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THESIS
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This is to certify that the

dissertation entitled

MICRODISTRIBUTION 0F CHRMATED
COPPER ARSENATE PRESERVATIVE
IN RUBBERHOOD
(HEVEA BRASILIENSIS WELL. ARG.)

presented by

Ismail Bin Jusoh

has been accepted towards fulfillment
of the requirements for

Ph.D. degree in Forestry

 

 

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Major professor

 

Date 6/9/2000

MS U is an Affirmative Action/Equal Opportunity Institution 0- 12771

 

 

LlIRARY
Michigan State
University

 

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE

DATE DUE

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dieingg

 

 

 

 

 

 

 

 

 

 

 

 

 

11100 cJCIRCJDateOuapes-p.“

 

MICRODISTRIBUTION OF CHROMATED COPPER
ARSENATE PRESERVATIVE IN RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG.)

By

Ismail Bin Jusoh

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Forestry

2000

ABSTRACT

MICRODISTRIBUTION OF COPPER-BASED PRESERVATIVES IN
RUBBERWOOD (HE VEA BRASILIENSIS MUELL. ARG.)

By

Ismail Bin Jusoh

Rubberwood is popular for making indoor furniture since rubberwood is
relatively abundant and sustainable. Currently more than 60% of the total annual
rubberwood produced by rubber plantation is used as fuelwood. Rubberwood has the
potential for both indoor and outdoor application. For exterior applications, preservative
treatment is needed to extend the service life of rubberwood. The objectives of this study
are to (1) assess treatability of rubberwood with chromated copper arsenate (CCA)
preservative, (2) evaluate the natural decay resistance and efficacy of CCA on
rubberwood, and (3) study the microdistribution of CCA components in rubberwood
cells. The treatability of rubberwood was determined by measuring the penetration and
retention of CCA type C preservative after a full-cell treatment. Natural decay resistance
and efficacy of CCA treatment on rubberwood was estimated using a laboratory soil-
block test according to AWPA ElO-91. The microdistribution of chromium, copper and
arsenic in CCA-treated rubberwood was studied using scanning electron microscope in
conjunction with energy dispersive X-ray analyzer (SEM-EDXA). As expected,
longitudinal permeability was found to be better than the radial and the tangential
permeability. The penetration and retention in the radial direction was about 3 times

better than in the tangential direction. Longer pressure period increased penetration and

retention of CCA type C in rubberwood. Complete penetration was achieved after 4
hours of pressure (1240 kPa) treatment. A pre-treatment steaming improved the
treatability of rubberwood regardless of the anatomical direction. The average weight
loss by white rot and brown rot was about 1.5 times higher than that of soft rot. A linear
relationship was found between the weight loss and the incubation period for all the six
test fungi. A CCA retention of 4.1 kg/m3 reduced weight loss to about 10% and retention
of 14.5 ltg/m3 reduced the weight loss of all test fungi at less than 2%. Vessels contained
high level of chromium, copper, and arsenic compared to fibers. Chromium level was the
highest, followed by arsenic and then copper in rubberwood cells. After the full cell
treatment, fibers contained about 0.42%, 0.63%, and 1.02% of copper after treatment
with 4.1 kg/m’, 10.5 kg/m’, and 14.5 kg/m3 of CCA, respectively. Highest levels of Cr,
Cu, and As were recorded in fiber-to-vessel cell corner (FVCC) and F iber-to-vessel middle
lamella (F VML) and the lowest was recorded in S2 layer of fiber. Linescan analyses
showed that higher count rates of carbon, oxygen, chromium, copper, and arsenic were
found in the middle lamella compared to the fiber 82 layer in CCA-treated rubberwood.
The increase of the solution strength in chromium, copper, and arsenic corresponds to an

increase in Cr, Cu, and As level in wood cells.

DEDICATION

To my beloved wife, Salviah, and children, Afiqah, Syamimi, Zulhusni, and
Khairulhamiz for their patience and sacrifices.

iv

ACKNOWLEDGEMENTS

I wish to express my sincere appreciation and thanks to my major professor, Dr.
D. Pascal Kamdem, for his guidance and assistance in all phases of my graduate program.
I deeply admire his endless patience, encouragement, kindness and understanding
throughout the course of this study. I am grateful and indebted to Dr. Stanley L. F legler
for his guidance and support in the scanning electron microscopy and X-ray
microanalysis works. I appreciate the keen interest, cooperation and valuable suggestions
of the other committee members, Dr. Melvin Koelling of the Department of Forestry,
MSU, and Dr. Eugene A. Pasek of Hickson Corporation, Conley, Georgia.

Special thanks and appreciation goes to Dr. Shirley Owens for her assistance in
Confocal Laser Scanning Microscopy works.

I am particularly indebted to Dr. Jun Zhang, Justin Zykowski and Weining Cui for
their helpful assistance, cooperation, support, suggestions, and time.

1 wish to thank the USDA-CSRESS Eastern Hardwood Utilization Program for

providing the funds, which made this graduate work possible.

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................. ix
LIST OF FIGURES ........................................................................................................... xi
CHAPTER 1
INTRODUCTION .............................................................................................................. 1
CHAPTER 2
LITERATURE REVIEW
2.1 Rubberwood — overview ................................................................................... 5
2.1.1 Rubberwood resource ........................................................................ 5
2.1.2 Properties of rubberwood ................................................................... 5
2.1.3 Utilization and uses of rubberwood ................................................... 7
2.1.4 Preservative treatment of rubberwood ............................................... 8
2.2 Performance of treated hardwoods ................................................................. 12
2.3 Fixation of CCA in wood ................................................................................ 15
2.4 Microdistribution of CCA in hardwoods ........................................................ 20
2.4.1 Microdistribution study using bulk samples of hardwoods ............. 21
2.4.2 Microdistribution study using thin samples of hardwoods .............. 22
CHAPTER 3

SOME CHEMICAL AND ANATOMICAL PROPERTIES OF RUBBERWOOD
(HE VEA BRASILIENSIS MU ELL. ARG.)

3.1 Introduction ..................................................................................................... 25
3.1.1 Chemical properties ......................................................................... 25
3.1.2 Anatomical properties ...................................................................... 27
3.2 Materials and Methods .................................................................................... 29
3.2.1 Chemical analysis ............................................................................ 29
3.2.2 Light and confocal laser scanning microscopy (CLSM) ................. 30
3.2.3 Scanning electron microscopy (SEM) ............................................. 30
3.3 Results and Discussion ................................................................................... 31
3.3.1 Chemical constituents of rubberwood ............................................. 31
3.3.2 Microscopic features of rubberwood ............................................... 33
CHAPTER 4
PENETRATION AND RETENTION OF CCA IN RUBBERWOOD (HE VEA
BRASILIENSIS MU ELL. ARG.)
4.1 Introduction ..................................................................................................... 40
4.2 Materials and Methods .................................................................................... 42
4.2.1 Wood samples .................................................................................. 42
4.2.2 Pre-treatment steaming .................................................................... 42
4.2.3 Anatomical direction ........................................................................ 42

vi

4.2.4 Pressure treatment ............................................................................ 43

4.2.5 Determination of CCA retention ...................................................... 43
4.2.6 Determination of CCA penetration .................................................. 44
4.3 Results and Discussion ................................................................................... 45
4.3.1 Retention and penetration ................................................................ 45
4.3.2 Effect of pre-treatment steaming of wood blocks ............................ 49
4.3.3 Gradient retention of Cr, Cu, and As ............................................... 50

CHAPTER 5
LABORATORY EVALUATION OF THE NATURAL DECAY RESISTANCE
AND THE EFFICACY OF CCA-TREATED RUBBERWOOD (HE VEA

BRASILIENSIS MUELL. ARG.)
5.1 Introduction ..................................................................................................... 53
5.2 Materials and Methods .................................................................................... 53
5.2.1 Sample preparation .......................................................................... 53
5.2.2 Sample treatment ............................................................................. 54
5.2.3 Chemical analysis ............................................................................ 55
5.2.4 Fungal exposure ............................................................................... 55
5.2.5 Determination of weight loss ........................................................... 56
5.2.6 Statistical analysis ............................................................................ 57
5.3 Results and Discussion ................................................................................... 58
5.3.1 Relation between moisture content and weight loss ........................ 58
5.3.2 Natural decay resistance .................................................................. 59
5.3.3 Relationship between weight loss and incubation period ................ 61
5.3.4 CCA efficacy ................................................................................... 63
CHAPTER 6

MICRODISTRIBUTION OF COPPER-CHROME-ARSENATE PRESERVATIVE IN
THE CELLS OF RUBBERWOOD (HE VEA BRASILIENSIS MUELL. ARG.)

6.1 Introduction ..................................................................................................... 66
6.2 Materials and Methods .................................................................................... 68
6.2.1 Wood treatment ................................................................................ 68
6.2.2 Samples preparation for X-ray microanalysis .................................. 68
6.2.3 Scanning Electron Microscope — Energy Dispersive X-ray
Analysis (SEM-EDXA) ................................................................... 69
6.2.4 Data handling ................................................................................... 72
6.3 Results and Discussion ................................................................................... 74
6.3.1 X-ray microanalysis of wood ........................................................... 74
6.3.2 Chromium, copper, and arsenic in wood cells ................................. 76
6.3.3 Relative composition of Cr, Cu, and As in wood cells .................... 78
6.3.4 Influence of treating solution concentration on distribution of
Cr, Cu, and As .................................................................................. 80
CHAPTER 7

MICRODISTRIBUTION OF CCA ELEMENTS IN RUBBERWOOD (HE VEA
BRASILIENSIS MUELL. ARG.) CELL WALLS

vii

7.1 Introduction ..................................................................................................... 84

7.2 Materials and Methods .................................................................................... 87
7.2.1 Wood treatment ................................................................................ 87
7.2.2 Samples preparation for X-ray microanalysis .................................. 87
7.2.3 Scanning Electron Microscope-Energy Dispersive X-ray
Analysis (SEM-EDXA) ................................................................... 89
7.3 Results and Discussion .................................................................................... 93
7.3.1 Microdistribution of Cr, Cu, and As ................................................ 93
7.3.2 Distribution of carbon and oxygen .................................................. 95
7.3.3 Comparison between the distribution of carbon and oxygen
and distribution of Cr, Cu, and As ................................................... 98
7.3.4 Cr, Cu, and As distribution in relation to decay fungi attack ........ 110
7.3.5 Influence of CCA solution concentration on Cr, Cu, and As
distribution ..................................................................................... l 10
CHAPTER 8
CONCLUSIONS .............................................................................................................. 1 12
CHAPTER 9
RECOMMENDATIONS ................................................................................................. l 15
LITERATURE CITED .................................................................................................... 117

viii

LIST OF TABLES

Table 1. Preservatives used for rubberwood dip treatment .................................................. 9
Table 2. Schematic diagram of fixation of CCA wood preservative according to Pizzi
(1982c) ............................................................................................................................... 17
Table 3. The chemical composition of hardwood and sofiwood (Haygreen and

Bowyer 1996) ..................................................................................................................... 25
Table 4. Chemical composition of rubberwood ................................................................. 32

Table 5. The effect of pressure duration on the retention and penetration in
rubberwood treated with 2% CCA-C solution ................................................................... 46

Table 6. The effect of pressure duration on the average chemical retention in the
assay zone (0-13 mm) of end sealed rubberwood samples ................................................ 48

Table 7. Average retention of Cr, Cu, and As in the outer (0-13 mm) zone and core
of end-sealed 2% CCA-treated rubberwood blocks ........................................................... 51

Table 8. Average CCA and copper retention from CCA-treated rubberwood blocks ....... 55

Table 9. Average biweekly moisture content (%) of untreated rubberwood cubes
exposed to different decay fungi for 12 weeks .................................................................. 59

Table 10. Average weight loss (%) of untreated rubberwood cubes exposed to
different decay fungi for 12 weeks .................................................................................... 60

Table 11. Regression equation of WL (%) vs duration (t) of rubberwood exposed to
decay fungi ......................................................................................................................... 62

Table 12. Weight loss (%) of CCA type C-treated rubbberwood exposed to
decay fungi ......................................................................................................................... 64

Table 13. Estimated threshold retention values of CCA type C for rubberwood using
intercept method (AWPA BIO-91) .................................................................................... 65

Table 14. Elemental composition in percent (%) of CCA-treated rubberwood as
obtained by SEM-EDXA after ZAF corrections ............................................................... 76

Table 15. Comparison of chromium, copper, and arsenic element composition in
percent in various rubberwood cells after treatment with different treating solution
strength ............................................................................................................................... 77

ix

LIST OF TABLES (Cont.)
Table 16. Relative ratios of elements concentration in various rubberwood cells at
different treating solution concentration ............................................................................ 79
Table 17. Dimension of cell layers in rubberwood ............................................................ 91

Table 18. Average elemental composition and proportion of various cell morphological
regions in CCA-treated rubberwood .................................................................................. 94

Table 19. Count rate of carbon and oxygen for cell comer, middle lamella, and the
adjacent 8; layer of untreated and CCA-treated rubberwood ............................................ 97

LIST OF FIGURES

Figure 1. World map of rubberwood distribution ................................................................ 2
Figure 2. CLSM image of transverse section of rubberwood ............................................ 35
Figure 3. SEM micrograph showing simple perforation plate in vessels .......................... 35

Figure 4. CLSM image of transverse section of rubberwood showing relative cell
wall thickness of fiber, parenchyma, and ray cells. The dark spots in ray and

parenchyma cell represents the pits ................................................................................... 36
Figure 5. CLSM image of radial section radial section of rubberwood showing pits of

fiber, parenchyma, and ray cells ........................................................................................ 36
Figure 6. SEM micrograph showing starch grains in ray and parenchyma cells ............... 37

Figure 7. CLSM image showing starch grains in parenchyma and upright ray cell .......... 38

Figure 8. SEM micrograph of transverse section of rubberwood showing 8; layer
of fiber, middle lamella, cell comer, and fiber-to-fiber pitting .......................................... 39

Figure 9. Average Cr, Cu, and As retention by outer and core zones of 2%
CCA-treated rubberwood ................................................................................................... 52

Figure 10. SEM micrograph of transverse section showing cell walls of vessel
(+1 and +2) and fiber (+3, +4, and +5) used for X-ray spot analyses ................................... 70

Figure 11. SEM micrograph of transverse section showing cells of parenchyma
(+1 and +2) and ray (+3, and +4) used for X-ray spot analyses ........................................... 71

Figure 12. A schematic diagram of electron beam/specimen interaction within
bulk specimen .................................................................................................................... 73

Figure 13. The effect of treating solution concentration on the Cr, Cu, and As
element composition in vessels and rays of CCA-treated rubberwood ............................. 82

Figure 14. The effect of treating solution concentration on the Cr, Cu, and As
element composition in parenchymas and fibers of CCA-treated rubberwood ................. 83

Figure 15. Sections of a 3 mm tungsten grid centered on aluminum stub ......................... 88

xi

LIST OF FIGURES (Cont.)

Figure 16. A schematic diagram of electron beam/specimen interaction .......................... 90

Figure 17. SEM micrograph of semi-thin (0.5 pm) section showing fiber-to-fiber
cell corner (FF cc), fiber-to—fiber middle lamella (FFML), and fiber 82 layer regions
used for analyses. (Magnification SOOOX) ......................................................................... 92

Figure 18. SEM-EDXA linescan of untreated rubberwood. (A) SEM micrograph
of transverse surface showing a line across two adjacent fibers used for linescan

analyses. (B) Carbon distribution and (C) oxygen distribution across two adjacent
fiber cells ........................................................................................................................... 99

Figure 19. SEM-EDXA linescan analyses of rubberwood treated with 0.93% CCA
solution. (A) SEM micrograph of transverse surface showing a line across two

adjacent fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen
distribution, (D) chromium distribution, (E) copper distribution, and (F) arsenic
distribution across the two adjacent fiber cells ................................................................ 101

Figure 20. SEM-EDXA linescan analyses for rubberwood treated with 2.12% CCA
solution (A) SEM micrograph of transverse surface showing a line across two

adjacent fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen
distribution, (D) chromium distribution, (E) copper distribution, and (F) arsenic
distribution across the two adjacent fiber cells ................................................................ 104

Figure 21. SEM-EDXA linescan analyses for rubberwood treated with 3.29% CCA
solution (A) SEM micrograph of transverse surface showing a line across two

adjacent fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen
distribution, (D) chromium distribution, (E) copper distribution, and (F) arsenic
distribution across the two adjacent fiber cells ................................................................ 107

xii

CHAPTER 1

INTRODUCTION

Rubber plantations are found in more than 30 countries around the world as
illustrated in Figure l. The total plantation surface area world wide is approximately 9
million hectares with almost 90% located in Asia and about 75% of these are in Malaysia,
Indonesia and Thailand (Ismariah and Norini 1994).

Rubber trees (Hevea brasiliensis Muell. Arg.) reach their prime in 25 years, after
which it is no longer economical to for latex production (Hong et al. 1994). After 25
years, rubber trees have a clear bole of 3 to 10 meters height depending on the clone. The
diameter can reach up to 50 centimeter at breast height.

Old rubber trees are simply burned in the field prior to planting new stock. Some
of the old trees are used for firewood for brick manufacturing and for production of
charcoal briquettes. In recent years, due to the shortage of forest timbers, rubberwood has
become an important source of timber particularly for furniture and wood composites
manufacturing (Hong and Sim 1994). Despite the rapid commercial use of the
rubberwood, it is estimated that 67% of the total volume of rubberwood obtained from
rubber plantations is bumed (Lew 1992).

Rubberwood has excellent potential for both interior and exterior wood products.
The supply is sustainable and is relatively low cost as it is a by-product of rubber industry
Today, by far the largest users of rubberwood are manufacturer of furniture for indoor
use. For exterior use, rubberwood is not included because of its susceptibility to

biodegradation and dimensional instability.

 

 

  

 

 

 

 

 

Indoneswm

 
 
  

. a”

 

 

Figure 1. World map of rubberwood distribution.

 

The protection of hardwood against deterioration is desirable for exterior
applications. The service life of wood can greatly be increased by proper treatment. The
opportunity for increasing utilization of many hardwoods species, especially for exterior
applications, is highly dependent on the development of wood preservation technology.
Chemical treatments can make the use of rubberwood in high decay-hazard environment
possible. The effectiveness of a wood preservative is dependent not only on the retention,
but also on the penetration and distribution of preservative in the wood cells (Janezic et
al. 1997; Ryan 1986).

Information on the location and distribution of the active ingredients in treated
wood is important with regard to the mode of action of the preservative, permeability of
wood, and impregnation process. Over the last three decades, the microdistribution of
preservative in treated wood has received considerable research. Several studies have
investigated the microdistribution of chromated copper arsenate (CCA) in softwood
species (Newman and Murphy 1996; Jeihooni et al. 1993; Greaves et al. 1983; Yata and
Nishimoto 1983; Drysdale et al. 1980; Chou et al. 1973; Petty and Preston 1968). Apart
from Eucalyptus, little work is reported on the microdistribution of metal elements in
tropical hardwoods. The location and amount of preservative elements present in the
complex wood microstructure of hardwoods need more study. The amount of
preservative in the cell walls may contribute to its efficacy (DeGroot and Kuster 1986).
Thus, it is necessary to understand the microdistribution of preservative in rubberwood

cells.

The objectives of this study are;

(1) To assess the treatability of rubberwood with chromated copper arsenate (CCA)
preservative.

(2) To evaluate the natural decay resistance and the efficacy of CCA on rubberwood.

(3) To examine the microdistribution patterns of CCA components in the wood cell walls

and selected morphological regions, at varying treating solution strength.

CHAPTER 2

LITERATURE REVIEW

2.1 Rubberwood - Overview
2.1.1 Rubberwood resource

Rubberwood is the timber produced from rubber trees. The rubber trees of
Malaysia, indigenous to Amazon forest of Brazil, were introduced in 1877 for latex
production (Hong 1994). Currently, Malaysia has more than 20 clones of rubber trees. In
1992 the total area planted with natural rubber in Malaysia was estimated to be 1.8
million hectares (ha.) (Anonymous 1993a). The rubber plantation contributes the largest
man-made forests in the South East Asia region (Ser 1990). Logs with diameter more
than 20 cm are used for sawn timber products while smaller diameter are used as fuel in
brick factories and processed into charcoal, chipboard and medium density fiberboard

plants (Ho 1994).

2.1.2 Properties of rubberwood

Rubberwood is white to pale cream, sometimes with a pinkish tinge, and aged to
light straw or light brown. It consists of only sapwood (Lim and Sulaiman 1994;
Anonymous 1982; Thomas and Landon 1953). The texture is moderately coarse with an
even grain. A characteristic smell of latex is distinct in freshly sawn timbers. The vessels
are moderately large and usually filled with tyloses (Lim and Sulaiman 1992). Wood
parenchyma cells are narrow and irregularly spaced. Rays are moderately fine and are

visible to naked eye. The structural elements of rubberwood consist of about 62% fibers,

9.5% vessels, and 29.0% parenchyma cells (Nagoshi 1970). The fiber length of
rubberwood varies from 1.1 to 1.8 mm, fiber width from 26 to 30 microns and cell wall
thickness from 5.1 to 7.0 microns (Peel and Peh 1960). Rubberwood has a lignin content
of 22 to 29%, holocellulose of 70%, pentosan content of 20%, alpha-cellulose of 40%
and extractives of 6 to 10% (Hong and Lim 1985; Peel and Peh 1960).

The green specific gravity of rubberwood is 0.53 (Lee et al. 1979). The air-dried
modulus of elasticity (MOE) and modulus of rupture (MOR) were 9,240 MPa (1.34
million lb/inz) and 66 MPa (9,500 lb/inz), respectively. The strength properties of
rubberwood are grouped under the strength group C (Rahman 1978), which is good for
light construction. Gnanaharan and Dhamodaran (1993) reported that a 35-year
rubberwood plantation from Kerala, India had an average MOE of 15,700 MPa (2.27
million lb/inz) and MOR of 98.4 MPa (14,200 lb/inz).

In the tropics rubberwood is classified as non-durable wood (Wong 1988; Jantan
and Tarn 1987; Hong et al. 1987; Scheffer and Cowling 1966). Wood in this class has the
natural durability of between 2 to 5 years and should require some protection if used in
decay or insect hazardous environment (Findlay 1985). The carbohydrates content of the
parenchyma makes rubberwood susceptible to decay attack (Azizol and Sudin 1989). In a
laboratory evaluation of susceptibility of rubberwood to the three major types of wood-
rot, the severity of attack are in the order of sofi rot > white rot > brown rot (Wong 1988).

Freshly sawn rubberwood is susceptible to sapstain and mold fungus. The
common fungus reported to be responsible for bluish discoloration is Botryodiplodia
theobromae (Hong 1976; Kaarik 1980; Tsunoda et. al. 1983). Other staining fungi that

have been isolated from rubberwood are F usarium decemcellulare, Aspergillus sydowii

and Penicillium citrium (Balasundram and Gnanaharan 1990). The main surface
colonizers or molds are species of Aspergillus, Curvularia, F usarium, Gliocladium,
T richoderma, Sphaeronaema and Penicillium (Hong et al. 1987; Tsunoda et a1. 1983;

Hong 1981; Sujan et al. 1980).

2.1.3 Utilization and uses of rubberwood

Rubberwood is valuable for furniture making because of its beautiful, light and
even colored texture, suitable strength, good machining and processing properties (Tee
1990). The creamish color and figured, ease of machining and high quality surface finish
make rubberwood suitable for mouldings and other joinery components, parquet and strip
floorings (Chew 1993). Particelboard made from rubberwood is extensively used in
furniture and joinery industries for making wardrobes, cabinets, side- boards, desks,
tables, room divider, door and kitchen cabinets (Hong and Sim 1994). Currently the main
raw material for making MDF in Malaysia is rubberwood (Yusoff 1995). The excellent
physical properties of rubberwood MDF (Yusoff 1992; Razali and Diong 1992;
Tomimura et al. 1990) made it excellent choice for furniture manufacture especially
mainly as table tops, cabinets, doors and headboards for beds. The cement-bonded
particleboard (CBP) manufactured in Malaysia from rubberwood is marketed under the
trade name Cemboard and has been widely used as building material in construction of
low-cost houses and multi-story buildings (Sudin 1994). Other uses of rubberwood are
for pulp and paper (Yusoff 1994), charcoal and briquettes (Hoi 1994) and when properly
treated rubberwood can be used as building material (Hong and Sim 1994; Teng and

Idrus 1990).

2.1.4 Preservative treatment of rubberwood

Newly felled rubberwood logs are extremely susceptible to staining fungi and
insect attacks (Jantan et al. 1994). To avoid deterioration the logs are usually converted to
sawn timber as soon as possible. However, delay in conversion to sawn timber is
unavoidable because of transportation and log yard operations (Ho 1994). To prevent log
deterioration during storage, preservative treatment is necessary.

Rubberwood logs can be protected from biodegradation by application of
chemical preservatives containing a fungicide and insecticide by means of spraying or
end-coating (Jantan et al. 1994; Lewis and Spencer 1987; Hong et al. 1980). For more
effective end-coating, the preservatives could be incorporated into Shellkote-3, a
bituminous based emulsion for end coating applied by brushing (Hong et al. 1980; Tan et
al. 1980). The end-coating serves as physical barrier to fungal infection and insect attack
and at the same time create an unfavorable condition for fungal development because of
moisture content fluctuation at the coated surfaces.

The most effective end coat preservatives are the combinations of 2% Captafol
and 1% F ennotox 82 (thiophanates, thiocarbamates and sodium nitrite) incorporated into
Shellkote-3 (Hong et al. 1980). The performance of Shellkote-3 is enhanced by addition
of either 4% sodium pentachlorophenate (NaPCP) or 1.5% of a proprietary fungicide
containing methylene-bis—thiocynate (MBT) or 4% Captofol (Lewis and Spence 1987).
Storage of rubberwood logs under water is another way of protection. Complete
protection of fresh logs can achieved by end coating prior to storing under water. A study
by Hong et a1. (1988) showed that without any prior treatment, fresh logs completely

submerged under water for up to seven months had little or no staining, and no

appreciable visual deterioration. Although this method has an added advantage in
protecting logs against splitting and insects, large log pond facilities are seldom available.
Storing logs under water emit a foul smell after a few days (Jantan et al. 1994).

Freshly sawn rubberwood are susceptible to fungal and insects attack. Two types
of treatments are employed in Malaysia for temporary and long-term protection (J antan et
al. 1994). Temporary treatment is used to protect rubberwood during air-drying and/or
prior to kiln drying. Temporary treatment is done by dipping rubberwood in a
preservative mixture of fungicide and insecticide for 1 to 2 minutes (Hong 1989).
Commonly used preservative mixtures available for dip treatments in Malaysia are listed
in Table 1.

Table 1. Preservatives used for rubberwood dip treatment.

 

 

Preservative Recommended amounts
per 1000 liters of water
NaPCP + 15 - 20 kg
gamma-BHC 7.5 kg
NaPCP + 15 - 20 kg
deltametrin/cypermethrin 0.125 L
TCMTB + 1 - 5 L
boron compounds 15 - 20 kg
TCMTB + 1 - 5 L
Deltametrin/cypermethrin 0.125 L
MBT + 4 - 10 L
boron compounds 15 - 20 kg
MBT + 4 - 10 L
deltametrin/cypermethrin 0. 125

 

* From Hong, LT. (1989)

TCMBT - Thiocyanomethylthiobenzothiazole
MBT - Methyl-bis-thiocynate

The growing concern on the use of highly persistent pesticides such as the cost-
effective NaPCP has resulted in the search for formulation of alternative fungicides.
Tsunoda et al. (1983) reported that 2% formulated mixture of 4-chlorophenyl-3-
iodopropagylformal and 2-(4-thiazoly)benzimidazole prevents sapstain and mold growth.
A study by Lewis and Spence (1987) showed that stain and mold development on
rubberwood can be controlled by using 1.5% Antiblu-3739 (MBT and TCMTB)
treatment. Wong and Woods (1997) reported that Tuff Brite CTM containing (36% w/w
chlorothalonil & 8% carbendazim) with or without borax provided complete control
against blue-stain and mold on rubberwood.

Dip treatment is essentially a temporary protective measure as preservative only
form a protective layer of about 2-5 mm deep from the surface of treated rubberwood
(Jantan et al. 1994; Hong, et al. 1982). During further processing to furniture and other
products the superficial preservative layer is removed, exposing fresh untreated surfaces.

For long term protection, preservatives need to penetrate deep into the
rubberwood wood rrricrostructure. Two methods employed for long-term protection are
dip-diffusion process and pressure impregnation process (Jantan et al. 1994). The dip-
diffusion process is a simple and economical method to treat fresh sawn rubberwood
(Anonymous 1969). The treatment consists of dipping freshly sawn wood in a 20-30%
solution mixture of borax and boric acid at 35-45°C for 5 to 40 nrinutes (Gnanaharan
1982; Tarn and Singh 1987). Addition of 0.5-1% NaPCP to the boron compounds prevent
staining of wood (Gnanaharan and Mathew 1982).

Pressure impregnation or pressure treatment gave satisfactory results for total

protection of rubberwood (Hong et al. 1982; Sonti et al. 1982; Hong and Liew 1989).

10

Chemicals that have been tested for pressure treatment of rubberwood are benzylkonium
chloride, copper naphthenate, pentachlorophenol, copper-chromium—arsenate (CCA), and
cresosote (Martawidjaja 1971; Tan et al. 1979; Hong et al. 1987). An average uptake of
507.2 l/m3 (31 lb/fi3) was achieved when rubberwood was treated with 3% CCA by full
cell process for the duration of 2.5 hours (Jantan et al., 1994). In recent study on
treatability of rubberwood, Salim (1997) reported retention of 32.58 kg/m3 and full
saturation of 40 x 40 x 750 mm specimen when 5% CCA was used in full cell process for
the duration of four hours.

If rubberwood is to be used for furniture making, CCA is seldom used to treat
rubberwood because of the undesirable color of treated wood, however if it to be used for
construction it is best to treat with CCA (Jantan et al. 1994). In a field test, pressure
treated rubberwood stakes with 100% and 50% creosote and 4 % copper naphthenate
showed no sign of rot after 20 years of ground contact (Martawidjaya 1971).

Boron-based preservatives have been used to treat green rubberwood using
pressure treatment (Tan et al. 1980, 1983, Hong et 01.1987; Hong and Liew 1989,
Salamah et al. 1988). Treatment of rubberwood of varying moisture contents using 3%
mixture of borax and boric acid has shown that freshly sawn rubberwood could absorb
187-214 kg/m3 of preservative solutions giving retention of about 0.36% boric acid
equivalent (BAE) and up to a depth of 10 mm (Hong and Liew 1989).

The opportunity for increasing the utilization of rubberwood and other hardwoods
in exterior construction is highly dependent on the preservative treatment. However,

satisfactory protection of hardwoods vary with species because of the different in

11

chemical contain, preservatives used, and permeability of various wood tissues (Smith et
al. 1996; Butcher and Nillson 1982; Butcher 1979).

Fungi decompose wood by secreting enzymes, which in present of moisture,
degrade cellulose and other wood constituents (label and Morell 1992). However, the
complexity of fungi metabolism and processes provide numerous potential points that can
be altered or blocked chemically. For instance, copper acts as a fungicide in which its
denatures protein within the fungi and interfere with enzyme reactions (Eaton and Hale
1993). Arsenic is a competitive inhibitor for phosphorus in adenosine triphosphate (ATP)
synthesis (label and Morell 1992) while chromium has strong affinity for wood lignin

which limits leaching (Hartford 1973).

2.2 Performance of treated hardwoods

Chromated copper arsenate (CCA) is a broad-spectrum wood preservative and its
effectiveness in protecting softwoods both in laboratory and field tests is well
documented and proven. The excellent performance of CCA-treated softwood,
particularly the Pinus species, is attributed to deep penetration of preservatives into the
cell wall of tracheids (Petty and Preston 1968), preservative loading (Ryan and Drysdale
1988), uniform preservative distribution at cell level (Bodner and Pekny 1991; Dickinson
and Sorkhoh 1976; Greaves 1972), and even preservative distribution within the cell wall
(Newman and Murphy 1996). However, the performance of CCA-treated hardwoods
against soft rot varies. Soft-rot fungi often attacked CCA-treated hardwoods that are used

in ground contact (Duncan and Eslyn 1966; Findlay 1984; Smith et al. 1996). For

12

instance, CCA-treated eucalyptus transmission poles in Australia were attacked by soft-
rot fungi (Greaves 1977; Butcher and Drysdale 1978).

In laboratory studies (Butcher and Drysdale 1978), specimens of twelve CCA-
treated hardwoods were severely attacked by soft-rot fungi. The same study also found
that it was possible to control soft-rot attack by increasing the CCA retention from 26
ltg/m3 to 44 kg/m3, depending on the density of the species. Ryan and Drysdale (1988)
noted that it required six times more copper retention in the fibers of Betula alba than in
tracheids of Pinus radiata to prevent soft-rot attack. Witheridge (1983) also suggested
that retention of approximately 35 kg/m3 of CCA can significantly extended the service
life of eucalyptus power poles in New South Wales. However, Leightley and Norton
(1983) reported that CCA retention of up to 40 kg/m3 did not protect eucalyptus poles
from soft rot in Australia.

Some hypotheses have been put forward to explain the reasons for the poor
performance of CCA-treated hardwood. The gross anatomy of hardwoods and softst
are very different. Hardwoods are composed of mainly fiber (IS-60%), vessel elements
(20-60%), ray (5-30%), and parenchyma (0-24%) (Haygreen and Bowyer 1996). The
vessel elements perform conductive function while fiber is responsible for support, which
usually possess a few slit-like simple pits (Greaves 1974). Preservative solution flows
principally through the open vessels, which form an easy and continuous pathway
(Wilkinson 1979; Siau 1984). It moves into the surrounding cells, through pits into cell
lumen, and penetrating the cell wall. Softwoods are compose of 90-95% tracheids, and
the remainder, 5-10% is make up of ray cells. In softwood, tracheids are conducting cells,

thin walled, with rounded ends and numerous bordered pits, which leads to more

13

invariable behavior in term of liquid penetration and distribution than in hardwoods.
Softwoods have a uniform arrangement of thin-walled tracheids, conversely hardwoods
composed of varying proportions of different kinds of cells couple with thick cell-wall
fiber, may posses many possibilities as regards to liquid pathways that will influence
penetration and distribution of liquids (N ilsson 1982; Greaves 1974). Studies showed that
preservatives distribution in softwood were relatively more even and penetrated deeper in
the cell wall than hardwood (Levy and Greaves 1978; Greaves 1974).

The differences in chemical make-up of hardwoods and softwoods affect the
fixation reactions. The softwoods have generally higher lignin content than hardwoods
(Haygreen and Bowyer 1996), and not only the content is different but there are also
structurally different. According to Butcher and Nillson (1982), lignin content determines
the susceptibility of hardwood to soft-rot, since lignin is encrusting the cellulose
nricrofibril, thus it provides protection from enzymes attack by soft-rot. Softwoods
contain a guaiacyl lignin whereas most hardwoods contain syringyl-quaiacyl lignin. Since
lignin is one of the reaction sites of CCA thus the amount of CCA in treated wood
corresponds to the amount of and distribution of lignin in wood (Buthcer and Nilsson
1982; Daniel and Nilsson 1987). In addition, it has been reported that CCA preferentially
react with guaiacyl lignin (Daniel and Nilsson 1987), which may suggests that since
hardwood cells are mostly made-up of syringyl-quaiacyl lignin thus its more susceptible

to fungi attack.

14

2.3 Fixation of CCA in wood

The term “fixation” as used in the field of wood preservation refers to the
mechanism by which preservative component become stabilized in the wood that resist
leaching by water or rain during service. However, there is debate whether the word
fixation is appropriate term to use. This is because even CCA, which is firlly bound to
wood, will leach to some degree. Thus some researchers suggested that CCA fixation
refer to the state of the chemical component of the preservative and wood or other
substrate when all chemical reactions are complete.

The interactions of CCA preservatives with wood during and after treatment are
complex and not completely understood (Eaton and Hale 1993; Lebow 1996). The
completion of CCA fixation may take few days, weeks or even months. However, some
reactions do occur during and immediately after treatment (Dahlgren and Hartford 1972;
Pizzi, 1981, 19820). In a series of papers published by Dahlgren and Hartford (1972 -
1975) suggested that the process is related to pH changes in wood following treatment.
According to their study based on wood flour from sapwood of pine and spruce, the
process of fixation undergo three periods namely, momentary initial reactions, primary
fixation reactions, and conversion reactions.

In the momentary initial reactions, that is immediately after CCA treatment there
is an increase in pH caused by ion exchange and adsorption reactions between copper and
chromium and wood components. It appears that some copper and chromium react with
wood almost instantly. The next process is the precipitation reactions. During
precipitation of the active elements, pH continues to increase but reaches a maximum (ca.
pH 5), when all the chromium is consumed. The reactions involve in this period are the

reduction of chromic acid to trivalent chromium (Cry) that causes a steady increase in

15

the pH of the solution. Following precipitation reactions, slow fixation reactions may
continue within the wood for several months. During the slow process, some of the early
reaction products, which are unstable, are slowly converted via dissolution into stable
compounds. For instant acid and tertiary copper arsenates are converted into basic copper
arsenate. During these conversion reactions the pH of the wood-CCA system increases
and decreases due to proton liberating and proton consuming reactions. In this reaction
liberated protons are consumed in the reduction of chromates and chromate-wood
complexes to trivalent chrome in the form of Cr(OH)3. The final equilibrium products
believed to be ion exchange fixation of copper to wood, CrAsO4, Cu(OH)CuAsO4, and

Cr(OH)3 (Dahlgren, 1974, 1975).

Studies by Pizzi (1981, 1982a, 1982b, 1982c) on the mechanisms of CCA fixation
using cellulose and lignin model compounds and also wood flour showed that a series of
reactions and fixation products occur in wood cell appear to have some similarity to those
described by Dahlgren and Hartford (1972). However, Pizzi (1982) suggested that during
the initial reactions, the initial fixation of copper was only physical absorption not
adsorption reactions as suggested by Dahlgren and Hartford (1972). He also concluded
that copper might also be involved in much slower reactions with cellulose and lignin.
According to Pizzi (19820), the main precipitation and fixation reactions, which follow
the initial reactions, are divided into three zones that occur within the first 2 hours. The

details of reactions in the three zones are described in Table 2.

16

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According to Pizzi ( 1982c) the products formed when CCA is reacted with wood
are composed of mainly the CuCrO4' —lignin complexes, CrAsO4' —-lignin complexes,
and CrAsO4 precipitates on cellulose. The actual proportions of various chemical species
are dependent on relative proportion of Cu, Cr, and As present in the formulation. About
10% of the copper in the system is bound to chromium. The rest of the copper is bound to
the cellulose and lignin. Copper is present in the treated wood in four different forms:

(1) CuCrO4 bound to guaiacyl units of lignin by Cr6+ (10 - 15%), (2) Cu2+ directly bound
to carbohydrates and lignin guaiacyl units (10 - 22%), (3) Cu2+ directly bound to lignin
functional groups other than guaiacyl units (40 — 70%), and (4) CuSO4 physically
adsorbed by the various wood constituents (5 —- 20%). It can be seen from the different
forms of copper, that the majority of copper is associated with lignin in wood. The
frxation reactions with wood and the products formed when CCA reacts with wood can

be summarized as follows (Pizzi 1982c):

CuCrO4 ____p Stable CuCrO4—lignin complexes
CrAsO4—lignin complexes
CrAsO4 —<:: Inorganic CrAsO4 precipitates on
CCA— cellulose

Cr2(OH)4CrO4 ——> Inorganic precipitates on cellulose
/—> Curl—lignin complexes
Cu2+ p Physically adsorbed on wood

\ constituents
Cu“ —cellulose complexes

Earlier work by Smith and Williams (1973) had shown that chromium was crucial

 

 

to the fixation process and was responsible for fixation of most of the arsenic and copper.

When chromium is reduced from Cr6+ to Cr3+ it react readily with arsenic to form

18

CrAsO4, which in turn, has the ability to complex with lignin and cellulose. In treated
wood, approximately 85% of the arsenic reacts with chromium, the remaining arsenic
forms fairly soluble complexes with lignin and cellulose (Pizzi 1982b).

In term of leach resistance, Pizzi (1981) postulated that the formation of
polymeric complex of guaiacyl—003 provides a significant amount of water repellency,
which contributes to the efficacy of CCA-treated wood against leaching.

In a study by Yata et al.(l982) on the distribution of chromium in cell wall
showed that chromium concentration was high in the primary wall and $1 layer, which
are areas of high lignin content, suggests that preferential association of chromium with
lignin.

The current trend of research on CCA fixation is to study the effect of fixation
reactions on wood. Ostrneyer et al. (1988, 1989) using x-ray photoelectron spectroscopy
(XPS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) on CCA-
treated southern pine, found that carbon-hydrogen bonds of the aromatic ring are being
oxidized, with the possibility that hexavalent chromium chromate esters being formed.
According to them, this suggest that the preservative components undergo substitution
reactions with aromatic portion of guaiacyl lignin only, because the second methoxyl
group on syringyl units would limit formation of stable wood-metal complexes. In a XPS
study by Yamamoto and [none (1990) on CCA-treated coniferous wood, detected an
increase in the proportion of carbon-carbon-hydrogen bonds, and a decrease in hydroxyl
concentration.

A study using infrared, nuclear magnetic resonance (NMR), and ultraviolet

spectroscopic analysis by Hon and Chang (1985) on model lignin compounds of quaicol

l9

and catechol demonstrated that phenolic hydroxyl compunds were altered by reaction of

chromium trioxide.

2.4 Microdistribution of CCA in hardwoods

The microdistribution of wood preservatives in hardwoods has been studied in
various ways. Most of the research was done with waterborne chromated copper arsenate
(CCA) preservative using scanning electron microscopy (SEM) in conjunction with X-
ray microanalysis (Greaves 1974; Dickinson and Sorkhoh 1976; Greaves and Levy 1978;
Greaves et al. 1982; Daniel and Nilsson 1987). Another method employed to study the
microdistribution of CCA was by electron probe microanalyser (EPMA) (Salamah and
Ani 1995).

Studies on the microdistribution of CCA components in wood using SEM and
EPMA employed bulk sections or specimen. For more detailed X-ray microanalysis the
transmission electron microscope (TEM) in combination of X-ray microanalysis has been
used to determine the microdistribution of CCA elements in wood cell walls (Dickinson
1974; Drysdale et al. 1980; Newman and Murphy 1996). The use of TEM-X-ray
microanalysis provides higher spatial resolution and eliminates the complication
encounters with the specimen electron interactions as in normal bulk specimen. However,
SEM fitted with X-ray microanalysis has been used to determine CCA microdistribution

in the cell wall of wood by employing semi-thin sections (Daniel and Nilsson 1987).

20

2.4.1 Microdistribution study using bulk samples of hardwoods

In some early works using SEM in conjunction with energy dispersive X-ray
analysis (EDXA), Greaves (1974) reported that CCA components were unevenly
distributed through different anatomical structures in which preservative was
accumulated in vessel of Eulyptus regnans, E. maculata and F agus sylvatica. A similar
instrument was used in the analysis of CCA-treated birch (Betula sp.) by Dickinson and
Sorkhoh (1976) and found that high levels of chromium (Cr) in vessels and rays together
with high levels of copper (Cu) and arsenic (As) in vessels and overall lower distribution
of the three elements in fibers. Similarly, in SEM-EDXA analysis of several hardwoods
species, Levy and Greaves (1978) noted that individual CCA component was unevenly
distributed with the exception of Alstom'a scholaris. In a more recent study using EPMA,
Salamah and Ani (1995) detected high concentration of copper in vessel and ray cells in
CCA-treated dark red meranti (Shorea leprosula).

It has been shown that X-ray generated from bulk sample is affected by three
known factors namely atomic number (Z), absorption (A), and fluorescence (F), or in
short ZAF factors. The atomic number correction Z, is concerned with the efficiency with
which an element generates X-ray. When an electron enters a specimen it may undergo
elastic scattering, in which case it may re-emerge (backseattered) before it has excited
any X-rays. Similarly, X-ray may not be generated because the electron may lose energy
so rapidly to excite further X-rays as it penetrates deeper into the specimen. Both of these
effects are dependent on atomic number, and if left uncorrected will cause error in due to
overestimation of X-rays. The absorption effect correction A, adjust for X-rays generated

at the surface of the specimen are emitted without loss, whereas X-rays produced from

21

deeper portion of the specimen have to travel through the specimen and are likely to be
absorbed before they can escape to the detector. Absorption corrections take into account
numerous factors such as accelerating voltage, take-off angle, mean atomic number and
mean atomic mass. However, in thin samples the effect is almost negligible. If correction
on absorption is not done it will underestimate the X-rays. The factor fluorescence F,
corrects for ‘secondary’ X-rays. The X-rays produced within the specimen may be of
high energy X-rays that are capable of fluorescing lower energy X-ray of another
element. The effect causes abnormally high counts in the lower energies. Although
generally considered the least important of the three corrections secondary fluorescence
can cause errors as large as 15% when analyzing elements in adjacent atomic numbers

(Goodhew and Hunphreys 1988).

2.4.2 Microdistribution study using thin samples of hardwoods

Study on the distribution of metal element in wood using SEM-EDXA employed
bulk sections. This means that the specimens are always thicker than the depth of electron
during irradiation (Daniel and Nilsson 1987). As a consequence, the results will always
be affected by electron backseattering, absorption and fluorescence (Williams and Carter
1996; F legler et al. 1993; Russ 1984). Furthermore, SEM-EDXA bulk analysis would not
reflect real loading in the 82 cell wall layer (Ryan 1986) due to the low spatial resolution.
However, the SEM-EDXA of bulk analysis is useful in evaluating the penetration
pathways of preservative in treated wood.

To overcome the low spatial resolution due to bulk sections, TEM-EDXA is the

method use for more detail X-ray microanalytical studies on wood cell wall layer (Daniel

22

and Nilsson 1987). A single cell wall layer could be analyzed in a thin section with
confidence that no X-ray had been generated from outside the region (Ryan 1986).
However, SEM-EDXA of semi-thin sections (0.5 pm) have shown to be useful in
analyzing the microdistribution of Cr, Cu, and As in wood cell walls (Daniel and Nilsson
1987). Although the spatial resolution with conventional SEM may not approach that of
TEM, sufficient resolution can be obtained to analyze many cell wall regions without risk
of overlapping such as 82 layers of fiber, ray, and vessel, cell comer, and middle lamella.
Due to the limited SEM resolution 81 and 83 layers cannot be analyzed for
nricrodistribution of CCA components. However, for routine CCA microdistribution
studies of large specimen areas, SEM-X-ray nricroanalysis of semi-thin sections provide
a convenient alternative to TEM-X-ray microanalysis (Daniel and Nilsson 1987).

In an early study of CCA distribution in cell walls of several hardwoods by TEM-
EDXA, Hulrne and Butcher (1977) reported that CCA component is well distributed with
the exceptions of three Eucalyptus species. However, Drysdale et al. (1980) using
electron microscope micro-analyser (EMMA) fitted with EDXA, reported that CCA
levels within the 82 cell wall layer varies and often low in Betula alba, F agus sylvatica,
Alstonia scholaris, and Acer psedoplatanus. Similarly, SEM-EDXA of thin section of
CCA-treated birch (Betula verrucosa), Daniel and Nilsson (1987) found that fiber and ray
S; cell wall layers have the least Cr, Cu, and As. It appeared that results fi'om the analyses
of thin section for microdisribution of CCA components varies. This is attributed to the
differences in the preparation of treated wood, sample preparation for X-ray
microanalysis, different species used and the use and capabilities of the electron

microscope and X-ray detector itself.

23

Studies on the microdistribution of CCA components in hardwood cell walls after
pressure treatment showed that the middle primary wall region between cell walls and
cell comers tends to be better treated than the adjacent S; layers (Daniel and Nilsson
1987; Drysdale et al. 1980). Drysdale et al. (1980) reported that increasing preservative
retention did not resulted in proportional increase of preservative in the 82 layers. Daniel
and Nilsson (1987) showed that relative microdistribution of CCA follow closely that of
lignin distribution.

An examination of the methods used in X-ray microanalysis to determine
microdistribution of Cr, Cu, and As in woods, both in bulk and thin samples, indicate two
approaches; X-ray counts in certain time interval and peakzbackground (PzB) ratios.
There are relatively few data that gave microdistribution of CCA components in terms of
elemental composition. It is important to quantified the present of Cr, Cu, and As in wood
in order to determine preservative threshold and to assist preservative formulation. High
or low X-ray counts would not reveal element quantities in treated wood. Similarly, P:B
ratios cannot be used for direct comparison between Cr, Cu, and As in different region of

cells and cell walls.

24

CHAPTER 3

SOME CHEMICAL AND ANATOMICAL PROPERTIES OF RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG.)

3.1 Introduction
3.1.] Chemical properties

There are three major chemical components in wood namely lignin (IS-35%) and
cellulose (40-55%), and hemicellulose (25-40%). There are complex and polymeric
materials. Minor amounts of extraneous materials, mostly in the form of organic
extractives and inorganic minerals (ash), are also present in wood usually 4-10%.
Overall, wood has an elemental composition of 50% carbon, 6% hydrogen, 44% oxygen,
and trace amount several metal ions (Fengel and Wegener 1984). The chemical
composition of cellulose is similar in all woods but the hemicellulose and the lignin
components differ between hardwoods and softwood. The approximate composition of

chemical components in both hardwoods and softwood are shown in Table 3.

Table 3. The chemical composition of hardwood and softwood (Haygreen and Bowyer
1996)

 

 

 

Type Dry weight percent (%)

Cellulose Hemicellulose Lignin Extractives Ash
Hardwood 40-44 15-35 18-25 4-10 2%
Softwood 40-44 20-32 25-35 4-10 <1%

 

Cellulose is the main structural components in wood cells consisting of D-
anhydroglucopyranose units linked by B l-O-4 glycosidic bonds (Eaton and Hale 1993).

The average degree of polymerization (DP) is about 8000-10000 arranged in linear chain.

25

It exists in the form of microfibrils which are reportedly more or less square in cross-
section (ca. 10 x 5 nm) of indeterminate length (Eaton and Hale 1993). The function of
cellulose microfibrils is to impart strength to the cell wall. Cellulose is insoluble in most
solvents including strong alkali. It is difficult to isolate because it is intimately associated
with the lignin and henricelluloses.

Hemicelluloses are relatively short, branched, and of much lower molecular
weight. There are made up of glucose and other hexose and pentose sugar and having DP
seldom exceeds 200 (Haygreen and Bowyer 1996; Eaton and Hale 1993). Hemicelluloses
exist as a matrix material and appear to contribute as structural components in plant.
They are soluble in alkali and easily hydrolyzed by acids.

Lignin is a complex three-dimensional polymer of phenylpropane units, which is
completely amorphous and serves as encrusting material surrounding microfibrils. Lignin
gives considerable rigidity to the cell wall and because of its hydrophilic properties; its
also influences the swelling and shrinkage properties of wood. Lignin can be isolated by
several methods. Acid hydrolysis of wood isolates Klason lignin, which can be
quantified, but is too severely degraded for used in structural studies. Milled wood lignin
procedure (Bjorkrnan) yields a lignin that is much less degraded and is more useful for
structural studies. Lignin for structural studies can also be obtained by enzymatic
hydrolysis of carbohydrates.

Extraneous components (extractives and ash) in wood are substances other than
cellulose, hemicelluloses, and lignin. They do not contribute to the cell wall structure and

most are soluble in neutral solvents. Extractive constitute 4-10% of the dry weight of

26

wood species that grow in temperate climates and as much as 20% of the wood in tropical
species (Eaton and Hale 1993; Pettersen 1984).

Ash is the inorganic residue remaining after ignition at a high temperature. It is
usually less than 1% of wood from temperate zones. It is slightly higher in wood from

tropical climates (Haygreen and Bowyer 1996).

3.1.2 Anatomical properties

The water-conducting elements in hardwoods are the vessel. Vessels make up of
about 20-60% of the total volume in hardwoods, composed of wide, cylindrical cells
arranged in vertical columns. Vessels only found in hardwoods and are often called
pores. They have relatively thin walls with overall diameter ranging from 25-500 um
(Eaton and Hale 1993). Majority of tropical and many temperate hardwood species,
including birch, beech and maple are described as diffuse-porous and exhibit little
difference in the size and distribution of the vessels across each growth ring. Other
temperate hardwood species are classifies as ring-porous such as ash, elm and oak. There
produce prominent large-diameter vessels in the earlywood and small vessels in the
latewood of successive growth rings. Some species are known as semi-ring porous,
showing large-diameter pores in the earlywood but a more gradual decrease in size
through to the latewood region of the grth ring.

In hardwoods, the main strength of the timber is provided by fibers. Fibers make
up 15-60% of hardwoods volume and are with narrow cells with finely tapering end.

Fiber cells can be more than 1.5 mm with thick cell wall surrounding the narrow central

27

cell lumen. The overall diameters of fiber cells are normally between 20 and 40 um
(Haygreen and Bowyer 1996; Eaton and Hall 1993).

Parenchyma is often seen in the transverse sections as lines or bands running
more or less at right angles to the rays. They make up 0-24% of the hardwood volume. In
some hardwood species parenchyma form a sheath surrounding the vessels and is known
as paratracheal parenchyma. Parenchyma that is not associated with vessels is known as
apotracheal.

Hardwood rays are much more variable in form than softwood rays and occur as
uniseriate and also multiseriate aggregation of cells. Rays consists of 5-30% of the total
hardwood volume. They show considerable variation in height. Rays in hardwoods
divided into two types. The upright cells are found at the upper and lower margin of the
ray; procumbent cells make up the remainder of the ray and more or less brick-shaped
with longest diameter oriented radially (Haygren and Bowyer 1999; Hoadley 1993).
Hardwood rays are described as homocellular when only procumbent cells are present or
heterocellular when both cell types occur in the ray.

In softwood 90-95% of the total wood volume is make up of tracheids. Tracheids
can be up to 5 mm long or even longer in some species. The tangential diameter of
tracheids ranges from 20 and to 70 pm but the radial diameter are variable depending on
their position in the annual ring and are quite narrow in the latewood zone (Hoadley
1990). In softwoods, the strength of the wood is derived largely from latewood tracheids.
The latewood tracheids are composed of thick-walled cells with small lumina. The wide
diameter and thin-walled tracheids in the adjacent earlywood zone in softwoods function

as water conducting and nutrient transfer in living trees. Rays make up the rest of the 5%

28

wood volume in softwood. Generally they are one cell wide or occasionally biseriate
extending from 1-15 and sometimes up to 50 cells in height (Hoadley 1990)

The objectives of this study are to ( 1) determine the chemical component of
rubberwood and (2) investigate the anatomical structures that are important to liquid

transport in rubberwood.

3.2 Materials and Methods
3.2.1 Chemical analysis

Rubberwood samples were cut into small pieces and milled (Wiley) to pass 20-
mesh. The sample was chemically analyzed for ash, extractives, Klason lignin, cellulose
and hemicellulose content. Ash content was determined using TAPPI T 211 om-85
(1992) procedure. Extractives content were determined based on TAPPI T 264 om-88
(1992) ‘Preparation of wood for chemical analysis’ procedure. To determine the amounts
and types of extractives approximately 2 g of oven dried-milled rubberwood was placed
in a thimble and successively extracted with ethanol-toluene (1:2 by volume), 95%
ethanol, and water in a soxhlet extractor. Each extraction time was about 10 hours. Total
extractives were determined on the weight residue remaining after the final extraction
with water. The residue was placed into a crucible and oven dried to constant weight and
placed into a desiccator prior to final weighing.

Klason lignin was determined using TAPPI T 222 om-88 (1992) procedure. One
gram of dried extractive free rubberwood was treated with 72% sulfuric acid, for Klason
lignin determination. Holocellulose content was determined by Ona’s et al. (1995)

procedure. Three grams of extractive free rubberwood samples were treated with 20%

29

sodium chlorite. The residues was filtered and washed prior to drying. To determine the
amount of (rt-cellulose, l g of hollocellulose was treated with 12% potassium hydroxide.
Then the residues was filtered, washed, and dried prior to weighing. Hemicellulose was
determined by subtracting hollocellulose content by a-cellulose obtained from the 12%

potassium hydroxide treatment.

3.2.2 Light and confocal laser scanning microscopy (CLSM)

Rubberwood samples were cut into 1 cm cubes. Prior to sectioning, the cubes
were softened by boiling in water for 48 hours. The transverse, radial, and tangential
sections were cut approximately to 20 pm thick using a sliding microtome. The sections
were stained with 1% Safranin-O and mounted permanently in resin. All three sections
were examined and photographed with both brightfield and confocal laser fluorescence
using Carl Zeiss confocal laser scanning microscope LSM 210. Fluorescence of the
sections was observed using a 488 nanometers (nm) argon ion laser line for excitation
and 520 nm long phase emission filters. Three transverse sections were used to measure
vessel diameter and frequency. Ten vessels were measured for diameters from each
transverse section. The number of vessels per square millimeter was determine by
counting individual vessels present in a field of 1 x 1 m. From each section five fields

were measured.

3.2.3 Scanning electron microscopy (SEM)

Rubberwood were cut to 2 x 2 x 10 mm specimen with lO-mm dimension in the

radial direction for SEM examination. The transverse, radial, and tangential surfaces of

30

the specimens were prepared by a razor blade (Exley et al. 1974). The prepared surface
specimens were dried in an oven of 60°C for 24 hrs. Dried specimen were mounted on
aluminum stubs and coated with approximately 28 nanometers (nm) of gold in Emscope
SC500 sputter coater.

Small matchstick samples of 0.5 x 0.5 x 10.0 mm were cut. The samples were
infiltrated and embedded in Spurr’s resin. Selected embedded samples were sectioned
using ultramicrotome to obtain semi-thin section of 0.5 pm thick. The sections were
mounted on copper grid. The semi-thin sections were used to examine the size of middle
lamella, fiber pits, cell comers and the cell wall thickness vessels, fibers, parenchyma,
and rays. The samples were examined in a JEOL 6400V scanning electron microscope

using a accelerating voltage of 20 kV.

3.3 Results and Discussion
3.3.1 Chemical constituents of rubberwood

The results of chemical studies are summarized in Table 4. The average
hollocellulose yield, corrected for extractives and ash content, was 77.5%. The yield
obtained for hollocellulose is comparable to those of other hardwoods ranging from 69 to
80% (Ona et al. 1995). Potassium hydroxide extraction for (rt-cellulose yield about 40.3%
and by subtraction, henricellulose is approximately 37.2%. Comparison of hollocellulose
data available for rubberwood is limited. In a chemical analysis of rubberwood pulp, Peel
and Peh (1960) reported a hollocellulose yields of 70%, (Jr-cellulose 40%, and pentosan
content of 20%. In wood cellulose exist as in the form of microfibrils and it is the main

structural component of wood cell walls.

31

The Klason lignin yields was about 18.5%. This compares well with result
showing 15.9 to 22.9% of Klason lignin in various hardwoods (Ona et al. 1995).

Total extractives content is about 6%. Ethanol-toluene extractives yield about
4.7% and water-soluble extractives were about 1.3%. Extractives are a variety of organic
compounds including fats, waxes, alkaloids, proteins, simple and complex phenolic,
simple sugars, pectins, mucilages, gums, resins, terpenes, starches, glycosides, saponins,
and essential oil (Pettersen 1984). Many of these functions as intermediates in tree
metabolism, as energy reserves, or as part of the tree’s defense mechanism against
microbial attack (Haygreen and Bowyer 1996). They contribute to wood properties such
as color, odor, and decay resistance (Eaton and Hale 1993; Hoadley 1990). Ash content is
about 1%.

Table 4. Chemical composition of rubberwood.

 

 

Chemical constituents Content (%)
Hollocellulose 77.5 :07

Hemicellulose 37.2 :06

(Jr-cellulose 40.3 3:09
Lignin 18.5 i0.8
Extractives 6.0 :05

Ethanol-toulene 4.7 $0.2

Hot-water 1.3 :02
Ash 1.0 2120.01

 

In general, cellulose microfibrils make up the backbone structure of the wall and
that hemicellulose and lignin exist as matrix materials around the microfibrils (Eaton and
hale 1993; Haygreen and Bowyer 1996). The individual chemical components vary
widely across cell walls. The distribution of wood chemical components can be

generalized as follows (F engel and Wegener 1984); cellulose is concentrated in the

32

secondary walls and is least abundant in the middle lamella and cell corner.
Hemicellulose concentrations are highest in the $1 and lowest in the S; of secondary wall
of tracheids and fibers. The hemicellulose types and distribution vary greatly among
species. High levels of lignin present in the cell corner, middle lamella, and primary wall
and lower but relatively uniform distribution in the secondary wall. However, because of
the thickness of the secondary wall 70 to 80% of lignin occurs in the secondary wall

(Eaton and Hale 1993).

3.3.2 Microscopic features of rubberwood

The shape of vessels or pores was round to oval, mostly in a group of 2 to 4 and
with tangential diameter (widest point) ranging fiom 150 to 300 um (Figure 2). Vessels
are diffuse, with average frequency of 3-4 vessels/mmz, and sometimes filled with
tyloses. The pores have simple perforation plates (Figure 3). Intervessel pitting
arrangement is scalarifonn and sometime opposite and is about 20-30 pm in diameter.
The cell wall of the vessel varies from 2.5 to 8 pm thick. The thickest part of the cell wall
is usually when the vessel cell walls are adjacent to each other while the thinnest are
when the vessel cell walls are adjacent to other cell. Vessel consists of about 9.5% of the
total rubberwood structural volume (N agoshi 1970).

Fibers have thick cell wall ranging from 4 to 7 pm and lumen width from 10 to 20
um (Figure 4). Fiber pits are confined to radial walls and approximately 0.3 to 0.5 pm in
diameter (Figure 5). Fiber makes up the bulk of rubberwood and it was estimated that

61.5% of rubberwood volume is made up of fibers (Nagoshi 1970).

33

Parenchyma consists of both apotracheal and paratracheal (Figure 2). Apotracheal
parenchyma appears as irregularly spaced bands, joining ray to ray to form a net-like
pattern (Figure 2). Close examination of apotracheal parenchyma show that they are
diffuse-in-aggregates and discontinuous lines up to 3 cells wide. Paratracheal
parenchyma is sparse and adjacent to the vessels. Cell wall of parenchyma is about 2.5 —
3.5 pm thick and is the thinnest cell. In rubberwood parenchyma is about 29% of the total
rubberwood volume (Nagoshi 1970).

Rays are moderately fine and visible to the naked eye. They are heterogeneous,
with 1 to 4 rows of square upright cells and 8 to 12 procumbent cells. Rays are mostly
about 0.5 mm in height but can reach up to 0.8 mm. The cell wall of ray ranged from 2.5
to 4 pm thick. Close examination of parenchyma and ray cells shows that they contain
considerable amount of starch grains (Figures 6 and 7). Azizol and Sudin (1989) reported
that rubberwood contains high starch reserves deposited in the parenchyma cells.
According to Esau (1977) starch are products of cell metabolism and deposition occurs
commonly in the parenchyma of stem tissue.

The middle lamella and cell comers of rubberwood are measured based on semi-
thin sections as examined by SEM (Figure 8). The examination of semi-thin sections by
SEM gave a high resolution that enables the cell walls, middle lamella, and cell corners
to be measured, but not high enough to resolve the $1 and 83 cell wall layers.

Measurements on middle lamella showed that it ranges from 1 to 1.8 pm while cell

comers is between 2 and 3.5 pm wide.

34

Vessel

 

 

Figure 3. SEM micrograph showing simple perforation plate in vessels.

35

Ray cells

 

Figure 4. CLSM image of transverse section of rubberwood showing relative cell wall
thickness of fiber, parenchyma, and ray cells. The dark spots in ray and parenchyma cell
represent the pits.

Parenchyma

)llS
/‘

‘1

Ray pits

 

Figure 5. CLSM image of radial section of rubberwood showing pits of fiber,
parenchyma, and ray cells.

36

Starch grain in ray cell Starch grain in parenchyma cell

 

Figure 6. SEM micrograph showing starch grains in ray and parenchyma cells.

37

Starch grains in parenchyma cell Starch grains in upright ray cell

 

Figure 7. CLSM image showing starch grains in parenchyma and upright ray
cell.

38

Middle lamella

Cell comer Fiber-to-fibcr

/ pitting

 

Figure 8. SEM micrograph of transverse section of rubberwood showing S2 layer
of fiber, middle lamella, cell comer, and fiber-to-fiber pitting.

39

CHAPTER 4

PENETRATION AND RETENTION OF CCA IN RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG.)

4.1 Introduction

The importance of Rubberwood in Malaysia was realized only two decades ago
when the supply of traditional forest timbers declined and pushed the price high make it
unaffordable for the furniture manufacturers. The properties and utilization of
rubberwood have been studied since the 1950’s, but the commercial utilization of wood
only began in the late 1970’s (Hong et al. 1994). Rubberwood is primarily used for
furniture making due to its, light and even texture, suitable strength, good machining and
processing properties (Hong and Sim 1994, Tee 1990). Rubberwood is also extensively
used for manufacturing particleboard, blockboard, medium density fiberboard and
cement-bonded particleboard (Hong and Sim 1994). Despite the rapid expansion of the
rubberwood industry, about 67% of the total rubberwood obtained from rubber
plantations are still used as fuelwood (Lew 1992).

Rubberwood is classified as non-durable and does not produce visible heartwood
(Wong 1988, Jantan and Tam 1987, Thomas and Landon 1953). Rubberwood is highly
susceptible to sapstain, mold and decay fungi (Tsunoda et al. 1983, Wong 1988). The
current use of rubberwood for making furniture and related products does not warrant
protection against decay fungi.

Forest land area in Southeast Asia has been in continual decline due to
agricultural conversion and urbanization. Thus, the future wood supply will increasingly

rely on forest plantations. The cost of establishing forest plantations is high, but some 9

40

million hectares of existing rubber plantations in Southeast Asia could produce 19 million
m3 of wood annually (Ser 1990). The supply is sustainable and is relatively low cost as it
is a by-product of rubber industry (Ismariah and Norini 1994). The utilization of
rubberwood can supplement the wood supply.

Using rubberwood for general outdoor application will depend on the ability to
effectively protect against decay and insect attack. Copper-chromium-arsenic (CCA) type
C wood preservative is a cheap and broad-spectrum pesticide that leaves wood paintable
after treatment. Treatability of wood with CCA type C is influenced by its permeability,
which is a function of anatomical structure (Nicholas and Siau 1973).

Permeability in the longitudinal direction is usually several thousand times greater
than in the transverse direction due to the vessels and fibers, and the pits arrangement on
the cell walls (Nicholas and Siau 1973). Hardwood permeability is generally higher in the
radial than in tangential direction although there are some exceptions (Hunt and Garrat
1953, Rudman 1965, 66). Variability in transverse penetration may be attributed to the
proportion of ray parenchyma (Siau 1984) and the presence or absence of aspirated pits.
A pre-treatment steaming may help in dissolving water soluble deposits in ray
parenchyma or weakening the adhesion between the pit membrane and overarching
border in the aspirated pits. The objective of this study was to determine the influence of
anatomical orientation, pre-treatrnent steaming and pressure duration on the treatability of

rubberwood.

41

4.2 Materials and Methods
4.2.1 Wood samples

Samples of sodium pentachlorophenol (NaPcP)-treated and kiln-dried
rubberwood (50 x 50 x 800 mm) from a 30-year-old Malaysian plantation were quarter-
sawn to 35 x 35 x 125 mm defect-free and uniform grain wood blocks. A set of 75 end-
matched blocks was prepared for modified full-cell treatment and another set of 25 end-
matched blocks was used for pre-treatment steaming. The blocks were labeled and
conditioned to constant weight at 20°C and 70% relative humidity. The average moisture
content (MC) before treatment was 10 i: 2% and average air-dry density was 670 kg/m3

(41.8 lb/fi’).

4.2.2 Pre-treatment steaming
A set of 25 end-matched blocks was autoclaved at 250°F (120°C) for 4 hours and

then conditioned for 10 to 14 days until the MC was about 10 :1: 2%.

4.2.3 Anatomical direction

Selected block surfaces of pre-treatment steamed and unsteamed blocks were
sealed with SCS 1200 GE Silicon Rubber Adhesive Sealant to permit chemical
penetration only in one or two anatomical directions. Unseal blocks allows preservative
penetration from all directions. End-seal blocks allow both tangential and radial
penetration while end- and radially-seal blocks expose only the tangential surface. End-

and tangential-seal blocks expose the radial surface permitting penetration in the

42

tangential direction. Sealing all four edges and leaving the end or the transverse surface

expose allows longitudinal penetration. Five replicates were used for each surface.

4.2.4 Pressure treatment

Pressure treatment of blocks used a modified full-cell process. The treating
schedule included an initial vacuum of 25 in Hg for 30 minutes followed by 1240 kPa
(180psi) pressure for 1, 2, or 4 hours, and a final vacuum of 85 kPa (25 in Hg) for 10
nrinutes. A 50% stock solution of CCA-type C from Hickson Corporation was diluted to
2% CCA. The actual concentration of CCA was determined by Atomic Absorption
Spectroscopy (AAS) and the oxides was calculated according to AWPA Standard A2-96
(1998). The concentration of 003, CuO, and A5205 used were 0.90, 0.41, and 0.66%,
respectively. For pre-treatment steamed blocks, the duration of pressure applied was 1

hour.

4.2.5 Determination of CCA retention

Each block was weighed before and after treatment to determine preservative
uptake. The retentions were determined on the basis of net weight gain after treatment,
using the actual solution concentration, the volume of the block according to the

following expression

Where R is the retention in kg/m3, G the net weight gain after the treatment in grams, and

C the concentration of CCA solution in percent, and V the volume of block in cm3.

43

The CCA retention was determined in the assay zone of the outer 13 mm-tlrick
portion of the blocks. The chemical analysis was performed according to AWPA
Standard A7-93 (1998). The retentions of chromium, copper and arsenic were expressed

on oxides basis then converted from a weight percent to kg of preservative per m3 wood

based on the measured density.

4.2.6 Determination of CCA penetration
CCA-treated blocks were air-dried for 14 days before been then cut in two halves.

The freshly cut surfaces were sprayed with 0.5% chrome azurol-S to reveal the presence
of copper at 2 25 ppm concentration (AWPA Standard A3-97, 1998). The penetration of

depth of copper in mm was obtained by measuring the depth of the colored area with a

digital caliper.
The penetration of CCA was assessed according to its penetration direction. The

radial and tangential penetrations were determined by measuring preservative penetration

at right angle to the block edge or face. The maximum penetration for both directions was

set as the half of the width or length of the treated blocks.

The percentages of preservative penetration in each block were measured by
t1Ticing the penetration pattern on tracing paper and redrawing the pattern on graph paper

The areas covered by the penetration pattern over the total cross-sectional area of each

b10ck were expressed as percentage.

4.3 Results and Discussion
4.3.1 Retention and penetration

Average values of retention, maximum penetration and percentage rating of cross
section penetrated for rubberwood are listed in Table 5. Observations of penetration
patterns of unsealed blocks due to pressure show that some sections were penetrated
completely. Others were penetrated only in the outer shell, and some had patchy
penetration. Full penetration of unsealed wood blocks was achieved by applying 4 hours
of pressure and the retention (13.3 i 0.6 kg/m3) was well above that recommended for
most applications as specified in the Malaysia Standard MS 360 (1991).

Hong et al. (1982) reported that complete penetration of CCA was achieved in 5
cm thick of rubberwood board with an average retention of 16 kg/m3 after 2 hours of full-
cell treatment. The concentration of the CCA treating solution used was not reported.
Hiziroglu (1997) reported CCA retention of 32.6 kg/m3 for CCA in rubberwood using a
5% CCA treating solution in a 4-hour treatment schedule at room temperature with 2
hours of pressure. Higher CCA retention may be achieved with increase concentrations
although special care should be given to the viscosity and the fixation rate of chromium
in such treatment. Treatment parameters such as duration and level of initial and final
vacuum, concentration of CCA, and pressure level and duration may significantly affect
the retention and penetration of preservatives.

Increased in retention and penetration values with increase pressure duration
suggests that pressure duration is an important parameter in the treatment of rubberwood.

Acidic solutions like CCA with pH varying from 1.5 to 3.0 can hydrolyze hemicellulose

45

89383 :50 8:885 ..

 

 

 

QR an 36 SK 32 .2 v 3.0
gm 0.2 New mac ode .3 N Bahama 55%
Se 3a «A... ”.8 e. a 3:83.235 no.5 co owsfiea
SA 3 ca 4.3. 36 .3 _ omega.
ode 3 ca «.2 .02 .5 v
34 3 ed as 2: .5 N
m.wm wd N.N_ and _ «WE .Efigfimdi A880 newshound
m.mm QN New :4 wd .E _ 8:2:er omega.
9: 3 2: o.: nu 5:.
E: S. 2: 2: on .2 N
E 2 an 3 2: _.: accesses A Ewes
md N.~ cs md ad .3 ~ 53:82 owfio><
3:8.st
accede: avenge :35 ea 33. 8826 .2 oases
baa—ta 22m

 

dog—cm 0-<00 o\oN .23 @285 6002398 5 cougocom was 83:88 05 co 5:85 83.8.:— 00 Soho 2E. .m 032.

46

(Winandy et al. 1983). Kamdem and Chow (1999) reported a 33% strength reduction in
CCA-treated hardwoods, which was attributed to the hydrolysis of hemicellulose.

The effect of anatomical direction on penetration and retention was obvious
(Table 5). Copper penetrated deeper in longitudinal direction than in the radial and
maximum longitudinal penetration was achieved after 4 hours of pressure. The cross-
sectional coverage was about 97%. Complete penetration and cross-sectional coverage
was observed in longitudinally penetrated blocks treated for 4 hours.

Penetration in longitudinal direction was almost identical to that of unsealed
blocks indicating that the longitudinal penetration was the dominant flow path in
rubberwood. In hardwood species, without tyloses, penetration in the longitudinal
direction is usually greater than in the radial and tangential direction because vessel
elements provide a flow path (Nicholas and Siau 1973; Greaves 1974; Siau 1984).

Transverse direction penetration results showed that radial and tangential
permeability were not similar. Retention and penetration in the radial direction was about
2 times greater than in the tangential direction (Table 5). Retention and penetration values
in the radially penetrated blocks were similar to those of end-sealed blocks, indicating
that radial penetration is more important than tangential penetration in rubberwood.

Radial permeability is generally attributed to the ray cells (Nicholas and Siau
1973; Siau 1984). The role of rays as penetration pathways in hardwoods varies. Hunt
and Garratt (1953) stated that ray cells in hardwoods do not assist penetration and
suggested that lateral movements are carried out by parenchyma. Rudman (1965, 1966)
observed that liquids of different polarities did not penetrate ray parenchyma of

Eucalyptus. Other studies have shown that hardwood rays are penetration pathways.

47

Hayashi et al. (1967) mentioned that rays of three Japanese hardwoods achieve good
penetration. Greaves (1974) found that ray tissues play a significant role in the
distribution of CCA in F agus sylvatica , Eucalyptus regnans and E. maculata. A more
recent study but Maturbongs and Schneider (1996) showed rays of 10 non-durable
Indonesian hardwoods are well penetrated by CCA after pressure treatment.

CCA retention in the O to 13 mm assay zone of end-sealed blocks and function of

the pressure duration during the treatment are listed in Table 6. End-sealed samples were

Table 6. The effect of pressure duration on the average chemical retention in the assay
zone (0 — 13 mm) of end sealed rubberwood samples.

 

 

Pressure duration Chemical retention (kg/m3, oxides basis)*
1 hr. 8.4
Pre-steam/ 1 hr. 10.2
2 hr. 11.8
4 hr. 15.8

 

* The chemical retention was obtained by multiplying the measured density by the
percent oxide determined by using AAS (AWPA Standard A7-93, 1998).

used in assaying the CCA in the outer 0 to 13 mm in order to minimize the longitudinal
penetration and exhibit a transverse penetration. The Malaysia Standard MS 360 (1991)
on pressure treatment of hardwood lumber with CCA specifies retention of 8 kg/m3 and
12 kg/m3 in the 0 to 12 mm assay zone for C5 and C4 commodity for above ground and
soil contact, respectively. The retention value of 15.8 kg/m3 CCA oxides for end-sealed
blocks after 4 hours pressure treatment satisfies the retention requirements for C4
commodity (MS 360 1991). C4 commodity is for ground contact application such as

railway sleepers, bridge decking, fence and gardening posts and stakes.

48

One-hour pressure duration was sufficient to satisfy the C5 commodity
requirement. Thus a 4 hours pressure treatment may be unnecessary. Two hours of
pressure resulted in 11.8 kg/m3 CCA retention in the 0 to 13 mm assay zone, satisfying
the C5 and C4 requirements. Subj ecting rubberwood to pressure treatment for more than
2 hours and less than 4 hours would result in satisfying C4 and C5 requirement (MS 360,

1991).

4.3.2 Effect of pre-treatment steaming of wood blocks

Full penetration was observed in unsealed and end-sealed blocks. The penetration
was improved by about 2.9 times for radial and tangential direction. The CCA retention
was improved from 9 to 73% depending on the direction of penetration. The chemical
retention was improved by 21% in end-sealed blocks (Table 6).

Pre-treatment steaming improved longitudinal permeability by 150%. It was
reported earlier that longitudinal permeability was increased in black walnut after
steaming at 210°F (100°C) prior to treatment (Chen 1975). In pre-treatment steamed
blocks, CCA penetrated deeper in both radial and tangential direction. The pre-treatment
steaming appears to improve lateral penetration. Retention was increased by 33% in
radially and 73% in tangentially penetrated samples. Increase in lateral penetration after
pre-stearning of wood was also observed in red oak (Simpson 1976). The chemical
retention was also increased by pre-treatment steaming (Table 6).

The mechanism responsible for increase permeability after steaming is not well
known. Simpson (1976) suggested that pre-treatment steaming of the wood caused the

cell walls and/or pit membrane to crack or check, and help in removing the encrusted

49

material in the pit membrane. Chen and Workman (1980) also mentioned the increase in
permeability caused by the removal of the encrusted material during pre-treatment
steaming. Their study showed that during steaming some of the water-soluble extractives
were removed and resulted in improved permeability of black walnut.

Nicholas and Thomas (1968) suggested that steaming affected pit aspiration. The
aspirated pits after a pre-treatment steaming formed weaker bond between torus and cell
wall, resulting in improved treatability. Further study is underway to assess the detail
effect of pre-steaming parameters such as different pre-steaming duration, pre-steaming
temperature, and pressure duration. The assessment on the effect of pre-steaming on the
wood mechanical and physical properties is necessary since pre-steaming can impact the

mechanical properties of wood.

4.3.3 Gradient retention of Cr, Cu and As

Average elemental retention values for outer and core sections of end-sealed
block are presented in Table 7. The amount of Cr, Cu, and As retained in the core section
was less than outer section. However, result of pre-treatment steamed and unsteamed
blocks did not show much differences in the retention of Cr, Cu, and As between the
outer and core section. The average Cr, Cu, and As retention for outer pre-steamed blocks
are 2.3 kg/m3, 1.8 kg/m3, and 2.3 kg/m3, respectively. Comparable values were obtained
for pre-steamed core samples.

The retention trend of Cr, Cu, and As between outer and core sections are
illustrated in Figure 9. The retention of Cr, Cu, and As of pre-treatment steamed blocks

are higher than and unsteamed blocks. In the core zone, an apparent improvement in the

50

retention of Cr, Cu, and As in pre-treatment steamed blocks can be observed. Retention
of Cr, Cu, and As in pre-steamed blocks of treated with 1 hour pressure surpasses the
retention values in unsteamed blocks treated with 2 hour pressure. This further
emphasized the improvement of CCA penetration and retention in pre-treatment steamed

rubberwood blocks.

Table 7. Average retention of Cr, Cu, and As in the outer (0-13) zone and core of end-
sealed 2% CCA-treated rubberwood blocks.

 

 

 

 

Pressure Outer (kg/m3) Core (kg/m3)
duration

Cr Cu As Cr Cu As
1 hr. 1.9 1.4 1.9 0.7 0.5 0.7
Pre-steam/ 1hr. 2.3 1.8 2.3 2.1 1.7 2.1
2 hr. 2.8 1.8 2.7 1.8 1.2 1.8
4 hr. 3.8 2.5 3.4 2.8 1.8 2.5

 

CCA retention and penetration increase as the pressure duration increased. Full
penetration of unsealed wood blocks was achieved by applying 4 hours of pressure. It
was reported that using two hours of pressure full penetration of CCA was achieved in 5
cm thick rubberwood samples. However, this study showed that two hours of pressure
resulted in only about 63% of the cross section penetrated with CCA in the end sealed
samples of 3.5 cm thick samples.

Retentions in the unsteamed rubberwood blocks treated with different pressure
duration were usually lower than pre-treatment steamed blocks. Pre-treatrnent steaming
resulted in the improvements of Cr, Cu, and As retentions in the outer and core zone of

rubberwood blocks.

51

 

 

 

 

Dlhr.

IPre-steam/l hr.

.2 hr.

Ill4 hr.

 

 

 

3.5 i

 

.2... \ 55.... .......\.\,\, ...\\ . \H\.\\\\\\\\c\\u\.\\.vw\a \ .
4. g...“ >5... v... \\\..\..t\\\.w....\x..%\uw.\xfi\\\q M .

As

 

,, L 5

Core

  

.M,,.,.,\....... ,. ,....\.,,\.,.. H..,_.\...\ .. mix. \\\\\.w.\...\\m\\\\\\\\x\5v 3.
x x .. \\\\\\&\\\\\.\N\\\x ,
, u , , L , ,

Cr

  

_, 5 w. . \\\\\5\v\\\\5\\\\\\\\\\\\\\\\\\\\\\\\\\5\\\\\w

 

Outer

 

 

fl _ q

4
3 5 2 5 l 5 0

$8th cows—88 Egan—m

 

 

Figure 9. Average Cr, Cu, and As retention by outer and core zones of 2% CCA-

treated rubberwood.

52

CHAPTER 5
LABORATORY EVALUATION OF THE NATURAL DECAY RESISTANCE

AND THE EFFICACY OF CCA-TREATED RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG).

5.1 Introduction

The opportunity for increasing the utilization of rubberwood is highly dependent
on the efficacy of the preservatives that will protect against biodegradation. Currently
CCA preservative has been shown to be effective in protecting some Malaysian
hardwoods species such as Koompassia malaccensis, Dipterocarpus spp., Shorea
leprosula, Shorea talura, and Drypbalanops spp. for exterior use (Jantan et al. 1994;
Aston 1985). Few studies were done on the natural decay resistance and the performance
of CCA-treated rubberwood.

The retention and penetration of CCA in rubberwood was established (Chapter 4).
The retention and penetration are established as function of protection. CCA-treated
cubes were tested against pure monoculture of [max lacteus, Trametes versicolor,
Gloeophyllum trabeum, Postia placenta, Chaetomium globosum and Phialophora sp.

after 12 weeks of incubation, using laboratory soil block test.

5.2 Materials and Methods
5.2.1 Sample preparation

Six 30—year-old rubber trees from a Malaysian plantation located at Kota
Samarahan, Sarawak were felled. The logs were sprayed with sodium pentachlorophenol

(N aPCP) to protect against mould and insect attacked. The logs were quarter-sawn to 50

53

x 50 x 800 mm boards and kiln-dried prior to shipment to East Lansing, Michigan, USA.
No attempt was made to separate the wood into sapwood and heartwood since the volume
of heartwood in rubber trees is negligible. The boards were further planed, ripped and cut
into 19 mm cubes. The cubes were conditioned at 20°C and 70% relative humidity until
they reached a constant weight. The average moisture content (MC) and the air-dried
density of the cubes before treatment were averaged at 6 :t 2 % and 670 kg/m3,

respectively.

5.2.2 Sample treatment

A 50% stock solution of CCA type C (CCA-C) obtained from Hickson
Corporation, Conley, Georgia was diluted with water to 1%, 2% and 3% total oxides and
used for treatment. The actual strength of CCA solution (total oxides) was determined by
using Atomic Absorption Spectroscopy (AAS). The cubes were treated with the three
different CCA solution strengths via a modified full-cell process. The control cubes were
pressure-treated with distilled water. The treatment schedule involved an initial vacuum
of 85 kPa for 30 minutes followed by 1240 kPa of pressure for 1 hour and a final vacuum
of 85 kPa for 10 minutes. Treated samples were blotted with paper towel and weighed to
determine the weight of the treating solution absorbed. Treated samples were stored in
conditioning room kept at 20°C and 68% relative humidity for 4 weeks.

After 4 weeks of drying in the conditioning room, the cubes were then
conditioned at 40°C in an oven to a constant weight. The treated and conditioned cubes
were weighed prior to the sterilization of the cubes. Cubes were sterilized by using

gamma irradiation according to the procedures describe in AWPA ElO-9l (1999).

54

5.2.3 Chemical analysis

Chromium, copper, and arsenic concentrations in treated cubes were determined
with atomic absorption spectrometer (AAS). Wood samples were digested in perchloric
acid according to the AWPA 97-93 (1999) standard. Chromium, copper, and arsenic
concentrations in the digested sample solution were determined by AAS. The retentions
of chromium, copper, and arsenic, expressed as oxides, were calculated based on
measured density of the treated samples in kg/m3. Table 8 contains the CCA retention
determined by weight difference and chemical analysis of CCA-treated rubberwood

blocks.

Table 8. Average CCA and copper retention from CCA-treated rubberwood blocks.

 

 

CCA solution CCA retention by CCA retention in Copper retention in
strength weight gain wood by AAS wood by chemical
determined by analysis and AAS
AAS (kg/m3) (kg/m3) (kg/m3)

(%)
Control (untreated) 0 0 0

0 0 0 0

0.93 5.18 4.12 0.97

2.12 13.24 10.54 2.68

3.29 20.90 14.48 3.57

 

5.2.4 Fungal exposure

The cubes were evaluated for resistance to attack by the white-rot decay fungi
Irpex lacteus Fries (PP-105915) and Trametes versicolor (L. ex Fr.) Pilat (R-105), the
brown-rot fungi Gloeophyllum trabeum (Pers. Ex Fr.) Murr (Madison 617) and Postia
placenta (Fries) M. Larsen et Lomb.(Madison 698), and the soft-rot fungi Chaetomium

globosum Kunze (ATTC 32237) and Phialophora sp. (ATTC 66725) by a slightly

55

modified soil-block test as described in AWPA standard method BIO-91. Polycarbonate
boxes of 400 m1 volume from Sigma Inc. were filled with 95 g of forest soil of about 70
percent MC. The forest soil was first screened for roots and other wood debris. Then the
soil clumps were broken into particles and passed through No. 6 sieve and stored in
plastics bag.

An aspen feeder strip measuring 3 x 25 x 30 mm was placed above the soil in
each box and then the boxes were autoclaved for one hour at 121°C. The boxes were then
inoculated with an agar plug cut from the edge of actively growing colony of the
appropriate test fungus. Culture boxes were incubated until the fungus covered the feeder
strips. Boxes with vigorous fimgus grth without contamination were selected for the
soil-block test. Treated and conditioned wood cubes were weighed prior to sterilization
using gamma irradiation. Sterilized cubes were aseptically placed on the feeder strip with
end exposed to the feeder strips. Twelve sterilized cubes from each treatment were used
for each decay fungus. Untreated and distilled water-treated cubes were included for
reference. Sterilized reference and treated cubes were placed in uninnoculated culture
boxes to determine the operational weight loss of the samples. The cubes were incubated

at 25°C and 75% relative humidity for 12 weeks.

5.2.5 Determination of weight loss

The degree of fungal attack was estimated by determining the weight loss after 2,
4, 6, 8, 10, and 12 weeks. Test cubes were removed from the boxes and the mycelium
was wiped with soft foam from the cube surfaces. Every two weeks five replicates per

sample treatment and per decay fungus were removed and their MC and weight loss were

56

determined. The clean cubes were dried in an oven set at 40°C to a constant weight. The

weight loss due to decay was calculated and expressed in percentage as follow:

Initial weight - Final weight
Initial weight

Weight loss (WL), % = x 100

 

Where;
Initial weight = Weight of conditioned cube prior to fungal exposure.
Final weight = Weight of conditioned cube afier fungal exposure.
To determine the cube MC afier decay, the cubes exposed for 2, 4, 6, 8, 10, and

12 weeks were weighed immediately after removal from culture boxes. The MC of each

cube was calculated as:

Weight of decay cube from box - Final weight
Final weight

x 100

 

Moisture content (MC), % 2

Where;
Weight of decay cube from box = Weight test cube immediately after removal
from box and after mycelium has been wiped.
Final weight = Weight of conditioned cube after fimgal exposure.

All data were subjected to statistical analysis.

5.2.6 Statistical analysis

Simple linear regression analysis was conducted to determine the relationship

between the weight loss and the incubation duration for each fungus. Covariance analysis

was used to determine whether the difference was statistically significant among the

57

coefficients. The incubation duration was used as covariate for the analysis of covariance
of the weight loss.

One-way AN OVA was used to compare and determine any significant difference
of weight loss and the CCA retention of treated samples exposed to a laboratory soil
block test. Tukey multiple comparison tests were used to further analyze the variation of

weight loss between treatments of different fungi using SYSTAT (SYSTAT 1996).

5.3 Results and Discussion
5.3.1 Relation between moisture content and weight loss

Fungus colonization of wood is reported to occur at moisture content around 20%
(label and Morell 1992; Eaton and Hale 1993). The optimal moisture levels for growth
of most decay fungi in laboratory evaluation lie between 40 and 80% (Scheffer 1973).
The moisture content in untreated test cubes exposed to different fungi for 12 weeks
show different trend for different decay type as shown in Table 9.

The moisture content in cubes exposed to white and brown rot fungi are in the
range of 44 to 87%, in agreement with Scheffer (1973). The MC of cubes exposed to
white rot, particularly [max Iacteus, increases with weight loss. However, the MC of
cubes exposed to brown rot showed a decreasing trend with weight loss. According to
label and Morell (1992), the reduction in MC associated with brown-rot attack is due to
the destruction of the cellulose. White rot decay fungi decompose lignin with little
cellulose modifications. Lignin is more hydrophobic than cellulose. This explain why

after white rot attack sample exhibit a higher moisture content compared to brown rot.

58

Table 9. Average biweekly moisture content (%) of untreated rubberwood cubes exposed
to different decay fungi for 12 weeks.

 

 

 

White rot Brown rot Sofi rot
Week Imax T rametes Gloeophyllum Postia Chaetomium Phialophora
lacteus versicolor trabeum placenta globosum sp.
2 49.7 43.9 86.9 70.7 39.0 27.9
(5.7)1 (17.1) (6.3) (9.1) (9.0) (5.4)
4 50.3 52.5 71.2 76.7 44.3 27.1
(5.7) (24.7) (1 1.6) (15.2) (8.5) (2.4)
6 54.4 65.2 75.9 64.2 46.2 41
(8.9) (17.2) (6.6) (12.3) (3.3) (16.7)
8 57.0 63.2 66.7 65.6 52.4 40.0
(14.8) (7.69) (10.4) (10.5) (5.9) (11.1)
10 57.0 63.2 66.5 54.9 48.4 41.6
(12.0) (1 1.0) (10.7) (10.5) (6.4) (7.9)
12 67.0 65.3 47.3 49.8 53.3 41.4
(15.5) (3.3) (5.5) (4.0) (7.6) (5.5)

 

IValues in parenthesis is the standard deviation of the mean.

For cubes exposed to soft-rot, the MC appears to increase as decay progresses.
Eaton and Hale (1993) stated that wood permeability increases as of soft rot cavity in
wood developed. Thus this explains the increasing MC in cubes exposed sofi-rot. High
level of MC not only supports the growth of soft-rot fungi, but also it increases the

availability of nutrients particularly nitrogen (Eaton and Hale 1993).

5.3.2 Natural decay resistance
The average WL of untreated rubberwood blocks due to decay afier 12 weeks
exposure are given in Table 10. Average weight losses of about 61 % were obtained after

12 weeks exposure to white (Imex lacteus and Trametes versicolor) and brown rot

59

(Gloeophyllum trabeum and Postia placenta). According to ASTM standard D 2017-81
“Standard Method of Accelerated Laboratory Test of Natural Decay Resistance of
Woods” an average weight loss of 25 to 44% is classified as moderately resistant.

Table 10. Average weight loss (%) of untreated rubberwood cubes exposed to different
decay fungi for 12 weeks.

 

 

Week White rot Brown rot Sofi rot
Imax T rametes Gloeophyllum Postia Chaetomium Phialophora
Lacteus versicolor trabeum placenta globosum sp.
2 3.2 2.1 3.9 0.9 1.0 1.4
4 8.4 12.3 16.9 5.5 2.3 4.9
6 19.5 23.4 24.1 13.0 6.7 9.7
8 27.4 33.6 33.8 31.6 20.1 19.2
10 44.3 40.4 42.2 39.4 27.6 26.6
12 63.2 61.8 61.4 59.1 35.9 39.5

 

Weight loss higher than 45% is classified as slightly resistant or nonresistant. Average
weight loss of 63.2% with [max lacteus and 61.8% with T rametes versicolor are
obtained after 12 weeks of incubation (Table 10). As for brown rot average weight losses
of 61 .4% and 59.1% were obtained with Gloeophyllum trabeum and Postia placenta,
respectively. According to ASTM criteria, rubberwood is nonresistant.

Findlay (1985) classified laboratory weight loss of 30% and higher as perishable,
which corresponds to the service life less than 2 years in tropical conditions and
maximum 5 years under temperate conditions. In some tropical countries the term
perishable is not used and non-durable or not durable is used to describe this class
(Findlay 1985, Eaton and Hale 1993). In this case moderately durable is used to describe

service life of 2 to 5 years and that correspond to weight loss between 10 and 30% in

laboratory evaluation.

60

In this study the susceptibility of rubberwood to white rot and brown rot is
identical. It has been reported that hardwood is relatively susceptible to white rot in field
test (Schultz and Nicholas 1997). In laboratory testing the samples are exposed to pure
fungus culture, with no or negligible competition and under artificial microbial
ecosystem. In rubber plantations, white rot fungi (Rigidoporous lignosus, Phellinus
noxius, Lenzites palisotii, Ganoderma applanatum) were reported to cause major damage
to rubber trees (Geiger et al. 1986; Sujan et al. 1980).

The highest weight losses after 12 weeks of incubation were observed with white
rot fungi, Imax lacteus (63%) and Trametes versicolor (62%) followed by brown rot,
Gloephyllum trabeum (61%) and Postia placenta (59%) and the lowest weight losses
were achieve with soft rot Phialophora sp. (40%) and Chaetomium globosum (36%).
White and brown rot weight losses were about 1.5 times higher than soft rot after 12
weeks of incubation. The slower decay rate of sofi rot fungi has been explained by the
lack of nutrients particularly nitrogen (Butcher and Drysdale 1974). Anagnost and Smith
(1997) reported a significant increased in weight loss due to Chaetomium globosum upon
addition of nutrient solution consisted of 1.5g/L NH4N03, 2.5 g/L KH2P04, 2.0 g/L
K2HPO4, 1.0 g/L MgSO4-7HzO, 0.1 mg/g thiamine and 2.5 g/L glucose at 8‘“ week of

incubation period.

5.3.3 Relationship between weight loss and incubation period
Simple linear regression equations for all decay fungi are summarize in Table 10.
Linear relationship exists between weight loss and incubation period. The coefficients of

determination (r2) range from 0.87 to 0.96 for all test fungi. The rate of decay of

61

rubberwood exposed to decay fungi used in this study significantly increased with
incubation period. The equations (Table 11) is only valid for the incubation period of 2 to
12 weeks and with the conditions used in this study.

The regression equations for brown rot and white rot were almost identical (Table
10). The slopes ranged from 5.3 to 5.9 and intercept from — 6.7 to —13.0. The highest
slopes were observed with weight loss due to [max lacteus (5.9). Postia placenta had the
next highest slope (5.87) followed by Trametes versicolor (5.6) and Gloeophyllum
trabeum (5.32). The soft rot fungi appeared to have lower regression slope than white and
brown rot fungi, which indicates that the their rate of decay was much slower than white
and brown rot.

Covariance analysis was carried out to determine the differences between the
regression equations in Table 11. The analysis revealed that differences for slope and
intercepts are significant at 1% level.

Table 11. Regression equation of WL (%)I vs duration (t)2 of rubberwood exposed to
decay fungi.

 

 

 

Coefficient of
Fungi Regression equation determination P3
(r’)

White rot

Imex lacteus WL (%) = 5.94*t — 13.00 0.90 **

T rametes versicolor WL (%) = 5.60*t — 10.31 0.96 **
Brown rot

Gloeophyllum trabeum WL (%) = 5.32*t — 6.67 0.96 **

Postia placenta WL (%) = 5.87*t -16.12 0.94 **
Sofi rot

Chaetomium globosum WL (%) = 3.77*t — 10.8 0.87 **

Phialophora sp. WL (%) = 3.79*t — 9.62 0.90 **
1 Weight loss in percent

2 Incubation periods in week
3 Significant at 1% level

62

5.3.4 CCA efficacy

Weight losses of CCA-treated rubberwood exposed to [max lacteus, Trametes
versicolor, Gloeophyllum trabeum, Postia placenta, Chaetomium globosum, Phialophora
sp. and no fungus (or operational weight loss) are summarized in Table 12. Operational
weight loss is defined as the weight loss associated with variation of equilibrium moisture
content of treated samples before exposure (AWPA 1999). The operational weight loss in
this study varies from 0.5 to 1.8%.

Treatment of rubberwood at CCA retention of 4.1 kg/m3 resulted in significant
reduction in weight loss (Table 12). The increase in CCA retention from 4.1 to 10.5
kg/m3 has reduce the weight loss due to decay by [max lacteus (2.8%), Trametes
versicolor (2.0%), Postia placenta (3.3%) and Phialophora sp. (3.1%). At retention of
14.5 kg/m3, the weight loss was similar to the operational weight loss, which indicates
that no significant fimgal attack occurred at 14.5 kg/m3 retention. The threshold values
(Table 13) shows that higher CCA retention is needed to control brown rot, followed by
white rot and then soft-rot. A study by Kamdem et al. (1996) also found that brown rot
fungi needed higher copper content, followed by white rot and soft rot for the protection
of northern white red oak (Quercus rubra) and soft maple (Acer rubrum) with water-
borne copper naphthenate.

This laboratory study showed that CCA-C could be used as preservative to
prevent rubberwood from decay fungi. Minimum retention of 14.7 kg/m3 is required

rubberwood against all test fungi. Field test is necessary to validate this result.

63

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64

Table 13. Estimated threshold retention values of CCA type C
for rubberwood using intercept method (AWPA E10—91).

 

 

Fungus CCA-C retention
(kg/m3)
[max lacteus 13. l
T rametes versicolor 12.8
Gloeophyllum trabeum 14.7
Postia placenta 13.8
Chaetomium globosum 13.1
Philophora sp. 12.3

 

65

CHAPTER 6

MICRODISTRIBUTION OF COPPER-CHROME—ARSENIC
PRESERVATIVE IN THE CELLS OF RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG.)
6.1 Introduction

It is well known that preservative effectiveness depends not only on the amount of
uptake or retention, but also upon the preservative distribution in the wood cells. The
efficacy of preservatives is also the function of its permanence in wood. The performance
of CCA in protecting softwoods both in laboratory evaluation and field tests is well
established and it is attributed to the deep penetration into the cell wall of tracheids of
Pinus species (Petty and Preston 1968), the preservative loading (Ryan and Drysdale
1988), the uniform preservative distribution in wood cells (Bodner and Pekny 1991;
Dickinson and Sorkhoh 1976; Greaves 1972), and within the cell wall (Newman and
Murphy 1996). In hardwoods, the poor performance of CCA has been associated with
uneven distribution of CCA components in hardwoods cells and within the cell wall
structure (Greaves 1972, 1974; Dickinson 1974; Butcher 1979).

Some hypotheses have been put forward to explain the poor performance of CCA-
treated hardwood. The gross anatomy of hardwoods and softwoods are different.
Hardwood species are composed of mainly fiber (15-60%), vessel elements (20-60%),
rays (5-30%), and parenchyma (0-24%) (Haygreen and Bowyer 1996). The vessel
elements function as conduction of liquids while fibers are responsible for mechanical
support. Hardwood fibers possess a few slit-like simple pits (Greaves 1974). Liquids are
reported to flow through open vessels, which form continuous pathway (Wilkinson 1979;

Siau 1984). Liquids move in the surrounding cells, through the pits into cell lumen.

66

Softwoods are composed of 90-95% tracheids, and the remaining 5-10% is make
up of ray cells. Tracheids are thin wall conducting cell with rounded ends and numerous
bordered pits. Hardwoods are composed of cells with thick cell-wall fiber, which
influence the penetration of preservative solutions into cell wall (Greaves 1974;
Wilkinson 1979; Siau 1984;).

The differences in chemical make-up of hardwoods and softwoods may affect the
permanence of preservatives in wood. Generally, softwoods have generally higher lignin
content that hardwood (Haygreen and Bowyer 1996). Softwoods lignin contain mostly
guaiacyl group whereas most hardwoods lignin contain syringyl and guaiacyl group. It
has been reported that CCA preferentially react with guaiacyl lignin (Daniel and Nilsson
1987). Softwood species with higher lignin content will be more reactive with CCA than
hardwood species.

The location and distribution of metal elements in copper-based treated wood is
reported to influence performance (Chou et al. 1973; Greaves 1978; Bodner and Pekny
1991). The uneven distribution of copper is suggested to be the cause of poor
performance of CCA-treated hardwoods against soft-rot. Soft rot fungi are known to
attack CCA-treated refractory hardwoods species. Uneven distribution of copper in S;
layers of fibers may explain soft rot decay in CCA-treated wood (Greaves and Levy
1978; Greaves and Nilsson 1982; Greaves et al. 1982). Some studies have pointed out
that an even distribution of copper in wood cell of hardwoods will still remain susceptible
to soft-rot decay (Butcher 1979; Drysdale et al. 1980; Ryan and Drysdale 1988). High
copper loading in CCA-treated hardwoods is required to protect against soft-rot decay.

Ryan and Drysdale (1988) reported that increasing CCA retention could control soft-rot

67

attack. Their study showed that it required six fold copper retention in the fibers of Betula
alba than in the tracheids of Pinus radiata. CCA retention of about 32 to 35 kg/m3 was
required to significantly extend the service life of hardwood poles in New South Wales,
Australia (Witheridge 1983). Field test data of CCA-treated Koompassia malaccensis and
Shorea leprosula indicate that service life of these timbers can be extended to 30 years
with a CCA retention of 15 kg/m3.

Numerous studies have been conducted to evaluate the microdistribution of CCA
in hardwoods (Greaves 1974; Dickinson and Sorkhoh 1976; Greaves and Levy 1978;
Greaves et al. 1982; Daniel and Nilsson 1987). Limited information is available on the
factors that may influence the performance of CCA-treated rubberwood. This chapter
reports on the distribution of CCA components in the rubberwood cells, at varying
treating solution strength using scanning electron microscope fitted with X-ray

microanalysis.

6.2 Materials and Methods
6.2.1 Wood treatment

Wood treatment was previously described in chapter 5.

6.2.2 Samples preparation for X—ray microanalysis

Three cubes from each treatment concentration were used. From each cube, two
small strips of l x 3 x 9 mm were cut perpendicular to each other from the transverse
section. The surface of the strips was cut with razor blade (Exley et al. 1974). The

samples were mounted on aluminum stub using double-sided adhesive tape and then

68

coated with a thin layer of carbon using a carbon string evaporator in Emitech K450

sputter coater.

6.2.3 Scanning Electron Microscope — Energy Dispersive X-ray Analysis (SEM-
EDXA)

The SEM-EDXA were performed using JEOL 6400V scanning electron
microscope fitted with Noran Vantage Energy dispersive X-ray system equipped with a
light element detector using a Moxtek window with detection capabilities down to
beryllium. A 20 kV accelerating voltage, 200 uamps, working distance 15 mm, and take
off angle 30° were used to examine the samples. The samples were analyzed for Cr - KCl
5.41 keV, Cu - K0 8.04 keV, and As - K0 10.54 keV. Each X-ray analysis was done at
500X magnification. Spot analyses of fibers, vessels, parenchyma, and rays (Figure 10
and 11) were made at 0, 3, 6, and 9 m depth from the outer surface. Each analysis was
repeated at 10 different spots of a specific cell for 100 second. For each CCA
concentration, three cubes were examined and a total of 30 examination spots on each
wood cell were performed. The data from matched depth from each strip were pooled

giving a total of 120 examination spots on each wood cell.

69

 

Figure 10. SEM micrograph of transverse section showing cell walls of vessel (+1 and +2)
and fiber (+3, +4, +5) used for X-ray spot analyses.

70

 

Figure 11. SEM micrograph of transverse section showing cells of parenchyma (+1 and
+2) and ray (+3, +4) used for X-ray spot analyses.

71

6.2.4 Data handling

The first step in the estimation of the concentration of an element in a specimen is
to measure the specific X-ray counts in a fixed time interval and to compare the specific
X-ray count to the total number of X-ray emitted from the sample in a similar time. The
ratio obtained is called k-ratio and represents approximately the elemental concentration
of the sample. It is an approximation because of some interference due to the matrix as
illustrated in Figure 12. The volume produced by specimen/electron interaction is
dependent on several factors: the accelerating voltage, the beam current, the specimen
density, the specimen atomic number, and the surface angle orientation. Since the
operating conditions are identical, correction is therefore needed for three factors: the
atomic number effect (Z), the absorption (A) and the fluorescence (F). The X—rays data
are expressed as elemental weight percent using the built-in computerized software
PROZOA, which uses ZAF and Phi Rho Z corrections as described in F legler et al.
(1993) and Russ (1984). The ZAF corrections are frequently used for quantitative
analysis of bulk sample. The following equation is used to adjust the k-ratio to get the

concentration (C) of an element (Flegler et al. 1993; Goodhew and Humphreys 1988):

The atomic number correction Z, refers to the adjustment for X-rays differences

due to the Z of samples. The Z correction is combination of stopping power and

backseattering effects.

72

Electron

 

 

 

 

beam
11 v
X Rays
A l/ llll "I
Specimen ” .
thickness Absorption path
3 m
Y
z 4.1 pm
§———>

 

 

Figure 12. A schematic diagram of electron beam/specimen interaction within a bulk
specimen.

73

The absorption effect correction A, is used to adjust for X-rays differences due to
absorption. X-rays produced from deeper portion of the specimen travel through the
specimen thickness and likely will be absorbed before they can escape and be detected
(Figure. 11). The absorption corrections take into account the accelerating voltage, the
take-off angle, the mean atomic ntunber and the mean atomic mass. With thin samples of
less than 0.15 pm the effect is almost negligible. If correction on absorption is not done,
it will underestimate the X-rays produced.

The fluorescence F factor, corrects for secondary X-rays. The X-rays produced
within the specimen may be of high energy capable of fluorescing lower energy X—ray of
another element. This may cause abnormally high counts for the lower energies element.
Although generally considered the least important of the three corrections, secondary
fluorescence could cause errors as large as 15% during analysis of elements of adjacent
atomic numbers (Goodhew and Humphreys 1988).

The Phi Rho Z corrects for the differences of areas of X-ray production. As
incident electron penetrates deeper into the specimen it loses energy. As a result X-rays
are generated from elements with a high Km and elements with a low Kw due to

differences in electron energy as it penetrates deeper into the specimen.

6.3 Results and Discussion
6.3.1 X-ray microanalysis of wood
The volume of wood tissue analyzed in bulk specimen is large. Based on the

operating conditions employed in this study, and using Electron Flight Simulator

74

software version 3.1 (1998) to estimate the volume of specimen-electron beam
interactions, the diameter of the analyzed volume in CCA-treated rubberwood is
approximately 3.6 - 4.1 pm, corresponding to a volume up to 36 m3 (Figure 12). In a
SEM-EDXA study of treated Hinoki (Chamaecyparis obtusa), Yata and Nishimoto
(1983) reported that 20 kV accelerating voltage produced an analyzed volume with a
diameter of 3.6 — 4.5 pm.

The cell wall thickness 4 to 7 pm for fibers, 4.3 to 8 pm for vessels, 2.5 to 4 pm
for rays, and 2.5 to 3.5 pm for parenchyma (Chapter 3), indicate that examination of
fibers and vessels lies well within the cell regions analyzed. For ray, x-ray microanalyses
were within the cell region provided that the widest points are used for analyses. For
parenchyma, X-rays analyzed may include X-rays generated from adjacent regions. Since
the thickness of parenchyma cells and the diameter of specimen-electrons beam
interactions are comparable, it is expected that effect of X-rays generated from adjacent
cells is minimal.

Variability in the X-ray microanalysis of wood in bulk samples is expected. It is
explained by the heterogeneous nature of the biological tissues. Although the operating
and analyses conditions were kept constant, the different types and the density of wood
cells influence the x-ray analyses. Therefore, X-ray microanalysis of biological material
can only be semi-quantitative (Doyle and Ruddick 1994; Greaves et al. 1982; Drysdale et
al. 1980).

The elemental composition of CCA-treated rubberwood from a spot analysis by
SEM-EDXA is listed in Table 14. Hydrogen content is not represented, because hydrogen

does not generate X-rays.

75

Table 14. Elemental composition in percent (%) of CCA-treated rubberwood as obtained
by SEM-EDXA after ZAF corrections.

 

 

 

CCA solution strength by AAS
Element 0.93% 2.12% 3.29%
C 50.46 54.67 55.23
0 41.91 38.68 34.83
N 5.87 3.98 6.12
Na 0.02 0.00 0.00
Mg 0.11 0.15 0.25
S 0.00 0.02 0.03
K 0.01 0.04 0.20
Ca 0.00 0.04 0.17
Cr 0.69 0.81 1.06
Cu 0.24 0.54 0.99
As 0.69 1.07 1.12
Total 100.00 100.00 100.00

 

6.3.2 Chromium, copper, and arsenic in wood cells

The average composition of Cr, Cu, and As from 60 spots of each wood cells is
shown in Table 15. Chromium appeared to be concentrated in the vessels. The
composition of chromium in vessels increased from 1.85% to 4.66% after treatment with
1% and 3% CCA. High levels of chromium were also present in ray cells. The
concentration of chromium in rays was about 1.72% in 1% CCA-treated samples and
increased to 3.32% in 3% treated samples. Fibers have the lowest concentration of
chromium (Table 15).

Copper appeared to be distributed in lower concentration in all wood cells
compare to Cr and As. Among wood cell, vessels recorded the highest concentration of
copper followed by rays, parenchyma, and fibers (Table 15). The concentration of copper

in the vessel was about 1.67% in 1% treated samples and increased to 3.26% in 3%

76

treated samples. Fibers, which constitute the major portion of wood cells in rubberwood

contain the lowest Cu concentration. The concentration of Cu in fibers was only about

0.42%, 0.63%, and 1.02% in 1%, 2% and 3% treated samples, respectively.

Table 15. Comparison of chromium, copper, and arsenic elemental composition in
percent in various rubberwood cells afier treatment with different treating solution

 

 

 

strength.
CCA-C Elemental composition (wt%)
solution Cell type
strength Cr Cu As
(%)
0.93 Vessel 1.85“ (0.34)M 1.67 (0.25) 1.85 (0.50)
Ray 1.72 (0.85) 1.01 (0.50) 1.55 (0.80)
Parenchyma 1.31 (0.28) 0.77 (0.34) 1.12 (0.60)
Fiber 0.67 (0.21) 0.42 (0.25) 0.58 (0.21)
2.12 Vessel 3.55 (0.55) 2.42 (0.37) 3.45 (0.45)
Ray 1.89 (0.95) 1.39 (0.65) 2.47 (0.67)
Parenchyma 1.40 (0.35) 0.88 (0.40) 1.23 (0.54)
Fiber 1.12 (0.35) 0.63 (0.22) 0.94 (0.57)
3.29 Vessel 4.66 (1.08) 3.26 (0.91) 3.73 (1.05)
Ray 3.32 (0.97) 2.47 (0.88) 2.76 (0.99)
Parenchyma 2.39 (0.45) 1.55 (0.66) 2.03 (0.93)
Fiber 1.71 (0.67) 1.02 (0.52) 1.45 (0.52)

 

"‘ Mean of 120 readings
** Standard deviation

Arsenic concentration in wood cells follows closely that of Cr. Concentration of
As was highest in the vessels. Composition of As in vessel was 1.85% in 1% CCA and
increased to 3.73% in 3% CCA. Fibers have the lowest concentration of As, about 0.58%,

0.94%, and 1.45% in 1%, 2%, and 3% CCA, respectively.

77

The uneven distribution of Cr, Cu, and As in different cells occurs regardless of
treating solution strength. Chromium and arsenic appeared to be concentrated in the
vessel (Table 15). High level of chromium was found in rays. Among the three elements,
copper concentration was found to be the lowest in all type of cells. This indicates that
CCA treatment did not result in a homogenous distribution of all three elements
throughout rubberwood structure. Fiber cells have the lowest concentration of Cr, Cu,
and As.

The result showed that microdistribution of CCA components differed according
to cells types. Previous work by Levy and Greaves (1976) and Greaves et al. (1982)
reported that the uneven distribution of Cr, Cu, and As in sapwoods of E. regnans, E.
maculata, F agus sylvatica, and E. obliqua occurred in different types of cells. They noted
that each timber has its own specific characteristics penetration and distribution of Cr,
Cu, and As within the wood structure. This study confirms that penetration and

distribution of Cr, Cu, and As occurs even between cells within one species.

6.3.3 Relative composition of Cr, Cu, and As in wood cells

The relative composition of Cr, Cu, and As in vessel, rays, parenchyma, and
fibers are given in Table 16. The relative compositions of individual CCA components in
the wood cells were expressed as a percentage of the total concentration of chromium,
copper, and arsenic as shown below;

Element(%)
Cr% + Cu% + As%

x100

 

Composition ratio (%) =

78

For CCA solution and CCA retention in wood, the relative composition of Cr, Cu, and As
is expressed as a percentage of the total amount in part per million (ppm) of chromium,
copper, and arsenic as shown below;

Element(ppm)
Cr(ppm) + Cu(ppm) + As(ppm)

 

Composition ratio (%) =

Table 16. Relative ratios of element concentration in various rubberwood cells at
different treating solution concentration.

 

 

 

CCA-C Composition ratio (wt%)
solution Cell type
strength Cr Cu As
(%)
0.93 Vessel 38 24 38
Ray 40 24 36
Parenchyma 41 24 35
Fiber 40 25 35
Cr, Cu, and As in treating 39 27 34
solution
2.12 Vessel 39 22 38
Ray 43 21 37
Parenchyma 40 25 35
Fiber 42 24 35
Cr, Cu, and As in treating 39 25 36
solution
3.29 Vessel 41 27 33
Ray 41 25 34
Parenchyma 40 26 34
Fiber 41 24 35
Cr, Cu, and As in treating 39 25 37
solution

 

There is a small variation in the proportion of Cr, Cu, and As in different cells and

treating solution strength (Table 16). The mean magnitude of CCA composition in

79

rubberwood is in the order of Cr > As > Cu and the order of magnitude is similar to that
of the Cr, Cu, and As in treating solution (Table 16).

The distribution of individual CCA components among all cell types in treated
rubberwood was uneven. It has been reported that the distribution of Cr, Cu, and As in
hardwood cells and tissues were even or uneven depending on species (Greaves and Levy
1978). They noted that species with uneven distribution tend to show a low proportion of
Cr, Cu and As in fibers. Among hardwood species that showed even distribution are
Alstonia scholaris, Antiarz's toxican'a, and Elaeocamus sphaericus (Greaves and Levy
1978). Hardwoods species showed more uneven than even distribution. Low proportion
of CCA components was observed in Betula sp. (Dickinson and Sorkhoh 1976),
Eucalyptus regnans, F lindersia pimenteliana, Magnifera minor, Pterygota horsfieldii,
and Sterculia conwenysii fibers (Greaves and Levy 1978).

Previous studies have showed that variation in distribution reflects the
performance of timber in field exposure (Greaves and Levy 1978, Greaves and Nilsson
1982, Greaves et al. 1982). After 9 years field exposure A. scholarz's, A. toxicaria, and E.
sphaericus were rated as 100 (sound), while S. conwentzii scored 82, P. horsfieldii 55, M.

minor 35 and F. pimenteliana l7 (Greaves and Levy 1978).

6.3.4 Influence of treating solution concentration on distribution of Cr, Cu, and As
The effect of an increase concentration on the microdistribution of CCA elements

in individual cells cell types is shown in Figure 13 and 14. The increase of chromium,

copper, and arsenic in vessel, ray, parenchyma and fiber cells with the increase of the

strength of treating CCA solution is evident. The highest concentration of chromium,

80

copper, and arsenic were observed in the vessels treated with the highest solution strength
(3%).

Treatment of samples with 0.93% and 2.12% CCA solution resulted in similar Cr,
Cu, and As concentration in ray and parenchyma, but in vessel the increased of Cr, Cu,
and As was about two fold, and in fibers the increased was about 1.5 fold. Increasing the
solution concentration to 3.29% increased the concentration of CCA component to about
two fold in ray and parenchyma and about 2.5 times in fibers. In vessels the increased in
solution treatment to 3.29% increased the concentration of Cu and As to about two times
and this is similar to 2.12% treatment but Cr increased was about 2.5 times.

Samples treated with different treating solution strength showed that the vessels
produced the highest CCA element. This indicates that the main flow path of CCA
preservative in rubberwood is the vessels (Levy and Greaves 1978; Greaves 1974) and it
is consistent with results reported for most hardwood species impregnated with CCA
(Nicholas and Siau 1973; Dickinson 1974; Levy and Greaves 1978). The ray cells
consistently have high level of Cr, Cu and As suggesting that preservative penetration
through my cells accounted for a significant proportion of CCA components in
rubberwood. Radial penetration of CCA through ray cells is common in pine species
(Greaves 1974; Bodner and Pekny 1991). Hardwood species with ray cells significantly
used for CCA penetration are F agus sylvatica , Eucalyptus regnans and E. maculata
(Greaves 1974). Maturbongs and Schneider (1996) showed that rays of 10 non-durable
Indonesian hardwoods are well penetrated by CCA afier pressure treatment, indicating

that CCA penetrated through rays.

81

 

 

ElCu

 

 

 

 

 

 

 

 

         

5 7 IAs
ECr
A 4 d
95 7/ E
g 3 l g; Vessel
§2~ , E
8 E;Z;E;S;/—— :3323332/__
1*
o - sfsisiz§/__ zigzag:
0.93% 2.12%
Concentration
4 1
A 3 a
g
.5
"is 2
e R...
8

pa
L

 

 

 

 

 

O iiiiéiii iiiéiiié 2
0.93% 2.12%

Concentration

 

 

Figure 13. The effect of treating solution concentration on the Cr, Cu, and As
composition in vessels and rays of CCA-treated rubberwood.

82

 

BCu

 

 

 

   

  

 

 

 
    
  

 

 

   

 

  

.As
3 ‘ ECr
8 2- g
I; Parenchyma
°
0, isssasas/._ §§§§/_ 3§3§3§3§/_
0.93% 2. 12% 3.29%
Concentration
2 _
1.5 a
......... Fiber

.....

  

.....

Composition (%)

.....
.....
.....

.....

.....

.....

    

.........

22252;; /A :féisésé 2 .5232: g
0.93% 2.12% 3.29%

Concentration

 

 

 

Figure 14. The effect of treating solution concentration on the Cr, Cu, and As
composition in parenchyma and fibers of CCA-treated rubberwood.

83

CHAPTER 7

MICRODISTRIBUTION OF CCA ELEMENTS IN RUBBERWOOD
(HE VEA BRASILIENSIS MUELL. ARG.) CELL WALLS

7.1 Introduction

Levy and Greaves (1978) reported that soft-rot attack of CCA-treated hardwoods
is related to the poor and uneven microdistribution of copper in the 82 layers of fibers.
Later, Drysdale et al. (1980) suggested that the microdistribution patterns of preservative
within cell walls was not the sole factor controlling soft-rot development, but the
retention was also critical. Hardwood species may require high load of preservative to
protect against soft-rot (Smith et al. 1996; Witheridge 1983) in the S2 cell wall layer
(Cooper 1998) because of their thicker S2 layer compared to that of softwood species.

The retention and the microdistribution of CCA in wood cells are therefore of
paramount importance to understand and predict the bioefficacy of CCA-treated
hardwoods. In this study X-ray microanalysis was used to study the microdistribution of
Cr, Cu, and As in CCA-treated rubberwood using semi-thin sections of 0.5 pm thick. The
microdistribution of wood preservatives in hardwoods has been studied extensively in
various ways. The microdistribution is defined by the quality and quantity of elements
present in each microstructure of wood components.

Most of the research were done on chromated copper arsenate (CCA) preservative
using scanning electron microscopy (SEM) in conjunction with X-ray microanalysis
(Greaves 1974; Dickinson and Sorkhoh 1976; Greaves and Levy 1978; Greaves et al.
1982; Daniel and Nilsson 1987). Electron probe microanalyzer (EPMA) was also

employed to study the distribution of CCB-treated red meranti (Salamah and Ani 1995).

84

Basically principles of electron probe microanalysis and scanning electron microscope X-
ray microanalysis are similar. The differences between the two instruments are that in
EPMA the region of the specimen to be analyzed is selected using the attached light
microscope and the microanalysis is operated using high beam currents of 10'11 to 10'12
amperes. In SEM-X-ray microanalysis, the region of interest to be analyzed is selected
using conventional SEM and the microanalysis is done using lower beam currents of

10° to 10'9 amperes. SEM-X-ray microanalysis has several advantages over EPMA. The
low beam current in SEM-X-ray microanalysis reduces over heating of specimen,
element migration and spot contamination (Greaves 1974; Ryan and Drysdale 1988).

Several researchers (Dickinson 1974; Drysdale et al. 1980; Ryan 1986; Newman
and Murphy 1996) also used TEM in conjunction with X-ray microanalysis to study the
microdistribution of CCA in wood cell walls. TEM provides higher spatial resolution and
eliminates the complication encounters with the specimen electron interactions obtain
with SEM. However, Daniel and Nilsson (1987) reported that the used of semi-thin
sections of 0.5 pm in thickness with SEM yield useful information on the distribution of
Cr, Cu, and As in treated wood. They concluded that SEM-X—ray microanalysis of semi-
thin sections provide a convenient alternative to TEM-X-ray microanalysis for routine
CCA microdistribution studies.

It is widely and generally accepted and established in the current literature that the
middle lamella, the primary cell wall layer and the cell comers tends to retains high levels
of Cr, Cu, and As than the adjacent S2 layers (Daniel and Nilsson 1987; Drysdale et al.
1980; Greaves 1974). Drysdale et al. (1980) reported that increasing preservative

retention do not result in proportional increase of Cr, Cu, As in the S2 layers. Daniel and

85

Nilsson (1987) showed that the microdistribution of CCA in wood is closely related to
the lignin distribution. All these studies used SEM and X-ray microanalysis observed
high count per seconds of Cr, Cu, and As in the cell corner, middle lamella, and primary
cell wall layers of CCA-treated wood.

In previous studies, no mention is made on the effect of the probable density
difference within the different cell wall layers. The middle lamella (ML), cell corner
(CC) and primary cell wall (P) are very rich in lignin compared to the secondary wall
(S2). The high retention of Cr, Cu, and As in ML, CC, and P have been thought to be due
to the interaction with lignin.

A factor that is difficult to take into account is the density of the different part of
the cell wall. Cell comer, ML, and P is rich in lignin which is a polymeric matrix richer
in carbon than the cellulose. It can be theorized that lignin may be more conductive and
more prone to produce X-rays during SEM-X-ray mcroanalysis than the cellulose. It can
be also be postulated that since the S2 layers have several orientation (Haygreen and
Bowyer 1996) the emission of X-ray will be reduced and then less X-rays detected. To
test this series of hypothesis, untreated and CCA-treated samples were analyzed for Cr,
Cu, As, C and 0 using SEM-X-ray microanalysis. The objective of this study is to
investigate the microdistribution patterns of Cr, Cu, As, C, and O in the cell walls of

CCA-treated rubberwood.

86

1.1

7.2 Material and Methods
7.2.1 Wood treatment

The wood treatment was previously described in chapter 5.

7.2.2 Samples preparation for X-ray microanalysis

Small matchstick samples measuring 0.5 x 0.5 x 10.0 mm were cut from the outer
portion (0 — 5 mm) of treated cubes to minimize the effects of uneven or poor
penetration. The matchstick size samples were infiltrated, embedded in Spurr’s resin and
ultramicrotomed to obtain semi-thin section of 0.5 pm thick. The sections were mounted

on tungsten 3 mm grid and centered on aluminum stub (Figure 15).

87

I

 

Figure 15. Semi-thin sections on a 3 mm tungsten grid centered on aluminum stub.

88

7.2.3 Scanning Electron Microscope — Energy Dispersive X-ray Analysis (SEM-
EDXA)

The SEM-EDXA were performed using similar operating conditions described in
Chapter 6. SEM-EDXA of thin sections of less than 0.15 pm is reported to have very
little to negligible impact on the absorption (A) and fluorescence (F) factors (William and
Carter 1996). The only correction factor that is important is Z. When 0.5 pm thick
sections are used, as in this study, it can be postulated that the A and F factors exists but
the effects are minimal. However, better precision can be achieved when all the Z, A, and
F factors are included for corrections. Electron Flight Simulator Software (1998) was
employed to estimate the volume of specimen-electron beam interactions of the semi-thin

sections of 0.5 pm. The diameter over which X-ray microanalyses were conducted was

approximately 0.300 — 0.375 um (Figure 16).

89

Electron beam

X Rays

 

Specimen thickness
z 0.5 pm

 

I z 0.375 um|

Figure 16. A schematic diagram of electron beam/specimen interaction.

90

The cell wall regions and their dimensions included in this study are summarized in Table

17.

Table 17. Dimension of cell layers in rubberwood.

 

 

Cell type Morphological region Dimension
Fiber S2 layer 4 — 7 pm
fiber-to-fiber cell corner (F FCC) 2 — 3.5 pm
fiber-to-fiber middle lamella (FFML) 1 — 1.8 pm
Ray S2 layer 2.5 — 4 um
Fiber-to-ray cell corner (FRcc) 2 — 3.5 pm
fiber-to-ray middle lamella (FRML) 1 — 1.8 um
Vessel S2 layer 2.5 — 8 um
fiber-to-vessel cell comer (FV cc) 2 — 3.5 pm
fiber-to-vessel middle lamella (FVML) 1 — 1.8 pm

 

The spot analyses were performed on cell comers (CC), middle lamella (ML) and
S2 cell wall layer of fibers, vessels and ray cells regions at a magnification of 5000 X
(Figure 17). Twenty spot analyses were collected at each region during 100-second
analysis time. To minimize variation, analyses were conducted on adjacent cell wall
regions of the same cell from the same sections. Analyses of ML and CC region were
done midway between adjacent cell wall. The S2 layers were analyzed almost at the
center of the layer to reduce the possible X-rays count from the primary cell wall (P)

Linescan analyses were performed on two adjacent fiber cell walls. The total
acquisition time for each linescan was about 10-15 minutes depending on the thickness of

the cell wall.

91

Fiber S;

FlbL‘l’ S}

 

Figure 17. SEM micrograph of semi-thin (0.5 pm) section showing fiber-to-fiber cell
comer (FFcc), fiber-to-fiber middle lamella (F FML), and fiber S2 layer regions used for
analyses. (Magnification 5000X).

92

7.3 Results and Discussion

7.3.1 Microdistribution of Cr, Cu, and As

The elemental composition and proportion of Cr, Cu, and As of various cell wall
regions detected from semi-thin sections of rubberwood are shown in Table 18. Each
value is the average of 20 analysis points, automatically expressed by the Noran Vantage
software as a percentage of Cr, Cu, and As present at each region analyzed. The
proportion from different region is expressed as percentages of the total composition of
Cr, Cu, and As.

There was a high level of Cr compare to Cu and As in all cell wall regions
analyzed for all three different treating solution strengths. The S2 layer of fibers exhibited
the lowest amount of Cr while fiber to vessel cell comer (FVcc) contained the highest
level of Cr regardless of the treating solution strength. Arsenic was present in slightly
lower concentration than Cr in all regions. Arsenic was the lowest in the S2 layer of fibers
and the highest in FVCC. Copper appeared to have the lowest level in all regions analyzed
compared to Cr and As. Similarly, as with Cr and As, the Cu level was the lowest in S2
layer of fiber and the highest in F Vcc.

Different regions have different elemental composition at various solution
strengths. High concentration of Cr, Cu, and As were observed in the CC followed by the
ML region. The F Vcc and ML appeared to have the highest level of Cr, Cu, and As. The
S2 layer of vessels contained higher amount of Cr, Cu and As compared to the S2 layers
of rays and fibers. The high concentration of Cr, Cu and As in the CC of rubberwood is in
agreement with studies reported for CCA-treated Betula verrucosa using SEM-EDXA
(Daniel and Nilsson 1987), Betula alba and Alsotnia scholaris using TEM-EDXA (Ryan

and Drysdale 1988).

93

Table 18. Average elemental composition and proportion of various cell morphological
regions in CCA-treated rubberwood.

 

 

 

Morphological Treating Elemental

region“ solution Elemental composition (wt%) proportion
strength

Cr Cu As Cr: Cu : As

Fiber S2 0.93 0.57 0.29 0.43 44 : 22 : 33

2.12 0.99 0.52 0.94 40:21 :38

3.29 1.52 0.89 1.60 38 : 22 :40

FFCC 0.93 0.95 0.47 0.91 41 :20 : 39

2.12 1.85 0.81 1.72 42: 19: 39

3.29 3.37 1.60 3.09 42 : 20 : 38

FFML 0.93 0.85 0.38 0.78 42 : 19: 39

2.12 1.81 0.78 1.65 43: 18:39

3.29 2.98 1.49 2.75 41 :21 :38

Ray S2 0.93 1.38 0.64 1.01 46 : 21 : 33

2.12 2.41 1.10 2.01 44:20:36

3.29 3.35 1.71 2.60 44 : 22 : 34

FRCC 0.93 1.93 0.79 1.48 46 : 19:35

2.12 4.58 2.01 4.22 42: 19 :39

3.29 6.77 3.09 4.90 46 : 21 : 33

FRML 0.93 1.83 0.77 1.39 46: 19: 35

2.12 4.21 1.58 3.16 47: 18:35

3.29 6.35 2.65 4.56 47 : 20 : 34

Vessel S2 0.93 1.82 0.91 1.79 40 : 20 :40

2.12 3.38 1.75 3.08 41 :21 :38

3.29 4.50 2.04 4.09 42 : l9 : 38

FVCC 0.93 2.01 0.91 1.88 42 : 19:39

2.12 5.21 2.78 4.90 40 : 22 : 38

3.29 7.51 3.45 6.50 43 : 20 : 37

FVML 0.93 1.98 0.89 1.75 43 : l9 : 38

2.12 4.80 2.50 4.40 41 :21 :38

3.29 6.95 3.20 5.48 44 : 20 : 35

 

* Fiber S2 - F iber’s S2 layer; F F cc — F iber-to-fiber cell corner; F F ML — F iber-to-fiber
middle lamella; Ray S2 - Ray’s 82 layer; F Rcc — F iber-to-ray cell corner; FRML — F iber-
to-ray middle lamella; Vessel S2 - Vessel’s S2 layer; FVcc — Fiber-to-vessel cell comer;
FVML - Fiber-to-vessel middle lamella.

94

In CCA-treated Cryptomeriajaponica, Lee at al. (1992) noted that Cr, Cu, and As were
located within the ML and CC in greater concentration than in the secondary wall. The
present study also showed that Cr, Cu, and As were accumulated in the ML, CC, and the
primary wall in agreement with published literature.

The cell comer and middle lamella are rich in lignin (Fengel and Wegener 1983;
Saka and Goring 1985). It has been suggested that lignin is one of the fixation sites for
Cr, Cu, and As. The microdistribution of CCA components in treated wood correlated
well with the distribution of lignin in wood (Daniel and Nilsson 1982, 1987). Petric et al.
(2000) reported that lignin is the preferential site for copper and other metal ions.
However, Thomason and Pasek (1997) suggested that copper from a copper ethanolamine
solution react with the carboxyl groups of hemicellulose. Using Fourier transform
infrared spectroscopy (FTIR), Zhang and Kamdem (1999) concluded that the carboxyl
groups in hemicellulose and phenolic hydroxyl, and ester groups of lignin are the major
bonding sites for copper. Craciun and Kamdem (1997) proposed that Cu interact with

carboxyl groups of hemicellulose and lignin.

7.3.2 Distribution of carbon and oxygen

The X-ray counts for carbon and oxygen in the S2 fiber layer and the adjacent cell
corner and middle lamella of untreated and CCA-treated rubberwood are presented in
Table 19. The count rate of carbon and oxygen counts of S2 layer of fiber, CC, and ML
were expressed in ratios with S2 layer of fiber count rate as 1.0. The ratio was calculated

as follow:

95

 

Carbon or oxygen count rate of cell wall region

 

Ratio value =
Carbon or oxygen count rate of S2 layer

The count rates of carbon and oxygen in the ML and CC were higher than that of
the S2 of the adjacent fiber cells. Carbon ratio values of ML and CC were higher than the
S2 layer in both treated and untreated samples (Table 19). Oxygen count rate are 1
relatively similar between CC and ML. The results indicate that higher amount of carbon
and oxygen present in the middle lamella and cell comer. However, studies on wood
component distribution strongly suggested that high lignin content and low cellulose
contents are found in the middle lamella and cell corner (Sjostrom 1981; Fengel and
Wegener 1983). Since wood lignin has a higher molecular weight than cellulose (Fengel
and Wegener 1983; Eaton and Hale 1993), thus at any unit area or volume of the middle
lamella and the cell corner have higher density than the S2 layer. Hence, the result of this
study suggests that density of the cell wall region might influence the microdistribution

of carbon and oxygen.

96

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7.3.3 Comparison between the distribution of carbon and oxygen and distribution of
Cr, Cu, and As

The distribution patterns of carbon and oxygen in untreated rubberwood cell walls
of fiber observed by using X-ray linescan are shown in Figure 18. The SEM-EDXA
linescans of CCA-treated rubberwood, counts corrected for the background for carbon,
oxygen, Cr, Cu, and As are presented in Figures 18 to 21. The count rate was assumed to
be proportional to the concentration of each element per unit volume since all the data
were from the same sample (Russ 1984; Goodhew and Humphreys 1988). The counts for
carbon and oxygen were low in the 8; layer and high in the middle lamella in both
untreated and CCA-treated samples.

The linescans show that Cr, Cu, and As were concentrated in the middle lamella
and on the lumen surface. The linescans show that count rates increases from the lumen
area toward the lumen surface then decreases across the S; layer and then increases again
in the middle lamella region. This suggests that higher concentration of Cr, Cu, and As
were present in the lumen surface and middle lamella region as compare to the $2 layer.

The count rate of Cr, Cu, and As increases with the concentration of treating
solution. However, no significant effect of increased treating solution concentration was
observed on the carbon and oxygen count rates. The linescan curve suggested that the
distribution of Cr, Cu, and As were similar to the distribution of carbon and oxygen. High
Cr, Cu, and As levels were observed in the region with high carbon and oxygen level.
Thus, the results of this study suggest that density of ML might influence the

microdistribution of CCA component in wood.

98

Figure 18. SBM-EDXA linescan of untreated rubberwood. (A) SEM micrograph of
transverse surface showing a line across two adjacent fibers used for linescan analyses.
(B) Carbon distribution and (C) oxygen distribution across two adjacent fiber cells.

99

(A)

(B)

(C)

 

 

 

00 Carbon

 

ollllllll
01234567

Micron

 

 

 

Counts

75

50

Oxygen
25

Ollllllll
01234567

Micron

 

 

100

 

 

 

Figure 19. SEM-EDXA linescan analyses of rubberwood treated with 0.93% CCA
solution. (A) SEM micrograph of transverse surface showing a line across two adjacent
fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen distribution, (D)
chromium distribution, (E) copper distribution, and (F) arsenic distribution across the two
adjacent fiber cells.

101

(A)

(B)

(C)

2 pm

 

 

 

 

Micron

Carbon

 

 

 

 

Counts

75

50

25

 

O

Micron

Oxygen

 

 

102

(D)

(E)

(F)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12 -
3
s 9‘
e 6-
3 — Chromium
0 f r r
0 2 4
Micron
3
S
8
Copper
0 2 4
Micron
15
12
g 9
O 6
U 3 Arsenic
O l I T
0 2 4
Micron

 

103

 

 

 

Figure 20. SEM-BDXA linescan analyses for rubberwood treated with 2.12% CCA
solution (A) SEM micrograph of transverse surface showing a line across two adjacent
fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen distribution, (D)
chromium distribution, (E) copper distribution, and (F) arsenic distribution across the two
adjacent fiber cells.

104

(A)

(B)

(C)

 

 

 

 

 

 

 

 

600
g, 450
8 300 Carbon
0
150
0‘ ‘ ' ' I‘T I 1 1 1
0 l 2 3 4 5 6 7 8 9
Micron
75
g 50
° Oxygen
U 25
0 l 1’ T T T I l l I l
0 1 2 3 4 5 6 7 8 9
Micron

 

 

 

105

 

 

 

 

 

 

 

 

 

 

 

 

 

25
20
g 15
8 10 Chromium
(D) 5
0 I I I r I I I I I I
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g 9
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207
:9 15 4
§ 10 «
(F) o 5-
Arsenic
O I I I I I I I I l
O l 2 3 4 5 6 7 8 9
Micron

 

 

 

106

 

Figure 21. SEM-EDXA linescan analyses for rubberwood treated with 3.29% CCA
solution (A) SEM micrograph of transverse surface showing a line across two adjacent
fibers used for linescan analyses. (B) Carbon distribution, (C) oxygen distribution, (D)
chromium distribution, (E) copper distribution, and (F) arsenic distribution across the two
adjacent fiber cells.

107

(A)

(B)

(C)

 

 

 

Counts

600

450

300 Carbon

150

Ollllvll.
01234567

 

Micron

 

 

 

Counts

75

50
Oxygen
25

 

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108

 

 

(D)

(E)

(F)

 

 

Count

 

 

0 —r

0 1

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2345

Micron

If I

I

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6

7

Chromium

 

 

 

 

 

 

Copper

 

 

 

 

 

 

I I

1234567

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Micron

I

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Arsenic

 

109

 

7.3.4 Cr, Cu, and As distribution in relation to decay fungi attack
According to Hedley et al. (1990) afier the Bethell or full cell process, the cell

lumina are filled with preservative solution. As the wood dries, more preservative
ingredients are deposited on the lumen wall. Deposition of CCA components in the
lumen surface was also reported in various softwood and hardwood species (Newman
and Murphy 1996; Drysdale et al. 1980; Greaves 1974).

It was noticed earlier that CCA-treated rubberwood at retention of 4.1 kg/m3 and
10.5 kg/m3 were not satisfactorily protected from soft-rot fungi (chapter 5). At these
retentions, SEM-EDXA data showed that the average Cu elemental composition in the S2
layer of fibers were 0.29% and 0.52%, respectively. Acceptable control of soft-rot was
achieved at CCA retention of 14.5 kg/m3. At this level of retention, the elemental
composition of Cu in the S2 layer of fiber was 0.89% which correspond to 3 times higher
than the Cu level in 10.5 kg/m3 retention. The loading of Cu in rubberwood treated at
14.5 kg/m3 retention was sufficient to prevent soft-rot attack in rubberwood in laboratory

test.

7.3.5 Influence of CCA solution strength on Cr, Cu, and As distribution

The composition of Cr, Cu, and As in the cell wall, middle lamella, and cell
comer increase with increasing treating solution strength (Table 18). However, the
relative proportion of each element in all regions seems to have little variation with
increasing CCA solution strengths. Both chromium and arsenic were present in larger
proportion in all regions. The increases in the amount of Cr, Cu, and As with increasing
treating solution strength in S2 layers of fiber, ray and vessel is not as much as in cell

corner and middle lamella. The S2 layer of fiber shows the lowest increased in all three

110

CCA elements. The increase of Cr, Cu, and As with increase treating solution strength
was also observed in Pinus radiata, Betula alba, Alstonia scholaris using TEM-X-ray
analysis (Ryan and Drysdale 1988). Drysdale et al. (1980) did not observe any increases
in the amount of Cr, Cu, and As with increased treating solution strength in S2 layer of
tracheid in Pinus sylvestris using EMMA. According to Ryan et al. (1988), Drysdale et
al. (1980) used a short analyses time of 10 seconds per spot, which may be not sufficient
to obtain a low noise background. In this study, 100 seconds analysis time per spot was

used for every cell types and morphological regions.

11]

 

CHAPTER 8

CONCLUSIONS

Based on the observations made in the study of chemical constituents in
rubberwood, hollocellulose averaged 77.5%, of which 37.2% was hemicellulose and or-
cellulose, respectively. Klason lignin content averaged 18.5%, whereas extractives
content averaged 6% and ash 1%. Rubberwood vessels are large ranging from 150 to 300
pm and its frequency of occurrence was 3-4 vessels/mmz. The vessel cell wall varies
from 2.5 to 8 pm thick in which the thickest part of the wall was the vessel cell walls
adjacent to each other. Fiber cell wall of rubberwood was thick ranging from 4 to 7 pm
and fiber pits were confined to radial walls. Examination of parenchyma and ray cell
revealed the presence of starch grains suggesting that rubberwood can easily be decay or
colonized by fungi.

Retention and penetration of CCA after full cell treatment are influence by the
pressure duration on rubberwood. Good penetration and retention were achieved after
four hours of pressure (1240 kPa). This finding suggests that rubberwood was not easily
treatable contrary to many studies stating that rubberwood is highly permeable to CCA
treatment.

The result on the fluid pathways showed that anatomical features influence the
penetration of CCA in rubberwood. Longitudinal permeability was the highest followed
by radial and tangential permeability. Pre-treatrnent steaming was beneficial to the CCA
penetration and retention. The substantial improvement in the retention and penetration of
CCA suggests that pre-treatment steaming can be used to improve the permeability of

rubberwood blocks.

112

The laboratory soil-block test showed that rubberwood was a nondurable species.
Weight losses due white rot and brown rot decay fungi were 1.5 times higher than that of
sofi rot. Exposure of the test fungi to varying retention of CCA resulted in marked
reduction in weight loss. Treatment of rubberwood with CCA at retention of 4.1 kg/m3
reduced the weight loss to about 10% after 12-week exposure to all test fungi. A higher
CCA retention of 14.5 kg/m’ was required to protect against Irpex lacteus, Trametes
versicolor, Gloeophyllum trabeum, Postia placenta, Chaetomium globosum, and
Phialophora sp. not to exceed 2%. Based on the threshold values (Table 13), protection
against all test fungi can be achieved with CCA retention of 14.7 kg/m3. Field test is
strongly recommended to validate this result.

There were differences in Cr, Cu and As microdistribution between cell types in
rubberwood. Chromium, copper, and arsenic were high in the vessels. Fiber recorded the
lowest level of CCA elements. Fibers, which constitute about 62% of rubberwood,
contain about 0.42%, 0.63%, and 1.02% of copper in CCA-treated wood samples with
retention of 4.1 kg/m3, 10.5 kg/m3, and 14.5 kg/m’, respectively. The microdistribution of
the individual CCA components in wood cells differ in the order of Cr > As > Cu similar
to the treating solution. The concentration of Cr, Cu, and As in the vessels followed by
rays suggests that vessels are the main pathway of CCA flow and the ray cells are the
secondary pathway in rubberwood. This study showed that the increase in the solution
strength of the treating solution resulted in the increase in the amount of CCA elements.
The proportion of Cr, Cu, and As did not vary much among cell types and treating
solution strength, suggesting that CCA solution did not disproportionate during their

application to rubberwood.

113

Regardless of treating solution strength, the highest levels of Cr, Cu, and As were
found in fiber-to-vessel cell corner (FVcc) and fiber-to-vessel (F VML)- The lowest level
was detected in the S2 layer. The concentration of Cr, Cu, and As in cell wall and
morphological region increased with increasing treating solution strength. The variation
of proportion of Cr, Cu, and As in all region analyzed regardless of treating solution
concentrations were insignificant. Linescan analyses showed that Cr, Cu, and As were
present on the surface of cell lumen. The results showed that even though the S2 layer of
fiber contains only about 0.9% copper after treatment with CCA retention of 14.5 kg/m3,
its still effective preventing decay fungi attack. This suggests that uneven distribution of
CCA in wood structure did not affect the performance of CCA-treated wood rather the
well-treated cell comer, middle lamella, and lumen surface prevent decay.

Using spot and linescan analyses of semi-thin section, the distribution of carbon,
oxygen chromium, copper, and arsenic can be compared. Spot analyses showed that the
composition of C, 0, Cr, Cu, and As were higher in the middle lamella and cell corner
than in the S2 layer. Linescan analyses also showed that higher counts were obtained
from middle lamella compared to the adjacent S2 layer of fiber. The density of cell wall
regions might influence the microdistribution of Cr, Cu, and As in CCA-treated

rubberwood.

114

CHAPTER 9

RECOMMENDATIONS

Recommendations for further study can be summed up as the followings:
( 1) More study is required to assess the effect of pre-treatment steaming on the strength

properties of rubberwood.

(2) Since wood in actual use is exposed to many decay hazards, field test is strongly

recommended to validate this result.

(3) More studies on microdistribution of preservative in hardwoods should be carried on
other wood preservative system in order to obtain complete understanding of

preservative efficacy.

(4) Future studies on preservative microdistribution in wood should employ SEM-
EDXA or TEM-EDXA in combination with UV microscopy or any in situ chemical
analyses method. This will elucidate the relationship between microdistribution of

preservatives elements and distribution of wood chemical components.

(5) Further research is needed to determine the relationship between the distributions of

carbon, oxygen and CCA elements in other wood species.

(6) More research is needed to determine how the ratios of Cr, Cu, and As affect and thus

provide protection against wood destroying organism.

115

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