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TH .

THE DURABEUTY QF A TWO SPECIES
FAR‘EiELE SQAEfi

Times}: 509 the Dame's of M. 5‘
MECHIGAN STAY’E UNI‘JERSIW
Bruce A. Wifitrup
1964

TH ESlS

 

LIBRARY

Michigan State
University

 

ABSTRACT
THE DURABILITY OF A TWO SPECIES
PARTICLE BOARD

by Bruce A. Wittrup

This study was undertaken to determine if a durable species
could protect a non-durable species when the two were combined in
particle board. Two durable woods, redwood (§equoig Sempervireng
(D. Don) Endl.) and northern white cedar ( hu a occidentalis L,)
were mixed with Jack pine (_13_1_n_g§ banksiana Lamb.) in varying per-
centages to see if a durable board could be produced.

Other factors investigated with redwood only were; 1) the effect
of heat on board durability, 2) the effect of adhesive (urea-formal-
dehyde and phenol-formaldehyde) on durability, and 3) the decay due
to different organisms.

The durability criterion was the weight loss of the blocks after
exposure in soil block decay chambers. The primary decay agent used
was Lenzites 353929; the fungus Polypgrus versicolor was used on cer-
tain redwood blocks.

A supplementary test was undertaken, in which thin pine veneers
were fastened securely to blocks of redwood. This was to determine
if the redwood could protect a non-durable species in close contact
with it.

The results show that, with the manufacturing methods used, the
durable wood imparts no protection to the non-durable species when

the two are combined in particle board. The results of the test with

Bruce A. Wittrup

thin pine veneers showed that with sufficient moisture movement
after contact, the redwood did impart a protective action.

The supplementary tests with redwood only, showed that; l)
boards produced with urea-formaldehyde adhesives are less durable
and more severely delaminated than blocks produced with phenol—
formaldehyde adhesives, 2) the heat used did not impair the decay
resistance of the redwood extractives, and 3) figlyporus versicglg;
is a less severe decay agent than'Lgnsiteg trabeg fer the species

tested.

THE DURABEH‘Y OF A TWO SPECIES

PART ICLE BOARD

By

\

t,p
Bruce.A?!Wittrup

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
fer the degree of

MASTER OF 33 IENCE

Department of Forest Products

1964

ACKNOWLEDGEMENTS

The author wishes to acknowledge the assistance and
encouragement given him by the f0110wing faculty members of
the Department of Forest Products at Michigan State University:
Dr. Eldon.A. Behr, who suggested the study and gave much assis-
tance throughout the work; Dr. Otto Suchsland for his advice
on the manufacture of the particle board and his photographic
work used in the thesis.

I would like to thank my wife, Renate, fbr*her encourage-

ment and patience throughout the course of this study.

11

TABLE OF COM‘ENI‘S

MRODUM ION O O O O O O O O O O O O O O O O C O O O O O O O O 1
mme REV mw O O O O O O O O O 0 O O O O O O O O O O O O O 2
Pm ICE mm TM 0 ' O O O O O O O O O O O O O O 0 O O O O O .11

’WoodSource.........

FlakeandBoardPreparation...............ll
ExposureProcedure....................13
Ream-t8 and Diacu881on O O O O O O O O O O O O O O O O O .15

mm rm 0 O O O O O O O O O O O O O O I O O O O O O O O O .26

Procedure. 0 O U C O O O O 0 C O C O O O O O O O O O O O .26
ResultsandDiscussion.. . . . .. . ... . . . . ...29

MICROSCOPIC Em‘um ION C O C O C O O O O O O O O O ,0 O O O O .32
CONC ms IONS O O C O O O O O O C O C C O O O O O O O O O O O O O 36
ECOWNENDM IONS FOR m m SIUDI O O O O O O O O O O O O O O O 37

BELIOGRAPIIIcoo0.0000000000000000000038

iii

LIST OF TABLES

Table No. Page

1. Board Preparation Data and.Test Results
for Redwood Particle Board . . . . . . . . . . 17

2. Board Preparation Data and Test Results for
Nerthern White Cedar Particle Board . . . . . 20

3. Test Results for "Veneer'Test' . . . . . . . . 30

iv

LIST OF ILLUSTRATIONS

Figug No.
1. Appearance of Decayed Redwood Particle Board..
2. Weight Loss versus Redwood Content in
Partic13 bard O O O O O O O O O O O 0 O O O O
3. Appearance of Decayed Northern White Cedar
Pafiicle Rard O O O O O O O O O O O O O O O O
4. Weight Loss versus Northern White Cedar
Content inParticle Board . . . . . . . . . .
5. Degree of Delamination in Redwood Particle
Ram O O O O O O O O O O O O O O O O O O O O
6. Method of Assembly and Complete "Veneer Test"
Assembly 0 O O O O C O O O O O O O O O O O O O
7. Appearance of Pine Veneers after Exposure
toLenzitestrabea....... .......
8. Photomicrographs of 25 percent redwood
Particle Board prior to Decay Tests . . . . . .
9. Photomicrographs of 25 percent Radwood Particle

Board after Decay Tests Showing fungus hyphae..

Page
18

19

21

28

31

34

35

INTRODUCTION

The purpose of this study was to establish whether a small percen-
tage of durable wood could protect a particle board comprised largely
of a nonsdurable species. A preliminary study indicated this principle
might prove true.

Two durable species were chosen; redwood (§gguoia gempgrviggns (D.
Don) Endl.) and northern white cedar (Thai; occidentalig L.). These two
species were to be mixed with Jack pine (Ping: banksiana) in varying
percentages.

Particle board is not now widely used in places where decay resis-
tance is an important factor. If a board could be produced in the above
manner, which had good decay resistance, it could expand the uses of
particle board without greatly increasing the cost.

A second test was undertaken to learn more about how durable wood
could protect a non-durable wood, if indeed it does. Thin veneers of a
non-durable wood were fastened to a durable wood and tested for decay
resistance. These veneers were varied in thickness to see how far this
protective action, if any, could extend into the non-durable species.
This test was meant to substantiate the results of the test on the
particle board.

The soil block test was chosen as the criterion of durability.
This method of testing has been questioned as a valid method of deter-
mining decay resistance, however it is widely used and its usefulness

is recognized hy many authorities.

REVIEW OF LITERATURE

W:
The extractive content of wood is the primary factor in a wood's

durability. The makeup and chemistry of these extractives is very
complicated and the exact structure of may is not known.

Of the two durable woods used in this work, only the extractives
of redwood have been investigated to arm great extent. One of the
most complete studies of redwood extractives was carried out by The
Institute of Paper Chemistry (1). In this work, they found that red-
wood extractives contained the following four classes of materials:
1) coloring matter, which included phlobamene, tannin, sequoyin, humic
acid material, and a material resembling tannin, but differing in that
it is insoluble in ethyl acetate, 2) sugars and polysaccharides, 3) cy-
closes (pinite and sequoyite), and I.) mineral salts. Of these four
groups, only the coloring matter portion is toxic to fungi and the only
fraction of the coloring matter found to be toxic was the tannin (l) .

The tannin content of redwood varies and has been reported by
different investigators as being between I. and 12 per cent (1, 2, 3).
The structure of tannin is not known exactly, however many complicated
structures have been proposed for it. One of these which has been syn-
thesized and found to be qualitatively equal to the natural pholobatannins
is bis-(7, 3', 4' trihydroxyflavopinacol) I. (2).

0\ H
,cHdoH
f“:

c-oH
c—oH
i”
0/, 0H

2

Tannins extracted from wood are never obtained as a pure substance,
but rather as a heterogeneous mixture. Tannins have the following pro-
perties in common (2): 1)a11 are polyhydroxylic phenols, 2) tannins are
soluble in.water, alcohol, acetone, and ethyl acetate, and 3) are easily
oxidized and give characteristic colorations or precipitates with me-
tallic salts.

Tannin is feund in wood, bark, leaves, and cones of trees. These
tannins are not all of the same structure and the difference is usually
quite distinct (2).

The taxicity of tannin is not great when compared with chemicals
such as sodium.pentachlorophenate. Data have shown that 823 times as
much tannin by weight as sodium pentachlorophenate is required to in-
hibit fungus growth (1). Therefore, it is only the very high percentage
of tannin found in redwood that is responsible for its durability. In
tests carried out on an agar medium containing 2.058 per cent tannin
extracted from redwood, no growth of the fungus Egggg annosus was ob-
served. As stated earlier, only the tannin fraction inhibited fungus
growth to any great extent.

The extractive content of northern white cedar is not as well
known as that of redwood. Compounds which have been identified in
northern white cedar are: O<and X thujaplicins, cedrol, white cedar
oil, and traces of thujic acid (2, 3, A). Thetwtthujaplicin is pre-
sent in concentrations of 0.08 percent compared to 0.008 percent for

% thuJaplicin. The thuJic acid, present only in trace amounts in

northern white cedar, is the major constituent in western red cedar

(Thuja icata 2. Don) extractives (A).

The extractive content in redwood or any species will vary with
position in the stem and age of the tree. The extractive content is
greatest in newly formed heartwood at the lower portion of the stem.
The extractive content decreases going up the stem or toward the pith.
Two possible reasons for this are given by Scheffer and Hopp (5);
they suggest I) ”That a greater quantity of the resistance factor is
produced per unit of newly formed heartwood each year and that this
resistance factor is not stable but subsequently deteriorates in effec-
tiveness with agen or 2) "that the quantity of the resistance factor
produced for a unit of new heartwood is about the same from year to
year, but is supplemented by a continuous outward diffusion or migra-
tion of previously fermed resistance factor.”

The position of the extractives within the wood has been investi-
gated by Tarkow and Krueger (6). They found that of the hot water solu-
ble extractives, 73 percent are found within the cell walls and the
remainder in the cell openings.

That the extractives of redwood are heat labile has been shown by
Anderson, Duncan, and Scheffer (7). They found no fungicidal action
on extractives removed with hot water. Extractives removed with cold
water and concentrated by freeze drying showed good fungicidal proper-
ties. To determine the effect on redwood durability, the above authors
(7) conducted decay weight loss tests on boards dried by different me-
thods. They feund that kiln drying, with temperatures not exceeding
180 degrees Fahrenheit, decreased durability only slightly. A pre-
steaming treatment at 212 degrees Fahrenheit for four hours prior to

kiln drying reduced durability to the extent that the weight loss

 

increased from 2 percent to 7 percent. Solvent drying in acetone

increased the weight loss to 12 percent.

Particle Board:
Particle board is a relatively new product in this country,

being introduced after World'War II. For this reason we do not have
extensive data on the durability of particle board.

In.a.three year test at the U. S. Forest Products Laboratory (8),
the following results were obtained: 1) phenolic resin adhesives were
more durable than urea or urea-melamine adhesives, 2) increased den-
sity improved the strength and durability (tested on an outdoor test
fence) and 3) painted specimens after three years' exposure on a test
fence were still in good condition. It was also found in.this study
that increasing the amount of adhesive (phenolic and urea) or the addi-
tion of 1 percent wax improved the boards' durability.

A test of particle board durability, using the soil block test,
was also conducted at the Forest Products Laboratory (9). This test,
in agreement with the above study, also feund that increasing the
amount of urea adhesive and the addition of 1 percent wax improved the
board durability. In this study, however, increasing the amount of
phenolic adhesive or increasing the density appeared to have no effect
on the durability.

One board tested in the above study contained ”About 50 percent
western red cedar and 50 percent alder flakes." This board showed a
very low weight loss (4 percent) when exposed to the fungus.225i§

monticola, however, when exposed to Lenzites trabea, the weight loss

parallelled that of boards produced with low to moderate decay

 

resistant woods. The low weight loss was "tentatively attributed to
the naturally occurring toxic extractives present in the 50 percent
western red cedar flake component.“ The fact that the above board
contained 50 percent hardwood flakes might better explain the low
weight loss from exposure to Eggig monticola. In all three boards in
the above study, which contained hardwood flakes, the weight loss was
less for Poria mongigglg than for Lenzites trabea. 0f 14 boards in
the same study containing all softwood flakes, only one lost more
weight with 225;; monticola. If the alder flakes were not susceptible
to decay by the organisms used, the "avenues of travel" proposed later
in the current study would not be present.

Much work has been done on the addition of a preservative to par-
ticle board. In most of these tests, the preservative has been incor—
porated in the adhesive.

In one of the early tests, Klauditz and Stolley (10) found that
pentachlorophenol in a urea-formaldehyde resin produced a chipboard
resistant to both fungi and termites. The amount of preservative
shown to be effective was 1.5 percent of the oven dry weight of the
chips.

Other investigators (11) found the optimum percentage to be 5
percent pentachlorophenol when incorporated with urea-formaldehyde.

Huber (12) incorporated pentachlorOphenol in both urea and phe-
nolic adhesives. He found that 0.6 percent of the oven dry weight
of the chips gave good protection in soil block tests with Lenzites
inane.

Brown and Aldon (13) sprayed the preservative on the flakes,

rather than mixing it in the adhesive. Using pentachlorOphenol at

1.25 percent of the dry chip weight, they produced phenolic resin
boards which were very resistant in twelve month Exposure tests.
Boards produced with urea, using the same method, did not prove
durable in the test.

Pentachlorophenol has been the primary preservative used in
this type of particle board test. However, others have been used.
Sokolova and.Timofeeva (14) used sodium fluoride and sodium fluosi-
licate at 0.5 and 1.0 percent of the dry chip weight. They obtained
good protection in this way when the blocks were exposed to gggi_-
phgrg cerebella.

Criterion of Durability:
There are many criteria for testing the durability of wood.

Probably the most accurate method is actual records kept of wood in
service. However, the length of time required rules out this method
for most practical purposes. The most widely used and accepted me-
thod of testing durability is the weight—loss method. This method
is outlined in the A.S.T.M. Standard D 1413-61. (15). The above pub-
lication includes the method for incorporation of a preservative in
the test blocks. A publication by McNabb (16) omits this procedure
and gives a good outline of both the soil-block and agar-block method.
Many other methods have been proposed, such as toughness tests,
hygroscopicity, crushing strength, and others. A method devised by
Brown (1?) involves tensile testing of very thin test specimens after
exposure to fungi. This method involves much less time (1 to 2 months)
in testing than the weight-loss method (4 to 5 months) and Brown ob-

tained good results using this test. Brown has stated that this pro-

cedure should be applicable to particle board testing as well as
solid woodl.

Some of these methods show merit and promise; however, Hartley
(18) states, "None of them has enough supporting evidence to justify
being substituted for the weight-loss test without further careful
study.“ The weight-loss method measures the loss of wood substance
due to metabolic conversion of wood to carbon dioxide and water.

In the weight-loss method, exposure chambers are prepared in
most cases with soil and feeder strips. There are many factors which
can vary in the preparation of the soil block bottles and if test re-
sults are to be compared, these factors must be as uniform as possible.
Some of these variable factors which require control are given by
Duncan (19) as: 1) soil characteristics, 2) effect of aeration and
3) moisture content of soil relative to its water holding capacity.
In tests on these variables, it was found that l) the soil character-
istics had little effect unless extreme soil types were involved, 2)
the moisture content of the soil should not exceed 150 percent of its
water holding capacity, and 3) to assure aeration, caps should be loosely

attached with no liners, or the cap vented with a glass tube.

WoodaFungi Relationship:
As mentioned earlier, the loss in weight accompanying decay in wood

is due to the metabolic conversion of wood to carbon dioxide and water.
This conversion is accomplished by enzymatic degradation of cellulose
by fungus hyphae moving through the wood substance. The fungus hyphae
can move through the wood either through natural openings, such as cell

lumens and pits, or through the cell walls.

1. Op. Cit.

The manner in which the hyphae penetrate the cell wall is given
by Proctor (20) as, nthe secretion of enzymes at the tips of pene-
trating hyphae, and the total dissolution of the cell wall by enzyma-
tic activity in advance of actual passage through the wall." The
hyphae are usually constricted as they move through the cell wall and
then expand as they enter the cell cavity.

The actual utilization of the cellulose by the fungi is divided
into two types of reactions (21): 1) the extracellular reactions in-
volving the conversion of wood to linear anhydroglucose chains and
these in turn to cellobiose, and 2) the intercellular reaction con-
sisting of the conversion of cellobiose to glucose which can be uti-
lized by the hyphae. This last conversion is accomplished by the
enzyme 9 Q-glucosidase .

The decay of wood usually takes place under conditions of good
aeration. However some growth can occur in anaerobic conditions (22).
In this case the products are substances such as alcohol and oxalic
acid, rather than carbon dioxide.

The production of water can be great enough to sustain the fungus
growth if it is well established (18). If evaporation of water is not
excessive, the fungus can thrive with no external source of water.

The growth of fungus is slowed down to a great extent in a dura-
ble wood or wood treated with a preservative; however, decay does occur
slowly in such wood. Lyr (23) has investigated this fact and suggests
reasons for its occurrence. He has shown that the extractives pinc-
sylvin-mono-methylether, pi-thujaplicin and the chlorOphenol preserva-
tives are no longer toxic after oxidation by fungal oxidases such as

laccase, tyrosinase, and peroxidase. One or more of these oxidases
are present in nearly all fungi which attack wood. Lyr gives the
following relative values of the ability of different substances to
resist oxidative degration: l) 5-chlor0phenol-100, 2) L-chlorophenol
-95, 3) 3-chlorophenol-86, I.) 2-chlorophen01260, 5) pinosylvin-mono-
methylether-20, 6) {3 -thujaplicin=15.

nyr also states that, "the tannins of the heartwood strongly
inhibit oxidases.a This would support the findings that it is the

tannins in redwood which are largely responsible for its durability.

10

PARIIDLE BOARD TEST

Wood Source:

Three species of wood were used in this study. The wood was to
be as fresh cut as possible and therefore could not be obtained from
regular commercial sources. The reason for this was that it was not
to be soaked in water before flaking as this could remove extractives.
A second reason being that any heat treatment, such as kiln drying,
could affect results.

The redwood (Seguoia sempgrvirens) was shipped from California
in waterproof paper. The wood was at a very high moisture content
and was shipped just after sawing. It was received as rough one
inch lumber.

The northern white cedar Qthig occidentalis) was shipped from
Northern Michigan in the form of eight to twelve inch diameter posts.
This was sawed to one inch lumber at the Forest Products Department
sawmill.

The Jack pine (gigg§,b§nkgigg§) was cut from the Michigan State
University Experimental Forest. This was also sawed into one inch

lumber at the Forest Products Department sawmill.

Flake and Board Preparation:
All three species of wood were converted to flakes measuring

1 inch by 0.75 inch by 0.015 inch. Flaking was done on a converted
lathe equipped with two knives attached to a steel plate. The flake
size was reduced by passing the flakes through a hammermill. A 3/1

inch screen was used on the hammermill for the jack pine and northern

cedar. No screen was used in hammermilling the redwood gs it is
more brittle and was broken up too much with the screen attached.

After reducing the flakes to the proper size, they were air
dried to approximately 10 percent moisture content. These flakes
were then placed in an equilibrium chamber for twenty-four hours to
attain a uniform moisture content of 6 percent. The conditions were
140 degrees Fahrenheit dry bulb and 110 degrees Fahrenheit wet bulb.

The conditioned flakes were then weighed to the correct percen-
tages fer each individual board and stored in sealed plastic bags.

All boards contained 275 grams of conditioned flakes and 8 per-
cent adhesTVe based on the oven dry weight of the flakes.

Two different adhesives were used for the boards; phenol-formal-
dehyde and urea-formaldehyde. Only the phenol-formaldehyde, due to
its moisture resistance, would be suitable for use where decay was
important. The urea—formaldehyde was used in a few boards to see
how this adhesive might affect results. The adhesive application
was accomplished in a rotating drum type mixer. This method not
only assured an even application of adhesive, but also blended the
mixture of two species. The adhesive was sprayed into the mixer us-
ing air pressure and total spraying time was two to three minutes.

In the pressing operation, most variables were held constant
and some were varied for a small number of boards. All boards were
pressed to a size of 8 inch by 8 inch using 3/8 inch stops on the
cauls. The press used was a single opening hydraulic press which
has a 200 ton capacity. The press temperature of 325 degrees Fah-

renheit and pressure of 500 p.s.i. were maintained for all boards.

12

Press time was changed on two boards to see if increased heating
might affect durability due to its action on extractives.

Tables 1 and 2 show the twenty-three types of boards produced
fer use in this study; certain of these boards were used in more
than one test.

After pressing, the boards were marked and stored in plastic

bags before cutting for the exposure tests.

Expgsure Procedure:
In preparing the specimens for exposure to the soil block test,

several methods for determining the oven dry weight were considered.
Actual oven drying was not used due to the question of the effect of
heat on the extractives responsible for the woods' durability. Con-
ditioning the blocks to an equilibrium weight is a time consuming
procedure and was not used for this reason. The method used was to
out twice the number of specimens required and use half of these to
determine the average moisture content of the board. From.the mois-
ture content and the weight of the test specimens, the oven dry weight

was computed using the following fermula:

WT . WT.g;
od M.C.+l
WTod - Oven dry weight, grams
Wgr - Original weight, grams
M.O. - moisture content at
original weight,
percent

The exposure chambers were the standard soil block bottles and

were prepared as outlined in the A.S.T.M. Standard lAlB-élT, with one

13

exception. This exception was that the feeder strips were inadver~
tantly cut with the transverse surface on the wide face. It is not
felt that this caused any great variation in the results.

The soil used in the bottles was a sandy loam with a water’hold-
ing capacity of 37.3 percent as determined by A.S.T.M. standards.
The pH of the soil was between 6.5 and 6.6 determined with a Beckman
pH meter.

The bottles were inoculated with fungus cultures obtained from
the U. S. Forest Products Laboratory at madison, Wisconsin. Lenziteg
trgbg§,(Madison 617) was the primary fungus used. This fungus is pri-
marily a softwood rotter and is commonly found on wood in service.

Two additional series of decay chambers were prepared using Polypgrus
versicolor (Madison 697). This is considered a hardwood decay agent
and was included for comparison.

The sterilized specimens were placed in the decay chambers and
these placed in a conditioning room at 80 degrees Fahrenheit and 67 percent
relative humidity. The relative humidity dropped to approximately 50
percent for a two week period due to a burned out motor, but the tempera-
ture was maintained at 801 1 degrees Fahrenheit throughout the entire

test.
The exposure period was twelve weeks and at the end of this time,

the specimens were removed, oven dried and weighed to the nearest 0.01

gram. The degree of delamination was determined and is shown in the

results.

Results and:2iscussion:

The results of the particle board decay tests are given in
Table 1 and‘Table 2. Table 1 gives the results for all boards pro-
duced using redwood and Table 2 gives results fer all boards contain-
ing northern white cedar.

The decay-composition relationship of boards 1 through 10 for
the redwood is plotted in figure 2, and of boards 1 and 18 through 26,
representing the northern white cedar, is plotted in figure 4. On
both of these graphs, the weight loss is plotted versus percentage of
durable wood present in the board.

Using a mixture of two species of wood in a single board, one of
three results should be expected; these three are discussed separately.

In case one, each wood would decay at its normal rate as though
the other wood were not present. In this case the plot of weight
loss versus percentage of durable wood should be a straight line re-
lationship represented by line "AF on both figures 2 and 4.

In case two, the durable wood could afford some protection to
the non-durable wood. In this case the above mentioned curve should
concave upward. This would be due to the following: the durable wood
would decay at its own rate, but the non-durable wood would decay at a
lower rate and move the curve down at all intermediate points.

In case three, no protective action is imparted, but rather, the
presence of the non-durable wood provides avenues of travel for the
fungus, through the board. In this case, the fungus should travel
through the avenues provided by the non-durable wood and branch out
into the durable wood. These mycelium branches could utilize the

durable wood as food substance until the toxic extractives stopped

15

their growth. In case three the percentage of decay of durable
wood should decrease as the thickness of durable wood that the myce-
lium must pass through increases. For the 100 percent redwood board
the decay would be limited to the outer shell of the particle board.
In the boards manufactured partially of redwood, this surface of
vulnerability is greatly increased.

The shape of the curve in this case should be concave downward.
The reasoning for this is analagous to that for the opposite case.
The non-durable wood should decay at its own rate, but the durable
wood would decay faster and raise the intermediate points.

The shape of the curve fer both species would seem to conform
to case three. The curve for northern white cedar starts at a lower
point; however, the upper portion of the curve is level, rather than
the lower portion. This fact would still indicate that fer the par-
ticular boards tested, case three would seem to be true.

The columns giving delamination data indicate the degree of de-
lamination after testing and subsequent drying. The rating system,
as stated on page 17, Table l, was taken from.Forest Products Labora-
tory Bulletin no. 2196. In this report they stated, "Severe delamina-
tion was not necessarily associated with high weight loss nor was the
lack of delamination closely correlated with a low weight loss.” In
the present study, this was not feund to be necessarily true. With
the exception of the 100 percent redwood board produced with urea
formaldehyde, the degree of delamination would seem to be correlated

with weight loss. Figure 5 illustrates this factor for representative

samples.

16

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Figure 1e

 

Appearance of decayed redwood particle board;

1) 100% pins, 2) 25% redwood, 3) 75% redwood, and
A) 100% redwood. Boards at left illustrate surface
in contact with feeder strips, upper face shown at
right.

18

 

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0 IO 20 30 40 50 CO 70 00 90 IOO

 

Percentage of redwood in board

Figure 2. weight loss versus redwood content in particle board.

19

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.oheoo. 303.30 .303 33: enmeshed no.“ magma." pump was spec scavenged 0.30m .0. 0.3.3.

 

Figure 3. Appearance of decayed northern white cedar particle board;
1) 100% pine, 2) 25% cedar, 3) 75% cedar, and 4) 100%
cedar. Boards at left illustrate surface in contact with
feeder strips, upper face shown at right.

21

 

30

N
O

leightleea, f of overdry weight

0

 

o I I l l l I J 1 1 l

 

 

~ 0 IO '20 30 40 50 60 70 00 90 IOO
Percentage of northern white cedar in board.

Figure l. leigit less versus northern white cedar content
in ”"101. was

22

Specimen groups 13, 14, and 17 were added to this study to see
what effect increased heating might have on durability. Specimen
groups 6, 13, and 17 were all produced with 25 percent redwood and 75
»percent pine. The amount of heat applied to these three groups is
quite different as shown in table 1, but the weight loss data are not
appreciably different. Specimen groups 10 and 14 also have the same
makeup, but different amounts of heat application. Here again, the
weight loss is not changed by additional heat.

Specimen groups 11 and 12 were produced with urea-formaldehyde,
which is not water resistant. In the 25% redwood group, the decay
loss increased and the boards were badly delaminated. The 100 percent
redwood board was not delaminated when removed from the exposure cham-
bers, but upon drying, delamination occurred. The weight loss of this
board was not increased due to the use of urea-formaldehyde adhesive.

Solid blocks of both redwood and northern white cedar were tested
for durability under exactly the same conditions as the particle board
specimens. The weight loss for the solid redwood blocks was 11.6 per-
cent, whereas the weight loss fer the solid northern white cedar
blocks was 0.9 percent.

In comparing the decay losses of solid blocks with the 100 percent
durable wood particle boards, we find the results are not well corre-
lated. Redwood particle board lost 4.1 percent of its weight, but the
solid redwood lost 11.6 percent. The most obvious factor causing this
reduction would seem to be the presence of the phenol-formaldehyde ad-
hesive which is toxic. However the 100 percent redwood board manufac-

tured with urea-formaldehyde adhesive lost no more weight than the 100

23

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percent redwood board manufactured with the phenol-formaldehyde.

Another factor which could account fOr the increased durability
would be the increased density of the particle board over the solid
wood. The density increased from 0.40 gram cm."3 to 0.76 gram cm'"3
(oven dry basis) for redwood and this could explain the variation. 6
Density is a questionable criterion of durability; however, Southam
and Ehrlich (24) concluded that, "For a single species of wood there
may be a tendency toward greater initial decay resistance in wood of
high specific gravity, but this tendency is nullified and may even
be reversed as decay progresses, and so is of little practical value."
The first half of this statement could explain the results obtained
in this study.

The decrease in durability of the northern white cedar particle
board compared to the solid block could not be explained in this way.
It is possible that some toxic component of the extractives reacted
with the phenol-formaldehyde and was lost in this way. There is no
comparable board produced with urea-formaldehyde and therefore it is

difficult to draw conclusions in this case.

25

VENEEB.TEST

Mars:

This test was designed to determine if a durable wood could
protect a thin layer of non-durable wood in close contact with it.

Thin veneers of southern yellow pine sapwood were cut at vary-
ing thickness measurements. The thickness began at approximately
0.005 inch and was increased by 0.010 inch intervals to a maximum
of 0.055 inch. These veneers were trimmed to 0.75 inch by 1 inch.
The oven dry weight of the veneers was determined by the same me-
thod used for the particle board specimens. The weight was deter-
mined to the nearest 0.0001 gram as the veneers were of very low
weight.

These veneers were fastened to the top of a small block of
redwood of the same dimension as the veneer. The veneers had to
be firmly attached so they would remain in close contact. This was
accomplished by having the veneers at a high moisture content be-
fore fastening them down on the redwood block. In this way they
would not swell in the moist decay chambers and buckle away from
the redwood block. The veneers were held down with two nichrome
wires placed and tightened around the entire assembly. It was felt
that the nichrome wire was so inert that it could have no effect on
the fungus growth. Figure 6 shows the completed test assembly and
the materials going into it.

Five assemblies of each veneer thickness were exposed in stan-

dard soil block bottles, to the fungus Lenzites trabea. The

26

specimens were exposed with the non-durable veneer resting directly
on the feeder strips in the soil block bottles. The same soil and
conditions were used for these exposure chambers as in the particle
board tests.

A control group of five veneers with no redwood contact were
also tested. These veneers were placed directly on the feeder
strips and held down with squares of heavy window glass.

The specimens were removed from the chambers at the end of
four weeks. The pins veneers were carefully removed and oven dried.
Some of the thinner veneers had to be oven dried in individual con-
tainers so that no particles would be lost. The specimens were then
weighed to the same accuracy as prior to test. Weighing was done
using closed weighing bottles so that no moisture could be picked

up and affect results.

27

 

 

 

 

 

Figure 6. Method of assembly and complete I'Veneer Test" Assembly.

28

Results and Discussion:

From the results of the veneer test, it is obvious that the
redwood imparted a protective action to the thin pine veneers.

This fact is not entirely in agreement with results obtained from
the particle board test. A possible reason for these differences
could be the difference in moisture conditions of the test speci-
mens. The thin pine veneers and redwood blocks were kept at a very
high moisture content prior to exposure. This was to keep the veneer
from buckling away from the redwood blocks in the moist decay cham-
bers. The completed assemblies, at this very wet condition, were
then sterilized for 20 minutes prior to exposure. This period of
heating should produce considerable movement of steam and carry some
of the hot water soluble extractives from the redwood through the
pine veneer.

At no time during manufacture and testing were the mixtures of
species in the particle board subjected to heat while at a moisture
content over approximately 6 percent.

Anderson (25) has found that when redwood lumber dries, water
solubles are carried to the outer surface of the lumber. He states
that, "As the moisture evaporates from the surface, it leaves a heavy
deposition of water solubles at and near the surface." The above
statement and the fact that the completed assemblies were above the
fiber saturation point could explain the increased durability of the

pine veneers attached to the redwood blocks.

29

Table 3.

Test results for veneer'test.

 

 

Veneer thickness, inches Wt. loss, % Wt. loss, grams
0.007 15.8 0.0060
0.014 11.2 0.0074
0.026 13.0 0.0191
0.037 4.9 0.0116
0.046 8.0 0.0215
0.053 8.3 0.0260
0.013* 64.1 0.0417

 

* Control, no redwood block

30

 

 

Figure 7. .Appearance of pine veneers after exposure to Lenzites trabea.
Thickness of veneers was: 1) 0.007 inch, 2) 0.014 inch,
3) 0.026 inch, 4) 0.037 inch, 5) 0.046 inch, and 6) 0.053

inch. Number 7 shows extreme of decay present in veneer
of 0.026 inch thickness.

31

MICROSCOPIC EXAMINAI ION

Microscopic slides were made of various redwood boards used in
this study to show board makeup and location of decay. Color photo-
micrographs were taken of the 25 percent redwood particle board before
and after exposure to decay organisms.

Figure 8 illustrates the cross section of the 25 percent board
prior to decay tests. This block was prepared for sectioning by im-
bedding the particle board in butyl—methacrylate; the procedure fol-
lowed is given in a publication by Rohm &:Haas Company (26). Section-
ing was done on a sliding microtome and the slide was stained with
safraninrfast green as outlined in Sass (27).

The photomicrographs in Figure 9 illustrate the fungus hyphae
present in a board of the same redwood percentage after decay tests.
These sections were cut on a freezing microtome using carbon dioxide
under pressure to freeze the block while cutting. These sections were
stained with safranin and picroanaline blue as outlined in Cartwright
and Findlay (22). The decayed sections were cut from a position as
close to the center of the test block as possible.

Sections were also cut from the center of the 100 percent redwood
particle board after exposure in the decay test. No fungus hyphae
were observed in these sections. The fact that hyphae were found in
the center of the 25 percent redwood board would seem to substantiate
the theory that the pine allows entrance of the fungus into the center
of the board. Numerous hyphae were found in sections made from redwood

flakes removed from the center of the 25 percent redwood board. This

32

gives evidence that once the fungus gains entrance through the
"avenues of travel“ furnished by the pine, it can attack the red-
wood in the center of the block. This means the redwood flakes
adjacent to pine flakes in the center of the 25 percent redwood
board are as susceptible to decay as the redwood flakes on the
exterior of the 100 percent redwood board. Hyphae were found in

the surface flakes of the 100 percent redwood board.

33

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u
\t'
\

a. 721

| \‘
\
|

"
.\..
'\ o
‘1‘.

\

r
I, no

 

b. 721

 

Figure 8. Photomicrographs of 25 percent redwood particle board
prior to decay tests.

34

a. 2761:

 

c. 5521

 

Figure 9. Photomicrographs of 25 percent redwood particle board
after decay tests, showing fungus hyphae.

35

CONCLUSIONS

From the results of this study, the principle of protecting
a non-durable wood with a durable species does not seem feasible
with the manufacturing methods used.

The results of the veneer test illustrate that the redwood
can protect a non-durable species under suitable conditions. Whe-
ther these conditions could be applied to particle board manufac-
ture cannot be answered in this paper.

The boards manufactured with urea-femaldebyde adhesive demon-
strate that even a durable species particle board is subject to
severe delamination with this adhesive.

The different degrees of heat had no effbct an the durability
of the boards produced. From these results it would seem that the
heat used in the normal production of particle board does not impair
the decay resisting effectiveness of the extractives in redwood.

Increasing the density of the redwood in particle board as com-
pared to solid wood increased its durability considerably. Whether
this increase is only in the initial stages of decay cannot be told

from the data.

36

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RECOMMENDATIONS FOR.FURTHER STUDY

This study was undertaken to determine whether a durable
species could protect a non-durable species from decay. With
the methods used in the production of the particle board tested,
it would seem that no protective action was imparted.

A primary factor deserving more attention is the movement
of extractives through the board. If the board were soaked in
water, some of the extractives might leach into the non-durable
species and protect it in this way. Another possibility is that
if the boards were pressed at a high moisture content, the in-
creased steam during pressing might carry extractives through the

entire board.
Density might also be a factor affecting the durability of a

board produced in this way. If the flakes were brought into closer

contact, the durable wood night prove more effective.

37

4.

5.

7.

9.

10.

11.

12.

13.

14.

BIBLIOGRAPHY
Mn; .1945. Redwood. The Institute of Paper Chemistry
Research Bulletin.

Wise, L. E. 1944. Wood Chemistry. Reinhold Publishing Cor-
poration, New York.

Hillis, W. E. 1962. Wood Extractives. Academic Press, New

' York and London.

Gripenberg, J. 1949. The Constituents of the (Heart) Wood
of Thuja occidentalisL. Acts Chemica Scandinavica, Copenhagen
3 (7). From Forestry Abstracts 1949-50. 11 (pp. 484)

Scheffer, T. C. and Hopp, H. 1949. Decay Resistance of Black
Locust Heartwood. U.S.D.A. Technical Bulletin 984.

Tarkow, H. and Krueger, J. 1961. Distribution of Hot Water
Soluble Material in Cell Walls and Cavities of Redwood. For.
Prod.Jour. ll (5)-

Anderson, A. 8., Duncan, 0. G. and Scheffer, T. C. 1962.
Effect of Drying Conditions on Durability of California Redwood.
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Hann, R. A., Black, J. M. and Blomquist, a. r. 1962. How
Durable is a Particle Board? For. Prod. Jour. 12 (12).

Clark, J. I. 1960. Decay Resistance of Experimental and
Commercial Particle Board. U. S. For. Prod. Lab. Report 2196.

Klauditz, l. and Stolley, I. 1954. Development and Manufacture
of Chipboards Resistant to Fungi and Termites. Holz. Rah-u.
Werkstoff 12 (5). From Forestry Abstracts 1955. 16 ( pp 292).

Narayanamurti, D., Prasab, B. N., and George, J. 1961.
Protection of Chipboard from Fungi and Termites. Norsk.
Skogind. 15 (9). From Forestry Abstracts 1962. 23 (pp. 336)

Huber, H. A. 1958. Preservation of Particle Board and Hardboard
with Pentachlorophenol. For. Prod. Jour. 8 (12).

Brown, C. E. and Aldon, H. M. 1960. Protection From Termites:
Penta for Particle Boards. For. Prod. Jour. 10 (9).

Sokolova, T. E. and Timofeeva, O. G. 1959. Biological Protec-

tion of Wood Chip Panels. Stroitelrve Materialy 5 (10). From
Forestry Abstracts 1960. 21 ( pp. 675).

38

at

.

. .

. .

.

.t

e
O
,
.
.
s ' ‘
.‘ 1‘
.- k,
. .0
l.
0 .’
.
.
‘l
G. u.
0
J n
. O
f
9.
' .
a
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v

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Assn-L. __ "_____ American Society for Testing and Materials.
1956. Method of Testing Wood Preservatives by Laboratory
Soil-Block Cultures. A. S.T. M .designation: D1413-61.

McNabb, H. S. 1958. Procedures of Laboratory Studies on
Wood Decay Resistance. Proc. Iowa Academy of Science
653150-159e

Brown, F. L. 1963. A Tensile Strength Test for Comparative
Evaluation of Wood Preservatives. For. Prod. Jour. 13 (9).

Hartley, 0. 1958. Evaluation of Wood Decay in Experimental
Work. U. S. For Prod. Lab. Report 2119.

Duncan, G. G. 1958. Studies of the Methodology of Soil-
Block Testing. For. Prod. Lab. Report 2114.

Proctor, P. 1941. Penetration of the Walls of Wood Cells by
the Hymae of Wood-destroying Fungi. Yale School of Forestry
Bull. 47.

Cowling, E.B. 1958. A review of Literature on the Enzymatic
Degradation of Cellulose and Wood. For. Prod. Lab. Report 2116.

Cartwright, K. St. G. and Findlay, W. P. K. 1958. Decay of
Timber and its vaention. Her Majesty's Stationery Office,
London.

Lyr, H. 1962. Detoxification of Heartwood Toxins and Chloro-
phenols by Higher Fungi. Nature 195.

Brown, H. P., Panshin, A. J., and Forsaith, 0.0. 1949. Textbook
of Wood Technology. Vol. 1. McGraw-Hill Book Comparw, Inc.
New York, Toronto and London. .

Anderson, A. B. 1961. The Influence of Extractives on Tree
Properties. 1. California Redwood (Sequoia Sempervirens).
Jour. Institute of Wood Science. 8.

ML.-- Embedding Specimens in Methacrylate Rosina. Rohm &
Haas Comparv, Philadelphia.

Sass, J. E. 1961. Botanical Microtechnique. The Iowa State
University Press, Amos, Iowa.

Colley, R. H. 1953. The Evaluation of Wood Preservatives.
Bell Telephone System, Technical Publication Monograph 2118.

39

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