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This is to certify that the
thesis entitled
The Effect of Cyclic Environments on the
Compression Strength of Boxes Made From High-Performance
(Fiber-Efficient) Corrugated Fiberboards
presented by

Antika Boonyasarn

has been accepted towards fulfillment
of the requirements for

 

M.S . degree in MIDL'

W

Bruce R. Harte, Ph.D.

Major professor

 

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TO AVOID FINES return on or betore date due.

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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MSU I: An Affirmative Action/Equal Opportunity Inuitution
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' 7} -H‘IH l"

THE EFFECT OF CYCLIC ENVIRONMENTS ON
THE COMPRESSION STRENGTH OF BOXES MADE FROM
HIGH-PERFORMANCE (FIBER-EFFICIENT) CORRUGATED FIBERBOARDS

By

Antika Boonyasarn

A THESIS

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

MASTER OF SCIENCE

_ School of Packaging

1990

ABSTRACT

THE EFFECT OF CYCLIC ENVIRONMENTS ON
THE COMPRESSION STRENGTH OF BOXES MADE FROM
HIGH-PERFORMANCE (FIBER-EFFICIENT) CORRUGATED FIBERBOARDS
By

Antika Boonyasarn

The compression strength of boxes made from high-performance (fiber-
efficient) linerboards subjected to cyclic environments was investigated. The
compression strength of two types of boxes made from fiber-efficient linerboards
(regular fiber-efficient linerboards and highly fiber-efficient linerboards) was
compared with the compression strength of boxes made from standard
linerboards, after exposure to cyclic conditions. The effect of moisture
absorption by box materials on compression strength was also investigated.

Exposure to the cyclic conditions used in this study caused significant
reduction in compression strength of all box types. Boxes made from regular
fiber-efficient linerboards experienced greater loss of strength than boxes made
from standard linerboards, after exposure to the cyclic conditions, however,
there was no significant difference in their final compression strength. Only
marginally significant differences in loss of strength were found for boxes made
from highly fiber-efficient linerboards and boxes made from standard
linerboards, in addition, no Significant difference in their final compression
strength was found. Differences in moisture absorption among the box materials
was a factor causing the variation in loss of strength among the box types.
Compression strength decreased as the moisture content of the box material

increased.

Dedicated to

uruufiu LLR: 5mm umruzmum

(my parents, Boonserm and Araya Boonyasarn)

ACKNOWLEDGEMENTS

I would like to thank the following people, without whom, this work would
not have been possible:

Dr. Bruce Harte, for his patience, support and professional advice, while serving
as my major advisor.

Dr. Diana Twede, for her understanding, support and guidance, while serving on
my committee.

Drs. Julian Lee and Lloyd Rinehart, for their guidance, assistance and time,
while serving on my committee.

Dr. John Gill, for his statistical know-how

and Jaruloj Eamsiri, John Hartzell and Kelly Pashos, for their friendship, support
and humor.

TABLE OF CONTENTS

Page
LIST OF TABLES v
LIST OF FIGURES vi
INTRODUCTION 1
LITERATURE REVIEW 4
l. Standard (Conventional) Corrugated box ............................................ 4
II. High-performance (Fiber-efficient) Corrugated Box .......................... 5
Ill. Compression Strength ........................................................................... 9
IV. Compression Strength Testing Method ............................................ 13
V. Effect of Temperature and Humidity on Compression
Strengthof Corrugated Box ................................................................. 17
VI. The Effect of Cyclic Condition on Paper Properties ....................... 23
VII. Distribution Environment .................................................................... 21
EXPERIMENTAL PROCEDURES 25
Test Materials .............................................................................................. 25
Process Techniques for Fiber-efficient Linerboard .............................. 27
Box Set Up ................................................................................................... 28
Pre-condltioning ......................................................................................... 29
Cyclic Conditioning .................................................................................... 29
Test Methods ............................................................................................... 31
Experimental Design ................................................................................. 32
RESULTS AND DISCUSSION 35
l. Boxes Made From Standard Linerboards vs Boxes Made From
Fiber-efficient Linerboards ..................................................................... 37
L! Loss of strength ................................................................................. 38
I." Final compression strength ........................................................... 47
II. Effect of Moisture Absorption ................................................................ 49
Ill. Effect of Cyclic Conditions ................................................................... 51
IV. Compression Strength After Re-conditioning .................................. 57

Page

SUMMARY AND CONCLUSIONS 66

APPENDICES
Appendix A ................................................................................................. 69
AppmkfixB ................................................................................................. 72
AppendxC) .................................................................................................. 73
Appendix D .................................................................................................. 75
AmpemflxE .................................................................................................. 76
AmpemflxF .................................................................................................. 77
AppemmXCB .................................................................................................. 78
Appendix H .................................................................................................. 79
Appemfixl .................................................................................................... 8O
AppemfixJ ................................................................................................... 81
AmpemfixKi .................................................................................................. 82
Appendix L .................................................................................................. 83

BIBLIOGRAPHY 84

iv

LIST OF TABLES

Page
Table 1 Physical properties of the box materials .............................................. 36
Table 2 Compression strength values of boxes made from 69-lb standard
linerboard and boxes made with 58-lb fiber-efficient linerboard... 39
Table 3 Results from the analysis of difference analyzing loss of strength
between boxes made with 69-Ib standard linerboard (box A)
and boxes made with 58-lb regular fiber-efficient linerboard

(box 8) for each cyclic condition ........................................................... 40
Table 4 Compression strength values for boxes made with 90-Ib standard
and boxes made with 69-Ib highly fiber-efficient linerboard ........... 44

Table 5 Results from the analysis of difference analyzing loss of

Strength between boxes made with 90-lb standard linerboard

(box C) and boxes made with 69-lb highly fiber-efficient

linerboard (box D) for each cyclic condition ...................................... 45
Table 6 Results from the analysis of difference in final compression

strength between boxes made from 69-lb standard linerboards

(box A) and boxes made from 58-Ib regular fiber-efficient

linerboards (box 8) for each cyclic condition .................................... 48
Table 7 Results from the analysis of difference in final compression

strength between boxes made from 90-lb standard linerboards

(box C) and boxes made from 69-Ib highly fiber-efficient

linerboards (box D) for each cyclic condition ................................... 50
Table 8 Percent mositure gain of box materials held at 73F, 85% RH ....... 52
Table 9 Loss of compression strength for each box type after exposure

to cyclic conditions ................................................................................. 55
Table 10 Percent moisture content of box material after exposure to cyclic

condition ................................................................................................. 56

Table 11 Compression strength of all four box types after exposure
to TAPPI standard conditions, cyclic conditions and
re—conditioning ...................................................................................... 60

LIST OF FIGURES

Page

Figure 1 Load-deflection curve from compression test .................................... 15
Figure 2 Outdoor relative humidity for Madison, 1-10 February, 1987 ......... 24
Figure 3 Testing sequence for determining compression strength of boxes

and moisture content of box materials ................................................. 33
Figure 4 Difference in loss of strength between box A and box 8 ................. 41
Figure 5 Difference in loss of strength between box C and box D ................ 46
Figure 6 Percent moiture gain for the four different box materials ................. 53
Figure 7 Loss of compression strength and material moisture content

after exposure to cyclic condtion for all box types ............................. 58
Figure 8 Relationship between loss of strength and material

moisture content ...................................................................................... 59

Figure 9 Compression strength determined after cyclic condition exposure
and after re-conditioning and moisture content of box materials... 61
Figure 10 Development of hydrogen bonds from water evaporation ........... 64

vi

lNIBQDlLQIIQN

Many warehouses are forced to stack containers as high as possible
because of their limited storage space. The compression strength of corrugated
fiberboard containers made from conventional materials may be inadequate to
provide the level of strength required. End-users may need containers that
provide greater compression strength at a cost-efficient price.

A conventional way to increase compression strength is to increase the
number of fibers in the linerboard and/or medium, or by using a multiwall
construction. Although higher levels of compression strength may be obtained,
the increased cost may make the container unaffordable. High-performance or
fiber-efficient corrugated materials have been developed in an attempt to
acquire the needed level of compression strength at an efficient price.

Several technologies are used in the production of high-performance
corrugated materials. The technologies that are commonly used in the industry
are classified into four categories: chemical enhancement, improvement of fiber
orientation, high-pressure forming and multiple medium (Spanlding, 1989).
Each of these processes can provide the additional stmctural strength, and the
different methods can be combined to produce one container.

One of the most commonly used techniques is chemical enhancement. In
this process, chemicals are impregnated into fibers to create bridging bonds
between fibers. The bridging bond welds the fibers together and results in
greater resistance to deformation under stressed conditions.

Improvement of fiber orientation redirects the fibers during paper

production. Typically most fibers mn parallel to the machine direction. Thus the

fibers lay horizontally around the box after the container is form. This results in
low top-to-bottom compression strength of the final box. If more of the fibers are
forced to run perpendicular to the machine direction, the final box will have
more fibers running vertically up and down its which results in the higher box
compression strength.

High-pressure board forming is a process that uses elevated mechanical
pressure to compress paper fibers during the manufacturing process. This
creates better fiber-to-fiber bonding and a denser sheet, and as a result there is
an increase in the material's strength. High-pressure forming also tends to
squeeze more water out of the pulp. This causes a decrease in material
moisture content and thus better strength.

Multiple medium is a technique that obtains better compression strength
by laminating two or more layers of medium together. This can create a single-
wall board which performs as well as double-wall boards weighing up to 10
percent or more.

However, despite these approaches, there is concern that high-
performance boxes may not perform as well as conventional boxes when
subjected to cyclic environments. A "cyclic environment" is defined here as one
where the climatical conditions of temperature and relative humidity fluctuate
through several levels. Simulation of real-life situations using cyclic
environments are used because most warehouses are often unable to control
the effect of rapidly changing weather conditions even with climate control
systems. In addition, containers that are shipped regionally, nationally‘ or
internationally may be sent from areas of low humidity conditions to high
humidity environments and vice versa.

Cyclic environments have been shown to have an adverse effect on

paper's performance under loads (Byrd, 1988). Cyclic changes in relative

2

humidity results in a more rapid decrease of compression strength in corrugated
fiberboards than a constant relative humidity condition. Thus, loaded boxes
exposed to cyclic. relative humidity conditions are most likely to fail before
similarly loaded boxes subjected to a constant relative humidity environment. A
box that performs acceptably in a constant relative humidity condition might not
be acceptable in a cyclic environment.

There have been extensive studies conducted to examine the
performance of various kinds of fiberboards under cyclic conditions. These
range from corrugated fiberboards made from high-yield, normal-yield, virgin
and recycled pulps to corrugated fiberboards made with press-dried and
conventionally-dried linerboard. Yet, the effect of cyclic environments on
corrugated boxes made from high-performance materials has not been
reported.

Compression strength is most widely used as a measure of final box
performance because of its relationship to box stacking performance. It also can
be used as an indicator of the overall quality of the materials and the efficiency

of the box manufacturing process.

The objectives of this study are:

- To measure and compare the compression strength of corrugated boxes
made from two types of high-performance linerboards, subjected to cyclic
and non-cyclic environments.

- To compare the compression strength of corrugated boxes made from
high-performance linerboards in a cyclic environment to that of corrugated
boxes made from conventional linerboards in the same cyclic environments.
- To determine the relationship between moisture content and compression

strength in high-performance corrugated fiberboard.
3

LW

A corrugated fiberboard box consists of two structural components:
corrugating medium and linerboard. The corrugating medium is the fluted or
corrugated center of the board, and the linerboard is the flat material attached to

the medium.

Corrugating Medium

The corrugating medium is mostly manufactured from semichemical
processed hardwood (Kline, 1982). Hardwood fibers are preferred over
softwoods because the hardwoods cost less and contribute to the particular
type of strength needed in corrugating medium. In the semichemical process,
the pulp is not washed thoroughly as with chemical pulp, therefore, lignin and
other hemicelluloses are left with the fibers. These chemicals help to bond the
web of paper together and form the rigid fluted shape needed. The short
hardwood fibers are less flexible than softwoods and, thus, provide stiffness to
the corrugating medium. Secondary (recycled) fibers are also used in the
corrugating medium, however, they cannot be used for more than 40% of the
weight of the paper, otherwise the stiffness will suffer. Fillers and sizing agents
are not needed for the medium unless wet strength agents are used to provide

water resistance.

Linerboard

Most of the linerboard used for corrugated board is unbleached kraft. The
kraft pulping process is basically an alkaline cook. The predominant raw
material used to manufacture linerboard is softwood fibers, though the
linerboard may contain up to 20% hardwoods or secondary fibers (Kline, 1982).
Softwood fibers are required to provide the necessary strength to the
linerboard. Mineral fillers are not normally used since they can reduce the
strength of the board, however, because of higher fiber costs, clay may be used
in order to add to the weight of the board and thus reduce the cost as long as
the strength is not reduced too severely. Chemicals may be used to provide

water resistance or increase wet strength of the board.

In recent years, there have been many research studies designed to
improve corrugated box performance by improving the compression strength of
boxes. Increasing fiber costs, expensive warehouse and tmck space, and high
quality standards are factors that contribute to this research effort. The
development of a process and/or material change which would allow
manufacturers to reduce raw material and operational costs without a
consequent reduction in paper properties would be enormously significant.

The development of high-performance or fiber-efficient corrugated
materials and containers have been extensively introduced to fulfil this need.
High-performance corrugated fiberboard is a product that provides substantially
more compression strength than the conventional corrugated fiberboard
(T alsma, 1989). Several technologies are being used in the production of high-

performance corrugated board. Processes as simple as laminating linerboards

5

and mediums together or as complicated as to require special mill process in
the papermaking machines are being used. Some use more medium in their
boxes than in conventional ones. Several of these techniques improve the
linerboard Since it is a key attribute which provides compression strength to the
corrugated container (Peterson and Fox, 1980). Each process adds a certain
amount of strength, different methods can be combined in one container.
Spanlding (1989) classified commonly used processes for the production
of high-performance corrugated board into four categories: chemical
enhancement, improvement of fiber orientation, high pressure forming, and

multiple mediums.

Chemical Enhancement

One of the most commonly used processes to increase compression
strength of corrugated board is chemical enhancement (Walthy, 1987). In this
process, chemicals are impregnated into wood fibers which can create bridging
bonds between the fibers. The bridging welds the fibers together and results in
greater resistance to deformation under stressed conditions.

Walthy (1987) reported that the two primary chemicals that are used to
create a high compressive strength board are sodium silicate and urea
formaldehyde. Both can improve compression strength of boxes made with
typical adhesives and processing techniques without sacrifying printability,
gluability, or runnability. In addition, both chemicals improve box compression
properties in a high humidity conditions.

Urea formaldehyde treated board maintains better strength
characteristics after prolonged exposure to high humidity than sodium Silicate
treated board. However, urea formaldehyde contains low levels of free

formaldehyde, which is a probable known carcinogen. This can cause a

6 .

potential health hazard. Sodium silicate, on the other hand, is less expensive
and has almost no negative environmental impact.

Walthy (1987) found that an approximately 10% addition of sodium
Silicate gave a 42-lb basis weight linerboard the same compressive strength as
that of a 69-lb linerboard. As a result, a 69-lb / 26-lb / 69-lb board can be
replaced by a treated 42-lb / 26-lb / treated 42-lb board which results in

substantial economic saving.

Improvement of Fiber Orientation

Improvement of fiber orientation or fiber cross-linking redirects the fibers
during the paper manufacturing process. Typically, fibers runs parallel to the
machine direction, thus the fibers lay horizontally around the box after the
container is formed. This is the worst direction to obtain high top-to-bottom box
compression strength.

Cross linking is a technique that forces more of the fibers to run 90
degree to the machine direction. It reduces the ratio of machine direction (MD)
to cross direction (CD). This causes more fibers to run vertically up and down
the panels of a container and, as a result, higher compression strength is
obtained.

The effect of the fiber orientation was studied by Whitsitt (1988). It was
concluded that by reducing the ratio of MD:CD of the linerboard, the CD
compression strength of the linerboards was increased and hence, box

compression strength.

High-pressure Forming
High-pressure board forming is another commonly-used process to

increase compression strength of linerboard. It is performed during paper

7

production. Spanlding (1989) explained that, this technique involves increasing
the degree of pressure on the paper fibers to more tightly compress them. This
creates better fiber-to-fiber bonding and a denser Sheet, the denser the paper
the stronger it becomes. As a result, box compression strength is increased.
High-pressure forming also tends to squeeze more water out of the pulp. This
results in a decrease moisture content of the paper and thus better strength. In
addition, Talsma (1989) added that tightly compressed board provides a
smoother surface as a barrier against abrasion during handling in the
distribution. The consistent porosity of the board also helps assure smoother
handling with vacuum-fed packaging equipment.

The influence of high-pressure forming on compression strength was
studied by Whitsitt (1988). He found that the highly pressed linerboard gained
more compression strength and combined boards made with these linerboards

exhibited improved edge cmsh values.

Multiple Medium

The lamination of two or more layers of medium together is another
innovation that offers increased compression strength (Spanlding, 1989) Two
or more layers of medium are laminated together combining them with
linerboard into a corrugated board. The glue can be a simple starch based
adhesive. Spanlding stated that double medium cornJgated boxes retain a thin,
single-wall construction, but they can perform as well as double-wall boxes

weighting up to 10 percent more.

"L W

The performance requirements of a corrugated shipping container range
from need for advertising appeal to mechanical strength to protect the product.
In transportation and storage of goods, sufficient strength is required to sustain
the load of several filled boxes placed on top, and to protect contents from
forces resulting from freight cars humping, from end thrust in a truck that stops
suddenly, or from forces caused by rough handling (Kellicutt, 1960). Kolseth
and Ruvo (1983) added that in many cases, additional strength is required to
resist vibrational load during the shipment.

Compression strength is generally considered to be the most prominent
indicator of final box performance. There are two reasons for this (McKee,
1961): (1) compression strength is directly related to warehouse stacking
performance and (2) laboratory tests of box compression strength is a useful
tool to evaluate the overall quality of the materials and the quality of its
manufacture.

In order to successfully design corrugated boxes for long-term storage,
package designers have to know how much strength containers must have
(Koning and Stern, 1977). Quite often, this has been decided based on design
curves of compressive strength and stacking time period, past experience, trial
and error, or guesswork. For instance, Kellicutt and Landt (1951) developed
design curves by conducting compression tests to find a relationship between
box compressive strength and the length of time that containers were exposed
to dead loads at a specific temperature and humidity. Their design curve shows
that, in general, for dead loads less than 75% of the box compressive strength,
each decrease of 8 percentage points in the ratio of the dead load to the

compressive strength resulted in extension of failure time by about eight times.

9

Before selecting materials and designing box stmcture to acquire the

necessary box compressive strength, it is important to examine how a

compressive load is distributed on corrugated boxes. McKee, et al (1961)

described the top-to-bottom compression behavior of most conventional,

vertical flute, corrugated boxes in tests as follows:

"As the applied load is progressively increased, a load level is
eventually reached where the side and end panels of the box become
unstable and deflect laterally. The beginning of bowing of the panels may
or may not be markedly evident , depending on whether the panel is
initially nearly flat or, on the other hand, is warped or bowed due to box
manufacture and setup. Having become unstable, the central region of
each panel suffers an appreciable decrease in its ability to accept further
increase in load.

Bowing of the panels, however, does not usually coincide with the
maximum load-carrying capacity of the box. The combined board near
the vertical edges of each panel is constrained to remain essentially flat
because the adjacent panels of the end thrust is capable of accepting
substantially greater load (by reason of its stable configuration) than the

most centrally located regions of the panel."

McKee, et al (1961) added that the centermost portions of the panels

carry only one-half to two-thirds the intensity of load sustained at the edges of

the box failure. The box reaches its maximum load when the combined board at

or near a comer of a panel mptures. Maltenfort (1980) also found that the edges

or corners of the box carried 64 percent of the total compressive load and that

10

the panels carried the remaining 36 percent. The load carried by any particular
corner did not differ from that carried by any of the other three.

There are several ways to evaluate box compression strength.
Compression testing of the empty box has been widely used to measure the
compression strength. It is probably the best "all-around” method for evaluating
the final box quality (Maltenfort, 1988). Box compression test reflects several
factors that contribute to box strength (McKee, 1963). Contributing factors
include grade of the combine boards, box dimensions, and quality of the
manufacture.

McKee, et al (1963) developed an equation which is known as the
McKee formula and is used to predict box compression strength. The formula is
as follows.

Top-to-Bottom Compression = 5.87 PmJ'Z_h

where: Pm edgewise compression, in lbs/in
Z = box perimeter (2L+2W), in inches

h

board caliper, in inches

McKee (1963) explained that in box compression, box failure is triggered
by failure of the combined board at the vertical edges. Both linerboards and
corrugating mediums are approximately uniformly stressed in edgewise
compression. Therefore, in the formula, the edgewise compression strength of
corrugated board (in the direction of the flutes) is primarily important to predict
the box compression strength.

According to McKee, et al (1961), the board at the center region of each
panel carries less load than the board near the edges, however, it is significant
and must be considered in predicting box strength. The load-carrying capacity
of the central region of each panel reflects the bending characteristics of the

combined board and the panel dimensions. Therefore, flexural stiffness, the

11

measure of the ability of the board to resist bending, should be included in any
analysis of box compression strength. Since determining the stiffness value of
corrugated board is very cumbersome, the board thickness, which is well
correlated with stiffness, has been introduced to modify the original equation.

Nordman, et al (1978) stated that the thickness of corrugated board has a
major influence on the compressive strength of boxes. Thus, it is important to
avoid subjecting the board to treatments which lead to a reduction in the
thickness of the board. However, during manufacture, board components or
combined boards may be damaged by compressive forces. For example, when
the board is run through printing or converting machines, perpendicular forces
applied to the surface of the board may cause considerable sidewall
compression. As a result, the board does not posses the ultimate strength
obtainable from its components.

The asymmetrical construction of corrugated board can also influence
the distribution of compressive loads on boxes. Asymmetrical construction
refers to the corrugated boards that have different weight grades, ie. different
stiffness levels on the inside and outside linerboards. In practice all boxes are
filled, so that any bulge is outward. That means the outside linerboard will be
stressed in tension while the inside will be in compression. Maltenfort (1980)
explained that as long as both linerboards have the same weight grades, load
distribution does not affect ”inside” and "outside” differentially. If the construction
is asymmetrical, then a heavier or stiffer linerboard inside the box will accept a
higher compression load than if the lighter or less stiff linerboard had been in
that position. Therefore, the heavier liner should be located inside in order to
acquire the most box compression strength.

There are several other factors that have an influence on the

compressive strength of corrugated boxes. These include: moisture content of

12

board, flute construction, misalignment in stacking, content's role in supporting

the load and cyclic environments.

IV. W

Estimation of box compression strength based on individual component,
combined board and box criteria can be used to determine, before the box is
manufactured, how much compression strength it will have (Maltenfort, 1988).
The need for such procedures has increased since more corrugated boxes are
being used as the shipping containers. There are a number of methods which

can be used to evaluate and predict compression strength of corrugated boxes.

Box Compression Test

According to Maltenfort (1988), the box compression test is considered to
be the best ”all-around" method for predicting the final box performance. McKee
et al (1961) stated that the box compression test, however, has a critical
limitation. The limitation is that the box compression test generally cannot
distinguish between several factors which contribute to box strength. These
factors are: (1) quality of the basic materials - linerboard and corrugating
medium, (2) box dimensions, (3) corrugating and conversion variables, and (4)
environmental effects (humidity, duration of loads, etc.). In the event of
inadequate box strength, it may not be apparent whether the fault is due to the
linerboards or corrugating mediums, or the manufacturing process, or the
conversion operation.

In a compression test for shipping containers, according to ASTM 0642-
76, a box is placed on the lower platen of a compression tester which is

connected either to a load cell or to a mechanical scale. The upper platen is

13~

lowered onto the box at a constant rate of 0.5 inch per minute until the box

collapses. A load-deflection curve is recorded as the test proceeds (see Figure

1).

Edge Crush Test

Stott (1988) believes that the edge crush or edgewise compression test
(ECT) is the best measurement of board properties. Among the different board
properties, the ECT value has the closest relationship with final box
performance. Moreover, it is the most important input into the McKee formula,
which is the most used equation for prediction of box compression strength.
McKee et al (1961) stated that the edgewise compression strength of the
corrugated board is a major factor in the top-load compression strength of a box
because in testing, it has the same type of failure which triggers box failure in
top-load compression.

In the ECT test, a rectangular specimen of combined board is placed on
its edge in a compression tester. The load is applied perpendicular to the flutes.
The largest force that the specimen can withstand without failure is reported as
the edge crush value.

There are several ECT methods being used in laboratories (Stott, 1988).
These methods include TAPPI, ASTM, FEFCO Method No.8, JIS 0402, FPL
proposal, IPC proposal and the Weyerhaeuser method. Stott reported that the
TAPPI method widely used in the United States is not well suited to routine use
due to the complications and delays resulting from the required edge-waxing
step. European Federation of Corrugated Board Manufactures (FEFCO)
recommended adopting FEFCO method No.8 as the international standard
method. One of the reasons is that this method is operationally convenient with

a known and acceptable level of interlaboratory agreement. Moreover, its

14

 

 

  

 

POINT or FAILURE
(0
O
2
D
O
A.
c;
3 DEFLECTION—w
.J

 

 

DEFLECT ION. INCHES

 

 

 

Eigure, 1 Load-deflection curve from compression test.

15

results correlate highly with results of other test methods that use more
elaborate and expensive methods. In FEFCO Method No.8, a Billerud cutter,
which Simultaneously cuts both loading edges of the sample in a clear and

precise manner, is required.

Flexural Stiffness

McKee, et al (1962) stated that the top-load compression strength of
corrugated boxes depends mainly on the edgewise compression strength of the
corrugated board in the cross-machine direction, and to a considerable extent
on the flexural stiffness in both machine and cross direction of the corrugated
board. Flexural stiffness is the ability of the board to resist bending.

McKee, et al (1961) explained that side and end panels of a vertical flute,
RSC box usually bow outward or inward when subjected to top-to-bottom
compression. Bending of the panels limits their load-carrying ability over the
central region of each panel. As a result, analysis of box compression strength
essentially includes consideration of the flexural stiffness of corrugated board.

One of the most commonly used methods to measure flexural stiffness is
the four-point beam test. In this test (TAPPI T 820 cm-85), a specimen out either
in the machine or cross machine direction is placed on two supporting anvils.
Two loading anvils are placed on the top of the specimen. The top anvils are
then successively loaded with weights of equal increments. The deflection
caused by each weight is measured with a micrometer. Flexural stiffness is

calculated as follows:

D = (1/16)(P/Y)(L3/w)(a/L)

Where, D = flexural stiffness

16

P = sum of the two weights

Y = sum of the deflection of the two weights

L = distance between the bottom support anvils, cm (in.)

a = distance between the bottom support anvil and upper
loading anvil

w = width of the specimen, cm (in.)

V. 0 u’ 3; 3 AL. I u. I .L .A.:, .L

The moisture content of paper has an important effect on paper
properties (Kline, 1982). Normally paper contains about 5% moisture when it is
dry. Since paper is made of cellulose, which is highly hygroscopic, it will absorb
water from the atmosphere if the two are not in balance. Generally, variations in
moisture content can cause the paper to curl, wrinkle, change dimension or lose
strength and can create other handling difficulties.

Kellicutt (1961) stated that the most serious factor limiting the use of
corrugated boxes has been the effect of moisture on box compressive strength.
As a result, paperboard components are specially treated by adding wet
strength agents in order to retain the dry stiffness when the box material is wet.
One of the most commonly used wet strength chemical is melamine
formaldehyde (MF) (Kline, 1982). The MF will react during the drying of the
paper to form a water-resistant compound. By adding the MF to the pulp stock
prior to paper web formation, it can adhere to the fibers and also be deposited
on the bond areas during web formation. The MP then functions in the paper to
protect the bonding and also to help hold the fibers together when the paper is

wetted. Therefore, when corrugated boxes are subjected to a damp condition,

17

wet strength agents will retard the absorption of moisture by the highly
hygroscopic wood fibers of the fiberboard. This is especially true when treated
boxes are subjected to high humidity for short periods of time. However, when
the same boxes are subjected to high humidity for prolonged periods of time,
water vapor will eventually reach the fibers and cause reduction of box
compressive strength. This reduction, on a percentage basis, is generally the
same as for the untreated ones. However, MF'S advantage is that it protects
boxes from the adverse effect of moisture in short time exposure.

Kellicutt (1961) stated that corrugated box material has the most
compressive strength when it contains the lowest moisture content. As moisture
content increases, there is a corresponding decrease in compressive Strength.
A relationship between compressive strength and moisture content was
developed by Kellicutt (1961) as follows:

(1o)-3.01x
Y = b

where, Y = compressive strength of box, in lbs.

b = compressive strength at 0 percent moisture content
x = moisture content

Kellicutt (1961 ) found that boxes made from different materials reacted in
essentially the same way for specific increases in moisture content. The
compressive strength of the box at a specific moisture content may be found by
relating the box to another for which the compressive strength and moisture

content are known. The formula is expressed as follows:

(10)3.01 X / (1o)3.01 X
P = P1 1 2

where, P = compressive strength to be determined, in lbs.

18

P1 -.- known compressive strength in lbs.

x1 = moisture content for box with P1 compressive strength
x2 = moisture content for which the compressive Strength is

to be determined

The effect of relative humidity (RH) and temperature on the tensile stress-
strain properties of softwood kraft linerboards was studied by Benson (1971).
The tensile properties investigated included tensile stress, modulus of elasticity,
strain to failure, and tensile energy absorption. Benson stated that the effects of
temperature on tensile properties consisted of two factors: (1) At any RH level,
change in temperature caused a change in the absolute water vapor available
to the paper, a change in the absolute vapor pressure acting on the paper, and
a resulting change in the paper equilibrium moisture content (EMC). (2)
Temperature change directly affects the behavior of paper that is subjected to
an external stress through changes in thermal energy levels. If moisture is
present, observed effects of temperature change on paper tensile properties are
dependent upon interaction between these two factors. Therefore, instead of
using conventional methods of interpretation that relate tensile properties to RH,
Benson evaluated the effect of RH in term of the specimen EMC. The
advantages for this are: (1) It would eliminate the need to know how specimen
EMC is reached, whether on an adsorption or desorption isotherm. (2) It would
eliminate the difficulty in maintaining fixed temperature and RH conditions. (3) It
would eliminate the problem of determining the calibration accuracy of
instruments used to measure RH.

The test results showed that as the EMC increased, the tensile properties
decreased and as the temperature increased, the tensile properties increased.

Both relationships were essentially linear.

19

Compression strength of boxes held under frozen conditions was studied
by Harte, et al (1985). In the study, boxes were held at -17.8 C and -31.7 C. The
compression strength of these boxes were compared to the compression
strength of boxes held at 22.8 C and 50% RH. From the result, boxes held at
22.8 C were found to have less compression strength than the ones held at
temperatures below 0 C. The increase in compression strength was partially
provided by the frozen water (ice) in the board. Stiffening of board fibers during
freezing was probably a contributing factor. In addition, it was found that
thawing of frozen boxes caused reduction in compression strength, however,
boxes regained strength when refrozen. Freezing-thaw cycling did not have

substantial effect on compression strength of frozen boxes.

VI. 1 C .L.l .L.L'A' i'i" :

The effect of cycling -relative-humidities on paper properties has been
studied by Byrd (1972). He investigated the compression creep response of
paper in a changing relative humidity (RH) environment. Creep is a time-
dependent deformation of a material under constant stress. In the study, short-
column corrugated fiberboard specimens were subjected to edgewise
compressive loads during exposure to both cyclic (90-35%) and constant (90%)
RH environment. The results Showed that creep rates were much greater for the
specimens in a cyclic RH environment than for the ones in a constant
environment. The creep strains for cyclically conditioned specimens were
higher than for the ones in a constant condition. From the results, Byrd
concluded that paperboard products under edgewise compressive loading and

cycled between 90 and 35% RH would fail sooner than in constant (90%) RH
20 -

environment even though the average board moisture content may be lower
under cyclic RH conditions.

Byrd and Koning (1978) studied the edgewise compression creep, of
corrugated fiberboard made from various materials, in cyclic RH environments.
Virgin, recycled, high-yield and roughwood southern pine pulps were selected
for this study. In comparing the relationship of creep rates of the various
materials in both constant and cyclic RH environments, the constant 90% RH
creep rates did not vary substantially for any of the corrugated fiberboard
specimens. Conversely, in cyclic RH conditions, significant differences in creep
rates between these specimens were found. High-yield pulp had the highest
cyclic RH creep rate and thus is expected to have the lowest stacking life. Byrd
(1988) explained that the poor performance was probably due to the lack of
conformability of the high-yield fibers resulting in lower fiber-to-fiber bonding
than with virgin conventional-yield pulps. Roughwood pulp, made by adding
bark with the chips during pulping, had higher creep rates than non-bark pulp
(about 25%). The creep rates of specimens made from recycled fiber were 7-
28% higher than for virgin material. The results revealed that increasing pulp
yield , adding bark or recycling is detrimental to cyclic RH creep performance.
Each of these factors leads to reduction in interfiber bonding. Improvement in
interfiber bonding generally results in improved cyclic RH creep performance
and thus improvement in expected box stacking performance.

Setterholm and Benson (1977) found that press-dried, high-yield,
hardwood fiberboard specimens performed as well in compression as
conventionally dried, normal-yield, softwood fiberboard specimens in cyclic RH
environment. The press-drying process provides improvement in moisture
resistance and increase in interfiber bonding which results in improved creep

performance of high-yield pulps in cyclic environments.

21

Byrd (1984) compared the creep response of board components
(linerboard and corrugating medium) that were compared to the results of his
earlier studies on combined board. He found that the combined board creep
was 2-5 times faster than board component measurement indicated. He also
found that press-dried, high-yield, oak linerboard did not creep as fast as
conventionally dried, softwood (virgin) linerboard in a cyclic RH environment.
Conventionally dried, low-yield, oak linerboards deformed at a greater rate than
either conventionally dried, softwood linerboards or press-dried, low-yield oak
linerboards.

Byrd (1984) stated that since different cellulosic materials absorb and
desorb moisture at different rates, it is not sufficient to only record ambient RH
changes during an experiment. Byrd, thus, investigated actual moisture loss
and gain during RH cycling of the board components in order to better
understand the causes of creep rate acceleration. The results showed that
linerboard made from high-yield pulp sorbed moisture much faster than virgin
linerboard did. Sorption rates and lignin content were found to be related: as
the lignin content in pulp is increased, the sorption rate rises. The recycled and
press-dried linerboards are two exceptions to this phenomenon. Recycling
reduces the rate of moisture sorption due to the debonding effects of drying. The
press drying process provides paper more moisture resistance which results in
less moisture sorption rate and hence less creep rate. Therefore, even though
press-dried linerboard has a relatively high lignin content, it creeps and picks
up moisture at about the same rate as virgin softwood linerboard.

Byrd (1984) concluded that the increase in creep rate is apparently
related to the moisture sorption rate. Therefore, linerboards made from high-
yield pulps creep faster and sorb moisture faster than specimens made from
virgin, conventional-yield pulps.

22

vu. W

Variations in! humidity and temperature can and do occur during
transportation, in warehouses, and even in retail stores. In many cases,
shipping containers are moved from low-humidity environments to high
humidity environments and vice versa.

Considine, et al (1989) stated that despite having control systems and
insulation, warehouses are often unable to prevent the cyclic humidity changes
caused by rapidly changing weather condition. Temperature and relative
humidity fluctuate every day and night. For example, Figure 2 shows wide
fluctuations of outdoor relative humidity (RH) for Madison, Wisconsin, between
1-10 February 1987, as measured by the National Weather Service. As a result
of the weather fluctuations and the lack of elaborate moisture control systems in
the manufacture plant, transportation and storage, most corrugated containers

experience moisture sorption during their service lives.

23

 

 

 

 

 

 

 

 

 

 

100
80-
§ 60-
I
E
g I
O
E
\°
° 40-
1
20 I I I I I 1
o 2 4 6 8 10 12

Elam Outdoor relative humidity for Madison, 1-10 February, 1987

24

25

W
IESLMAIEBIALS

The fiberboard materials and corrugated fiberboard boxes used in this
study were suppplied by a commercial manufacturer of corrugated packaging.
Description of the fiberboard materials and corrugated fiberboard boxes is as
follows:

1. Boxes made from two types of standard linerboards and two types of
fiber-efficient linerboards were provided to determine effect of cyclic
environments on box compression strength.

B S '[j I'

Corrugation: C Flute, Single-wall

Basis Weight (linerboard / medium / linerboard) (lb / 1000 ftz):

- 69-Ib standard I 33-lb / 69-lb standard (Box A)

- 58-lb regular fiber-efficient / 33-Ib / 58-lb regular fiber-efficient
(Box B)

- 90-lb standard / 33-lb / 90-Ib standard (Box C)

- 69-lb highly fiber-efficient / 33-lb / 69-lb highly fiber-efficient (Box
0)

Box Dimension (LxWxD): 14.00" x 10.00” x 8.08”

Box Style: Regular slotted container (RSC)

2. Two types of combined boards, made from standard linerboards and
two types of combined boards made from fiber-efficient linerboards were
provided to determine the edge crush value for their material physical property
specification.

B I S '[i I'

Corrugation: C Flute, Single-wall

Basis Weight (linerboard / medium / linerboard) (lb / 1000 ft2):
- 69-lb standard / 33-lb / 69-lb standard
- 58-lb regular fiber-efficient / 33-lb / 58-lb regular fiber-efficient
- 90-lb standard / 33-Ib / 90-Ib Standard
- 69-lb highly fiber-efficient / 33-lb / 69-lb highly fiber-efficient

3. Four types of linerboards and corrugating medium were provided to
determine basis weight, thickness and ring crush value for their material
physical property specification.

| . I I S T I'

Basis Weight (lb / 1000 it?) :

- 69-lb standard linerboard

- 58-lb regular fiber-efficient linerboard
- 90-lb standard linerboard

- 69-lb highly fiber-efficient linerboard

C . II I' s ‘l' I.
Basis Weight (Ib/ 1000 I12): 33-lb

Heavy weight linerboards'were selected for use in this study Since fiber-
efficient linerboards are usually used to replace heavy weight conventional
linerboards. In the study, 69-lb standard I 33-lb / 69-lb standard box (box A) was
compared with 58-lb regular fiber-efficient / 33-Ib / 58-lb regular fiber-efficient
box (box B), and 90-lb standard / 33-lb I 90-lb standard box (box C) with 69-Ib
highly fiber-efficient I 33-lb / 69-lb highly fiber-efficient box (box D). The two box
types in each comparison were claimed by the manufacturer to have similar

compression strength under standard condition.

26

10. u! 0: = .- k L 3:“:-

Two types of fiber-efficient linerboards were used to manufacture the
boxes in this study. They were regular fiber-efficient linerboard (used in box 8)
and highly fiber-efficient linerboard (used in Box D). According to the
manufacturer, the regular fiber-efficient linerboards used in Box 8 were different

from standard linerboards used in Box A and C in the following ways:

1. Addition of a special species of wood fibers e.g., Southern Pine.

These fibers provide more flexibility and are flatter than regular wood
fibers (like Douglas Fir). The flexibility and flatness provides added surface area
for fiber-to-fiber bonding. The flexibility of fibers allows the fibers to collapse
from tube shape to flat ribbon shape during the drying process and thus
increases contact area between fibers (Kline, 1982).

2. The use of more refining.

The refining process is a mechanical process that breaks down the

ordered structure of the fiber in order to improve fiber-to-fiber bonding.
3. Application of a fiber orientation technique.

mm the fiber orientation technique, fibers are forced to run
perpendicular to the paper-making machine direction. This eventually causes
more fibers to run vertically up and down the panels of a container which results
in better compression strength.

4. The use of more virgin fibers versus recycled fibers.
5. Application of ENP (extended nip press) or high pressure forming

technique.

27

The ENP was used during the papermaking process to press the fibers
together under high pressure loads. It creates a denser sheet with more fiber-to-
fiber bonding.

The highly fiber-efficient linerboards used in box D were manufactured
using the same techniques and processes as used in the regular fiber-efficient
linerboards. However, additional refining, beyond what was used for the regular
fiber-efficient linerboards was used in manufacturing the highly fiber-efficient
linerboards. In addition, a chemical was added to the highly fiber-efficient
linerboards to provide extra chemical linkages (covalent bonds). Adding the
chemical also imparts wet strength properties to the linerboard.
meme

Knocked-down boxes with the manufacturer's joint attached by adhesive
(starch adhesive with wet strength resin added) were obtained from a
commercial manufacturer of corrugated packaging. The boxes were set up and
sealed top and bottom with pressure sensitive tape using 3M adjustable case

sealer.

28

W

Prior to conditioning all test fiberboard materials and knock-down boxes
at TAPPI standard conditions, they were conditioned at a low humidity
environment of 70:2F, 35i3% RH for 5 days. After that, they were transferred to
condition at TAPPI standard condition of 73 :t 3 F, 50%RH for at least 48 hours

before testing.

W

After box set up and pre-conditioning, boxes were transferred to an
environmental chamber. Two identical environmental chambers were used.
Even though the chambers have temperature (T) and relative humidity (RH)
measuring instruments, chamber conditions were manually measured using a
psychrometer, model No.566 (Bendix Corporation), which records both RH and
T. The measurement was repeated approximately every 12 hours (see
Appendix A).

Boxes were rotated through a cyclic condition in 6 days. For each cyclic
condition, three different RH and T conditions were combined where each
combination was maintained for 2 days (48 hours). Boxes were remained in the
same chamber for the entire cyclic condition. Five different cyclic conditions
were studied and are as follows:

1) 41 F, 85% RH 9 73 F, 50% RH 9 41F, 60% RH

2) 99 F, 85% RH -) 73 F, 85% RH -) 99 F, 85% RH

3) 99 F, 85% RH -> 41F, 85% RH -) 73 F, 50% RH

4) 99 F, 30% RH -) 73 F, 50% RH 9 41 F, 85% RH

5) 41 F, 85% RH -) 73 F, 50% RH 9 99 F, 30% RH

29

These cyclic conditions were designed to simulate the real-life conditions
that boxes are subjected to. Descriptions of the simulation of each RH and T
condition (Powers and Witt, 1972) are as follows:
i. 41 F, 85% RH = Refrigeration
ii. 73 F, 50% RH = Controlled room condition (T APPI standard condition)
iii. 41 F, 60% RH = Nighttime in Spring and Fall in Great Lakes states.
(e.g., Michigan, Illinois and Vlfisconsin)

iv. 99 F, 85% RH = Daytime in Summer in Central states.
(e.g., Missouri, Kansas and Arkansas)

v. 73 F, 85% RH = Nighttime in Summer in Mid-Atlantic states.
(e.g., Kentucky, Tennessee and Virginia)

v. 99 F, 30% RH = Summer in Southwest states.

(e.g., Arizona, New Mexico and Western Texas)

A total of 24 boxes of each box type were rotated through each cyclic
condition in the sequence of T, RH combinations as shown. After being
subjected to a cyclic condition, 12 boxes of each box type were tested for
compression strength and the moisture content of the box material immediately
determined. Another 12 boxes of each box type and condition variable were
transferred to re-condition at TAPPI standard condition of 73 F, 50% RH for 2
days and their compression strength and material moisture content determined.

In addition to testing at the five cyclic conditions, all four box types were
subjected to two non-cyclic conditions, 73F, 50% RH and 73F, 85% RH, and
their compression strength measured. The moisture content of each box
material type was also determined following compression testing. To determine
the initial box compression strength, boxes were conditioned at 73F, 50%RH.
Boxes were conditioned at 73F, 85% RH to determine material moisture gains

and effect on box compression strength.

30

IESLMEIHQQS
B 'III'II III'I I! l

The basis weight and thickness of linerboards and mediums conditioned
at TAPPI standard conditions were determined in accordance with ASTM D
646-67-74 and ASTM D 645-67-74, respectively. Ten samples for each board
type were used.

W

The ring crush values of linerboards and mediums conditioned at TAPPI
standard condition were determined in accordance with ASTM D 1165-60-73.
Ten samples for each board type were tested.

W

The edge crush values of combined boards conditioned at TAPPI
standard conditions were determined in accordance with ASTM D 2808-69. Ten
samples of each board type were used.

C . I I'

The compression strength of the boxes were determined in accordance
with ASTM D 642-76, using a fixed platen. The fixed platen, as opposed to a
floating platen, was used because only the differences in the quality of box
materials were examined in this study. If the compression test is performed
using the floaten platen, the compression strength value will also reflect the
variations of the quality of the box fabrication process. Compression testing was
performed using a Lansmont compression tester. The room was conditioned at
73:3 F, 50¢3% RH. During testing, two boxes at a time were transported from
the chamber to the compression tester. The distance between the chamber and
the compression tester is about 10 meters which takes less than 20 seconds to

transport. One box at a time was placed on the lower platen of the tester and the

31

compression test was performed. The upper platen was lowered onto the box
until the box collapsed and the maximum load was recorded. The test was
usually completed within 1.5 minutes for the lower compression strength boxes
and 2.0 minutes for the higher compression strength boxes.

II'I C | IDI 'I'

The moisture content of the box material was determined on each box
tested for compression strength. Immediately after compression testing, the top
flap of each box was cut into 4" x 4" samples and the moisture content was

determined in accordance with ASTM D 644-55.

E . | I D .

The testing sequence is shown in Figure 3. A total of 12 boxes of each
box type were used for each treatment. Due to the difficulty in maintaining the
environmental chamber condition, the experiment was designed in such a way
that this variation would be minimized. For each treatment, the 12 boxes were
separated into three sets and one set was rotated through each cyclic condition
at a time. Thus, four boxes of each box type were rotated through each cyclic
condition together and their compression strength and material moisture
content determined. The same procedure was repeated three times in order to

obtain 12 replicates for each treatment.

1].}: ._ .‘zo, o I::“|: 1‘01 01 one: o. :gol o :0,

1. Fiber-efficient linerboards and standard linerboards
The compression strength of boxes made from 58-lb regular fiber-
efficient linerboard was compared with the compression strength of boxes made

from 69-Ib standard linerboard. Another comparison studied was between

32

 

 

Box A‘ Box B“ Box 0' Box D‘

 

 

 

 

 

 

 

 

73F&50% RH A

41 F 81 85% RH (Cyclic Condition I) .

73 F & 50% RH ‘

—41F&60% RH H 7 ~ ‘ A V H

 

73 F 8: 50% RH

 

’

CT = Compression Test MC - Moisture Content Determination

' Eight box sanples were used. ’“ i. Cyclic condition I = 41 F, 85% RH - 73F, 50% RH - 41 F, 60% RH
.. ii. Cyclic condition II - 99F, 85% RH . 73F, 85% RH - 99F, 85% RH
F°”' b°x samp'es we“ ”sed' Iii. Cyclic condition III = 99F, 85% RH - 41 F, 85% RH - 73F, 50% RH
iv. CycrIc condition lV . 99F, 30% RH - 73F, 50% RH - 41F, 85% RH
v. Cyclic condition v = 41F, 85% RH - 73F, 50% RH - 99F, 30% RH

Note: This procedure was repeated three times in order to obtain 12 replicates for each treatment.

figure; Testing sequence for determining compression strength of boxes
and moisture content of box materials.

33

boxes made from 69-lb highly fiber-efficient linerboard and boxes made from
90-Ib standard linerboard.
2. Cyclic conditions
All boxes were tested for compression strength and material moisture
content after rotation through each cyclic condition The cyclic conditions were:
- 41 F, 85% RH 9 73 F, 50% RH 9 41 F, 60% RH
- 99 F, 85% RH 9 73 F, 85% RH 9 99 F, 85% RH
- 99 F, 85% RH 9 41 F, 85% RH 9 73 F, 50% RH
- 99 F, 30% RH 9 73 F, 50% RH 9 41 F, 85% RH
- 41 F, 85% RH 9 73 F, 50% RH 9 99 F, 30% RH
3. Re-conditioning
Twenty four boxes of each box type were rotated through each cyclic
condition, with 12 being tested immediately. The other 12 boxes were re-
conditioned at standard TAPPI condition of 73F, 50%RH for 2 days and their
compression strength and material moisture content determined.
4. Standard condition and high humidity condition
Twelve boxes of each box type were conditioned at 73F, 50% RH to
determine initial compression strength. Another twelve boxes of each type were
conditioned at 73F, 85% RH to determine material moisture gains and effect on

box compression strength.

34.

35
W

In this study the compression strength of boxes made from fiber-efficient
(high-performance) linerboards was examined under cyclic conditions. The
compression strength of boxes made from fiber-efficient linerboards was then
compared to boxes made from standard linerboards after exposure to the same
cyclic conditions. Over 500 corrugated boxes were subjected to five cyclic
conditions and their compression strength evaluated. The moisture content of
box materials was also determined. After exposure to each cyclic condition,
noncompressed boxes were re-conditioned at TAPPI standard conditions (73F,
50% RH) and their compression strength and moisture content determined.

The ”basic” physical properties of the box samples, the combined boards
and the board components (linerboards and cormgating mediums) used in this
study are shown in Table 1.

A 3-factor factorial experiment was conducted to investigate the effect of
the experimental variables on box compression strength. Three variables were
evaluated in this study. These were:

- Box types (2 types)

i. Boxes made from standard linerboards
ii. Boxes made from fiber-efficient linerboards
- Cyclic conditions (5 conditions)

i. 41 F, 85% RH973 F, 50% RH94‘I F, 60% RH

lama; Physical properties of the box materials.

 

69-lb 58-lb 90-Ib 69-Ib 33-lb
Standard Regular Standard Highly Medium
Linerboard Fiber-efficient Linerboard Fiber-efficient

 

 

 

 

Linerboard Linerboard
Basis Weight* 68 59 91 67 33
(lb/1000 112)
Thickness’ 17.9 13.8 22.8 16.6 10.8
(pt)
Ring Crush“ 96.7 98.6 157.2 137.5 54.2
(lb)
W
69-Ib 58-lb 90-Ib 69-lb
Standard Regular Standard Highly
Linerboard Fiber-efficient Linerboard Fiber-efficient
Linemaard Linerboard
Edge Crush Test" 42.1 44.3 58.2 54.3
(Weyerhaeuser

Method) (Io/In)

 

* An average of 10 test samples
** An average of 15 test samples
Note: See Appendix A for standard deviation of the data.

36

ii. 99 F, 85% RH 9 73 F, 85% RH 9 99 F, 85% RH
iii. 99 F, 85% RH 9 41 F, 85% RH 9 73 F, 50% RH
iv. 99 F, 30% RH 9 73 F, 50% RH 9 41 F, 85% RH
v.41 F, 85% RH 9 73 F, 50% RH 9 99 F, 30% RH
- Re-conditioning
i. After cyclic condition exposure
ii. Re-conditioning
A 3-way analysis of variance (ANOVA) for a completely randomized
design was performed (Appendix C). Boxes made from 69-lb standard
linerboards were compared with boxes made from 58-lb regular fiber-efficient
linerboards. The results of the ANOVA test suggest that there were 2-way
interactions between box types and cyclic conditions, and cyclic conditions and
re-conditioning. A 2-way interaction means that the two variables act together'to
affect the compression strength. In addition, there was a 3-way interaction
between all three variables. This indicates that the three variables act together
to affect the compression strength. The second comparison was between boxes
made from 90-lb standard linerboards and boxes made from 69-lb highly fiber-
efficient linerboards. The results of the ANOVA test shows that there was a 2-

way interaction between cyclic conditions and re-conditioning.

I.“ 112.. i.“ ALIA]. L EHAEI 30., HAD 3.“

W

In this study, examination of the difference in loss of strength due to the
cyclic conditions, and comparison of the final compression strength after
exposure to the cyclic conditions were conducted to compare the potential

Stacking performance of two box types under cyclic conditions. Boxes made

37

from 69-lb standard linerboards was compared with boxes made from 58-lb
regular fiber-efficient linerboards, and boxes made from 90-lb standard

linerboards with boxes made from 69-Ib highly fiber-efficient linerboards.

l-ILQSSDLSIBENQIB

o-o <1..'.._ rev-.0 3‘9330 -. 'v- I =1 run!

The average compression strength of boxes made from 69-lb standard
linerboards (box A) and boxes made from 58-Ib regular fiber-efficient
linerboards (box 8), after exposure to TAPPI standard conditions (73F, 50% RH)
and five cyclic conditions are summarized in Table 2. Based on an Analysis of
Variance (ANOVA) (Ott, 1989), the initial compression strength of boxes held at
TAPPI standard conditions was significantly different between the two box types
at 99.9% confidence level (Appendix D). Box 8 was 1661-60 lbs (approximately
13%) higher in compression strength than box A, after conditioning at 73F, 50%
RH. The average box compression strength loss due to cyclic conditions was
compared using a t-test analysis (Gill, 1978) (Appendix E). The results from the
analysis are shown in Table 3. At a confidence level of 99%, significant
differences between the two box types were found under cyclic conditions I, II, III
and IV. Box B experienced significantly greater loss of strength than box A. For
cyclic condition V, the results showed a marginally significant difference in the
loss of strength between both box types at a confidence level of 90%. The loss
of strength for each box type is shown in Table 3. A graphical presentation of
the loss of strength is shown in figure 4.

The 58-lb regular fiber-efficient linerboard used in box B contains less
fibers than the 69-Ib standard linerboard used in box A. However, box 8 has

higher compression strength than box A by 166+60 lbs, after conditioning at
38

mm Compression strength values of boxes made with 69-lb standard
linerboard and boxes made with 58-lb regular fiber-efficient linerboard.

 

Box Type Storage Condition" Compression Std. Deviation
Strength (lbs)“

 

69-lb Standard TAPPI Standard 1249 78.8

(Box A)
Cyclic condition I 1054 71.2
Cyclic condition II 976 77.7
Cyclic condition Ill 1120 44.0
Cyclic condition IV 738 29.7
Cyclic condition V 1226 87.9

58-Ib Regular TAPPI standard 1415 63.4

Fiber-Efficient

(Box B) Cyclic condition I 1128 82.2
Cyclic condition II 978 67.1
Cyclic condition Ill 1176 59.6
Cyclic condition IV 761 58.2
Cyclic condition V 1336 45.9

 

* TAPPI standard = at 73F, 50%RH
Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition lll = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

** An average of 12 test samples.

39

Iablej Results from the analysis of difference analyzing loss of strength
between boxes made with 69-Ib standard linerboard (box A) and
boxes made with 58-lb regular fiber-efficient linerboard (box 8) for
each cyclic condition.

 

 

Storage Condition‘ t-test value“ Lo§§_oj_§tr_e_ngm_flb§)
69-lb Standard 58-lb Fiber-efficient
(Box A) (Box B)

Cyclic condition I 3.14 195164 2871-62
Cyclic condition II 5.60 273166 437355
Cyclic condition Ill 3.76 129:54 239152
Cyclic condition IV 4.88 511:24 654,351
Cyclic condition V 1.91 23:34 73:47

 

* Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition III = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

’* Calculated t-value for the difference in strength loss between boxes made
with standard linerboard and boxes made with regular fiber efficient
linerboard.

Critical t-value = 2.819 at confidence level of 99%
’ = 1.717 at confidence level of 90%

4O

 

800

I BoxA
I BoxB

\.

\

.
I. e.
I... ‘p
I. I" u
.°
'0’.)
I" .-
I".
4‘
J .
’ I

1..

. 4

Loss of Strength (lbs)
its?“ \

J"
91/ .
i

." I .'
r‘./.‘
.1 .-

.‘.' \

 

 

 

Cyclic Condition

figures, Difference in loss of strength between box A and box B.

41

73F, 50% RH. This extra Strength in the regular fiber-efficient linerboard was
obtained by the special techniques used in the papermaking process. The
techniques are: (1) the use of more refining than that used for standard
linerboard, (2) addition of special species of fibers e.g., Southern Pine fibers, (3)
application of a fiber orientation technique, (4) the use of more virgin fibers, and
(5) the extended nip press technique.

The refining process is a mechanical process that breaks down the
ordered structure of the fiber to expose more hydroxyl groups for fiber-to-fiber
bonding (Kline, 1982). The strength of the hydrogen bond that forms between
two hydroxyls is fixed and the only way to increase the strength of a sheet of
paper is to increase the number of hydrogen bonds between fibers. Therefore,
more refining adds strength by increasing the fiber-to-fiber bonding. The
Southern Pine fibers added in regular fiber-efficient linerboard provide more
flexibility and are flatter than regular fibers (e.g., Douglas Fir) that are used in
standard linerboards. The flexibility and flatness provide added surface area for
fiber-to-fiber bonding. The flexibility of fibers allows the fibers to collapse from
tube shape to flat-ribbon shape during the drying process which results in more
contact area between fibers. Theextended nip press technique used during
papermaking presses the fibers together under a high pressure load. This
creates a denser sheet with more fiber-to-fiber bonding. Therefore, the strength
in regular fiber-efficient linerboard is increased due to the greater number of
hydrogen bonds between fibers.

Hydrogen bonds are a intermolecular force and their strength can be
dramatically reduced by the presence of water (Kaufman, 1977). Water tends to
disrupt the hydrogen bonds between molecular chains and thus reduces the
intermolecular forces. As a result, when the regular fiber-efficient linefooards

were exposed to the cyclic conditions with high relative humidity conditions, a

42

significant number of hydrogen bonds were probably lost. This most likely
caused the large reduction in compression strength when boxes made from
regular fiber-efficient linerboards were subjected to the cyclic conditions.

,._ . 4.-" .“mm .._ . I.” '-.: _ . .u .lzm' .

The average compression strength of boxes made from 90-lb standard
linerboards (box C) and boxes made from 69-lb highly fiber efficient linerboards
(box D), after exposure to TAPPI standard conditions and five cyclic conditions
are summarized in Table 4. The initial compression strengths of the two box
types, after subjection to TAPPI standard conditions, were found to be marginally
different by an ANOVA analysis at a confidence level of 93% (Appendix F). Box
C was 77182 lbs (approximately 5%) higher in compression strength than box D.
The average compression strength loss after exposure to cyclic conditions was
also compared. The statistical procedure used to determine the difference in
strength loss between these two box types was the same as previously
described for comparing box A and box 8. The analysis is detailed in Appendix
G. The results from the analysis (Table 5) indicated that at a confidence level of
90% there were only marginally significant differences in loss of strength
between the two box types under cyclic condition I, IV and V and no Significant
differences under cyclic conditions II and III. A graphical presentation of the
difference in strength loss is Shown in Figure 5.

Although the 69-Ib highly fiber-efficient linerboard used in box D contains
less fibers than the 90-Ib standard linerboard used in box C, box C had slightly
higher compression strength than box D. The highly fiber-efficient Iinerboard's
strength was aided by the same special techniques used in the regular fiber-
efficient linerboard (box 8). In addition to these techniques, a chemical was

added to impart wet strength properties to the linerboard. The

43

18919.4. Compression strength values for boxes made with 90-lb standard
linerboard and boxes made with 69-Ib highly fiber efficient linerboard.

 

Compression Std. Deviation

Strength (lbs)**

Box Type Storage Condition"

 

90-lb Standard TAPPI standard 1674 103.6

(Box C)
Cyclic condition I 1297 99.5
Cyclic condition II 1166 92.0
Cyclic condition Ill 1451 94.5
Cyclic condition IV 1007 61.1
Cyclic condition V 1649 91.8

69-Ib Highly TAPPI standard 1597 90.1

Fiber-Efficient

(Box D) Cyclic condition I 1305 102.6
Cyclic condition Il 1143 87.7
Cyclic condition Ill 1405 184.4
Cyclic condition IV 855 62.4
Cyclic condition V 1571 138.0

 

" TAPPI standard = at 73F, 50%RH

Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition III = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

** An average of 12 test samples.

44

Iablej Results from the analysis of difference analyzing loss of strength
between boxes made with 90-Ib standard linerboard (box C) and
boxes made with 69-Ib highly fiber-efficient linerboard (box D) for each
cyclic condition.

 

Storage Condition" t-test value“ LQSSJILSILQDQIMDS)
90-lb Standard 69-lb Fiber-efficient

 

IBQLC) (BOX D)
Cyclic condition I 1.71 377:86 292:82
Cyclic condition II 1.34 508:83 454:139
Cyclic condition Ill 0.77 259:84 192:123
Cyclic condition IV 1.86 667:72 742:66
Cyclic condition V 1.93 25:83 26:99

 

* Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition Ill = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

** Calculated t-value for the difference in strength loss between boxes made
with standard linerboard and boxes made with regular fiber efficient
linerboard.

Critical t-value = 1.717 at confidence level at 90%
= 2.074 at confidence level at 95%

45

I BoxC
I BoxD

 

 

H /..,.,.HH.,.H.,...,.,,...H
h. /.7fl%,%7//

   

   

          

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

 

 

800

400 -'
200 -

as: .355 so 83

Cyclic Condition

EiguLej Difference in loss of strength between box C and box D.

46

chemical also provides extra chemical linkages (covalent bonds) beyond
hydrogen bonds. After exposure to the cyclic conditions with high humidity
conditions, box C and box D showed only marginally significant difference in loss
of strength. This may be because in the highly fiber-efficient linerboard the
chemical, acting as a wet strength agent, helped to protect the hydrogen bonds
and hold the fibers together when the box was exposed to high humidity. As a
result, the box strength was retained. Furthermore, the covalent bonds provided
by the chemical are not sensitive to moisture as are the hydrogen bonds.
Apparently, the addition of the chemical was an important attribute that enabled
the box made from the 69-Ib highly fiber-efficient linerboards to retain their
compression strength as well as the box made from the 90-lb standard
linerboards under the cyclic conditions used in this study.
I.II.E|NAL_QQMEBES.S.IQN§IBENGII:I

.-. 4.0.10 l:|o‘o-p ;-. ;:. ._ .: -:. ':.. fume."

Final box compression Strength after cyclic condition exposure was
compared between boxes made from 69-lb standard linerboards (box A) and
boxes made from 58-Ib regular fiber-efficient linerboards (box B) using a Host
analysis (Appendix H). The results from the analysis are shown in Table 6. At a
confidence limit of 95%, a significant difference was found only under cyclic
condition I. The final compression strength of box 8 was 74:65 lbs higher than
that of box A. The differences in the final compression strength between the two
box types are shown in Table 6. Although box 8 experienced greater loss of
strength than box A under all cyclic conditions, box B's final compression
strength was not significantly different from box A's. The final compression
strength is an indication of the box stacking ability. The results thus suggest that

47

1am Results from the analysis of difference in final compression strength
between boxes made from 69-lb standard linerboards (box A) and
boxes made from 58-Ib regular fiber efficient linerboards (box 8) for
each cyclic condition.

 

Storage Condition“ t-test value Difference in
Final Compression Strength (lbs)

 

Cyclic Condition l 2.36 74:65
Cyclic Condition II 0.07 2:61
Cyclic Condition lll 1.07 56:109
Cyclic Condition IV 0.49 23:96
Cyclic Condition V 1.75 110:145

 

* Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition Ill = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

** Calculated t-value for the difference in strength loss between boxes
made with standard linerboard and boxes made with regular fiber
efficient linerboard.

Critical t-value = 2.074 at confidence level at 95%

48»

the two box types should perform similarly under all cyclic conditions used in

this study except cyclic condition I.

I O O .- I
O O
I-o .10.. |:|oe._o e-o.o| o:-:| :3 1:10....

The final compression strength of the boxes made from 90-Ib standard
linerboards (box C) and boxes made from 69-lb highly fiber-efficient linerboards
(box D), after subjection to cyclic conditions, were also compared using the t-
test analysis (Appendix H). The results from the analysis (Table 7) shows that
there was no significant difference under all cyclic conditions except under
cyclic condition IV. The final compression strength of box C was 152:62 lbs
higher than that of box D. The differences in the final compression strength for
each box type are shown in Table 7. The results indicate that the two box types
should perform Similarly under all cyclic conditions except under cyclic

condition IV.

li- EEEEQLQEMQISIUBEABSQBEIIQN

Cellulosic materials respond to shifts in relative humidity differently. They
absorb or desorb moisture at different rates (Byrd, 1984). This response can be
critical in the performance of a corrugated fiberboard box. Byrd (1984) assumed
from his study that increased creep rates (used to predict final box stacking
performance) resulted from increased moisture sorption by fiberboards.
Therefore, differences in loss of compression strength among the four box types
in this Study may partially be as a result of the differences in moisture absorption
among the box materials.

The moisture content of the different materials used for each box type

and held at 73F, 85% RH for 2 days was measured to determine the percent

49

1am Results from the analysis of difference in final compression strength
between boxes made from 90-lb standard linerboards (box C) and
boxes made from 69-Ib highly fiber efficient linerboards (box D) for
each cyclic condition.

 

Storage Condition“ t-test value Difference in
Final Compression Strength (lbs)

 

Cyclic Condition l 0.08 8:210
Cyclic Condition II 0.26 23:186
Cyclic Condition "I 0.31 46:304
Cyclic Condition IV 2.46 152:62
Cyclic Condition V 0.66 78:243

 

* Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition Ill = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

*‘ Calculated t-value for the difference in strength loss between boxes
made with standard linerboard and boxes made with regular fiber
efficient linerboard.

Critical t-value = 2.074 at confidence level at 95%

50

moisture gain. In Table 8, the percent moisture gains of the four materials are
shown and a graphical presentation is shown in Figure 6. An ANOVA analysis
suggested that the moisture gains by box materials used for the 69-lb standard
linerboards (box A) and box materials used for the 58-lb regular fiber efficient
linerboards (box 8) were significantly different at 99% confidence level
(Appendix I). The box 8 material absorbed more moisture than the box A
material. The higher moisture gain in box 8 was at least in part responsible for
its greater compression strength loss when compared with box A.

The difference in moisture gain by the box materials used for the 90-lb
standard linerboards (box C) and box materials used for the 69-lb highly fiber-
efficient linerboards (box D) was found to be significant at a confidence level of
99% (Appendix J). The box D materials absorbed less moisture than the box C
materials. This may be a factor influencing the marginal difference in strength
loss between the two box types. 'The lower moisture gain in box D is probably
due to an addition of the wet strength chemical in the 69-lb highly fiber-efficient
linerboard. The chemical imparts wet strength properties to linerboard and
provides added covalent bonds which are not sensitive to moisture as are the
hydrogen bonds. Thus, the addition of the chemical was probably partially

responsible for the marginal difference in loss of strength between box C and
box D.

Ill. W
To determine the significance of the cyclic conditions on the compression
strength of each box type, an Improved Bonferroni t-test (Gill, 1990) was used to
compare the initial box compression strength after exposure to TAPPI standard
conditions with the box compression strength after exposure to the cyclic
51

Iablej Percent moisture gain of box materials held at 73F, 85%.

 

Box Type %Moisture Content % Moisture Gain
at 73F, 50%RH at 73F, 85%RH

 

Box A 7.13 13.01 82.0:3.0
Box 8 7.12 13.32 87.0320
Box C 6.90 13.07 89.5325
Box D 7.00 12.84 83.5:2.5

 

52

80
.E
3 so
2
a
(n
2
0\o4o
20
0
Elam

 

 

 

 

BoxAvs BoxB Bovas BoxD

Percent moisture gain for the four different box materials.

53

conditions for all four box types. A significant difference was found at the 99%
confidence level (Appendix K) for all four box types. The cyclic conditions used
in this research caused significant reduction in compression strength. The
reduction in compression strength due to exposure to the cyclic conditions for
each box type is shown in Table 9.

The largest reduction in box compression strength occurs as a result of
exposure to cyclic condition IV (99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH). It
is probably the final condition (41F, 85%RH) that most adversely affected box
strength. The box materials subjected to cyclic condition IV contained the
highest moisture content (Table 10). The presence of moisture in a corrugated
fiberboard causes a decrease in fiber-to-fiber bonding. A decrease in fiber-to-
fiber bonding generally results in low compression strength and hence
negatively affects box stacking performance (Byrd, 1989). Therefore, it is highly
probable that the high moisture content of the box materials subjected to cyclic
condition IV was at least partially responsible for the reduction in compression
strength.

The strength reduction under cyclic condition lI (99F,85%RH 9
73F,85%RH 9 99F, 85%RH) was smaller than that under cyclic condition IV,
although the boxes were exposed to high humid environments for the longest
period of time. This may have been due to the effect of temperature on the
relationship between moisture content of paper and humidity in the atmosphere.
If relative humidity is kept constant, an increase in temperature decreases the
moisture content of paper (Ott, et al, 1954). In cyclic condition II, the boxes were
held at a constant high humidity (85% RH) and the temperature increased to
99F. This resulted in a smaller moisture content. The decreased moisture

content caused a smaller reduction in compression strength.

54

1am Loss of compression strength for each box type after exposure to cyclic

conditions.

 

Storage Condition’

Loss of Compression Strength (lbs)

 

Box A Box B Box C Box D
Cyclic condition I 195:64 287:62 377:86 292:82
Cyclic condition ll 273:66 437:55 508:83 454:139
Cyclic condition Ill 129:54 239:52 259:84 192:123
Cyclic condition IV 511:24 654:51 667:72 742:66
Cyclic condition V 23:34 73:47 25:83 26:99

 

* Cyclic condition I = 41 F, 85%RH 9 73F, 50%RH 9 41 F, 60%RH

Cyclic condition II = 99F, 85%RH 9 73F, 85%RH 9 99F, 85%RH
Cyclic condition Ill = 99F, 85%RH 9 41 F,85%RH 9 73F, 50%RH
Cyclic condition IV = 99F, 30%RH 9 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH 9 73F,50%RH 9 99F, 30%RH

55.

lam Percent moisture content of box material after exposure to
cyclic conditions.

 

 

Q I. Q ill.
I II III N

Box A 10.7 11.8 8.7 15.5 6.0

Box B 11.3 11.8 8.6 15.3 5.7

Box C 10.8 12.1 8.7 14.6 5.6

Box D 10.5 11.8 8.5 14.7 5.5

 

56

The boxes exposed to cyclic condition V (41 F, 85%RH 9 73F, 50%RH 9
99F, 30%RH) experienced the least strength reduction. This is most likely as a
consequence of the lower moisture level existing in the box material.

The moisture level in a box material is a very important factor which
impacts the box compression strength. The compression strength of a box after
exposure to cyclic conditions is substantially affected by the final moisture level
in the box material. The reduction in box compression strength and material
moisture content after exposure to cyclic conditions for all four box types is
shown in Figure 7. A graphical presentation of the relationship between loss of
strength and material moisture content is shown in Figure 8. The high
correlation coefficient values depict a very strong linear relationship. The figure
generally illustrates that the box compression strength decreased as the

moisture content increased.

N W

The average compression strength of all box types, after box re-
conditioning (73F, 50% RH) is shown in Table 11. The difference between the
compression strength of the boxes after cyclic condition exposure and the
compression strength of the boxes after box re-conditioning was found to be
statistically significant using an improved Bonferroni t-test at 99% confidence
level (Appendix L). The compression strength of the different boxes, after cyclic
condition exposure and after re-conditioning is shown in Figure 9. The boxes
exposed to cyclic condition I, II, III and IV partially regained their compression
strength after re-conditioning at TAPPI standard conditions for 2 days. Since
paper is made of cellulose, which is highly hygroscopic, it will absorb and

desorb moisture with the environment if the two are not in balance. As water

57

- BoxA
I BoxB
BoxD

I BoxC
Z

 

 

Moisture: Content

I

Z

  

as; £5.26 so 83

 

. ”MW/7%”

          

Cyclic Condition

EiguLel Loss of compression strength and material moisture content

after exposure to cyclic condition for all box types

58

 

800

Loss of Strength (lbs)

 

—¢-— BoxA
—-O— BoxB

 

 

 

 

 

 

 

% Moisture Content
800
A 600 -
.8
.2
E’ 4m -1 R 8 0.998 —D— BOXC
g —0— Box D
m I
“'6 \
B
o 200 -
.J
k R = 0.982
O I V I f I ‘ 7 ' 1 v
4 6 8 1 0 12 1 4 1 6
% Moisture Content
R = Coefficient of Correlation

EiguLej Relationship between loss of strength and material
moisture content.

59

IabLeJJ. Compression strength of all four box types after exposure to TAPPI
standard conditions, cyclic conditions and re-conditioning.

 

Box Type Storage Condition‘

Initial After Cyclic Condition Re-conditioning

 

69-lb

Standard
(Box A)

58-lb

Regular

Fiber

Efficient
(Box B)

90-lb

Standard
(Box C)

69-lb

Highly

Fiber

Efficient
(Box D)

73F, 50% RH 1249
Cyclic condition I

Cyclic condition II

Cyclic condition Ill

Cyclic condition IV
Cyclic condition V

141 5
Cyclic condition I
Cyclic condition lI
Cyclic condition III
Cyclic condition IV
Cyclic condition V

1674
Cyclic condition I
Cyclic condition II
Cyclic condition lll
Cyclic condition IV
Cyclic condition V

1597
Cyclic condition I
Cyclic condition II
Cyclic condition Ill
Cyclic condition IV
Cyclic condition V

1054
976
1 120
738
1226

1 128
978
1 176
761
1336

1297
1 166
1451
1007
1649

1305
1 143
1405

855
1571

1154
1161
1129
1121
1259

1300
1245
1 173
1296
1264

1 467
1 475
1 482
1 482
1 598

1518
1508
1442
1438
1561

 

" Cyclic condition I- = 41 F, 85%RH 9 73F, 50%RH -) 41 F, 60%RH

Cyclic condition II = 99F, 85%RH -) 73F, 85%RH -) 99F, 85%RH
Cyclic condition lll = 99F, 85%RH -) 41 F,85%RH -) 73F, 50%RH
Cyclic condition Iv = 99F, 30%RH -> 73F, 50%RH -) 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH -) 73F,50%RH -> 99F, 30%RH

60

I After Cyclic Condition
After Pie-conditioning

 

 

6.1 ‘— moisture content

60

   

aw

 

1500

500 -

_
o
o
0
1

3: 5955 8385500

4

3

Cyclic Condition
For boxes made with 69-Ib standard linerboard (box A).

2

I After Cyclic Condition
After Re—conditioning

 

 

2000

 

2 I , 4 247, .. ,7, ...4
e /////////////////%//%

8.7 5.7

8.6 8.5

 

3 .. , 4., / :4.........;.y/.,H.,U,.,.,..U.
a ///////////%///////7///
8

1|

m V////////////x/~V///////a

4|
1|

1000 -

3: 59.9.6 co_mwo.ano

    
 

          

       

4

3
Cyclic Condition
For boxes made with 58-lb regular fiber-efficient linerboard (box B).

M Compression strength determined after cyclic condition exposure and

after re-conditioning and moisture content of box materials.

61

I After Cyclic Condition
After Re-conditioning

 

 

5.6 6.0

   

              
      

5.
8

/////

6

 

2000

_
o
o
o
1»

3: 59.25 :28an00

Cyclic Condition
For boxes made with 90-Ib standard linerboard (box C).

I After Cyclic Condition
4:? After Re-conditioning

 

 

59

5.5

8

5
o
:i

85

   

 

   

 

2000

1000 '-

3: £9.25 seamen—:8

4

Cyclic Condition
For boxes made with 69-Ib highly fiber-efficient linerboard (box D).

3

62

evaporates from the paper, the fibrils (or fiber parts) are drawn together and
thus the hydroxyl groups are aligned for bonding (Kline, 1982) (see Figure 10).
The box materials exposed to cyclic condition I, II, III and IV contained high
moisture levels. They, thus, desorbed water during re-conditioning at TAPPI
standard conditions. The moisture content of box materials after cyclic condition
exposure and after re-conditioning is shown in Figure 9. As a result, the boxes
exposed to cyclic condition I, II, III and IV regained their compression strength
due to an increase in hydrogen bonding after re-conditioning at TAPPI standard
conditions. All boxes regained part of their compression strength, after re-
conditioning for 2 days, probably due to the fact that the box materials had not
reached their equilibrium moisture content at the time when the boxes were
tested. Table 12 shows moisture content of box materials after initial subjection
to TAPPI standard condition and after re-conditioning. The box materials used
in this study may need a longer period of time to stabilize their moisture level
with the atmosphere.

The boxes exposed to cyclic condition V lost compression strength after
re-conditioning (except for box A). Due to the final condition (99F, 30% RH) in
cyclic condition V, the moisture content of box materials after subjection to cyclic
condition V was very low. The box materials thus absorbed water from the
atmosphere when exposed to TAPPI standard conditions. The increase of water
in the paper caused a reduction in fiber-to-fiber bonding which results in lower

compression strength.

63

m

D.

S a
w.

am m
\ mm ..w
b

H \ mm m
H H ...m We
0 a r
\/ mm.

H mm.
/ ww
mm

aw.

//////////W. 0\ W
o A ax M 3

%MH AW

0/
H
v...
H

 

lam Moisture content of box materials after initial subjection to TAPPI
standard condition and after re-conditioning.

 

Storage Condition" W
Box A Box B Box C Box D

 

TAPPI Standard Condition 7.13 7.12 6.90 7.00
Cyclic Condition I 8.59 8.65 8.47 8.53
Cyclic Condition II 8.53 8.34 8.65 8.36
Cyclic Condition lll - 8.55 8.58 8.54 8.44
Cyclic Condition IV 8.71 8.75 8.55 8.12
Cyclic Condition V 6.09 6.17 6.00 5.94

 

* Cyclic condition I = 41 F, 85%RH -) 73F, 50%RH -) 41 F, 60%RH
Cyclic condition II = 99F, 85%RH 9 73F, 85%RH -) 99F, 85%RH
Cyclic condition lll = 99F, 85%RH -) 41 F,85%RH -) 73F, 50%RH
Cyclic condition IV = 99F, 30%RH -) 73F, 50%RH 9 41 F, 85%RH
Cyclic condition V = 41 F, 85%RH -) 73F,50%RH -) 99F, 30%RH

65

66

W

The summary of the results from this study are:

1. Boxes made from 58-lb regular fiber-efficient linerboards experienced greater
loss of compression strength than boxes made from 69-lb standard linerboards,

after exposure to the cyclic conditions used in this study.

2. There were only marginally significant differences in loss of compression
strength between boxes made from 69-lb highly fiber-efficient linerboards and
boxes made from 90-Ib standard linerboards under cyclic condition I (41 F, 85%
RH -) 73F, 50% RH 9 41 F, 60% RH), IV (99F, 30% RH -) 73F, 50% RH 9 41 F,
85% RH) and V ( 41 F, 85% RH -) 73F, 50% RH -) 99F, 30% RH) and no
significant differences under cyclic condition ll (99F, 85% RH -) 73F, 85% RH
-)99F, 85% RH) and Ill (41 F, 35% RH -> 41 F, 85% RH -) 73F, 50% RH).

3. There was marginally significant difference in final compression strength
between boxes made from 69-lb standard linerboards and boxes made from
58-lb regular fiber-efficient linerboards under cyclic condition I, and no

significant difference under cyclic condition II, III, IV and V.

4. The final compression strength of boxes made from 90-lb standard
linerboards and boxes made from 69-Ib highly fiber-efficient linerboards was
not found to be different under all cyclic conditions, except under cyclic

condition IV.

5. The differences in moisture absorption among the box materials were found
to be at least a partial factor causing the differences in loss of compression
strength among the four box types after exposure to the cyclic conditions.
Compression strength decreased with an increase in moisture absorption by

the box material.

6. All cyclic conditions used in this study caused significant reduction in

compression strength for all four box types.

7. The boxes subjected to cyclic condition I, II, III and IV partially regained their
compression strength after re-conditioning at TAPPI standard condition (73F,
50% RH) for 2 days, boxes subjected to cyclic condition V lost compression

strength after re-conditioning.

The results in this study indicate that although the boxes made from 58-lb
regular fiber-efficient linerboards lost more compression strength than the
boxes made from 69-Ib standard linerboards under cyclic conditions used in
this study, they may perform similarly under the cyclic condition II, III, IV and V.
No significant differences in final compression strength between the two box
types were found. The final compression strength is an indication of the stacking
performance of the boxes. The results of the marginal difference in loss of
strength and no difference in final compression strength (except cyclic condition
lV) suggest that boxes made from 90-lb standard linerboards and boxes made
from 69-lb highly fiber-efficient linerboards should perform similarly under cyclic

conditions used in this study.

67

This study demonstrated that even though two types of corrugated
fiberboard containers perform similarly in a non-cyclic environment, one may
fail before the other in a cyclic environment. One box type may lose its
compression strength greater or faster than the other under the cyclic
environment. It is thus important to report the stacking performance of the

cormgated fiberboard containers under cyclic environments.

68

APPENDICES

APPENDIX A

Temperature and percent relative humidity in the environmental chambers

m1

CW2

12819 S g !'|' if E IE IT 5 Q I" G I: E IE I..

 

 

 

 

 

 

 

 

Condipn (bncflpn
3-3-90 41 F, 85% RH l 41 F, 87% RH
' I 41 F, 89% RH
3-4-90 " l 42F, 88% RH
" I 41 F, 87% RH
3590 73F, 50% RH I 72F, 54% RH
" I 73F, 52% RH
3-6-90 " I 72F. 53% RH
" I 73F, 51% RH
3-7-90 41 F, 60% RH I 42F, 65% RH
" I 41 F, 62% RH
3—8-90 ' I 41 F, 63% RH
" I 41 F. 65m
39-90 41 F, 85% RH V 41 F, 88% RH
" V 42F, 89% RH
3-10-90 " V 41 F, 87% RH
" V 41 F, 91% RH
3-11-90 73F, 50% RH V 73F. 53% RH
" V 72F, 54% RH
3-12-90 " V 72F, 54% RH
" V 73F, 52% RH
3-13-90 99F, 30% RH V 99F. 34% RH
" V 99F. 32% RH
3-14-90 ' V 99F, 30% RH 41 F. 85% RH I 42F.85% RH
" V " I 41 F, 87% RH
3-15-90 99F, 30% RH N 99F, 31% RH " I 41F, 88% RH
' N 99F, 30% RH " I 41 F, 88% RH
3-16-90 " N 99F, 32% RH 73F, 50% RH I 74F, 54% RH
" N 99F. 31% RH " I 73F, 55% RH
3-17-90 73F.50% RH N 73F, 53% RH ' I 73F, 56% RH
" N 73F, 51% RH " I 73F, 55% RH
3-18-90 " N 72F, 53% RH 41 F, 60% RH I 41F, 64% RH
" N 73F, 50% RH ' I 42F, 64% RH
3-19-90 41 F, 85% RH N 41 F, 95% RH " I 41 F, 65% RH
" N 41 F. 90% RH " l mu
3-20-90 " N 41 F, 92% RH 41 F, 89% RH V 41 F, 89% RH
" N 42W " V 41F. 88% RH
3-21-90 99F, 85% RH I 99F, 84% RH " V 41 F, 89% RH
" I 98F, 87% RH " V 41 F, 89% RH
3-22.90 " I 99F, 87% RH 73F, 50% RH V 75F, 54% RH
" I 99F, 86% RH " V 73F. 56% RH
3-23-90 73F, 85% RH I 73F, 86% RH " V 73F. 53% RH
" I 73F, 91% RH " V 73F, 53% RH
3-24-90 ' I 72F, 89% RH 99F, 30% RH V 98F, 31% RH
" I 73F, 86% RH " V 99F, 30% RH
3-25-90 99F, 85% RH I 99F. 85% RH " V 99F, 31% RH
' | 99F. 86% RH " V W
3-26-90 ' I 99F, 87% RH 99F, 85% RH I 99F, 88% RH
" " I 99F, 87% RH
3-27-90 99F, 85% RH I 99F, 87% RH " I 98F, 85% RH
" I 99F. 87% RH " l 99F, 85% RH

69

 

 

 

 

 

3-28-90 " I 98F, 86% RH
" I 99F, 85% RH
3-29-90 41 F, 85% RH I 41 F, 98% RH
" I 41 F. 95% RH
3-30-90 " I 42F. 94% RH
' I 41 F, 95% RH
3-31-90 73F, 50% RH I 73F, 55% RH
' I 74F, 53% RH
4-1-90 " I 73F, 51% RH
4-2-90 99F, 85% RH I 99F, 86% RH
" I 99F, 87% RH
4-3-90 " I 98F. 85% RH
" I 99F, 86% RH
4- 4-90 73F, 85% RH I 75F, 89% RH
“ I 73F, 89% RH
4-5-90 " I 73F, 88% RH
" I 73F, 89% RH
4-6-90 99F, 85% RH I 99F, 85% RH
" I 99F, 84% RH
4-7-90 " I 99F. 85% RH
" ll W
4-8-90 99F, 85% RH I 99F, 85% RH
" I 99F, 86% RH
4-10-90 ' I 98F, 86% RH
" I 99F, 85% RH
4-11-90 41 F, 85% RH I 41 F, 95% RH
" I 41 F, 92% RH
4-12-90 " I 42F, 90% RH
" I 41 F, 93% RH
4-13-90 73F, 50% RH I 73F, 56% RH
" I 74F, 53% RH
4-14-90 " I 73F, 54% RH
" ll W
4-15-90 99F, 30% RH N 99F, 31 % RH
' N 99F, 32% RH
4-16-90 " N 99F, 31 % RH
" N 99F, 34% RH
4-17-90 73F,50% RH N 73F, 54% RH
" N 73F, 53% RH
4-18-90 " N 72F, 56% RH
" N 73F, 53% RH
4-19-90 41 F, 85% RH N 41 F, 89% RH
" N 41 F, 87% RH
4-20-90 " N 41 F, 90% RH
" L__52E..92%.BI:I
4-21-90 41 F, 85% RH I 41 F, 88% RH
" I 41 F, 87% RH
4-22-90 " I 42F, 87% RH
" I 41 F, 88% RH
4-23-90 73F, 50% RH I 72F, 56% RH
" I 73F, 54% RH
4-24-90 " I 72F, 54% RH
' I 73F, 51 % RH
4-25-90 41 F, 60% RH I 41 F, 65% RH
" I 42F, 66% RH
4-26-90 " I 41 F, 65% RH
" l 4] F. 64%
4-26-90 41 F, 85% RH V 41 F, 88% RH
" V 42F, 87% RH
4-27-90 " V 41 F, 86% RH
" V 42F, 87% RH
4-28-90 73F, 50% RH V 73F, 55% RH
" V 73F, 56% RH

70

73F. 85% RH

99F, 85% RH

 

99F, 85% RH

41 F, 85% RH

F"""""""""'

73F, 89% RH
73F, 89% RH
73F, 91 % RH
74F, 90% RH
98F, 85% RH
99F, 86% RH
99F, 88% RH
Wt!
99F, 86% RH
99F, 89% RH
99F, 87% RH
99F, 87% RH
41 F, 98% RH
41 F, 95% RH
41 F, 94% RH
41 F, 96% RH
73F, 54% RH
73F, 53% RH
73F, 51% RH

w

 

 

4-29-90 V 72F, 54% RH
" V 74F, 52% RH
4-30-90 99F, 30% RH V 99F, 32% RH
' V 99F, 32% RH
5-1-90 " V 98F, 31 % RH
" V W
5-2-90 99F, 30% RH N 99F, 32% RH
" N 99F, 33% RH
5-3-90 " N 99F, 30% RH
' N 99F, 31 % RH
5-4-90 73F,50% RH N 73F, 56% RH
" N 73F, 56% RH
5-5-90 " N 72F, 52% RH
" N 73F, 53% RH
5-6-90 41 F, 85% RH N 41 F, 92% RH
" N 41 F, 90% RH
5-7-90 " N 41 F. 89% RH
" N WEI
5-8-90 73F, 85% RH “ 73F, 86% RH
" " 72F, 87% RH
5-9-90 " " 73F, 87% RH
" " 73F, 86% RH
5-10-90 " " 74F, 86% RH
" " 73F, 86% RH
5-11-90 " " 73F, 85% RH
" " 73F, 87% RH
5-12-90 " " 73F, 85% RH
" " 73F, 85% RH
5-13-90 " " 73F, 86% RH
" " w

 

“ Non-cyclic condition at 73F. 85% RH.

71

APPENDIX B

Results of the physical properties of the box materials.

 

69-lb 58-Ib 90-lb 69-Ib 33-lb
Standard Regular Standard Highly Medium
Linerboard Fiber-efficient Linerboard Fiber-efficient

 

 

 

 

 

Limm Unerbqard
Basis Weight* 68 59 91 67 33
(lb/1000 f12)
Thickness“ 17.9 13.8 22.8 16.6 10.8
(pt.) SD = .18 .20 .50 .15 .26
Ring Crush" 96.7 98.6 157.2 137.5 54.2
(lb) SD = 4.75 4.56 4.32 3.58 2.52
Combinedjcam
69-lb 58-lb 90-lb 69-Ib
Standard Regular Standard Highly
Linerboard Fiber-efficient Linerboard Fiber-efficient
Linerboard Linerboard
Edge Crush Test" 39.7 44.3 58.9 54.2
(Weyerhaueser SD = 1.9 1.9 3.9 4.7

Method) (lbfin)

 

* An average of 10 test samples
** An average of 15 test samples

72

APPENDIX C

An analysis of variance for 3-factor factorial experiment.

- For 69-Ib standard and 58-Ib regular fiber efficient linerboards

 

 

E | . I}! . I ll
Source Degree of Sum of Mean F

Freedom Square Square Value Prob.
FactorA 1 318024.037 310824.037 60.0261 0.0000
FactorB 1 1551880837 1551880837 299.6980 0.0000
AB 1 21489.338 21489.338 4.1500 0.0428
FactorC 4 2188003708 547000.927 105.6364 0.0000
AC 4 43995.192 10998.798 2.1241 0.0788
BC 4 1812765392 453191.348 87.5200 0.0000
ABC 4 116807.142 29201.785 5.6394 0.0002
Error 220 1139192750 5178.149
Total 239 71 84958.396

 

Factor A = Boxes with 69-Ib standard linerboard vs boxes with 58-lb regular
fiber-efficient linerboard

Factor B = Compression strength obtained immediately after cyclic conditions
vs Compression strength after re-conditioning

Factor C = Cyclic conditions

Critical F-value (1,220) ~ 3.88 at 95% confidence level
Critical F-value (4,220) ~ 2.41 at 95% confidence level

73

APPENDIX c (Cont'd)

- For 90—Ib standard and 69-Ib highly fiber efficient linerboards

 

 

E | . I}! . I H
Source Degree of Sum of Mean F

Freedom Square Square Value Prob.
FactorA 1 66101.204 66101.204 6.5354 0.0112
FactorB 1 2701093838 2701093838 267.0558 0.0000
AB 1 38329.537 38329.537 3.7896 0.0528
FactorC 4 4196661.892 1049165473 103.7305 0.0000
AC 4 126043.442 31510.860 3.1155 0.0161
BC 4 2470086058 617521.515 61.0540 0.0000
ABC 4 15345.775 3836.444 0.3793
Error 220 2225155417 10114.343
Total 239 11838817.163

 

Factor A = Boxes with 90-lb standard linerboard vs boxes with 69-lb highly
fiber-efficient linerboard
Factor B = Compression strength obtained immediately after cyclic conditions
vs Compression strength after re-conditioning
Factor C = Cyclic conditions

Critical F-value (1,220) ~ 3.88 at 95% confidence level
Critical F-value (4,220) ~ 2.41 at 95% confidence level

74

APPENDIX D

One way Analysis of Variance for determining difference in initial compression
strength between boxes made with 69-lb standard linerboard and boxes made
with 58-lb regular fiber efficient linerboard.

 

 

E | . I}! . I II
Degree of Sum of Mean
Freedom Squares Square F-value Prob.
Between 1 164838.375 164838.375 32220" <0.001
Within 22 1 12552.583 51 16.027
Total 23 277390.958

Critical F-value = 14.4 at 99.9% confidence level

* Statistically significant

75-

APPENDIX E

A t-test analysis for determining the significance of the difference in strength
loss between two box types.

I = As - Ag
lV(As—Ac)I"2

V(As—Ac) = [V(As)+V(Ac)]

V ( As ) = (standard error of compression strength at TAPPI condition )2
V ( Ac ) = (standard error of compression strength after cyclic condition )2

A5 = Difference of initial compression strength a Ya1 - Yaz
Ac = Difference of compression strength after cyclic condition = Yb1 - sz

Ya1 = Average compression strength of standard box at TAPPI condition

Yaz = Average compression strength of fiber efficient box at TAPPIcondition

Yb1 = Average compression strength of standard box after cyclic condition

sz = Average compression strength of fiber efficient box after cyclic
condition

QaIQuIatinn
I V(As—Ac)]"2 = [{(20-65)2+(2’0-77)2}I"2
= 29.29

- Cyclic condition I: t = 92 / 29.29 = 3.14

- Cyclic condition ll: t= 164/29.29 = 5.60

- Cyclic condition III: gt= 110 / 29.29 = 3.76

- Cyclic condition IV: t: 143/ 29.29 = 4.88

- Cyclic condition V: t = 56 / 29.29 = 1.91

Critical t-value = 2.819 at confidence level of 99%

76

APPENDIX F

One way Analysis of Variance for determining difference in initial compression
strength between boxes made with 90-lb standard linerboard and boxes made
with 69-Ib highly fiber efficient linerboard.

 

 

E I . I]! . I ll
Degree of Sum of Mean
Freedom Squares Square F-value Prob.
Between 1 3561.042 35651.042 3.786‘ 0.0646
Within 22 207183.917 9417.451
Total 23 242834.958

Critical F-value = 2.95 at 90% confidence level; 4.30 at 95% confidence level

* Statistically significant

77

APPENDIX G

A Host analysis for determining the significance of the difference in strength
loss between two box types

1 = A§_-_Ag
l V(AS-AC)I1/2

V(AS—AC) = [V(As)+V(Ac)I

V ( As ) = (standard error of compression strength at TAPPI condition )2
V ( Ac ) = (standard error of compression strength after cyclic condition )2

As = Difference of initial compression strength = Ya1 - Yaz
Ac = Difference of compression strength after cyclic condition = Yb1 - sz

Ya1 = Average compression strength of standard box at TAPPI condition
Yaz = Average compression strength of fiber efficient box at TAPPI condition
Yb1 = Average compression strength of standard box after cyclic condition
sz = Average compression strength of fiber efficient box after cyclic
condition

Catculatinn

I v(As—Ao)1“2 = [{(28-01)2+(29-03)2}]

= 40.34
- Cyclic condition I: t: 69 / 40.34 a: 1.71
- Cyclic condition II: t: 54 / 40.34 = 1.34
- Cyclic condition Ill: t= 31 /40.34 = 0.77
- Cyclic condition IV: t: 75 / 40.34 = 1.86
- Cyclic condition V: t= 78 / 40.34 = 1.93

Critical t-value = 1.717 at 90% confidence level; 2.074 at 95% confidence level

78

APPENDIX H

A Host analysis for determining the significance of the difference in final
compression strength between two box types.

t= (U1 -U2) / Sy1_372

U 1 = Average final compression strength of box A after exposure to cyclic
condition
U 2 = Average final compression strength of box B after exposure to cyclic

condition
371 - 72 = Pooled estimate of variance

Calculation

1. For box A and box B
- Cyclic condition I: t = (1128 - 1054) / 31.39 = 2.36
- Cyclic condition II t = (978 - 976) I 29.60 = 0.07
- Cyclic condition Ill: t = (1176 - 1120) / 52.38 = 1.069

- Cyclic condition IV: t: (761 - 738) / 46.20 = 0.49
- Cyclic condition V t: (1336 - 1226) I 62.92 = 1.75

1. For box C and box D

- Cyclic condition I: t = (1305 - 1297) / 101.06 = 0.08
- Cyclic condition II t = (1166 - 1143) / 89.87 = 0.26
- Cyclic condition Ill: t= (1451 -1405)/146.51 = 0.31

- Cyclic condition IV: t = (1007 - 855) / 29.77 = 2.46
- Cyclic condition V t: (1649 - 1571) / 117.20 = 0.66

79

APPENDIX I

One way Analysis of Variance for determining difference in moisture gains
between boxes made with 69-Ib standard linerboard and boxes made with 58-

lb regular fiber efficient linerboard.

 

 

E I . I]! . I II
Degree of Sum of Mean
Freedom Squares Square F-value Prob.
Between 1 0.572 0.572 8.086* 0.0094
Within 22 1.555 0.071
Total 23 2.127

Critical F-value = 7.95 at 99% confidence level
* Statistically significant

80

APPENDIX J

One way Analysis of Variance for determining difference in moisture gains
between boxes made with 90-Ib standard linerboard and boxes made with 69-

lb highly fiber efficient linerboard.

 

 

E I . I}! . I II
Degree of Sum of Mean
Freedom Squares Square F-value Prob.
Between 1 0.313 0.313 8.619* 0.0076
Within 22 0.799 0.036
Total 23 1.112

Critical F-value = 7.95 at 99% confidence level
‘* Statistical significant

81

APPENDIX K

An Improved Bonferroni t-test for determining the difference between the initial
compression strength and compression strength after cyclic conditions.

t3 = {v1 - Y2} / {[32/dr1]+ [ MSE Idfz) )1/2
Y1 = Average compression strength of boxes held at TAPPI standard

condition
Y2 = Average compression strength of boxes after exposed to cyclic

condition
82 = Variance of measures in Y1
MSE = Mean Square Error of measures in Y2

df1 = degree of freedom for Y1
df2 = degree of freedom for Y2

Calculation
— For 69-lb standard and 58-Ib regular fiber efficient linerboards

to = “33%-1049} / {[12060/231-1-[5178/119]}1/2

- For 90-Ib standard and 69-lb highly fiber efficient linerboards
1636-1285} / {[10558/23]+[10114/119]}1/2

505*
Critical t-value = 3.08 at 99% confidence level

te={
=1

82‘

APPENDIX L

An Improved Bonferroni t-test for determining the difference between the in
compression strength obtained immediately after cyclic conditions and the
compression strength after re-conditioning.

te= {Y1 - Y2} / {[812/df1]+[822/df2)}1/2

Y1 = Average compression strength of boxes held at TAPPI standard

condition
Y2 = Average compression strength of boxes after re-conditioned
S12: Variance of Y1

$22 = Variance of Y2
(111 = degree of freedom for Y1
df2 a: degree of freedom for Y2

Caloulation

- For 69-lb standard and 58-lb regular fiber efficient linerboards

t3 ={121o-1049} I {[5178/119]+[5178/119]}1/2
— 17.3*

- For 90-lb standard and 69-lb highly fiber efficient

to = Iggy-1285} / {[10114/119}+[10114/119]}1/2

Critical t-value = 3.08 at 99% confidence level

83

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86

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