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thesis entitled

THE EFFECTS OF CYCLIC HUMIDITY ON COMPRESSION STRENGTH OF
CORRUGATED PALLETS

presented by

Michael Steve Dennis

has been accepted towards fulfillment
of the requirements for

M.S. Packaging Engineering

degree in

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THE EFFECTS OF CY CLIC HUMIDITY ON COMPRESSION STRENGTH OF
CORRUGATED PALLETS

By

MICHAEL STEVE DENNIS

ATHESIS

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

MASTER OF SCIENCE

School of Packaging Engineering

1995

ABSTRACT

THE EFFECTS OF CY CLIC HUMIDITY ON COMPRESSION STRENGTH OF

CORRUGATED PALLETS

By

Michael Steve Dennis

Corrugated material is affected by temperature and humidity during
storage and use. Recently, the effects of cyclic humidity have been studied by
various groups. This study looks at the effects of cycling conditions on the
compression strength of corrugated cores for Stone Container’ s Cordeck pallets.
Test methods included a moisture content study, edge crush test evaluation, and
compression test simulations under dynamic and constant loading. It was
determined that as the cycle time increases, the moisture content of the
corrugated increases as well. This leads to lower compression strengths in both
the dynamic and constant loading tests. Furthermore, it was determined that
54% i 5% of the maximum dynamic load of the cores is the upper limit for safe

stacking weights during long term storage.

I dedicate this thesis to all of the people involved in pushing me to go one step further in
life. To my Mom & Dad, who taught me the value of an education. To my
Grandparents, for being in my corner. To my Sister, who is always determined to
succeed. To my Brother, who is always there to pick me up. And to my family,
Rebecca, Meighan, Zachary, and Newt for helping me along to be successful in my
pursuit of Love, Happiness, and God. I Love all of you just because I do!

iii

ACKNOWLEDGMENTS

I greatly appreciate all of the support and guidance from my committee
members Gary Burgess, Paul Singh, and George Mase. Special accolades go out
to my Major Professor, Gary, for his wisdom and guidance throughout my
experience in graduate school. Special thanks to Stone Container Corporation
for supplying the Cordeck samples for this study.

iv

TABLE OF CONTENTS

 

 

LIST OF TABLES ................................................................................. vi
LIST OF FIGURES ............................................................................... vii g
1.0 INTRODUCTION ......................................................................... 1-4
2.0 EXPERIMENTAL DESIGN .......................................................... 5-17
2.1 Conditioning ..................................................................... 5-6
2.2 Tests ................................................................................... 10
2.3 Materials ............................................................................ 11
2.4 Methods ............................................................................. 12-14
2.5 Limitations ......................................................................... 15-17
3.0 DATA & RESULTS ....................................................................... 18-37
3.1 Moisture Contents .............................................................. 18
3.2 Edge Crush Tests ............................................................... 23
3.3 Compression Tests - Dynamic Loading ........................... 27-33
3.4 Compression Tests - Constant Loading ........................... 34-37
4.0 ERROR ............................................................................................ 38
5.0 CONCLUSIONS ............................................................................ 39-42
LIST OF REFERENCES ........................................................................ 43

 

 

LIST OF TABLES

 

 

 

Title Page it
Table 1 Sample Weights ........................................................... 19
Table 2 Sample Weights After Conditioning ........ - 21
Table 3 Sample Weights After Drying .................................... 21
Table 4 Moisture Content on Dry Basis .................................. 21
Table 5 ECT Values .................................................................. 24
Table 6 Conversion of ECT Results ........................................ 25
Table 7 Calculated Compression Strength ............................. 25
Table 8 Actual Compression Strength ..................................... 25
Table 9 Dynamic Compression 5" X 5” .................................. 28
Table 10 Dynamic Compression 5” X 8” .................................. 29
Table 11 Dynamic Compression 8” X 8” .................................. 30
Table 12 Test Schedule ................................................................ 32
Table 13 Constant Loading 5” X 5” ........................................... 35
Table 14 Constant Loading 5” X 8” ............................ i ............... 36
Table 15 Constant Loading 8” X 8” ........................................... 37
Table 16 Maximum Safe Long Term Loading -_ 42

 

 

 

 

 

LIST OF FIGURES

 

 

Title Page #
Figure 1 Two Cycles Per Day ..................................................... 7
Figure 2 One Cycle Per Day ....................................................... 8
Figure 3 Half Cycle Per Day ............................. 9
Figure 4 Sample Weights After Conditioning .......................... 20
Figure 5 Average Moisture Content Dry Basis ........................ 22
Figure 6 Actual vs. Calculated Compression Strength ............ 26
Figure 7 Average Dynamic Compression ................................. 33
Figure 8 Maximum Constant Loading ...................................... 40

Compression Strength

 

vii

 

1.0 INTRODUCTION

Corrugated material has been used in the transportation of consumer and
industrial goods for many years. It is light, durable, and versatile. It is
relatively lower in cost when compared to other materials making it one of the
most widely used packaging mediums in the world today.

Corrugated is being used for many applications traditionally reserved for
wood. One such example is the corrugated pallet. Stone Container makes the
Cordeck corrugated pallet for use in the distribution of some products found in
grocery stores and retail outlets.

There are several distinct advantages in using the Cordeck pallets. First,
they are lighter in weight in comparison to wood. This translates into savings
during distribution. They are also relatively strong for the amount of material
used in comparison to wood. In addition, they can be recycled and used in other
packaging applications. Lastly, they can be custom engineered for use in many
situations.

Cordeck pallets have some limitations as well. Research done by Gary
Greywall, of Michigan State, showed that they performed worse in the pallet

durability and stiffness tests in comparison to similar wood and plastic models.

Consequently, they have limited use in racking applications due to the lack of
bending stiffness in combination with the current rack designs. He also
concluded that multiple trips would decrease the strength of the pallets
significantly. (Greywall, 1994)

His study was based on ASTM D-1185, The Test Methods for Pallets and
Related Structures Employed in Materials Handling and Shipping. These test
methods were written for wood pallets in distribution systems with multiple trip
capabilities. They lack guidelines for corrugated pallets like the Cordeck, which
is primarily designed for one trip. In addition, there are no test methods for
determining compression strength of corrugated pallets in typical non-racking
situations. Therefore, the test methods in ASP M D-1185 do not represent an
accurate measure of performance in the real distribution environment for
Cordeck corrugated pallets.

However, there are other tests that are common to the corrugated
industry which would be applicable in this situation. Two of these areas of
testing are interrelated in regard to a corrugated material subjected to a
warehouse storage environment. They are atmospheric conditioning during
storage, and top to bottom compression strength over time. Atmospheric
conditions consist of many variables. In packaging, the areas of primary concern

include temperature, humidity, and relative humidity. These factors have an

impact on the performance of corrugated materials because they effect the
moisture content of the board at any given time.

Temperature is a measure of the degree of heat in the air. Humidity is the
term used to describe the water vapor content of the atmosphere. Relative
humidity is the ratio of actual moisture content of a sample of air to the same
volume of air that can hold the same temperature and pressure when saturated.
It is usually expressed in percentage form. (Ayoade, 1983)

Relative humidity has an inverse relationship with respect to temperature.
Generally speaking, as the temperature rises, relative humidity falls. Most
climates have diurnal cycles, or two cycling patterns per day in which
temperature and humidity fluctuate. There are also weather fronts or systems
that move across land and water creating shorter or longer cycles depending on
the type of system. (Ruffner, 1981)

In 1992, a symposium at the Forest Products Laboratory brought together
the industry experts in corrugated packaging to discuss the effects of cyclic
humidity on paperboard packaging. These individuals discussed their
experiences with cyclic humidity and the various aspects related to testing and
performance of corrugated packaging.

Craig Leake and Robert Wojcik of the National Starch and Chemical
Company in Bridewater, New Jersey, lectured on their study titled ”Humidity

Cycling Rates: How They Effect Container Life Spans.” Their results showed

that corrugated containers under a constant load crept faster and failed quicker
in cyclic humidity conditions when compared to constant conditions at high
temperature and high relative humidity. (Leake 8r Wojcik, 1992) The
implications are that moisture content increases in the corrugated over time at a
quicker rate when exposed to cycling conditions. Furthermore, as the cycle time
increases, the amount of moisture absorbed increases. The study also implies
that cycling test conditions are more like distribution environments for
corrugated materials. The cycling effects can be recreated in the laboratory to
represent normal and extreme conditions in a distribution system.

The practical application of these findings in relation to the Cordeck
pallets is understanding compression strength performance in climates where
high humidity and high temperature cycle over time. From there, one can
determine safe stacking limits for the Cordeck pallets when subjected to certain
cycling atmospheric conditions. This information could be used as a general
guideline to create a ”safe zone" for the stacking strength of the Cordeck pallets

used in temperate climates for long term loading.

2.0 EXPERIMENTAL DESIGN

2.1 Conditioning

Environmental conditioning was based on climates with moderate
to high relative humidities and temperatures. Large changes in these
conditions from day to night were also-factored in the decision. It was
found that the following cities in the Southeastern section of the United
States met these specifications: Orlando, FL; Atlanta, GA; New Orleans,
LA; Jackson, MS; Raleigh, NC. (Pearce, 1990) The conditions used for
this study were:

1. Standard conditions - 72°F 6: 50% RH

2. Temperate conditions - 85°F 8: 85% RH
These environmental factors were used conjointly to create the cycling
effect of the real world climate. The cycles were based on a twenty-four
hour time interval. The shortest amount of time in either condition was
six hours. The longest amount of time was twenty-four hours.
The four different cycling conditions were:

1. Standard constant conditions

2. Two cycles per twenty-four hours

3. One cycle per twenty-four hours

4. Half cycle per twenty-four hours
These different cycles are graphically depicted in Figures 1, 2, and 3. The
Leake and Wojcik study showed that the longer it takes to complete a
cycle, the more severe the impact on corrugated material. Thus, the half
cycle simulation should be considered the most severe, followed by one

cycle, two cycles, and the standard.

 

 

Relative Humidity (%)

Two Cycles Per Day

 

20-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1

 

 

 

 

Relative Humidity (°/o)

One Cycle Per Day

 

100

 

20 4

10 ‘4

 

 

 

 

 

 

 

 

 

Figure 2

 

 

 

 

 

 

Relative Humidity (“/o)

Half Cycle Per Day

 

1M

 

70 -~

 

 

 

 

20 +

10 m.

 

 

 

 

Figure 3

 

2.2 Tests

10

Four different procedures were utilized in order to analyze the

Cordeck pallets under cycling conditions. They were:

1.

2.

3.

4.

Moisture content of board
Edge Crush Test
Compression Test - Dynamic Loading

Compression Test - Constant Loading

Each test was done to understand the relationship of the corrugated

structure to the specific cycling environments.

11

2.3 Materials
1. Stone Container Cordeck Pallet
A. Nine cores per pallet - 275# burst corrugated
1. 5” X 5” cores
2. 5” X 8" cores
3. 8” X 8” cores

B. Two decks, upper and lower - doublewall
corrugated

II. Environmental chamber
(85°F :t: 5°F, 85% RH :I: 5% RH)
III. Compression testers

A. Lansmont
(force lb. :1: .51b., deflection in. :1: .005 in.)

B. Clarke
(force lb. :t 2.5 lb.)

C. TMI
(1b. 1: .05 lb. Per unit edge length)

N. Drying oven (°C i 2.5 °C)
V. Hand micrometer (in :1: .0005 in.)

VI. Mettler balance (g :1: .0005 g)

12

2.4 Test Methods

2.4.1 AST M D-644 Standard Test Method for Moisture
Content of Paper and Paperboard by Oven Drying

1.

Choose four samples from each size core (12
total samples)

Precondition samples for three days:

Three at two cycles (85°F and 85% RH)

Three at one cycle (85°F and 85% RH)

Three at half cycle (85°F and 85% RH)

Three at standard Conditions (72°F and 50% RH)

Weigh samples every six hours for three days

Heat three samples representing standard
conditions in oven for two hours at 105i 3°C

Weigh oven dried samples to determine
weight after drying

Calculate moisture content based on oven dry
weight using:

Moisture, % = [M1 - W2)/ W2] X 100
Where:

W1 = original weight of the specimen
W2 = weight of the specimen after oven drying

13

2.4.2 ASI‘ M D-2808 Test Method for Compressive Strength

2.4.3

of Corrugated Fiberboard

1. Choose one sample from each size core (3 total
samples)

2. Precondition samples for three days at 72°F
and 50% RH

3. Cut 15 specimens (1.25” by 2.00”) for each core
size using the sample cutter with flutes parallel
to the shorter side

4. Center specimen between platens with guide
blocks on each side of the specimen so that the
flutes are perpendicular to the platens

5. Compress specimen at 2.0 in. / min. with a
force increasing at 20.0 lb. / sec.

6. Record the maximum load value of specimen

AST M D-642 Test Method for Determining
Compressive Resistance of Shipping Containers,
Components, and Unit Loads

1.

Choose twenty samples from each size core
(sixty total)

Precondition samples for three days:

Fifteen at two cycles

Fifteen at one cycle

Fifteen at half cycle

Fifteen at standard conditions

Center test specimen between fixed platens
with flutes perpendicular to the platens.

Bring the upper platen down in contact with
test specimen

l4

Compress specimen with pre-load at 50 lb. and
platen speed at .5 in. / min.

Record maximum load value and deflection at
failure

2.4.4 AST M D4577 Test Method for Compression
Resistance of a Container Under Constant Load

1.

Develop criteria for constant loading to be
applied to samples through previous testing
using AST M D-642 test method

Choose twelve samples from each size core
(thirty-six total)

Precondition samples for three days:

Nine at two cycles

Nine at one cycle

Nine at half cycle

Nine at standard conditions

Center test specimen between fixed platens
with flutes perpendicular to the platens.

Compress specimen at predetermined constant
level for twelve hours or until failure

Record deflection at predetermined time
intervals: T=0 min., T=15 min., T=30 min.,
T=1 hr., T=6 hr., T=12 hr.

15

2.5 Limitations
The design of this experiment was developed based on
several ASI' M Standards for corrugated testing. At the present time, there
are no specific tests related to corrugated pallets. However, there are
standards that relate to physical properties of corrugated materials. Some
of the procedures have been modified due to limitations of available
equipment, or the practicality of using certain methods given the
circumstances of this study. These modifications are identified as follows: .
2.5.1 Test Specimens
The corrugated cores were tested individually as opposed to
an entire assembled pallet due to machine limitations. The type of
pallet used in this study had a thirty thousand pound maximum
rating for compression strength. (Stone Container, 1995) In order
to test complete pallets for compression strength, the tester must be
able to equal or exceed the maximum rating of the pallet. In this
case, the pallets were broken down into their respective parts in
order to accomplish this requirement. The additional compression
strength that might have been gained from the top and bottom
sheets of the pallet is minimal. Thus, the results from this

experimental design are comparable to using an entire pallet.

16

2.5.2 Ramping Procedure

All samples were conditioned for testing without the
ramping procedure to produce the cycling effect. The ramping
technique allows temperature and relative humidity to gradually
increase and decrease as the cycles are created in the laboratory
environment. The conditioning of samples in the study by Leake
and Wojcik used the ramping procedure. Unfortunately, there are
no facilities to create this kind of simulated condition at Michigan
State University. Instead, samples were moved directly from one
condition to the other to create the cycling effect. The consequences
of ramping versus direct contact are unknown at this time.
2.5.3 Loading Modification

The constant load testing was modified due to a machine
limitation. The motor governing the test equipment had a limited
running time. In order to meet time and load specifications for this
test, the procedure was altered to a creep and relax simulation.
Loading was constant at the predetermined level for the first hour
of the test. Then the machine was shut down for three hours while
the load remained on the specimen. As the specimen deflected

under the load, it was allowed to relax until the tester reapplied the

17

predetermined load. The effects of creep and relax versus a strict
constant load method are unknown at this time.
2.5.4 Load Application Range

It was reasoned through trial and error that a 40-65% test
range capability, based on the maximum compression strength of
the cores, satisfied the requirements for this study. Below 40% of
the maximum load, test samples showed no signs of failure.
Above 65% of the maximum load, test samples failed immediately.
The range of accuracy to describe the upper limit of the ”safe zone”
was chosen to be :1: 5% due to variations in the corrugated material
and the production process.
2.5.5 Load Application Time

It was reasoned through trial and error that twelve hours
was long enough to determine core failure in the constant load test.
Samples from each size core were tested at a constant load within
the application test range for seven to ten days without a

significant change in deflection. Twelve hours represents the

amount of time that the most significant measurable failure occurs.

3.0

DATA 8: RESULTS

3.1 Moisture Contents

Moisture Content was calculated for each of the different test
conditions. The sequential weights of the sample cores shows that the
moisture in the corrugated increased and decreased while experiencing
the cycling atmospheric conditions (Table 1). There were some minimal
changes in the constant condition samples as well. It is beneficial to note
the final weights after seventy-two hours of conditioning (Figure 4).
There is an increasing trend in moisture gain in all of the samples
subjected to the various cycling conditions. The average dry weight
(Table 3) for each size core was used to calculate moisture content values
for each sample in every condition (Table 4). The corrugated material in
the cores was assumed to be the same for every sample. Thus, the
moisture content values should be similar, regardless of the size of the
core. Table 4 shows that the values are grouped closely together. A
graphical representation of the average moisture content for each test
condition clearly shows that as the length of the cycle increases, the

moisture content of the cores also increases (Figure 5).

18

19

 

 

 

 

 

 

 

 

 

 

 

 

Table 1
Sample Weights (g.)

5" X 5"
10T6_112118124T:0736_T42_T48154T60166T72
Standard 148.55 148.72 14889 148.59 148.45 148.54 148.67 148.78 148.62 148.58 148.50 148.53 148.40
“170 Cycles 148.72 152.61 150.49 154.” 150.28 154.09 150.38 154.50 151.46 154.56 150.” 154.36 150.72
OneCycle 148.68 153.44 154.84 150.58 150.14 154.63 155.62 151.50 150.86 154.” 155.89 151.50 150.83
|Halnycle 14930 153.55 155.46 156.20 156.51 152.08 151.23 150.78 151.12 155.28 156.63 156.48 156.84

5" X 8"
I T0 T6 T12 T18 124 T30 T36 T42 T48 154 T60 T66_ T72
lsumdard 189.32 189.10 189.25 189.35 189.41 189.32 189.22 189.35 189.29 189.39 189.43 189.52 189?
“No Cycles 190.60 195.89 192.67 198.49 198.21 198.59 198.66 198.82 194.55 198.60 194.33 198.45 193.80
OneCycle 193.32 199.34 201.32 195.82 194.92 ”1.30 2172.47 197.22 196.25 ”1.38 ”2.” 196.73 196.01
IHalf Cycle 196.53 202.27 ”4.74 205.77 206.11 2m.53 199.59 198.85 199.28 ”5.11 206.42 ”6.41 ”6.83

8" X 8'
T0 T6 T12 T18— T24 T30 T36 T42_ T48 T54 T60_ ‘ T66 T72
Standard 207.79 207.58 207.65 207.77 207.69 20754 207.48 207.72 207.86 207.75 207.67 207.54 207.61
Two Cycles 206.92 213.44 20834 214.91 208.46 214.97 209.01 215.38 209.77 214.78 209.91 215.22 209.32
Cycle ”7.30 214.11 216.24 209.53 ”8.86 216.41 216.62 ”9.73 ”9.65 215.61 217.05 210.35 210.01
Half Cycle 208.35 215.08 217.73 218.73 218.86 211.43 210.31 209.75 210.26 217.20 218.88 218.83 219.20

 

 

20

Sample Weights After Conditioning

 

W
I One Cycle
DTwo Cycles

 

 

 

8'X8'

5"X8'

SIXSI a................

 

~x

120.00 140.00 160.00 180.00 200.00 220.00

 

240.00

Weight (3.)

Figure 4

21

Table 2

Sample Weights After Conditioning

 

 

 

 

 

 

 

 

 

Size Standard Two Cycles One Cycle Half Cycle
5" X 5" 148.40 150.72 150.83 156.84
5" X 8" 189.47 193.80 196.01 206.83
8" X 8" 207.61 209.32 210.01 219.20
Table 3
Sample Weights After Drying
Size Avg. Dry Weight (g)
5" X 5" 138.39
5" X 8" 177.56
8" X 8" 207.61
Table 4
Moisture Content on Dry Basis (g. moisture / 100 g. dry product)
Size Standard Two Cycles One Cycle Half Cycle
5" X 5" 7.23 8.91 9.00 13.33
5" X 8" 6.71 9.15 10.84 16.50
8" X 8" 7.08 7.96 8.32 13.06
Average 7.01 8.67 9.39 14.30

22

Average Moisture Content Dry Basis

 

 

 

86.6 :8:

o—ohU ofiO

uo—uhU 93H

"Envy—Sm

 

16.00

14.00 0

12.00 -*

400
2.00 --
000

m... w. 8.
new 8 6

85.388 to .o 8" \ 83862 .0

Figure 5

23

3.2 Edge Crush Tests

The Edge Crush Test was used to determine the compression
strength of a sample taken from the middle section of the manufactured
corrugated core (Table 5, Table 6). Three trials were conducted for every
core size. The calculated compression strength values were compared to

the actual test values of the cores and shown to be very similar (Figure 6).

24

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5
ECT VALUES (lb/2")
Trial 1 Trial 2 Trial 3
79.7 85.9 86.5
77.9 81.2 94.3
5" X 5" 79.1 83.8 82.4
77.6 91.5 83.8
81.2 80.8 87.4
Averages 79.1 84.6 86.9
Standard Dev. 1.5 4.4 4.6
Overall Avg. 83.5
Trial 1 Trial 2 Trial 3
71.8 87.2 97.4
92.7 89.3 89.1
5" X 8" 94.1 84.3 104.6
104.1 103.0 96.4
89.0 85.1 93.6
Averages 90.3 89.8 96.2
Standard Dev 11.8 7.6 5.7
Overall Avg. 92.1
Trial 1 Trial 2 Trial 3
84.5 99.2 102.1
107.4 102.1 98.6
8" X 8" 102.7 102.0 103.1
111.4 115.2 108.3
101.4 105.6 98.4
Averages 101.5 104.8 102.1
Standard Dev 10.3 6.2 4.0
Overall Avg. 102.8

 

 

 

25

 

 

 

 

 

 

 

Table 6
Conversion of ECT Results
-5"x5" 5"x8" 8"x8"
lb. / 2" 83.5 92.1 102.8
lb. / 1" 41.7 46.1 51.4
Table 7

Calculated Compression Strength

 

 

 

5" x 5" 66.6 X 41.7 '- 2782.9
5" x 8" 88.6 X 46.1 - 4079.1
8" x 8" 86.8 X 51.4 - 4458.9

 

 

 

Edge Length (in) X ECT Value (Ib./ in) - Compression Strength (1b.)

 

 

 

 

Table 8
Actual Compression Strength
Size Force (Ib.) Deflection (in)
5" x 5" 2642 0.18
5" x 8" 4029 0.22
8" x 8" 4326 0.29

 

 

 

 

 

 

 

26

Actual vs. Calculated Compression Strength

 

 

 

 

 

8" x8"

 

 

 

D Calculated Value
I Actual Value

 

 

5"x8"

 

 

 

 

 

5" x5"

 

 

 

 

l I I I I I I I I I I

0500100015002000250030003500400045005000

Force (1b.)

Figure 6

27

3.3 Compression Tests - Dynamic Loading

The dynamic compression tests on the 5” X 5” corrugated cores
produced interesting results (Table 9). There was some variation in the
data between conditions, which was expected. However, there was also
some significant variation of compression strengths within the same test
conditions. During the testing, it was noted that some of the samples had
a half inch machine produced cut intersecting all of the layers of the
corrugated cores. The cuts were noticed on more than one sample in this .
core size. The damage occurred on all four sides of the core near the top
or the bottom.

Tables 10 and 11 show results with respect to the 5" X 8” and the
8” X 8” core samples. Variations of compression strengths within the

same test conditions were also prevalent with these core samples.

28

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 9
Warden—5M
Sample Conditions Sample # Force (lb) Deflection (in)
1 2734 0.17
2 2843 0.18
Standard 3 2731 0.17
4 2726 0.19
5 2176 0.14
Average 2642 0.17
St. Dev. 265 0.02
1 2531 0.17
2 2415 0.16
Two Cycles 3 2190 0.17
4 2140 0.16
5 2297 0.17
Average 2315 0.17
St. Dev. 161 0.01
1 2603 0.19
2 2378 0.14
One Cycle 3 2553 0.16
4 2485 0.17
5 2544 0.17
Average 2513 0.17
St. Dev. 86 0.02
1 1856 0.16
2 2565 0.19
Half Cycle 3 2309 0.16
4 2258 0.16
5 2287 0.14
Average 2255 0.16

St. Dev. 255 0.02

 

 

29

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 10
WELL"
Sample Conditions Sample # Force (10.) Deflection fin.)

1 4011 0.21

2 4352 0.23

Standard 3 4N1 0.21
4 4251 0.22

5 3531 0.2

Average 4029 0.21

St. Dev. 317 0.01

1 3643 0.22

2 3488 0.18

Two Cycles 3 3492 0.18
4 3337 0.19

5 3266 0.2

Average 3445 0.19
St. Dev. 147 0.02

1 3769 0.23

2 3666 0.19

One Cycle 3 2997 0.18
4 3526 0.19

5 3435 0.21

Average 3479 0.20

St. Dev. 298 0.02

1 3026 0.17

2 3382 0.19

Half Cycle 3 3079 '0.18
4 3274 0.18

5 3299 0.17

Average 3212 0.18

St. Dev. 152 0.01

 

 

30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 11
WW
Sample Conditions Sample # Force (1b.) Deflection (in)
1 4321 0.38
2 4557 0.27
Standard 3 4145 0.27
4 4449 0.31
5 4157 0.24
Average 4326 0.29
St. Dev. 180 0.05
1 3557 0.33
2 3773 0.33
Two Cycles 3 3911 0.37
4 3648 0.18
5 3626 0.49
Average 3703 0.34
St. Dev. 140 0.11
1 3904 0.28
2 3516 0.19
One Cycle 3 3904 0.23
4 3666 0.26
5 3861 0.29
Average 3770 0.25
St. Dev. 173 0.04
1 2676 0.47
2 3446 0.34
Half Cycle 3 3666 0.33
4 3898 0.31
5 3023 0.51
Average 3342 0.39

St. Dev. 493 0.09

 

 

31

Some of the 5” x 8” samples had the same half inch cut that was described
on the 5” X 5” samples. In addition, it was noted that some of the samples
were shifting towards a parallelogram configuration, rather than the
designed rectangular shape.

Some of the 8” X 8” cores were non-uniform in the top to bottom
height dimension. Others had frayed rough edges on the top and bottom
of the samples. All of these types of samples were noticeably weaker in
compression strength in comparison to those that did not exhibit the
problems listed above.

The average value for each sample lot was used as the best estimate
for the maximum compression strength. A test schedule (Table 12) was
designed for the constant loading procedure based on the values from the
dynamic compression tests. A comparison of the average values shows
that as the cycling length increases, the compression strength

decreases (Figure 7).

32

 

 

Table 12
Test Schedule
5"X5" Average Force (1b.) 40% 45% 50% 55% 60% 65%
Standard 2642 1057 1189 1321 1453 1585 1717
Two Cycles 2315 926 1042 1157 1273 1389 1504
One Cycle 2513 1005 1131 1256 1382 1508 1633

 

 

5"X8" Average Force (1b.) 40% 45% 50% 55% 60% 65%
Standard 4029 1612 1813 2015 2216 2418 2619
Two Cycles 3445 1378 1550 1723 1895 2067 2239
One Cycle 3479 1391 1565 1739 1913 2087 2261
Half Cycle 1445 1606 1767 1927 2088

  

 

 

 

 

8" X 8"

Standard

Two Cycles 3703 1481 1666 1852 2037 2222 2407
One Cycle 3770 1508 1697 1885 2074 2262 2451

Half Cycle 3342 1337 1504 1671 1838 2005 2172

33

Average Dynamic Compression

 

 

Standard
Two Cycles

One Cycle

Half Cycle

Figure 7

34

3.4 Compression Tests - Constant Loading

Constant loading of the sample cores is a representation of the real
world storage conditions. The 5” X 5” samples remained intact up to 52% :t:
5% of the maximum compression force with respect to the dynamic testing
and conditioning (Table 13).

It should be noted that the standard conditions samples were able
to withstand the most force, followed by the one cycle samples, the two
cycle samples, and the half cycle samples. The 5” X 8” samples remained
intact up to 56% :t 5% of the maximum compression force with respect to
the dynamic testing and conditioning (Table 14). The order of
compression strength for these samples was the same as mentioned
above. The 8” X 8" samples remained intact up to 55% :1: 5% of the
maximum compression force with respect to the dynamic testing and
conditioning (Table 15). There was more variation with these samples in
comparison to the others. The one cycle samples withstood the most
force, followed by the standard samples, the two cycle samples, and the

half cycle samples.

35

Table 13

Constant Loading 5" X 5"

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

| I
Standard I I Two Cycles I
Force (1b.) 1380 I 1525 1650 Force (1b.) 1240 I 1360 1480
Creep Measurements (in.) Creep Measurements (in.)
T-O min. 3.529 3.542 3.53 T-0 min. 3.568 3.558 3.510
T315 min. 3.521 3.522 f=5 min. T-15 min. 3.557 3.532 f=9 min.
T-30 min. 3.515 3.502 T-30 min. 3.552 f-20 min.
T=45 min. 3.510 f-35 min. T=45 min. 3.551
T-1 hr. 3.508 T-l hr. 3.550
T-6 hr. 3.500 T-6 hr. 3.542
T-12 hr. 3.495 T-12 hr. 3.540
% Avg. Maximum % Avg. Maximum
,C Load 52% 57% 62% E 'c Load 53% 58% 63%
Deflection (in.) 0.034 N / A N/ A Deflection (in.) 0.028 N / A N/ A
One Cycle Half Cycle
H l
Force (1b.) 1250 I 1380 I 1500 Force (1b.) 1175 I 1295 1400
Creep Measurements (in.) Creep Measurements (in.)
T-O min. 3.600 3.615 3.59 T-O min. 3.548 3.600 3.574
T315 min. 3.588 3.510 f-6 min. T-15 min. 3.529 3.555 f-5 min.
T-30 min. 3.587 {-25 min. T-30 min. 3.522 f-20 min.
r-45 min. 3.582 r-45 min. 3.516
T81 hr. 3.582 T-l hr. 3.513
T=6 hr. 3.578 T=6 hr. 3.508
T-12 hr. 3.577 T-12 hr. 3.505
% Avg. Maximum % Avg. Maximum
E 'c Load 50% 55% 60% E 'c Load 52% 57% 62%
Deflection (in.) 0.023 N / A N / A Deflection (in.) 0.043 N / A N/ A

 

Constant Loadin

Table 14

5 51x11" '

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Standard . I Two Cycles
Force (1b.) 285 1 2460 I 2660 ‘ Force (1b.) 1895 I 2070 I 2240
Creep Measurements (in.) Creep Measurements (in.)
T80 min. 3.631 3.560 3.529 T80 min. 3.629 3.591 3.582
T815 min. 3.615 3.541 f82 min. T815'min. 3.615 3.566 f88 min.
T830 min. 3.600 3.499 T830 min. 3.613 3.532
T845 min. 3.595 f840 min. T845 min. 3.610 f832 min.
T81 hr. 3.593 T81 hr. 3.610
T=6 hr. 3.590 T86 hr. 3.595
T812 hr. 3.589 T812 hr. 3.593
% Avg. Maximum % Avg. Maximum
'c Load 56% 61% 66% E 'c Load 55% 60% 65%
Deflection (in.) 0.042 N / A N / A Deflection (in.) 0.036 N / A N / A
One Cycle Half Cycle
Force (1b.) 1950 I 2120 I 2290 Force (1b.) 1825 1990 2157
Creep Measurements (in.) Creep Measurements (in.)
T80 min. 3.583 3.598 3.568 T80 min. 3.606 3.605 3.607
=15 min. 3.574 3.579 f85 min. T815 min. 3.594 3.582 f84 min.
T830 min. 3.571 3.562 T830 min. 3.590 3.560
T845 min. 3.570 3.554 T845 min. 3.589 3.530
r-1 hr. ' 3.569 3.528 T-1 hr. 3.589 {-50 min.
T86 hr. 3.565 f=70 min. T86 hr. 3.585
T812 hr. 3.564 T812 hr. 3.581
% Avg. Maximum % Avg. Maximum
E ‘c Load 56% 61% 66% E 'c Load 57% 62% 67%
Deflection (in.) 0.019 N / A N/ A Deflection (in.) 0.025 N / A N/ A
mm

 

37

Table 15

Constant Loading 8" X 8"

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Standard Two Cycles
Force (1b.) 2075 2290 2510 Force (1b.) 2050 2250 2430
Cree Measurements (in.) Creep Measurements (in.)
T80 min. 3.653 3.629 3.59 T80 min. 3.622 3.579 3.554
T815 min. 3.641 3.601 f85 min. T815 min. 3.616 3.555 f83 min.
T830 min. 3.641 3.575 T830 min. 3.614 f829 min.
T845 min. 3.638 f837 min. T845 min. 3.613
T81 hr. 3.638 T81 hr. 3.612
T=6 hr. 3.636 T86 hr. 3.605
T812 hr. 3.634 T812 hr. 3.602
% Avg. Maximum % Avg. Maximum
WC Load 48% 53% 58% Dynamic Load 55% 60% 65%
Deflection (in.) 0.019 N/ A N/ A Deflection (in.) 0.020 N/ A N/ A
9ne Cycle Half Cycle
Force (1b.) " 2078 2260 2450 Force (1b.) 2020 2170 2340
Creep Measurements (in.) Creep Measurements (in.)
T80 min. 3.634 3.591 3.578 T80 min. 3.642 3.613 3.575
T815 min. 3.621 3.458 £82 min. T815 min. 3.634 3.590 f84 min.
T830 min. 3.615 f816 min. T830 min. 3.630 f825 min.
T845 min. 3.609 T845 min. 3.628
T81 hr. 3.607 T81 hr. 3.626
T86 hr. 3.605 T86 hr. 3.620
T812 hr. 3.604 T812 hr. 3.618
% Avg. Maximum % Avg. Maximum
lynamic Load 55% 60% 65% MC Load 60% 65% 70%
Deflection (in.) 0.030 N / A N / A Deflection (in.) 0.024 N/ A N/ A
h— I

 

4.0

ERROR

The error associated with this study centers around the test
specimens. It was determined through inspection and testing that some
of the samples arrived with damage due to manufacturing production
defects. Furthermore, it was assumed that all of the sample cores were
made from the same type of 275# burst corrugated board. Through some
independent tests, it was discovered that some of the 8” X 8” samples
were made from a heavier weight board. Thus, some error entered into
the outcome of the results. However, it was determined that the errors
were not significant due to the probability of similar cores being used in
actual Cordeck pallets in distribution environments. Therefore, the study

simulates the use of the cores as they would appear out in the field.

38

5.0 CONCLUSIONS

Cycling environmental conditions have a negative impact on corrugated
material. The results of the moisture study for the core samples subjected to the
various cycling conditions suggests that moisture content increases as the length
of the cycle increases. The impact of this effect is a decrease in the compression
strength of the cores. This can also be seen in the comparison of the compression
strengths of samples subjected to constant loading following the various cycling
conditions (Figure 8). This information could be useful to users of the Cordeck
pallets in temperate climates.

The production of the cores is of vital importance to the compression
strength for long term loading. The effects of the various damage to the cores
during production was significant in relation to the compression strength. These
faults caused premature failure of the damaged cores leading to lower values in
comparison to the higher quality samples.

The half inch cuts and the rough edges decreased the stiffness of the
corrugated in contact with the test platens. This resulted in folded edges and

lower compression strength values. The tendency of the 5” X 8” samples to

39

40

Maximum Constant Loading Compression Strengths

 

2500

1750

 

I Standard

 

El Two Cycles
I One Cycle

I Half Cycle

 

 

1500

2:
086m

1250

1000

750

500

250

S'XS'

Figure 8

41

lose their rectangular shape also caused a loss in compression strength. The top
to bottom height of the cores was crucial as well. When the height was not
uniform, the strength of the core was reduced.

Ultimately, the information from this study can be used to determine safe
stacking weights for long term loading on the individual cores and the pallets.
Table 16 shows safe stacking percentages derived from the average maximum
dynamic load for constant loading test conditions. Based on these numbers, the
”safe zone” includes loads up to 54% of the maximum rating. The margin of
error for the ”safe zone” is :t 5% . Loads which exceed this recommended

guideline may fail during long term storage.

 

Table 16

Maximum Safe Long Term Loading"

42

 

5"X5" 5"X8"

8"X8"

 

Standard 52% 56%
Two Cycles 53% 55%
One Cycle 50% 56%
Half Cycle 52% 57%

i i

Average % 52% 56%

 

 

 

 

48%
55%
55%
60%

i

55%

*percentage of maximum dynamic

compression strength for each condition

 

 

I Maximum Safe ZoneI

 

54%+or-5% I

LIST OF REFERENCES

 

43

LIST OF REFERENCES

 

ASI‘ M Committee D-10. Selected AST M Standards on Packaging, Third
Edition. Philadelphia, PA 1991.

Ayoade, J. 0. Introduction to Climatology for the Tropics, Department of
Geography, University of Ibaden. John Wiley 8: Sons, New York, NY
1983. P 109-113.

Greywall, Gary. Performance Comparison of Plastic and Wood Pallets for Static
and Dynamic Tests, Michigan State University. East Lansing, MI 1994.

Leake, Craig & Wojcik, Robert. Proceedings: Cyclic Humidity Effects on
Paperboard Packaging. ”Humidity cycling rates: How They Effect
Container Lifespans”, Forest Products Laboratory. Madison WI,
September 1992.

Pearce, E. A. 8: Smith, Gordon. Times Book World Weather Guide. Random
House. New York, NY 1990. P 126-159.

Ruffner, James A. & Bair, Frank. The Weather Almanac, 3rd Edition, Gale
Research Company. Book Tower. Detroit, MI 1981. P 229-230.

Stone Container Corporation. Cordeck Marketing and Technological Center
Brochure, Cordeck Group. Naperville, IL 1995.

 

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