The Effects of Relative Humidity and Temperature on the Strength Properties of Corrugated Board

Western Michigan University ScholarWorks at WMU

Paper Engineering Senior Theses Chemical and Paper Engineering

11-1972

The Effects of Relative Humidity and Temperature on the Strength Properties of Corrugated Board

James E. McFarland Western Michigan University

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Recommended Citation McFarland, James E., "The Effects of Relative Humidity and Temperature on the Strength Properties of Corrugated Board" (1972). Paper Engineering Senior Theses. 319. https://scholarworks.wmich.edu/engineer-senior-theses/319

This Dissertation/Thesis is brought to you for free and open access by the Chemical and Paper Engineering at ScholarWorks at WMU. It has been accepted for inclusion in Paper Engineering Senior Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact wmu- [email protected]. 11 THE EFFECTS OF RELATIVE HUMIDITY AND TEMPERATURE ON THE STRENGTH PROPERTIES OF CORRUGATED BOARD"

James E. McFarland-,,-

A Thesis Submitted To The Faculty of the Department of Paper Science & Engineering in Partial Fulfillment of the Degree of Bachelor of Science

Western Michigan University Kalamazoo, Michigan November, l 972 ABSTRACT

The objective of this t hesis was the determination of the effect of temperature and relative humidity on the strength properties of corrugated board. A testing laboratory was set up in a controlled humidity room. Both temperatures and humidities were varied to form testing levels. The temperatures ranged from 32°F to 92°F. The humidity varied from 25% to 75 %. Extreme conditions in either direction were not used so as to avoid damage to the room and testing equipment. Three tests were performed on the exposed board. They were H & D flat crush test, G.E. puncture test, and the mullen test. All were performed in accordance with TAPP! and Astm Standards. Results of the tests showed temperature and humidity to both have a definite effect on the strength properties of corrugated board. For example the mullen and G.E. puncture showed an increase in strength at a lower temperature with a 50% humidity. Yet at 75% humidity the strength is lost. The board at this point has reached or passed its saturation point causing the fibers to pull out of the lattice rather than stretch. The test results also proved temperature and relative humidity and also had an effect on strength due to what the board is made up of. A certain set of conditions could cause the liner board to add to the strength in a mullen test, while the corrugated medium of the board, under the same conditions, could completely destroy the crush strength. The major controlling factor of all tests was the relative humidity. The amount of rooisture absorbed by the board controlled the strength abilities. The results formed in this thesis are con- clusive enough to show that relative humidity and temperature do effect strength properties and should be controlled within the plant when possible. TABLE OF CONTENTS

Page

HISTORICAL BACKGROUND AND DEVELOPMENT. 1

EXPERIMENTAL SECTION ...... 3 Measurement of Moisture Content. 4 Fl at Crush. . 5 Mullen Test . 6 Puncture Test. 6

DISCUSSION OF DATA. 8 CON CL US IONS . 27

BIBLIOGRAPHY. . 30 -1-

HISTORICAL BACKGROUND AND DEVELOPMENT

The historical background on a topic of this nature is very limited. There have been very few articles published on this topic. Through talking to people in the industry there is evidence that this type of a study has been done on a limited basis, but not recorded. Many articles have been published pertaining to the effects of relative humidity on corrugated board in extreme conditions, but none have been centered around the effect of relative humidity on board under normal plant operating conditions. Recent articles published in 1970 give insight to these studies. Cxte article states in relation to corrugated board that, "Relative humidity is the critical factor, temperature changes alone do not have much effect 11 (l). This in itself leads to an assumption that the moisture in the corrugated board that can be gained from relative humidity while sitting in the plant can have a definite effect on the strength properties. "Material strength characteristics of corrugated boas:d vary appreciably with moisture content; for example, under extremely hot and humid conditions (90-100 degrees, 85-90% relative humidity), boxes lose 40-50% of their compression strength and flat crush 11 (_g_). These statistics are from studies for conditioning of board but can be applied to plant storage conditions. It is quite possible that board sitting in a plant during the summer months could be exposed to conditions nearing these extremes. If so then, the results of the experimental should demon- -2-

strate a loss in the strength in the other properties being tested. Another paper written in the past year was on the hygroexpansi- vity of corrugated board. Although this article does not relate to the strength properties of corrugated board, it does dwell upon the matter of expansion and contraction of corrugated board when exposed to different relative humidities. Some of the findings stated,

11 Dimensional changes were nonlinear with increases in relative humidity. There was approximately l .1 per cent dimensional movement parallel to the flutes (cross-machine direction), and 0.5 per cent movement perpendicular to the flutes (machine direction), when the material was moved from a relative humidity of 30 per cent to one of 90 per cent (constant

11 temperature 80 degrees F.) (~). Articles of this type show there is a definite relation between strength properties and relative humidity. To what extent remains to be seen. Hopefully the results of this experiment will demo.nstrate the extent of the effect, and possibly suggest a range of conditions under which corrugated board can be stored without appreciable loss of its strength properties. -3-

EXPERIMENTAL SECTION

The samples of corrugated board being used are basically made up of 9 point Semi Chemical Hardwood Kraft Medium. Its caliper is .009, and has a basis weight of 26 pounds per 1000 square feet. The following Table (I) will indicate the basic information for each pound test of board used.

TABLE I

125 200 275 350 500 Test Flute C

Liners & Medium

Combined Facings 52 75 84 138 180 92 11 0 126 222

Combined Board Wt. 97 120 129 183 225 179 197 313 309 #Wt/Mft.

All samples will be preconditioned at 72 degrees F. and 50% relative humidity. The samples used in testing will start in the form of a 6 inch square and will be cut down to fit appropriate testing qualifi- cations. Minimum time for conditioning will be at least 24 hours of exposure to the simulated plant conditions, prior to testing. The reference point for conditions of testing \'ii 11 be the same as the above standard conditions (72 degrees F. and 50% R.H.). This re- -4-

ference point shall be used in determination of the point of equilibrium for each of the different conditions. Equilibrium will be reached when the increase in moisture content of the sample has leveled off after exposure to the different atmospheric conditions. The strength tests that will be run on the samples after reaching equilibrium under the different atroospheric conditions are as follows: l . Determination of Moisture Content. 2. Flat Crush Test. 3. Mullen Test. 4. G.E . Puncture Test. An outline of experimental procedures of each of these tests is included in this section. The conditions to which the samples will be exposed will consist of temperatures held constant and the relative humidity being varied from high to low for that temperature. The temperatures will be 32 degrees F., 52 degrees F., 72 degrees F., and 92 degrees F.. For each of the five constant temperatures the relative humidity will vary within a range of 25% to 75%. Starting with 25% and increasing by 25% each time until 75 % relative humidity is reached. Every tine the relative humidity is changed, a new set of samples will be brought in from the standard conditions. Measurenent of Moisture Content Moisture content will be neasured by the weight increase or decrease (., -5-

decrease of the sample from the weight of the same sample at standard conditions. The rooisture con t en t measurement of the sample will also serve as an indicator for when the samples have reached equilibrium under the conditions they are exposed to. When the weight of the sample has become constant then equilibrium has been reached and the tests will then be conducted. Flat Crush 11 The flat-crush test evaluates the resistance of the flutes in corrugated board to a crushing force applied perpendicular to the surface of the board 11 (!). The flat-crush test measures the rigidity of the corrugations themselves. High flat-crush indicates good corrugated medium and proper formation. At the same time low flat-crush indicates a poor quality corrugated medium and poor formation. the following procedure will be used in accordance with A.S.T.M. Standard D. 1225-54, using the H. and D. Flat Crusher: 1. 2 inch square samples will be used from undamaged and unprinted board. 2. Six tests will be rrade on one sample and an average computed. 3. In single wall board, the pressure will be recorded at collapse of the corrugated nedium. 4. In double wall, the first .complete failure of flute will be recorded. -6-

Mullen Test The mullen test measure s bur sting strength. "Bursting strength is defined for ths method of t est as the hydrostatic pressure required to produce rupture of a circular area of the material under test 1.2 inches in diameter, ,v hen applied at a controlled, increasing rate, as described in Section 7. During the test, the specimen must be free to bulge under influence of the increasing pressure, but the periphery of the test area must be rigidly fixed so that it does not

11 move while the pressure is being applied (~). The following procedure will be followed:

1. Samples of 6 inch squares wi 11 be used with four pops being made on each side and being recorded as top and bottom. The recorded value wi 11 be the average.

2. Any pop not tearing in as 11 H" fashion or shape wi 11 be disregarded and another reading will be taken. 3. If any one pop is unusually low it will also be disregarded with another test being made. Puncture Test This test wi ll be conducted with the use of the General Electric puncture tester. The machine itself will measure puncture resistance and stiffness of board, either in single sheets or in double wall form. -7-

This type of a test si mulates damage in use, similar to that occuring in shipping or in the plant. The tester actually 11 rrea- sures the energy required to puncture the container board with a point affixed to a pendulum arm (ohe scale unit equals 0.305 cm-kg or 0.265 in-lb). These energy units actually are made up of two major components: the energy to tear the material and the energy to bend it out of the way of the point"(§). The procedure for testing puncture will be done according to the procedure outlined in this section and in accordance with Tappi Standard T 803ts - 50. The testing will be done as follows: l. Samples will be six inches square. 2. Five tests will be made on each type to get an average value. 3. Weights on the puncture arm will vary as to the poundage of the sample board being used. 4. The tested sample shall be clamped between plates with the corrugations running perpendicular to the angle swing of the puncture arm. -8-

DISCUSSION OF DATA

The data collected was limited due . to the limited capabilities of the humidity room used for testing. Extreme conditions at either end of the spectrum were eliminated beca~se of possible damage to the humidity room. The data collected under the various conditions does however indicate a definite effect on the strength properties of corrugated board. The mullen test data shows an increase in board strength as the humidity increases. Here the increase in humidity tends to make the board more plyable and able to stretch. A moisture increase in the board from the increased relative humidity is accountable for this effect. The effect of temperature is exemplified in the 85% relative humidity data. Here the board at 32°F with a high humidity shows in almost all cases the greatest amount of strength. The increase in temperature in this R.H. range consistently, on all types of board, shows a definite decrease in mullen strength. As the temperature increases the moisture content also is increasing. By the time 92°F is obtained the corrugated board has reached a moisture content where the board has become so plyable that it begins to tear rather than stretch. In comparing a certain temperature at various humidities the data does not indicate any definite pattern. Basically the mullen strength of the board does show a loss with increased humidity and increased -~

temperature within a given % R.H. range. This is probably due to the amount of moi sture content in the board. The moisture satu- rates the board both inside and out causing a breakdown in the fiber lattice of the liner board and a loss in strength. The medium used would also be highly susceptible to strength loss because of increased moisture content. The medium is the first area for the breakdown in strength by it's being a low density sheet of board with a more avid attraction for moisture. The H & D flat-crush data indicates a decrease in strength with an increase in humidity and temperature. Unlike the mullen test results the H & D indicated either temperature of humidity could be held constant while the other was raised, and a decrease in strength would be recognized. If either the 72°F temperature or the 92°F is followed across any of the different type of boards the increase in % R.H. causes strength loss. At the same time all types of board at the 75% R.H. show a lower strength at 32°F with an increase to a maximum strength at either 52°F or 72°F, with a consistent drop in strength at 92°F. The basis for strength in this type of test is how well the medium can withstand moisture. As the temperature and relative humidity increased, the moisture content of the board also increased. The flutes of the board, which are the basis for strength against crush, are the most succeptible to moisture absorption. The low grade of paper used -10-

for medium will readily absorb rooisture, thus accounting for the loss in strength. This effect can be roost critical to a plant in the area of printing. To much impression from the ink rol .ls could cause severe crush and accordingly a poor quality box. In the testing it was noticed that regardless of the temperature or humidity the C flute always gave out before the B flute. The greater strength of the B flute can be accounted for by the increased number of flutes per inch, than in C flute. 11 811 flute has 52 flutes/ inch, where-as C flute only has 42 flutes/inch. The C flute therefore has roore exposed surface areas of flutes per inch than B flute, and 'l«>Uld logically be capable of absorbing a greater amount of rooisture causing a loss in strength. The fluted mediums succeptability to moisture absorbtion and subsequently a strength loss is well indicated by the data collected in the H & D test results. Variation in flute size is one possible way to cut down the amount of strength lost. The strength of board in this area could definitely by helped by in plant controlled humidity. The results of the G. E. Puncture test data showed many of the same effects as the mullen test data. An increase in humidity, holding the temperature constant, in roost cases shows an increase in strength. This happens for much the same reasons as in the mullen test. The G.E. Punc- ture test also is de pend ent on the strength of the liner board. With a -11-

rise in humidity the liner board gains more flexibility or stretch with the increase in moisture co ntent. The brittle effect of the board caused by a low temperature and humidity is eliminated . Again though, the temperature has a detering effect at a high temperature. At 75 % relative humidity, as the temperature increases the board is becoming saturated with moisture. Consequently the board loses strength because the fiber lattice becomes so moist, there is a breakdown in the lattice rather than a stretch effect. The cooler temperatures (32°F & 52°F) keep the board brittle enough to offset the effect of the high percentage humidity. The medium has much the same effect caused by humidity and temperature. The medium reaches it's saturation point much sooner than the liners. As a result, this can cause the liners to collapse against each other at the point of impact of the puncturing object. Here the effectiveness of the doublewall style of board can be helpful for re- taining strength. The middle liner and the second fluted medium can offer additional resistence against a puncture or a mullen test. -12-

TABLE II MULLEN TEST RESULTS

Percent Relative Humidity

Temeerature 25 % 50% 75% 25% 50 % 75% OF Single Wa 11 [bubl e Wa 11 125 C 200 CB 32 214 359 52 155 160 365 355 72 143 233 166 315 371 361 92 128 161 166 273 323 318 Single Wa 11 [bubl e Wa 11 175 C 275 CB 32 268 455 52 215 243 362 385 72 235 281 270 341 388 397 92 205 238 225 313 343 378 Single Wa 11 [bub le Wa 11 200 C 350 CB 32 320 501 52 315 267 470 483 72 265 300 300 418 430 460 92 243 310 275 390 424 457 Single Wa 11 275 C 32 507 52 453 427 72 406 386 438 92 423 425 355 Single Wa 11 350 C 32 560 52 481 500 72 432 390 460 92 518 447 480 -13-

TABLE III H & D FLAT CRUSH RESULTS Percent Re lative Humidity

Temperature 25% 50% 75 % 25% 50 % 75 %

Single Wall Double Wall 125C 350C 32 284 261 52 307 315 372 345 72 297 261 258 396 353 302 92 376 281 236 383 335 289

Single Wall Double Wa 11 175C 200 CB 32 263 322 52 366 322 269 338 72 371 352 305 352 300 265 92 352 319 254 402 336 165 Single Wa 11 Double Wa 11 200 C 275 CB 32 268 208 52 338 293 355 295 72 344 317 252 401 369 333 92 35 4 330 213 432 332 267 Single Wall Double Wall 250 C 350 CB 32 260 248 52 345 285 354 262 72 351 338 289 363 308 216 92 388 341 246 397 314 213 -14-

TABLE IV G.E. PUNCTURE RESULTS Percent Relative Humidity

Tem~erature 25 % 50 % 75 % 25 % 50 % 75% OF Single Wa 11 [x)uble Wall 125 C 350 C 32 47 127 52 44 45 105 117 72 40 37 41 109 l 05 117 92 42 39 42 l 07 114 114 Single Wa 11 Double Wa 11 175 C 200 CB 32 59 l 09 52 56 57 100 l 07 72 56 53 54 88 99 l 02 92 52 51 54 90 l 03 l 06 Single Wall [x)ub le Wa 11 200 C 275 CB 32 66 112 52 61 67 l 08 112 72 57 59 60 l 02 l 07 l 08 92 58 57 61 98 l 06 l 08

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CONCLUSIONS

The data collected for this thesis, although limited, is indi- citative of the fact that humidity and temperature do have a definite effect on the strength properties of corrugated board. The conditions used for testing could easily be found in any corrugated plant anywhere in the world. In two of the three tests, Mullen and G.E. Puncture, it was found that an increase in percent humidity at a lower constant temperature can effectively increase the strength of the board. This increase in humidity creates moisture in the liner board that eliminates brittle- ness of the fibers and gives them the ability to stretch when subjected to force. But at the same time the fibers can only stand so much moisture absorption. When the telll)erature is increased at a higher constant humidity (ex. 75%), the fibers become increasingly saturated with rooisture and begin to lose strength. Here the fiber lattice of the liner board has reached the point where an exerted force on them causes pull-out and separation rather than strength. As exemplified above the liner board is the critical point of strength in the two types of tests. The medium in this case deters the resistence of the board. It is easily saturated and can collapse, causing the resistance of force to be put on the liners. The effect of the rredium is shown in the results of the H & D flat-crush test. Here the medium is the critical factor for strength. As the medium gained rooisture from increased humidity it weakened. The medium which is a much lower grade of paper, more -28-

readily absorbs the 111 oi sture. Although this gives a certain fl exi- bi l i t y, it also ca use s the f l utes formed by the medium to collapse when pressure is exerted . Consequently the strength for the medium is best at lower tempera tures and humidities where the fibers are somewhat brittle.

In all three types of tests, % Relative Humidity, is the key factor. The humidity puts the moisture in the air that the board can absorb. If the hu midity is low the temperature can be high or low and ca use little change. Yet if the humidity is high the temperature can be cool and help the board retain its stiffness thus adding to the strength. But if the temperature is high the v1arm air can increase the mois ture of the air and correspondingly cause the boards moisture content to reach it's saturation point, yielding a · loss in strength. The effects of humidity and temperature illustrated by this thesis indicated a nee d for controlled conditions in the plant situa- tion. To determine the amount and type of control would take many more years of research and testing of all types of board. Much research has been done on paper and its products in relation to plant conditions under which they are produced. Unlike this corrugated board has had most of it's studies done on sub-zero and tropical conditions. With the industry growing as it is today, much more research as done in this thesis will be conducted. Hopefully it will find the overall -29-

effect of temperature and humidity on all the strength properties of corrugated board produced in the plant -30-

THESIS BIBLIOGRAPHY ..

1. Nelson, H.G., "Process Capability Studies in Corrugated Box Plant", Tappi 49, No. 7:33-8A, (July, 1966), A.B.I. PC 37:229.

2. Am. Soc For Testing & Materials, 11 Tentative Method of Test For Puncture and Stiffness of Paperboard, Corrugated and Solid Fibreboard"., ASTM designation, D78l-65T, 1966 Book of ASTM Stds part 15:217-22.

3. Root H.C., TAPP!: 11 Fiberboard Shipping Container Test Comm. Puncture and Stiffness Test of Containerboard-Proposed Revision of T803 ts 50 Tappi 49, No. 9:l70-2A, (September, 1966), ABIPC 37: 403.

4. Weiss G. Heiss, R. & Garling, P., 11 Studies of the Internal Climate in Shipping Containers as a Function of Changes in Ext. Climate", Verpackuaigs Rundschau 16, No. 8: Suppl 59-67, (August, 1965), ABIPC-36-1965. 5. Novak, M; Beznoska, J., "The Resistance of Corrugated BO Con- 11 tainers To Storage Under Various Climatic Cond , Obaly 12, No. l: 20-6, (Jan/Feb 66) ABIPC 37: 1968. 6. Novak, M; Jakowski, S., "Tests of Cartons in the Conditioning Chamber", Obaly 14, No. 6: 172-175, (1968), ABIPC Vol. 41, No . l , ( July , l 97 0) .

11 7. Maltenfort, 6.6, "Structural Aspects of Corrugated Board , Tappi 53, No. 7: 1223-39, (July, 1970).

8. Maltenfort G.G., 11 Converibility of Shipping Container Data For 50 to 65% R Humid", Tappi 52, No. 6: 1120-5, (June, 1969), ABIPC 40-2044