V 3-. 5...“: {pa nOlrovlmd;b.-.. p OF‘ .lo '24:}: ,Vov.zuuv:lhlufi.nk 4‘ ;l 6 “uric “HO-i, #- 1a 1" 4. has '1’; 'a loft. Inlliiilo'ur‘). 61-Oct ‘2'! 1': t .2!" E o! I) rind-n. I. . 2?..16 I.l«auuv.lcl . .91.?! 3:13.“.9” gout” u I... u, o. in. .3 (til. 5}! 3-» “tutti“ .J.’. §§!'§ Jhant‘fltgiiu In!- ‘8' I .‘zv‘bl I- ‘11:?!) inéxpfi .l . 9 31:3. a 7 9.. a. {HESIS 3w LIBRARIES llllll\l\\l\lll\\l\\\l\ll \m lllzllll This is to certify that the them entitled PERFORMANCE OF RECYCLED CORRUGATED FIBERBOARD UNDER VARIOUS TEMPERATURES AND'HUMIDITIES presented by Supawadee Thewasano has been accepted towards fulfillment of the requirements for M.S. degree in PACKAGING Date /__al-([3 0-7639 M5 U i: an Affirmative Action/Equal Opportunity Institution LIBRARY Mlchlgan State Untverelty PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE MR l a “394' 7:241 I?» t’ 51192; J e -.-l 1 Q ma 0 2 199° “’4” 0 9 ma § 3&0 7' I & W ,— W” MSU Is An Affirmative Action/Equal Opportunity Institution Em PERFORMANCE OF RECYCLED CORRUGATED FIBERBOARD UNDER VARIOUS TEMPERATURES AND EUKIDITIES BY Supawadee Thewasano A THESIS Submitted to nichigan state University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Packaging 1993 ABSTRACT PERFORMANCE OF RECYCLED CORRUGATED PIEERBOARD UNDER VARIOUS TEMPERATURES AND EUMIDITIES BY Supawadee Thewasano Strength properties of recycled corrugated board such as box compression strength, edge crush, flat crush, pin- adhesion, puncture resistance, and bursting strength were determined for various board recycled contents and humidity conditions. The moisture content of the conditioned recycled fiberboard under three temperatures and humidities was also determined. In addition, the box compression strength predicted by the Mckee formula was compared to the actual box compression strength. The compression strength of the boxes and the strength properties of the recycled board itself were not found to decrease uniformly with moisture content as expected. This was due most likely to differences in manufacturing processes and the type of recycled fiber used. The moisture content of the recycled board was found to have a negative influence on edge crush, flat crush and pin-adhesion but a slightly positive influence on puncture and bursting strength. Dedicated to my parents, Chalaw and Nipa Thewasano iii ACKNOWLEDGEMENTS I would like to thank the following people and companies for their valued contributions to the completion of this study: Dr. Gary Burgess, for his patience, understanding, guidance and professional advice, while serving as my major advisor. Dr. Julian Lee, for providing me with employment during my graduate study and serving on my committee. Dr. Larry Segerlind, for his assistance and time while serving on my committee. Dr. Bruce Harte, Dr. Ruben J. Hernandez, and Dr. Paul Singh, for their advice on valuable texts for the literature review. Mr. Ralph A. Young of the Georgia-Pacific Corporation for his.guidance and.time spent in contacting the corrugated.board companies, and for providing the pin-adhesion instruments for this study. Also Viking Paper Corporation, J&J Southeast, Willamette, Industries, Inc., Weyerhaeuser, 4-m Corporation, Stone Container Corporation, and Corru-Kraft Co., for supplying the recycled corrugated board for this study. Wimol Taoklam, for his patience and professional advice in statisticis: Kitti Wangwiwatsilp, Sorawit Narupiti and Prapassara Nilgupta, for their support, friendship, and typing part of this study after I got in a car accident: Yossawan Boriboonthana, Booma Matur, for their friendship, support, and humor. iv TABLE OF CONTENTS LIST OF TABLES ...... ..... .................... ...... Vi LIST OF FIGURES ......... ....... .... ........... ...... viii INTRODUCTION ..................................... 1 LITERATURE REVIEW ..................................... 5 I. Box compression strength .......... ... ........ 5 II. Board properties ............................. 7 III. Manufacturing and strength .................... 20 EXPERIMENTAL PROCEDURES .............................. 27 Test materials ... ........... .................... 27 Apparatus ....................................... 28 Sample preparation .............................. 3O Conditioning .................................... 32 Test methods .................................... 32 RESULTS AND DISCUSSION 0 O O O O O I O O O I O O O O O I I 0 I O I O O O I O O O O O 37 I. Box compression strength versus medium recycled . content 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O I O O 37 II. Box compression strength versus edge crush reSiStance O O O O O O 0 O O O O O O O O O O O O O O O O O O 0 O O I O O O O O O 57 III. Properties versus recycled content ...... ..... 59 IV. Properties versus moisture content ............ 66 CONCLUSIONS AND FUTURE RESEARCH ...................... 70 APPENDIX ......OOOOOOOOOOOOOOO ..... 0...... 0000000000000 72 BIBLIOGRAPHY ...... . ...................... ... ......... . 73 Table 1 10 11 12 13 14 15 16 17 18 LIST OF TABLES Manufacturer, burst strength, basis weight of linerboard/medium, and %recycled content of 15 board types OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Board No.1 ............ .......... . ...... ............ Board No.2 ............... .......................... Board No.3 ........................... ...... ........ Board No.4 ..... .......... .. ....... . ...... .......... Board No.5 ........... .............................. Board No.6 ......................................... Board No.7 ..................................... .... Board No.8 ................. .. ............. ......... Board No.9 ......................................... Board No.10 .............................. . ......... . Board No.11 ...... ......... . ...... ......... ........ ... Board No.12 . ............................. . ......... . Board No O 1 3 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O Board No O 14 O O O O OOOOO O O O O O O O O O O O O O O OOOOO O O O O O O O O O O O O O Board No O 15 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O Predicted box compression strength versus actual compression strength ....... ....... ................. Values listed are mean/standard deviation for pin- adhesion strength of the 15 board types for three humidity conditions ............ ......... ...... ..... vi Page 29 38 39 40 41 42 43 44 45 47 48 49 50 51 52 58 Table Page 19 Linear regression between Edge Crush (EC), Flat Crush (FC), Pin-adhesion (PA), Puncture Resistance (PU), Bursting Strength (BS), and Moisture Content (MC) for all 15 board types . ......................... ....... 68 vii Figure Page 1 Bending Stiffness Measurement ...................... 9 2 Ring Crush Test ............................... ..... 10 3 Edge cruSh Test OOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 12 4 Waxed specimen used for the edge crush test, according to ASTM 2808-69 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 14 5 Flat crUSh Test SChematic OOOOOOOOOOOOOOOOOOOOOOOOOO 16 6 Pin-adheSion Test OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 17 7 Schematic of Puncture Resistance according to TAPPI 803 om-88 OOOOOOOOOOO O OOOOOOOOOOOOOOOOOO OOOOOOOOO OOOOO OO 19 8 Schematic of the Mullen Test according to TAPPI 810 om-so OOOOOOO OOOOO OOOOOOOOO OOOOO OOOOOOOOOOOOOOOOOOOO 21 9 Combined Board process ....... ...................... 23 10 Box blank for the compression tests ................ 33‘ 11 Box compression strength versus medium recycled content at TAPPI standard conditions ............... 53 12 Box compression strength versus medium recycled content for a 110 lb/1000 ft2 board basisweight at TAPPI standard conditons . .......... . ............... 55 13 Actual and predicted box compression strength versus edge crush resistance at TAPPI standard conditions OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 6o 14 Edge crush resistance versus medium recycled content for three humidity conditions .............. 61 15 Flat crush resistance versus medium recycled LIST OF FIGURES content for three humidity conditions .............. 62 viii Figure Page 16 Puncture resistance versus average liner recycled content for three humidity conditions .............. 63 17 Bursting strength versus average liner recycled content for three humidity conditions .............. 64 ix INTRODUCTION Recycling' plays an important role in ‘the packaging industry. Recycled plastics made from foam packaging are an example of an area where recycling has proven to be cost- effective. Corrugated fiberboard is another material which is used in packaging and is environmentally friendly. Corrugated fiberboard is biodegradable which means that it decomposes by biological means and therefore can be disposed of in a landfill (Anon, 1992: pg 25). The use of recycled fiber reduces the problem of the solid waste in landfills and also decreases the amount of virgin fiber needed (Kishbaugh, 1990: pg 27-28 and Uutela and Black, 1990: pg 50). Due to the solid waste problem, the use of recycled board is supported by the government in terms of recycling laws. For example, some states in the U.S. and all government entities, including schools, are required to develop recycling programs for at least.high-grade paper and corrugated cardboard (Glenn, 1992: pg 35-36). Solid waste management programs at the state level have been created to solve the solid waste problem. The paper industry is involved in recycling not only for the benefit of waste management but also by political command. About half the states in the U.S. have comprehensive laws on 2 the books to increase recycling (Cartledge, 1991: pg 152, 154) . Corrugated fiberboard consists of a corrugating medium sandwiched in between two linerboards. The corrugating medium is the fluted or corrugated center of the board and the linerboard.is the flat.material outside. In the manufacture of corrugated cases, about two-thirds of the raw materials used consists of recycled fiber. This shows that the amount of recycled fiber is becoming the chief raw material used in the manufacturing process (Anon, 1982: pg 6). The trend is to incorporate more recycled fiber into both the liner and medium to satisfy consumer demands and recycling laws for environmentally friendly packaging (Kelsey, 1992: pg 18). It is well known that the corrugated container plays an important role in protection. Its function is to restrain the product as it moves through the distribution system and to protect it from environmental hazards such as impact, vibration, compression, humidity and temperature. Moreover, its role is to reserve enough strength to support high compressive loads for long periods in warehouse storage, especially at high humidity. To fulfill these requirements, corrugated board must be fabricated to satisfy the requirements of Rule 41, Item 222 (Bever, 1986: pg 927-928). There are several tests carried out by container makers on corrugated fiberboard containers to ensure that there is maximum protection provided for the least use of materials to avoid "over packaging" (Anon, 1992: pg 25). In the past, it 3 was discovered that use of high-performance corrugated containers provided better stacking strength (Wallace, et al, 1991: pg 25-26). According to Boonyasarn's study (Boonyasarn, 1990: pg 1-68) on the effect of cyclic environments on the compression strength of boxes made from fiber-efficient corrugated fiberboard, boxes made from regular f iber-eff icient linerboards experienced greater strength loss than the ones made from standard fiberboard after exposure to cyclic conditions while both fiberboard boxes performed similarly under non-cyclic environments. This was thought to be due to differences in moisture absorption between the two different box materials. The general trend was that compression strength decreased as the moisture content of the box material increased. Although recycled fiber is still not as strong as virgin fiber, it has improved (Pels, 1991: pg 63-64). There are many problems associated with using recycled fiberboard. Recycled vegetable container boards for example are too weak to serve as fresh vegetable boxes, especially at high relative humidities (Anon, 1985: pg 13-14). The blend of recycled paper and virgin pulp also creates printing problems even if the printing is made by flexography which requires less pressure than other printing systems. Recycled fiber does not allow for fine detail: the more detail that is required, the more the flutes are damaged by the printing rollers, which then affects the strength of the finished corrugated box (Anon, 1987: pg 13). 4 Because containers are stacked as high as possible in warehouses, the compression force on the bottom box in the stack can be substantial. Compressing a box normally causes it to bulge outward which in turn causes the board to bend. Because the board bends, the outside and inside linerboards are stressed differently during stacking: the outside linerboard is in tension and the inside linerboard is in compression. Therefore, the percent of recycled pulp in both linerboards and the medium is important. The purpose of this study is to evaluate the effect of recycled content and basis weight on the box compression strength, and the edge crush, flat crush, bursting, puncture strength, and pin-adhesion strengths of recycled corrugated fiberboard, and to compare performance when the boards have different moisture contents. A secondary objective is to compare the compression strength of boxes made from various recycled boards to each other and to calculated values based on prediction equations. LITERATURE REVIEW I. BOX COMPRESSION STRENGTH The compression strength of a corrugated board box is an indicator of the stacking strength of corrugated board packages (Markstrom, 1988: pg 9). Since the shipping container encounters various environmental and handling hazards related to compression, it should satisfy the minimum requirements of Rule 41, item 222, so that box failure does not damage the product inside (Fibre Box Handbook Supplement, 1991: pg 8 and Maltenfort, 1988: pg 41). Due to an increase in the use of recycled materials, rule 41 has been changed to support recycled corrugated fiberboard by reducing the minimum requirement of performance. This includes reducing the amount of material by using lower weight, high-performance packages and decreasing the basis weight 10 to 20% on average to reduce over packaging. According to ASTM 0642-72 (revised 1983), the compression strength of a box is determined by placing the box at the center of the lower platen of a compression tester that is connected either to a load cell or to a mechanical scale. To ensure definite contact between the specimen and the platen, 6 an initial pressure or preload of 50 lb is applied. The upper platen is then lowered onto the box at a continuous rate 0.5 in/min until the maximum load has been reached. The compression strength is defined.to be the maximum load carried by the box. Although the compression strength from the test can be used to predict package performance and strength, there are differences between actual performance and laboratory tests. The difference can be attributed to a number of different factors. Hand-made boxes for example will generally have higher compression strengths than production made boxes by up to 8% (Maltenfort, 1988: pg 271, 273). Another factor which accounts for the difference between the laboratory and warehouse is that the environment for the former is usually 72°F and 50%RH and the latter is constantly- changing. The weakening of the box is greatest under changing conditions when the container tries to equilibrate to new conditions under the load (Leake, 1988: pg 74—75). Both temperature and humidity affect final box performance. This is because the corrugated fiberboard is made of paper and paper is composed of cellulose which absorbs moisture. The moisture content in turn is affected by the temperature (Back, 1989: pg 101). Normally, the moisture content of the liner or medium should be between 6% to 7%. Too much moisture weakens the board and lowers box compression strength. Moisture absorption by the adhesive at the interface between the linerboard and medium also affects the stacking 7 performance of corrugated fiberboard (Byrd, 1986: pg 99). The decrease in compression strength as moisture content increases is given by the equation below (Kellicutt, 1959: pg 80). It has been found that boxes made from many different types of board obey this equation. wet cs = (dry cspaorm' .............. (1) where: CS = compression strength of box, (lbs) dry CS = compression strength at zero percent moisture content x = board, moisture content, (grams 190/100 grams dry board) II. BOARD PROPERTIES Box compression strength is related to various strength properties of the corrugated board from which it is made. Sheet density, or basis weight, for example is known to be correlated to box strength. The lower the sheet density, the lower the compression strength (Bristow and Kolseth, 1986: pg 307) . Direct measurements of board strength are even more highly correlated to whole-box compression strength. Examples are flexural stiffness, ring crush resistance, edge crush resistance, flat crush resistance, pin-adhesion strength, puncture strength, and burst strength. The effect of each of these strength measurements on box strength will be discussed in detial. Flexural stiffness Flexural stiffness measures the bending strength of the combined board. A related property, bending stiffness, measures the bending strength of the components (Whitsitt, 1988: pg 163). Figure 1 illustrates the test procedure for measuring bending stiffness. Flexural stiffness of the combined board is dependent upon tensile stiffness of the components in the combined board. The higher the tensile stiffness, the greater the bending stiffness. For instance, kraft liner provides a higher tensile stiffness than a test liner. Kraft liner consists of 85% or more virgin kraft wood pulp while test linerboard satisfies the requirements of Rule 41 (The Dictionary of Paper, 1965: pg 267, 439). This leads to a higher box compression strength (Markstrom, 1988: pg 11). Ring—crush Test (RCT) RCT is a measure of the compression resistance of the individual linerboard and medium materials used in the corrugated board. Figure 2 shows the test procedure for measuring ring crush strength. The RCT value has been used to gauge total package strength. However since the RCT value takes into account only the strength of the containerboard components, it cannot compensate for poor converting quality or insufficient package design (Santelli, 1991: pg 28). KWAE Figure 1: Bending Stiffness Measurement 10 Force 1. J, liner or medium 6“ circumference yr RCT = Force to crush Figure 2: Ring Crush Test 11 Edgewise Crush Tbst (ECT) The edge crush resistance of corrugated board is the strength property most widely used to predict whole box compression strength. Figure 3 shows the test set up for measuring edge crush resistance. There are two reasons for using the edgewise compression resistance of corrugated board to predict box strength. The first is that the edge crush strength measures the necessary force to collapse a short vertical sample of corrugated board and therefore simulates box compression. The second is that it appears in the McKee formula as follows (Santelli, 1991: pg 33, Kelsey, 1992: pg 18, Fibre Box Handbook Supplement, 1991: pg 70, and Thielert, 1986: pg 77). cs = 5 . 87*ECT* (211)”? .................. (2 ) where: CS top-to-bottom compression strength, (lbs) ECT = edge crush resistance, (lbs/in) Z = box perimeter (2L+2W), (inches) h = board caliper, (thickness in inches) The ECT has been used as an index for the estimating the stackability of boxes stored on pallets in warehouses. The higher the edgewise compression resistance, the better the stacking properties of the boxes (Thielert, 1986: pg 77). The ECT is related to both the stacking strength and the overall transportation performance of a corrugated board box 12 load __> upper- plate 5/ 4” > samp Ie spec 1 men (flutes vertical: 16 lower- plate ”W”///////// Figure 3: Edge Crush Test 13 (Markstrom, 1988: pg 17). There are several ECT methods in use. Examples are ASTM D2808-69 and FEFCO method No.8. According to ASTM 02802-69 (Figures 3 and 4), the edges of the samples are first dipped in molten paraffin wax. The wax is used to reinforce the loaded edges of the specimens to prevent edge failure. For board grades with an ECT higher than 86 lb/in, paraffin wax impregnation alone cannot prevent edge failure however (Markstrom, 1988: pg 18 and Koning, 1986: pg 74). Other factors which affect the ECT are badly cut samples, a compression tester with non-parallel plates, and uncontrollable stress concentrations in the test piece. The compression speed also affects the ECT value. Edgewise compression resistance is usually higher when the compression speed is higher (Thielert, 1986: pg 78) Another important factor that affects the ECT value is the manufacturing process. Combined boards made with more highly wet-pressed or densified liners and stronger mediums exhibit higher values for edgewise compression testing (Whitsitt, 1988: pg 163, 167). ECT can vary by as much as 40 percent due to poor corrugator practices that affect the quality of the liner and medium. Process controls such as adhesion, tension on the medium and liner webs, temperature, preconditioning, single face glue line width, and viscosity of the starch adhesive also greatly affect the ECT (Galvin, 1992: P9 22) - Since the medium carries most of the load in an edge 14 Srrm C ’I/ 4 i n) / Paraffin T— 32mm L [1- ’1/4In) 51”" C21,») 6mm \U (’1/4in) Figure 4: Waxed Specimens used for the edge crush test, according to ASTM D2808-69 15 crush test, properties of the medium such as recycled content and basisweight are expected.to have the greatest influence on ECT and on whole box compression strength. Flat crush Tbst (PCT) PCT is a measure of the ability of the corrugated board to resist being crushed under the action of a compressive force perpendicular to the board surface. Figure 5 shows the test procedure for measuring flat crush resistance. The flat crush resistance is a critically important property of corrugated board that is related to the strength of the corrugating medium (Daub, Hoke and Gottsching, 1990: jpg 174). The stronger medium increases the flat crush strength and reduces crushing' during conversion and. product ‘use (Maltenfort, 1988: pg 248 and Whitsitt, 1988: pg 167). About 30-40% of the flat crush potential is lost during fluting (Whitsitt and Sprague, 1987: pg 91). Pin-adhesion Pin adhesion is a test for the dry bond strength.between the liner and medium as shown in Figure 6. This test is used in the manufacturing process as a quality control tool to monitor adhesive penetration and spotty adhesion (Daub, Hoke and Gottsching, 1990: pg 171 Maltenfort, 1988: pg 262 and TAPPI 821 om-87). Bond failure can occur from cohesive failure, adhesive failure, or substrate failure. Cohesive failure is failure within the adhesive layer itself; adhesive failure appears at 16 l oad Figure 5: Flat Crush test Schematic 17 /. O '!;I‘ . _,, A li.’ 1., l 1"; In- I..- _ _ Pressure Pins (Top) and Support Pin: (Bottom! End View ol Pressure Pine and Support Pins 0 mm Pins IO Smwoann Figure 6: Pin-adhesion Test 18 the adhesive-substrate interface, and substrate failure happens within the paper itself (Shires, 1988: pg 67). Low'pin adhesion strength is correlated to a:reduction in stacking performance particularly under long-term loads and high humidity conditions (Lorenz, 1990: pg 137). Low pin adhesion strength can occur in the manufacturing process as a result of the rapid drying of small amounts of glue before the corrugated medium comes into contact with the linerboard. An insufficient amount of glue to fill the cavities on the surface of rough papers can also cause low pin-adhesion strength (Daub, Hoke and Gottsching, 1990: pg 174). It has also been found that increased production speeds lead to decrease pin adhesion strength (Whitsitt and Baum, 1987: pg 111). Puncture Test According to TAPPI 803 0M-88, the puncture test is a measure the total energy required.to crush.the board before it can be punctured (Figure 7). Puncture strength is not as much dependent upon what the mill and the converter do but on the quality of the individual components, flute geometry, board design, and fabrication quality. The liner is the dominant factor in the puncture test of combined board in terms of improving stiffness. 19 Clamping W W r. Liner Jaws <"" "V‘ e—"991 W W \ um " Puncture Head In” Figure 7: Schematic of Puncture Resistance according to TAPPI 803 om-88 20 Burst Test In the burst test, a circular-shaped region of the corrugated board is stretched by a rubber membrane or diaphragm pushed by a piston until it bursts as shown in Figure 8 (Markstrom, 1988 : pg 42 and Kelsey, 1992: pg 17). The bursting strength measures the containment capability of the board (Howes, 1990: pg 21) and therefore is influenced most by the strength of the liners. Burst strength does not however correlate directly with box compression strength (Markstrom, 1988: pg 42). In addition, the test results are sensitive to the way the specimen is tested. According to TAPPI 810 om-80, there is no standard requirement for the clamping pressure used to hold the specimen in place (Maltenfort, 1988: pg 245). III. MANUFACTURING AND STRENGTH Corrugated fiberboard may be made of singlewall, doublewall or triplewall corrugated fiberboard. In any case, the corrugated fiberboard. is composed. of two structural components, the corrugating medium and the linerboard, which must be then combined in a high-speed fluting, gluing, and drying process. The corrugating medium is paperboard is shaped to form the fluted or corrugated center of the board. Manufacturers have discovered that the strength of the medium is very important to the overall strength of the board (Kelsey, 1992: 21 J:——————— Sample AVAVAVAVAVAVAVA AVAVAVA Jill—JV- . .. -.. I I - : ‘\ l I \\\\\‘ Rubber Diaphragm Figure 8: Schematic of the Mullen test according to TAPPI 810 om-80 22 pg 16-19). Performance results such as flat crush strength and edgewise compressive strength are strongly dependent on the strength of the medium. The compressive strength of the medium can be significantly reduced by the fluting process. During fluting, the corrugating medium is exposed to high tensile, bending, and compressive stresses in order to form the fiber-to-fiber bond between the fluting and the linerboard. These stresses can cause lower combined board compressive and flat crush strengths (Whitsitt and Sprague, 1987: pg 91 and.Bever, 1986: pg 928). During the combined board process, the corrugating medium must contact the glue as shown in Figure 9. Minimizing contact stresses during the fluting and combining processes enhances edgewise crush and flat crush strength in the combined board (Whitsitt and Baum, 1987: pg 110). Recycling lowers strength properties such as edge crush flat cush, burst, tear, fold, ring crush, tensile strength, etc. because the fibrils on the surface of the fibers collapse somewhat upon drying and rewetting and lower the strength of the hydrogen bond between the fibers (Bever, 1986: pg 4125, and Koning and Godshall, 1975: pg 40). Cleaning also affects strength. The cleaner the recycled board, the greater the decrease in the strength properties. For example, postconsumer waste pulp with lighter cleaning has proved to be stronger than more heavily cleaned plup due to the process employed in cleaning the pulp. Losses have tended to increase as the 23 ....................... h-“.”_“-”-n,n-“ Preheater Medium \r Upper Corrugator Roll Applicator """" Roll Single-facade ,- ’ ‘ “ ------------------- Lower corrugator board Roll ..................... Press Roll ‘. Liner ........ Preheater Figure 9: Combined Board Process 24 percentage of the recycled fiber increases (Fahey and Bormett, 1982: pg 110). Therefore, it is believed by some boxmakers that the best quality corrugated fiberboard is recycled material made of only Old Corrugated Containers (OCC) whenIthe ratio of virgin kraft to recycled materials is 80:20 (Huck, 1991: pg 23). Most corrugated fiberboard mills produce 100% recycled medium with 100% Old Corrugated Containers (OCC) (Huck, 1991: pg 23). The corrugated industry has been using a certain amount of OCC and Double-lined kraft (DLK) cuttings in the manufacture of linerboard for years. Virgin kraft now consists of linerboard with 80% virgin fiber and 20% recycled fiber (Huck, 1991: pg 23-24). Because of the shorter fibers, recycled fiber leads to converting problems in the corrugator and manufacturing problems on the paper machine. Since the recycled medium tends to fracture, the corrugating speed and web tension has to be reduced to complete runs. It has been found that the refined material showes a greater tendency to crack than the unrefined (Koning and Godshall, 1975: pg 38, 146-147 and Kroeschell, 1992: pg 35) . The medium has become more susceptible to cracking on the corrugator when recycled fiber is repeatedly used. Because .repeatedly’ recycled fibers continue 'to Jbe shortened as they are refined, this has also caused a decrease the drainage rate on the paper machine and a reduction in the production rate due to lower speeds. The greatest loss in strength properties occur between the virgin material and the first recycling, rather than between subsequent recyclings 25 (Koning and Godshall, 1975: pg 40 and Kroeschell, 1992: pg 34). Corrugated manufacturers today are expected to make 100% recycled linerboard even if they believe that the recycled content should not exceed 20% in high performance liners (Kelsey, 1992: pg 18 and Kishbaugh, 1990: pg 28). Since cylinder linerboard differs in physical properties from Fourdrinier linerboard, an evaluation of the effects\ of recycling on the strength properties might be different (Koning and Godshall, 1975: pg 38). To overcome the reduction in strength properties of recycled linerboard and corrugated containers, the recycling fiber should be more refined. But this leads to a decrease in the production rate and this is a more serious problem for recycled fiber use (Koning and Godshall, 1975: pg 37, 40). In the United States, OCC has been added to kraft liners in higher proportions to improve the strength properties of the linerboard (Uutela and Black, 1990: pg 51). It has been found that the addition of recycled OCC to the furnish improves impact resistance of the container (Horn, Bormett and Setterholm, 1988: pg 146). 4 When recycled paper is used, delamination is a common problem. This is because recycled.paper is less porous so that adhesive penetration becomes a problem. To solve the problem of delamination, better adhesive formulations must be used by the corrugating industry: a lower viscosity adhesive provides a thin texture and penetrates or interacts with the paper 26 faster than a viscous or thick texture material, for example (Wallace, Young and Pitt, 1991: pg 26-27). EXPERIMENTAL PROCEDURES TEST MATERIALS The fiberboard.materials used.in this study were supplied by seven commercial manufacturers of recycled corrugated board. The range of properties of the boards used were as’ described below: Board Specifications Corrugation: C-flute, Single-wall Basis weight of linerboard: 35-100 lb/1000 ft2 Basis weight of corrugating medium: 26 and 33 lb/ 1000 ft2 Quoted Burst Strength: 173 to 275 psi Caliper: 5/32 inches Recycled content of liner board: 0-100 % Recycled content of medium: 0-100% Type of recycled content: Old corrugated container(0CC) Double line Kraft (DLK) Post-consumer waste Sheet size: 58"X24" (flute direction perpendicular to the length) 27 tl Ta cc A] cc 24 re ma n0 is AP Th. te: 28 There were 15 types of corrugated fiberboard supplied by the seven commercial manufacturers. The details are given in Table 1. No "control" board with zero percent recycled content could be used because none is presently manufactured. All corrugated board presently referred to as "virgin kraft" contains at least 20% recycled content (Huck, 1991: pg 23- 24). The basisweights, recycled contents, and.burst strengths referred to in Table 1 are all values quoted by the 'manufactureru ‘The accuracy and variability of these number is not known. .Also, the type of recycled content (OCC, DLK, etc) is not known for all of them. APPARATUS The following equipment was used to conduct the performance tests on the recycled board 1. Environmental Chamber Brand: Nor-Lake Scientific no.3 and Chrysler Koppin refrigerator 2. Coolers: Used to protect conditioned samples during transfer from chambers to test equipment. Brand: Coleman 3. Thermo-hygrometer Brand: Cole-Parmer, model 3309-60 4. Sample Making Machine Brand: 8&8 Coorugated Paper Machine 29 Table 1: Manufacturer, burst strength, basis weight of linerboard/medium, and % recycled content of 15 board types board manufac Quoted Basis weight recycled no. -turer Burst (lb/1000ftfi content (%) Strength 1i me li (psi) / / 11 me 1 A 200 42/26/42 20 100 2 B * 35/26/35 0 35 3 B * 42/26/42 10 35 4 c * 42/26/42 44 70.5 5 C * 42/33/42 44 70.5 6 D 173 35/26/35 27 33 7 0 195 42/33/42 37 33 8 D 186 42/26/42 5 33 9 D 187 42/26/42 37 35 10 E 200 100/26/100 100 O 11 F * 42/26/42 100 100 12 G 175 42/26/33 32 100 13 G 200 42/26/42 30 100 14 G 275 69/26/69 21 100 15 G 250 55.5/26/55.5 25 100 E Note: * - unavailable 11 - Linerboard me - Medium. Maufacturers; A QWMUOU’ II II II II II II II Viking Paper Corporation J&J Southeast Willamette Industries, Weyerhaeuser 4-M Corporation Stone Container Corporation Corru-Kraft Co. Inc. 30 5. Sample Cutter for Edge Crush Test Brand: TMI Size: 2"X 1.25" 6. Circular Sample Cutter for Flat Crush Brand: TMI Radius size: 1.784" 7. Crush Tester Model no. 17-36 Brand: TMI 8. Oven for Moisture Content Test Brand: Precision Scientific P/S Model 524 9. Mass Balance Brand: Mettler AB 160 10. Beach Puncture Tester Brand: TMI 11. Mullen Tester Brand: Perkins Holyoke 12. Compression Tester Brand: Lansmont SAMPLE PREPARATION The board samples supplied by the manufacturers were used to make test specimens for the various board tests (edge crush, flat crush, etc.) and for the whole-box compression strength test. For boards 10, 11, and 14 in Table 1, the samples supplied*were either already scored by the manufacturer or not large enough so that the chosen test box for compression (a 31 16"X12"X10" RSC) could not be made. Prior to testing, test specimens for various boards were conditioned in one of three environments; the TAPPI standard condition, a refrigated storage condition, and a tropical condition. In this way, the effect of moisture content on strength could also determined. The boxes were conditioned only at TAPPI standard conditions. The number and size of the samples were as follows: 1. Five board specimens per humidity condition measuring 12 inches wide and 12 inches long for each type of board for bursting strength testing. 2. Eight board specimens per humidity condition measuring 10 inches wide and 10 inches long for each type of board for puncture strength testing. 3. Ten board specimens per humidity condition measuring 3 inches wide and 4 inches long for each type of board for moisture content determination. 4. Two strips, 2 inches wide and 12 inches long, per humidity condition for each board type for edge crush testing. The flutes were parallel to the long axis of the strips. Each strip was then cut into 5. specimens 1.25 inches wide and 2 inches long with the TMI sample cutter. Ten specimens were made for each board type. The edges of the cut specimens were dipped into wax according to ASTM D 2808-69. 5. Ten circular specimens of each board type for each humidity condition for flat crush testing. 6. Ten specimens per humidity condition of each board 32 type measuring 2 inches wide and 6 inches long, with the flutes running parallel to the width for pin-adhesion testing. 7. Ten RSC style boxes measuring 16"X 12" x 10" for each board type for compression testing. The blank for the box is shown in Figure 10. The size of box was chosen because it represents the average size used in the grocery industry. CONDITIONING TEST The 63 specimens per board type and the two coolers were conditioned for 5 days as follows before testing: 1. TAPPI standard condition: 73.4:2°F and 50:2 %RH 2. Refrigerated storage: 41.0:4°F and 85:5 %RH 3. Tropical conditions: 104i4°F and 85:5 %RH The temperatures and humidities for the refrigerated and tropical conditions are consistent with the recommendations of ASTM 04332-89. All boxes were conditioned only at TAPPI standard conditions. METHODS Edge Crush Testing The.edge crush values for the conditioned board specimens were determined using the test procedure outlined in ASTM 02808-69. Ten specimens or replications of each board 33 /i\ If U U 5 ------------------------------ x """"""""" HILII Is -)lK X X X A". '11/8" '16" 12" 18" ’12" Box slze : 16”x12”x10” CLxWxD) Figure 10: Box blank for the compression tests 34 type were used for each condition. There were 3 conditions and 15 board types so that the total number of tests for edge crush testing was 10 replications X 3 conditions X 15 board types = 450 tests. Flat Crush Testing The flat crush values for the conditioned board specimens were determined using the test procedure outlined in TAPPI 808 om-86. Ten specimens or replications of each board type were used for each condition. There were 3 conditions and 15 board types so that the total number of tests for flat crush testing was 10 replications X 3 conditions X 15 board types = 450 tests. Mgisture Content Determigatiog The moisture content values for the conditioned board specimens were determined using the test procedure outlined in ASTM 0644-55. Ten specimens or replications of each board type were used for each condition. There were 3 conditions and 15 board types so that the total number of tests for moisture content determination was 10 replications.x 3