Recycled Fiber Properties As Effected by Contaminants

RECYCLED FIBER PROPERTIES AS AFFECTED BY CONTAMINANTS AND REMOVAL PROCESSES

USDA FOREST SERVICE RESEARCH PAPER FPL 223

1974

U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY MADISON, WIS. ABSTRACT Five materials were applied to either a kraft pulp furnish or to a kraft paper and were removed by conventional removal processes. Uncontaminated kraft paper subjected to the same removal processes determined that the process, not the contaminant, was responsible for changes in sheet properties. Handsheet tensile properties, an indication of fiber bonding, ranged from a 48 percent decrease to no change from the original. Zero-span tensile tests, a measure of fiber strength, ranged from 46 percent decrease to a 19 percent improvement over the original control. Aqueous polyethylene removal and deinking processes restored fiber bonding and strength almost to their initial levels. Wet strength removal, hot melt, and polyethylene solvent extractions resulted in fiber property reductions similar in magnitude to that of the recycled control. Asphalt dispersion caused the largest decrease in fiber properties. Results suggest a potential for extending the market for recycled fibers through the development of chemical processes for upgrading secondary fibers as well as removing contaminants. MATERIALS RECYCLED The contaminants selected for study were those that are used in large volume, those that require special unit operations FIBER PROPERTIES for their removal, or both. Printing, writing, and related papers account for 26 percent of the total paper AS AFFECTED and paperboard production in the United States (11). Thus, a commonly used solvent based rotogravure ink was selected as one BY CONTAMINANTS contaminant. Urea- and melamine-formaldehyde resins for imparting wet strength to paper and paperboard (either in the sheet AND REMOVAL or applied with the coating processes) have been estimated to be used by the paper industry at 49,900 tons annually (6). Assuming PROCESSES that they are added at 1 percent of the weight of fiber, 10 percent of current production would contain one of these wet strength resins. A melamine-formaldehyde resin was select- By ed as this is more difficult to remove than JOHN H. KLUNGNESS, Research the other commonly used wet strength resin Chemical Engineer urea-formaldehyde (2). 1 About 159,000 tons of low density Forest Products Laboratory, polyethylene (PE) and 125,000 tons of wax Forest Service U.S. Department blends, hot melts, and fortified waxes are of Agriculture applied annually to paper and paperboard production (5). Assuming these materials are present at 20 percent of the fiber weight, each of these two classes is contained in 1 percent of current paper and paperboard INTRODUCTION production. Production of asphalt-treated paper and In order to increase the quality of re- paperboard (excluding construction sheeting cycled fibers, and thus their market potential, such as roofing felt) is currently about 185,000 sound information on the effects of contami- tons per year (11). This is less than 1 percent nants and their removal processes on fiber of current total paper production. quality is needed. Establishing how fibers PE, hot melts, and asphalt are all low are affected, by contaminants or removal volume contaminants, but require special processes or both, will provide means for unit operations for removal. A low density increasing the quality of recycled fibers. PE, a vinyl copolymer resin hot melt, and a This can suggest priorities for future research, standard laminating asphalt were selected. methods for avoiding current problems, and An unbleached southern pine kraft pulp at establish what fiber properties need to be 33.8 Kappa and 31 percent moisture was restored in order to increase the number of chosen for several reasons: All of the con- products in which recycled fibers can be taminants are commercially applied to some used. It can also establish criteria by which degree to this type of pulp; this pulp is pro- other current or proposed recycling proc- duced mainly for strength-the property esses may be rated as to their effect on affected most by recycling (4); and this pulp wood fibers. is the most commonly produced. TAPPI In a recent bibliography (12)2 listing over beater data for this pulp are shown in figure 1. 1,100 citations devoted to the topic of reclaimed fibers, only 26 pertained to properties of these fibers. Past work has centered more on how to remove objectionable materials 1 Maintained in Madison, Wis., in cooperation with the from wood fibers than on how the fibers are University of Wisconsin. affected by the contaminant or removal 2 Numbers in parentheses refer to literature cited at processes. end of report.

1 Figure 1.-Relationship of beating to properties of the original pulp. (M 141 977) METHODS Removal of the Contaminants Unit operations are described in the Preparation of the Base Paper literature for the recovery of wood fiber from Pulp was slushed at 6 to 8 percent products containing ink (10), wet strength consistency with warm water in a hydrapulper, resin (9), hot-melt-resins and/or PE (1)3 and refined in a twin disk refiner to 250 milliliters asphalt (2). In addition, for our study, base Canadian Standard Freeness (CSF) in a single paper not treated with contaminants was pass at 3 to 4 percent consistency. The furnish subjected to each removal process. was sized with 1 percent rosin size using The wet strength resin was removed by sulfuric acid for initial pH adjustment with treating the paper in the hydrapulper with the final pH controlled at 4.5 to 5 with alum. about 0.7 percent sulfuric acid. Four furnishes were identically prepared Because a small commercial asphalt (except for a portion of one containing dispersion unit was not available, a small melamine-formaldehyde resin) and each was Asplund Defibrator was selected. The chamber converted into three rolls on the experimental of the Defibrator was subjected to steam Fourdrinier paper machine. The paper had a pressure and intermittent agitation to sim- nominal weight of 37 pounds per 3,000 square ulate the conventional pressurized auger-fed feet and an apparent density of 0.65 gram tube. This pretreated stock was then disper cubic centimeter. persed by constant agitation at atmospheric pressure. Application of the Contaminants By means of a two level fractional Application of the contaminants and the factorial experiment, variables of chamber processes of removal are described in table 1. time, chamber pressure, and dispersion Three percent melamine-formaldehyde time were optimized for reduction of dirt resin was added to the final third of one count (TAPPI Method T 213 ts-65) (8). Selec- furnish before the addition of rosin size. ted were the least severe conditions resulting This portion was then converted into a roll in the minimum dirt count: 4 minutes cham- of paper. ber time, 40 pounds per square inch gage Ten pounds of the base paper were chamber pressure, and 2 minutes of disper- slurried in a small hydrapulper at 3 percent sion. consistency for 30 minutes. This stock was The deinking conditions were developed then dewatered to 22 percent solids by using bench scale equipment and the simplest pressing. Commercial laminating asphalt of known deinking methods. An experiment (petroleum type M.P. 180° - 200° F) was based on a two-level fractional factorial added at 0.5 percent with the stock when design was used to determine the mildest charging the Defibrator. No roll was made. conditions required to completely remove The solvent based rotogravure ink the ink. The variables investigated were was applied as a solid print to one side of consistency, time of agitation, temperature, one roll of paper using a commercial roto- and amount of sodium hydroxide. The ink gravure press. applied was fluorescent and the ink removal Low density PE was applied to a roll of efficiency was easily evaluated by use of paper by a standard commercial PE extrusion ultraviolet light. The conditions listed in process. This consisted of electrostatic table 1 were selected from this bench work. pretreatment of the paper to increase the Inspection of the deinked stock for the paper surface receptivity for bonding with PE, machine furnish showed no ink remained followed by extrusion of PE at 610° F. after the deinking and side hill washing-an The thickness of this one side coating was accepted method of washing the removed a nominal 0.002 inch, weighing 28.8 pounds ink from the slurry. per 3,000 square feet. There was very little One-half of the PE-coated roll, the hot- penetration into the sheet. melt coated roll, and a control roll were sub- Another roll was coated with a commer- jected to the Polysolv process4 This is a cial high molecular weight molten vinyl batch type, three-stage, counter current, copolymer resin followed by cooling to pro- solid-liquid extraction process employing duce a continuous coating. This hot- trichlorethylene as a solvent (1). Our material melt-resin was applied at 220° F and gave a total coating weight of 15 pounds per 3,000 3 Unpublished flow chart of an aqueous, 50-ton-per-day square feet. The application was to one side plastics recovery system, in use by B.J. Fibers, Inc. of the web but this penetrated well into the 4 The author wishes to thank Riverside Paper Corporation sheet. for allowing the use of their solvent extraction process. 3 Table 1.--Contaminant treatments and removal processes was included with a much larger charge of Sheet Properties wax-treated paperboard, so no attempt was In figure 2 the processes are ranked in made to optimize the operation for the order of decreasing sheet density. The experimental material. Because PE remained original value of the apparent density on the papers after one complete 3.5-hour (0.655 g/m3 ± 2.7 pct-95 pct confidence extraction process, all the experimental limits) is indicated by the dashed line along material was once again subjected to the the top of the figure. All processes showed a process. decrease in apparent density, except for the The balance of the PE-coated roll was deinking process. This process resulted subjected to an aqueous removal process. in no significant change from the original. This consisted of slurrying the paper in water It is also shown that while significant reduc- adjusted to a pH of 10 with sodium hydroxide. tions in apparent density resulted from the This aided in the wetting of the fiber so that various processes, no significant differences the fiber was completely washed free of the resulted from the earlier presence or absence PE film. The film floated to the surface and of contaminants. That is, the measurable was easily removed. effect on apparent density resulted from the process not the contaminant. If it is assumed Remaking Rolls that the reduction of apparent density is due Each of the contaminated rolls subjected to reduced fiber bonding, it would be expected to a removal process and the correspondingly that sheet strength properties would also processed uncontaminated control rolls generally decrease. was separately recycled into paper rolls. Bursting strength, corrected to a common As necessary for each case, the freeness 0.65 gram per cubic centimeter apparent was adjusted to 250 milliliters CSF and the density, is shown in figure 3. Again, the burst sizing procedure repeated. An overall control showed a general decrease for each proc- (listed in table 1) was also included which did ess except for that of deinking which re- not receive either a contaminant treatment sulted in no significant change from an nor a removal process. This roll was merely original of 46 pounds per square inch. The reslushed, sized, and remade into a roll on processes are arranged in the order of the paper machine. decreasing burst. Again, no measurable difference was observed whether the proc- Evaluation of the Pulps and Papers essed paper originally contained contami- The pulp in the paper machine chest nants or not. for each furnish was sampled (before sizing) In figure 4 the processes are ranked in and converted into handsheets. The hand- order of their effect on tear corrected to sheets were evaluated for strength properties. 0.65 gram per cubic centimeter apparent Testing of samples taken from each of the density. The order of increasing tear was four separate and identical initial runs, before the same as that for decreasing burst. If sizing and after the paper machine, allowed it is assumed that the observed decreases an estimation to be determined of the intrinsic in apparent density resulted from decreased variability of similar tests used in the balance fiber bonding, and that corresponding of the study. decreases in burst confirmed this, the Evaluations on all papers, as well as corresponding increases in tear may be handsheet preparation and evaluations, similarly explained. Earlier work (3) has followed TAPPI procedures. shown that the tearing strength depends on the forces required to rupture the individual fibers and to pull fibers intact from the web RESULTS AND DISCUSSION network. The force required to pull fibers from the network (which occurs when fiber Properties of the finished paper produced bonding decreases) is much greater under on the paper machine are given in table 2. normal conditions than that required to rupture Results obtained from pulp samples and individual fibers. from handsheets prepared from these samples are given in tables 3-5 and figures 2-6. Table Fiber Properties 2 does not include results of paper subjected Fiber lengths as measured by fiber to asphalt dispersion since the equipment used classification (table 4) showed no significant was not large enough to produce a sufficient change as a result of any of the processes quantity of stock for a paper machine run. except for the shortening of the longest Pulp results (table 3) support the paper data. fraction of the fibers subjected to asphalt

5 Table 2.--Properties1 of recycled paper after contaminant removal processes 1 Table 3.--Properties of handsheets from pulp recycled after contaminant removal processes Table 4 .-- Fiber length classification 1 Table 5.-- Chance of tensile and zero- span tensile from original values resulting from contaminant removal processes Figure 2. -Effect of removal processes on apparent density of handsheets with and without prior contamination. (M 141 976) dispersion. The effect of the processes on the However, the processes did affect the resulting values of tensile and zero-span conventional tensile strength (hereafter tensile suggested that fiber bonding and referred to as tensile) of the sheets. The fiber strength are both changed due to effect of the various processes on the result- processing. The comparative percentage ing tensile, again corrected to 0.65 gram per changes from the original are listed in table cubic centimeter apparent density, is illustrat- 5. The recycled control shows a greater ed in figure 5. Each process, except for decrease in tensile (32 pct) than zero-span deinking, reduced the tensile from the tensile (14 pct). This indicates a greater original value of 6,580 pounds per square decrease in fiber bonding with a lesser inch. Deinking resulted in no change from decrease in fiber strength. This has been the initial level of tensile. Again, the measurable reported earlier for uncontaminated unsized effects are due to the process, not the presence fibers (4). Wet strength removal, hot melt, or absence of contaminants. and PE solvent extraction showed decreases Zero-span tensile, an indication of of similar magnitude as the recycled control individual fiber strength, also was affected both with and without contamination. Asphalt by processing (fig. 6, corrected to 0.65 g/cm3). dispersion resulted in a larger decrease Deinking and aqueous PE removal result in both values, 46 percent for zero-span in slight measurable improvements in the tensile and 42 percent for tensile-for the zero-span tensile, while all other processes uncontaminated sample. The sample con- lowered the values from the original value of taining dispersed asphalt had values similar 10,550 pounds per square inch. to the overall control which may be due to 10 Figure 3.-Effect of removal processes on burst of handsheets with and without prior contamination. (M 141 978) the presence of asphalt. similar results in zero-span tensile increasing The aqueous PE removal and deinking the zero span 10 percent over the original processes not only showed less of a loss in for the unprinted and 11 percent for the tensile and zero-span tensile than the control, printed paper, and resulted in essentially no but resulted, in certain instances, in an change in the tensile values. improvement over the original values. The Sodium hydroxide was used in only decrease in tensile for the aqueous PE the deinking and aqueous PE removal removal process was 20 percent and 12 processes. The fibers apparently benefited percent for the uncontaminated and contami- from this mild chemical treatment. The nated paper respectively. This is less than process used for the aqueous PE removal the 32 percent decrease for the recycled was similar mechanically to that of the over- control. The value for zero-span tensile all control. Whether the sodium hydrox- increased 14 percent and 19 percent for ide restored the bonding potential by removing the uncontaminated and contaminated paper the initial internal size from the fibers or by respectively over the original values, compared chemically restoring the bonding potential to a 14 percent decrease for the recycled of the fibers or both was not determined. control. The deinking process showed 11 Figure 4.-Effect of removal processes on tear of handsheets with and without prior contamination. (M 141 979)

12 Figure 5. -Effect of removal processes on tensile of handsheets with and without prior contamination. (M 141 980)

CONCLUSIONS

Significant differences in properties of recycled fibers result not from the presence or application of the five contaminants selected for study, but from the processes used in their removal. Fiber bonding and strength can be restored to essentially their initial values by the chemical treatments used in the aqueous PE removal and deinking processes. The other removal processes investigated do not restore the fiber properties, and result in lower fiber bonding and fiber strength levels similar to those of recycling the control. Improved recycled fiber properties may be obtained through chemical treatments used in the removal of the problem contaminants. Further work in the area of contaminant removal should include efforts to chemically restore the original fiber properties either as part of the removal process as such, or as an added posttreatment. Literature Cited 1. Anonymous 1969. Secondary fibers-Many facets of processing and usage explored. Pulp and Pap. 43(13): 109-112. 2. Felton, A.J 1971. Handling the problem papers-wet strength, asphalt, polycoated, etc. Pap. Trade J. 155(37): 70. 3. Institute of Paper Chemistry n.d. Instrumentation Studies XLVI. Tearing strength of paper. Pap. Trade J. 118(5): 13-16, 18, 19. 4. McKee, R.C. 1971. Effect of repulping on sheet properties and fiber characteristics. Pap. Trade J. 155(21): 34. 5. Modern Packaging Encyclopedia 1971. McGraw-Hill Inc., New York, N.Y. Vol. 44, No. 7A. 6 Swanson, J.W. 1970. Chemical additives: New dimensions for papermaking. American Paper Institute. New York. Mar. 7. Technical Association of the Pulp and Paper Industry 1964. Fiber length of pulp by classification. TAPPI Suggested Method T 233 sv-64. Atlanta, Ga. 8. 1965. Dirt in pulp. TAPPI Method T 213 ts-65. Atlanta, Ga. 9. 1965. Wet strength in paper and paperboard. Tappi Monograph Series No. 29. Mack Print- ing Co., Easton, Pa. 10. 1967. Introduction to deinking. Tappi Monograph Series No. 31. Mack Printing Co., Easton, Pa. 11. U.S. Department of Commerce n.d. Current Industrial Reports Series. Bureau of Census. M26A (68)-14. 12. Weiner. J., and Black, V. 1971. Reclaimed fibers, Bibliographic Series No. 168. The Institute of Paper Chemistry, Appleton, Wis.

U.S. GOVERNMENT PRINTING OFFICE 1974-650-247/5 16 4.5-17-7-74 ACKNOWLEDGMENT

The author thanks Bowaters Southern Paper Corporation for supplying the pulp and Milprint Incorporated for paper roll treatments. The assistance of the following Laboratory staff is gratefully acknowledged: R.W. Shilts for assistance with bench scale investigations, C.L. Coens, J.F. Wichmann, and G.R. Henseler for pulp and paper testing, and especially R.D. Hilton and C.W. Polley for roll preparation and recycling.

Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the U.S. Depart- ment of Agriculture.