Methods for enzymatic deinking of waste paper

Details Methods for enzymatic deinking of waste paper Methods for enzymatic deinking of waste paper

1999-08-04

2002-07-30

Gitomer, Ralph (Department: 1623)

Chemistry: molecular biology and microbiology

Micro-organism, tissue cell culture or enzyme using process...

Preparing compound containing saccharide radical

C435S018000

Reexamination Certificate

active

06426200

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains to a method and composition for deinking printed wastepaper. More particularly, this invention relates to a method and composition for deinking noncontact-printed wastepaper, particularly xerographic and laser-printed paper, and mixtures of contact and noncontact-printed wastepaper, using an enzyme mixture characterized by a high ratio of &bgr;-glucosidase activity to filter paper units (FPU) activity. The present invention also relates to an assay for evaluating enzymes for use in deinking wastepaper based on the ratio of &bgr;-glucosidase activity to FPU activity.
BACKGROUND OF THE INVENTION
Recycling of waste papers and paper products has generated considerable interest in the pulp and paper industry. In response to increasing environmental awareness and regulatory pressure, the paper industry expects to recover and recycle at least 40% of all paper produced in the U.S. by 1995. Proposed regulations require even higher recoveries of certain grades of paper. (Darlington, W. E. (1992) Tappi 1992 Pulp. Conf. Proc., p. 857.) As the demand for recycled fiber content in paper products grows, the need for improved fiber deinking technologies increases accordingly.
Conventional deinking processes require large amounts of expensive, environmentally hazardous chemicals. Current recycling protocols use caustic soda and other chemicals throughout the recycling process. Because these chemicals tend to discolor the pulp, peroxide is typically added to whiten the pulp to the required brightness. These chemicals are eventually washed away in the waste water, causing serious environmental problems. In addition to their high cost and environmental impact, deinking chemicals disintegrate the paper fibers, resulting in lower quality pulp with poor physical properties.
As an alternative to conventional chemical deinking, enzymatic deinking of wastepaper has received increasing attention during the last few years. Several studies have shown that enzymes such as cellulases, hemicellulases, xylanases and lipases effectively deink “contact” printed wastepaper, i.e., papers produced by traditional offset printing using oil-based inks. For example, cellulases have been used to deink old newspaper when used alone or in combination with conventional deinking chemicals. (Fukunaga, N., et al. (Jap. Pat. 0280683); Kao Corp. (Jap. Pat. 59 09,299); Eom, T. J., et al. (1991) Kami Pa Gikyoshi 45(12):1377-82; and Prasad, D. Y., et al. (1992) Prog. Pap. Recycling 1(8):21.) Ow, S. K. and Eom, T. J. (1990) Proc. EUPECA Symp., Barcelona 37:85-94, reports that newspaper can be deinked without conventional deinking chemicals using a cellulase and hemicellulase-containing culture filtrate. Baret, J. L., et al. (PCT Int. Appl. WO 91/14819) reports efficient deinking of wastepaper comprising old newspapers, colored wood-free shavings and magazines using alkaline cellulase together with conventional deinking chemicals. Neo, P., et al. (1986) J. Wood Chem. Tech. 6(2):147, reports that xylanases promote “enzyme beating” during conventional chemical deinking. Finally, incorporation of an alkaline lipase in the conventional alkaline deinking process reportedly improves the brightness and fiber quality of the deinked pulp. (Sugi, T. and Nakamura, J. (Jap. Pat. 03,249,291); and Sharyo, M. and Sakaguchi, H. (Jap. Pat. 02,160,984)).
While the enzymatic deinking of “contact” printed wastepaper has been achieved, relatively little effort has been devoted to the development of alternative methods for deinking “noncontact” printed papers, the principal component of “mixed office waste.” Noncontact-printed papers, including xerographic and laser-printed papers, are notoriously difficult to deink by conventional deinking methods. (Vidotti, R. M., et al. (1992) “Comparison of Bench Scale and Pilot Plant Flotation of Photocopied Office Waste Paper,” 1992 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 643-652.) The noncontact inks (toners) used in xerographic and laser printing consist of colored pigments combined with a thermoplastic resin binder, the latter component comprising synthetic polymers such as polyester, styrene-butyl methacrylate or styrene-butadiene copolymers. (Vidotti et al., supra, p. 643.) The polymers become fused together and permanently affixed to the paper during the “fixing” stage of the printing process. During repulping, these fused polymers dissolve into thin, flat particles varying in size from a few to several hundred or more microns in diameter. (Vidotti et al., supra.) Because of this broad range of ink particle sizes, dislodged toner particles are not readily separated from the paper fibers. The larger ink particles, ranging in size from about 100 to about 300 &mgr;m in diameter, are too massive to be removed using conventional washing or flotation techniques, yet too small to be screened with existing devices. Moreover, their flat, disk-like configuration prevents toner particles from being separated by conventional centrifugal cleaning. Alteration of the size and shape of these dislodged toner particles requires harsh chemical and/or mechanical treatments such as high shear mixing or kneading. (Okada, E. (1991) 1991 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 857-864.) However, such actions are not specific, decrease fiber length, and create excessive fines and debris, resulting in reduced fiber strength. Finding efficient, cost effective and innocuous means for deinking toners from xerographic and laser-printed paper represents perhaps the greatest challenge for the pulp and paper industry.
Jeffries, T. W., et al. (1993) Tappi 1993 Recycling Symposium Notes, TAPPI Press, Atlanta, Ga., p. 183, discloses the use of a commercial cellulase to deink homogenous xerographic-printed wastepaper produced from a defined styrene/acrylate toner stock. Jeffries et al. compare the deinking capacity of cellulase (Celluclast™, Novo Nordisk Bioindustrials, Inc., Danbury, Conn.) with standard deinking chemicals using identical steps of high-consistency pulping. The authors report that this particular cellulase used alone was more efficient than chemicals alone or enzymes used in combination with chemical deinking. However, Jeffries et al. note that additional studies are necessary to evaluate the efficiency of enzymatic treatment on heterogenous office wastepaper which contain a mixture of hard-to-remove noncontact toners.
Jeffries, T. W., et al. (1994) Tappi J. 77(4):173-179, compare the deinking efficiency of several commercial cellulases in pilot plant trials. Although the authors could not attribute toner removal to a specific enzymatic activity, they report that “enzymes with the highest FPU values performed best for deinking” whereas the enzyme with the highest cellulase activity (Enzyme C) was among the “least effective in removing toner” (p. 177). Jeffries et al. further note that efficiency of enzymatic deinking depends on the particular paper source, i.e., whether the paper was acid- or alkaline-sized. This reference thus suggests that the cellulase be selected based on the pH range of the pulped paper stock, and that a high filter paper units (FPU) value may be more important to the efficiency of deinking than cellulase activity per se.
Kim, T. J., et al. (1991) Tappi 1991 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 1023-27, purport to provide an enzymatic method for deinking laser-printed computer printout (CPO) paper. [See also Eom, T. J., et al. (Can. Pat. App. 2,032,256).] Kim et al. report a slight improvement in fiber physical properties and a reduction in dirt count by substituting a cellulase for caustic soda during pulping. Although this preliminary report suggests the use of this enzyme to deink laser-printed white ledger paper, the reference provides no evidence that this cellulase (or any other enzyme) could effectively deink heterogenous office wastepaper, i.e., mixed grades and/or colored papers. The reference does not associate deinking with any specific enzyme activity, nor does it provide a basis for evaluating or identifyin

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