Page 459 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: GPB/GAM P2: GQT Final Pages
Encyclopedia of Physical Science and Technology EN013A-619 July 26, 2001 19:32

264 Pulp and Paper

additives are being developed that increase wet strength These wastes are disposed of either by incineration or land
without affecting absorbancy. disposal.
Once recycled pulps are produced they are either
blended with virgin fiber for use in paper products or used
VII. RECYCLING IN PULP AND PAPER exclusively. Blending affords the opportunity to gain the
characteristics of strength and brightness associated with
Recycling is one of the traditional sources of fiber for longer fibers from virgin (wood) sources. Typically, for
the pulp and paper industry, and in recent years, it has example, repulped newsprint is blended with TMP pulps
become an increasingly important element of fiber sup- as a means to produce acceptable feeds for making new
ply. Periodic fiber shortages coupled with governmen- newsprint. The TMP pulps provide the long fiber and con-
tal policies have encouraged the increased utilization of sequent strength required for high-speed paper machines
recycling. Currently several grades of fiber are used signif- and high-speed printing equipment. Blending also may
icantly as secondary fiber, including old corrugated con- take the form of multi-ply sheet forming in the papermak-
tainers (OCC), old newsprint, old magazines, and high- ing process. Typical products that have high secondary
grade deinking. Much of the fiber being recycled comes fiber utilization include newsprint, folding boxboard, cor-
either from industrial scrap (e.g., trimmings from con- rugating medium, moulded pulp trays, and certain con-
verting facilities), newspaper and magazine overruns, or struction papers. Recycling, then, provides an alterna-
selected office wastes. tive source of fiber to the pulp and paper industry. This
Postconsumer waste paper is being used increasingly, source of fiber is used as a consequence of both raw ma-
although such materials as mixed waste paper still have terial and governmental pressures. It is used in specific
limited market acceptance. In 1975 wastepaper recy- processes and in selected products, depending upon the
cling was about 25%, but due to environmental pressures source of the secondary fiber and the consumer acceptance
the paper industry now recycles 45% of the stock (47 of the final product with characteristics imparted by uti-
million metric tonnes). Even higher recycling levels, up lization of recycled product. Recycling, then, has become
to 60%, are possible and fiber poor countries such as the an increasingly important element of the pulp and paper
Netherlands and Japan are near this level. The use of re- industry.
cycled fiber is limited by the extent of contamination plus
final paper and paperboard product specifications such as
tear strength, brightness, and regulatory issues (e.g., paper SEE ALSO THE FOLLOWING ARTICLES
from secondary fiber cannot come into direct contact with
food products). BIOPOLYMERS • CARBOHYDRATES • ENERGY FLOWS IN
The processing of secondary fiber typically involves ECOLOGY AND IN THE ECONOMY
hydropulping, a mechanical pulping process for fiber lib-
eration from waste products. Hydropulpers also provide
for removal of large tramp objects through “raggers” BIBLIOGRAPHY
and “junkers.” After hydropulping, the fibers are cleaned
through a series of screens. Deinking processes are then Aho, W. (1983). Advances in chemical pulping processes in progress.
used. The selection of deinking process is dependent upon In “Progress in Biomass Conversion,” Vol. 4, Academic Press, New
the secondary fiber being processed and the product being York.
made. Certain waste papers are proving increasingly dif- Biermann, C. J. (1993). “Essentials of Pulping and Papermaking,” Aca-
demic Press, New York.
ficult to deink, particularly office papers from dry copiers
Breck, D. H. (1985). “Technological advances hold the key,” Tappi 68(4),
and laser printers. Deinking may be followed by sec- 71–72.
ondary fiber bleaching, depending upon the quality of the Casey, J. P. (1980). “Pulp and Paper Chemistry and Technology,” 3rd
fiber being processed and the final product characteristics Ed., Vol. 1, Wiley (Interscience), New York.
required. Secondary fiber pulping and bleaching concen- Fengel, D., and Wegener, G. (1984), “Wood: Chemistry, Ultrastructure
and Reactions,” Walter de Gruyter Pub., New York.
trates contaminants contained in the waste paper. Typi-
Hersch, H. N. (1981). “Energy and Materials Flows in the Production
cally pulping and bleaching of secondary fiber can gen- of Pulp and Paper,” Argonne National Laboratory, Chicago, IL.
erate 400–800 lb of wastewater treatment solids (sludge) Libby, C. E. (1962). “Pulp and Paper Science and Technology,” Vol. 1,
per ton of incoming secondary fiber, depending upon the Pulp. McGraw-Hill, New York.
type of fiber accepted and the final product produced. Fur- Mark, R. E. (1983). “Handbook of Physical and Mechanical Test-
ing of Paper and Paperboard,” Vols. 1 and 2, Marcel Dekker, New
ther, secondary fiber operations generate significant quan-
York.
tities of waste from the ragger and from the primary and Tillman, D. A. (1985). “Forest Products: Advanced Technologies and
secondary screens used to clean the hydropulper product. Economic Analyses,” Academic Press, Orlando, FL.