Page 163 - Materials Chemistry, Second Edition

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134 Waste Management Practices: Municipal, Hazardous, and Industrial
Production of paper continues to increase in the United States and, therefore, more paper waste
continues to be produced. Over the past decade paper recycling trends have continued to increase.
According to the American Forest and Paper Association, between 1987 and 1999, the paper and
paperboard recovery rate increased from 28.8 to 45%. The United States used more than 72 million
tons of paper products, but only 25.5% is made from recycled paper. This compares with 35% in
Western Europe, almost 50% in Japan, and 70% in the Netherlands (Liu and Liptak, 2000).
Waste paper can be classified as bulk or high grade. The highest grade includes manila folders,
hard manila cards, and similar computer-related paper products. High-grade waste paper is used as
a pulp substitute. Bulk grades consist of newspapers, corrugated cardboard, and mixed paper waste
(unsorted office or commercial paper waste). Bulk grades are used to make paperboards, construc-
tion paper, and other products. The Institute of Scrap Recycling Industries has established standards
and practices that apply to paper stock for repulping in the United States and Canada (ISRI, 2002).
Common paper grades are listed in Table 6.2.
Paper manufacture from recovered paper and paperboard utilizes a different pulping process
compared with pulping virgin fibers. A significant mechanical component needed for pulping recy-
cled fibers is the continuous pulper. In this unit, the input material is ground into a smooth pulp, and
extraneous materials (glues, plastic, metal and clips) are removed. Recovered pulps are then de-
inked by a process of chemical disintegration or chemical treatment. In some plants a washing step
is incorporated to further clean the pulp. The pulp is washed free of ink and other contaminants on
a fine mesh screen. An optional flotation process may be used in which chemicals are added to the
pulper to create air bubbles that separate and float ink droplets away from the pulp. The pulp may
also be bleached (Rhyner et al., 1995). Apart from washing and flotation, the resultant pulp is
screened and thickened. Once processed, the pulp, whether from virgin or recycled fibers, enters the
paper manufacturing process.
Each time paper is recycled, some of the longer fibers are shortened, generally losing their flex-
ibility and bonding ability. This is due to a process called “hornification,” which is collectively a
number of partly irreversible physical changes. Virgin pulp is added to maintain the paper strength
required for efficient runnability at fast speeds, both on the paper mill and during conversion (e.g.,
printing press), as well as for the end-use. Besides strength, brightness also deteriorates each time
the paper is recycled. In summary, waste paper tends to downgrade in quality as it is recycled.
However, recycled fibers possess some advantages in that the twice-dried stock may drain
faster than its virgin equivalent, require less refining, be co-refined with hardwood pulp or com-
bined hardwood and softwood pulps without significant damage, and impart improved opacity
(Ferguson, 2001).
As with many other materials, the waste paper market is volatile and strongly influenced by
region. Economic conditions continue to affect progress in paper recycling. In some locations, mixed
paper waste is of little value. One recycling marketer from the Midwest recently lamented, “Right
now we can get $5 per ton for recovered paper. For that amount you can’t start the collection truck.”
One limitation on the amount of waste paper that can be recycled in a year is the capacity of
paper mills. Construction or modification of such mills is capital-intensive; therefore, investors
must be assured that there will be an adequate supply of waste paper to the mills and at a compet-
itive price. Much waste paper is shipped to markets along the Pacific rim (e.g., South Korea), where
timber resources are scarce. China is a major influence in the mixed waste paper market. Imports
from the United States have increased from 209,000 tons in 1993 to 2.2 million tons in 2000. The
mixed waste paper is sorted and processed in the recipient country. The demand is expected to grow
further (Paper Technology, 2001).
Over the past decade, legislative programs have been developed in several countries that require
a certain percentage of recycled fiber content in newspaper, office paper, and other products. Such
initiatives increase the demand and the quantity of paper available for recycling. However, there
may be resistance on the part of waste paper recyclers to make the large capital investments neces-
sary to increase plant capacity (Pfeffer, 1992).