Page 237 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology EN012F-600 July 26, 2001 11:16

746 Polymers, Recycling

a result of a 5% improvement in car gasoline needs, which of paper is not necessarily the wisest choice since the
could readily be achieved by weight reduction. production of paper can be a polluting and water- and
As petroleum becomes more scarce and expensive, as energy-consuming process. Also, the lighter plastic bags
is bound to happen, industry will turn to more value- lead to lower shipping costs and a consequent reduction in
added use. Thus, there will be diversion toward the more fuel needs. Some of the properties of plastic bags such as
profitable petrochemical applications, and more of the moisture resistance and better “wet strength” are superior
burden will result from increased fuel costs. Thus, a to those of paper. An advantage over paper is the ability
wiser investment of research resources would be into they offer to carry a greater number of plastic bags because
energy-saving schemes and alternate energy production of their handles. Thus, the decision is dependent upon the
approaches, many of which are aided by the use of poly- environmental efficiency of production (and disposal) of
mers for applications such as fuel cell membranes, solar the alternative products.
panels, and wind turbine blades. These considerations point to two important factors:
Alternate feed stock such as natural gas, coal, or bioma- (1) reuse is often superior to recycling and (2) energy sav-
terials for polymer production is feasible, but, at present, ing as well as materials saving should be considered. By
not economical. It may be that as petroleum becomes adopting the common European practice of not supplying
scarcer, such approaches will become more favorable, but new shopping bags, but expecting consumers to supply
this does not appear to be so in the immediate future. their own, a “good” plastic shopping bag could be reused
Recycling certainly has a role in reducing the need to perhaps 50 times, while if its plastic content were recy-
produce new polymers (as well as other materials), but cled, only two or three cycles might be possible before
without governmental intervention, such as subsidies or deterioration of properties occurred.
tax rebates, society is unlikely to adopt uneconomical For energy considerations, the production, use, and dis-
measures. Of course, the total cost of polymer use, in- posal of any product require energy. The production of
cluding that of disposal of waste polymers, needs to be such energy often requires use of petroleum or other feed
considered. Measures such as subsidizing recycling based stocks common to the production of new polymers. There-
upon savings of disposal might be reasonable. While im- fore, both energy and materials need to be considered to-
proved means for recycling should be strongly encour- gether in the choice. For example, some environmental-
aged, it should be realized that there are limits on the frac- ists contend that natural fibers such as wool and cotton
tion of plastic waste that can be economically recycled. are a better choice than synthetic ones such as nylon and
Such limits depend upon petroleum costs, recycling tech- polyester. In making this decision, one needs to compare
nology, and the associated infrastructure costs involved in the energy and materials necessary to produce the syn-
collecting and sorting. At present, this fraction may be in thetic fiber with that needed for fertilizer, tractor fuel,
the range of 30–40% of the polymer waste, but this num- harvesting, and processing the natural one, along with
ber is bound to increase as petroleum becomes scarcer, a consideration of the greater maintenance requirements
technology improves, and infrastructure develops. (laundering, ironing, dry cleaning) necessary for the prod-
uct produced from the natural fibers. The choice is not
always clear-cut and depends on societal factors and the
II. MEANS FOR DEALING WITH
PLASTIC WASTE efficiency of utilizing these alternatives. For much of the
“third world,” food is scarce, and the production of the nat-
ural product competes with the agricultural requirements
A. Use Reduction
for food production.
For some purposes, particularly in the “first world,” there
is probably excessive polymer use. Consumer products of- B. Recycling
ten have too much packaging, and polymer can be saved
by distributing liquid products as more concentrated so- Recycling, next to reduced use and use of substitutes, is
lutions. (There is no point in packaging water.) Improved often the best environmental approach. This is the main
technology can result in less need for polymers. With im- focus of this article and will be considered in detail in later
proved polymer technology resulting in better mechanical sections.
properties, plastic bags and bottles can be made thinner.
The choice of substitute materials should be made with
C. Degradation
care. The consumer at the supermarket is often offered the
choice of “plastic or paper” in choosing a shopping bag. Polymers can be intentionally made so as to degrade by
Of course, the best choice is to say “neither” and bring an photolysis or bacterial action during a predetermined time
old bag for reuse. However, the choice of the alternative period. Until recently, the efforts of polymer scientists