Issue Date: May 21, 2012
The article “Old Plastics, Fresh Dirt” is concerned with degradable plastics (C&EN, March 19, page 12). These certainly have their place, but I’d like to call attention to the second law of thermodynamics, which tells us that entropy—a measure of disorder of an isolated system—will spontaneously increase. Thus, without intervention, as we can readily observe, the world becomes increasingly disordered.
Large molecules such as polymers have lower entropy than their decomposition products, so degradation of plastics follows the second law and adds to disorder. We should have environmental concern about this, in addition to concerns about energy, largely dealt with by the first law of thermodynamics. We can avoid an entropy increase by maintaining polymers as large molecules rather than their higher entropy decomposition products. This is the virtue of recycling.
Thus, to aid the environment, we should recycle rather than degrade plastics whenever possible. To do this, the plastics capable of being recycled should be readily identified and collected, and the products of recycling should have sufficient economic value. This has been true for soda bottles, for example, made mostly from the high-value-added polymer polyethylene terephthalate, which can be recycled to produce products including carpets, trays, and more. Collection is facilitated by imposing deposits and having reverse-deposit machines.
An example where this is not done, but I believe should be, is with Styrofoam clamshells that are sometimes used by fast-food chains for hamburgers. These can be readily identified, collected, and cleaned, and the polystyrene can be profitably recycled to make useful products. However, the practice has largely been abandoned, primarily because of public pressure, driven largely by the misconception that replacing them is more environmentally favorable. This illustrates the need to better educate the public.
There are cases where recycling is not feasible. For example, the economics of dealing with thin plastic bags is doubtful. Customers can be encouraged to use fewer of them by bringing their own bags and by charging for the plastic ones. Improper disposal results in pollution problems, so making them from degradable plastics is an option. The economics of this option must be compared with the possibility of disposal in trash-to-energy facilities, since the plastic has fuel value that is lost when the bags degrade. This option also meets with public objection, however, when such facilities are related to polluting incinerators. Here again, one must show that it is possible to economically have state-of-the-art facilities that do not pollute.
By Richard S. Stein
I enjoyed the article “Old Plastics, Fresh Dirt.” It would be great if someone could make a biodegradable cigarette filter—one that would decompose within 60 days in the presence of sunlight and/or moisture. Anyone who has ever participated in roadway or beach cleanups knows that the most common form of litter is cigarette butts. They are not only unsightly, but they are harmful to the fish and birds that ingest them.
By Wayne H. Martin
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