according to polymer type, and a uniform identification system has been agreed to by the industry to aid segregation by the consumer. Reprocessing of comingled waste leads to poor physical properties. Compatibilization may be technically possible, but it is quite expensive in relation to the value of the products produced. On the other hand, some plastic products appear to be easily recycled. For example, poly(ethylene terephthalate), which is used for soft drink bottles, is easily identified and is usually relatively free of contamination. A number of ways of reusing these materials have been identified, and some are in use. Perhaps the most significant are those that cause the polymer to revert chemically to oligomeric species that can be repolymerized into poly(ethylene terephthalate) or other polymeric products.
While innovations in polymer recycling are needed, other options must also be pursued. Opportunities include source reduction and design of products with recycling in mind. The potential value of biodegradable polymers as part of the solution to the solid waste and litter problem needs to be better understood. Such materials are likely to be much more expensive than the relatively inexpensive polymers currently used, and their performance may not be as good. It is not clear that any materials biodegrade in landfills. In any case, the release of the low-molecular-weight degradation products into the environment could lead to more serious air or water contamination concerns. Incineration for fuel value is another, and perhaps the ultimate, form of recycling of polymers. Most polymers are derived from oil, and about 95 percent of all the oil produced is burned for its energy value; thus oil converted into polymers is simply being borrowed for a while to be used as a material prior to returning to its ultimate fate of being burned for its energy. Of course, concerns about the impact of incineration on health and the environment need to be resolved.
Polymer interfaces are key to the performance of composites, blends or alloys, lubricants, adhesives, coatings, and thin films. Advances in the fundamental understanding of these interfaces and methods to engineer desired performance of these surfaces will no doubt lead to improved products and a competitive edge.
New engineering plastics, including some blends or alloys, with ever-increasing performance characteristics continue to be introduced and in many cases are being used for structural applications traditionally dominated by other materials, mainly metals. Ease of fabrication into dimensionally precise parts with high-quality surface finish is one driving force.
For polymer-based materials being used in highly critical structural applications, there is need for a better understanding of the mechanical, chemical, and environmental factors that affect their useful lifetimes and for methodologies to predict lifetimes in complex situations. Fracture mechanics techniques are not yet used to the same extent for polymers as for other structural materials.
There are opportunities for new polymer systems with controlled permeability properties for use in food packaging, medicine, clothing, agriculture, industrial