in part on starch. These materials are often water sensitive and may offer a way to produce biodegradable polymers. Such materials would be more susceptible to composting than most synthetic polymers, but their properties appear to be limited. In principle, polymers that degrade at controlled rates are possible, but the logistics of their use can be a problem. In addition, if degradable polymers are mixed with other polymers, the resulting mixture will be less satisfactory for recycling.

HOUSING AND CONSTRUCTION

Polymers have made important inroads into the construction of housing and other buildings, despite the difficult competition presented by traditional materials—such as wood, brick, stone, concrete, glass, asphalt, plaster, slate, iron, and copper—that are economical and are entrenched in terms of aesthetics, artisans' skills, and existing U.S. building codes. The market has been penetrated by synthetic polymer products, often used in combination with traditional materials, across a broad range of applications. Demonstration houses already exist in Massachusetts and New Jersey that showcase an impressive array of uses, as pointed out in the vignette "Plastic Houses."

As the acceptance of factory-built (prefabricated) structures grows, economies of scale will arise that will strongly favor the use of polymeric materials in many areas. Complicated shapes can be fabricated economically if the costly tooling can be depreciated over large numbers of copies. Synthetics offer greater uniformity than natural materials, a factor that will grow in importance as factory production increases. Further, as synthetics continue to improve, it is likely that polymers, composites, and combinations will become superior in those properties that are valued by the consumer.

Polymers have already become dominant in fabrics for household furnishings. Carpeting, draperies, and upholstery are now usually made of synthetic polymers because of their superior properties. Substitutions are also evident in appliances such as refrigerators, coffee makers, and mixers.

Progress in the use of polymeric materials in housing will probably continue to be incremental, as each application is tested on the basis of its merits with existing materials of choice. Although societal inertia is particularly large in the construction trades and housing, the movement to increased use of polymer-based materials is unmistakable.

ENERGY AND TRANSPORTATION

The United States consumes energy out of proportion to the size of its population, and a large fraction of this energy is consumed by our extensive transportation system. While rail is still significant for shipping freight, the highway network is the defining transportation mode for the twentieth century. Automobiles



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