Generally, the greater the number of plastic components in a blend, the poorer are its properties. Few products are currently being manufactured from recycled multi-material plastics, although limited ways do exist to improve the mechanical properties of products made from mixed plastics. While recycling of composite plastics is currently extremely limited, when recycled, such plastics might be used to make landscaping lumber, farm animal pens, roadside posts, industrial pallets, marine pilings, benches, and picnic tables. The lack of any significant recycling of this material reflects the current need to subsidize such activity to be cost-effective. In 1988, that amounted to 180 million tons.
Plastics are synthetic materials consisting of molecules called polymers.
The polymers that make up plastics are derived from petrochemicals, as compared to natural polymers such as cellulose, starch, and natural rubber. The synthetic polymer that constitutes plastics is a large molecule consisting of a long chain of chemically linked subunits called monomers.