Page 430 - Solid Waste Analysis and Minimization a Systems Approach

408 PLASTIC AND RUBBER MANUFACTURING

rubber products manufacturing subsector because the core technologies for these
activities are diverse and involve multiple materials.
Within the plastics and rubber products manufacturing subsector, a distinction is
made between plastics and rubber products at the industry group level, although it is
not a rigid distinction, as seen from the definition of industry 32622, rubber and plas-
tics hoses and belting manufacturing. As materials technology progresses, plastics are
increasingly being used as a substitute for rubber; and eventually, the distinction may
disappear as a basis for establishing classification.
The simplest definition of a polymer is something made up of many units. Polymers
are chains of molecules. Each link of the chain is usually made of carbon, hydrogen,
oxygen, and/or silicon. To make the chain, many links, are hooked, or polymerized,
together.
To create polymers, petroleum and other products are heated under controlled
conditions and broken down into smaller molecules called monomers. These
monomers are the building blocks for polymers. Different combinations of monomers
produce plastic resins with different characteristics, such as strength or molding
capability.
Plastics can be divided into two major categories: thermosets and thermoplas-
tics. A thermoset is a polymer that solidifies or sets irreversibly when heated. They
are useful for their durability and strength, and are therefore used primarily in
automobiles and construction applications. Other uses are adhesives, inks, and
coatings.
A thermoplastic is a polymer in which the molecules are held together by
weak bonds, creating plastics that soften when exposed to heat and return to
original condition at room temperature. Thermoplastics can easily be shaped and
molded into products such as milk jugs, floor coverings, credit cards, and carpet
fibers.
Plastic resins are processed in several ways, including extrusion, injection
molding, blow molding, and rotational molding. All of these processes involve
using heat and/or pressure to form plastic resin into useful products, such as con-
tainers or plastic films.

31.2 Waste Management Goals

and Opportunities

The majority of solid waste generated by this sector is mixed plastics and mixed
office paper. Table 31.1 displays the composition breakdown based on survey
results.
As shown in the table, the recycling rate for this sector is approximately 37 per-
cent. As derived from the solid waste evaluation model discussed in Chap. 12, the