Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-20 GTBL042-Callister-v3 September 21, 2007 19:48

796 • Chapter 20 / Economic, Environmental, and Societal Issues

Table 20.1 Recycle Codes, Uses of the Virgin Material, and Recycled Products for Several

Commercial Polymers

Recycle

Code Polymer Name Uses of Virgin Material Recycled Products

1 Poly(ethylene

terephthalate) (PET

or PETE)

Plastic beverage containers,

mouthwash jars, peanut butter

and salad dressing bottles

Liquid-soap bottles, strapping,

fiberfill for winter coats,

surfboards, paint brushes, fuzz on

tennis balls, soft-drink bottles,

film, egg cartons, skis, carpets,

boats

2 High-density

polyethylene (HDPE)

Milk, water and juice containers,

grocery bags, toys, liquid

detergent bottles

Soft-drink bottle base caps, flower

pots, drain pipes, signs, stadium

seats, trash cans, recycling bins,

traffic-barrier cones, golf bag

liners, detergent bottles, toys

3 Poly(vinyl chloride) or

vinyl (V)

Clear food packaging, shampoo

bottles

Floor mats, pipes, hoses, mud flaps

4 Low-density

polyethylene (LDPE)

Bread bags, frozen-food bags,

grocery bags

Garbage can liners, grocery bags,

multipurpose bags

5 Polypropylene (PP) Ketchup bottles, yogurt containers

and margarine tubs, medicine

bottles

Manhole steps, paint buckets,

videocassette storage cases, ice

scrapers, fast food trays, lawn

mower wheels, automobile

battery parts

6 Polystyrene (PS) Videocassette cases, compact disc

jackets, coffee cups; knives,

spoons, and forks; cafeteria trays,

grocery store meat trays, and

fast-food sandwich containers

License plate holders, golf course

and septic tank drainage systems,

desktop accessories, hanging files,

food service trays, flower pots,

trash cans, videocassettes

Source:American Plastics Council.

Biodegradable polymers have been synthesized, but they are relatively expensive to

produce. On the other hand, since some polymers are combustible and do not yield

appreciable toxic or polluting emissions, they may be disposed of by incineration.

Thermoplastic polymers, specifically poly(ethylene terephthalate), polyethylene,

and polypropylene, are those most amenable to reclamation and recycling, since they

may be reformed upon heating. Sorting by type and color is necessary. In some coun-

tries, type sorting of packaging materials is facilitated using a number identification

code; for example, a “1” denotes poly(ethylene terephthalate) (PETE). Table 20.1

presents these recycling code numbers and their associated materials. Also included

in the table are uses of virgin and recycled materials. Plastics recycling is complicated

by the presence of fillers (Section 14.12) that were added to modify the original prop-

erties. The recycled plastic is less costly than the original material, and quality and

appearance are generally degraded with each recycle. Typical applications for recy-

cled plastics include shoe soles, tool handles, and industrial products such as pallets.

The recycling of thermoset resins is much more difficult since these materials

are not easily remolded or reshaped due to their crosslinked or network structures.

Some thermosets are ground up and added to the virgin molding material prior to

processing; as such, they are recycled as filler materials.