What is Plastic?

What is Plastic?

Plastics are synthetic polymers that are made of long interwoven polymer chains. Each polymer chain is composed of many repeating “mer” units. Each “mer” unit is usually made of carbon, hydrogen, oxygen and/or silicon, by polymerization, the “mer” units are joined together to form a long polymer chain. Differences in “mer” units cause plastic to have various properties. The arrangement of polymer chains can affect the physical properties of a polymer.

There are two different ways of arranging polymer chains. First by quenching the polymerization process, polymer chains can not arrange themselves in certain orientation therefore forms a random amorphous arrangement. Amorphous polymers are generally transparent and are used in many applications that require transparency.
Second by controlling cooling rate of the polymerization process, polymer chains can arrange themselves into distinct patterns; crystalline regions are then produced. The higher the degree of crystallinity, the less transparent the polymer is. Translucent and opaque polymers generally have a larger portion of crystalline arrangement.

Plastics are divided into to groups, thermoplastics and thermosets. Polymers with amorphous arrangements are generally thermoplastics. Thermoplastics soften when heated and harden when cooled. These processes are totally reversible and can be repeated. Thermosets become permanently hard when heat is applied and degenerates upon subsequent heating.

Plastics’ versatility allows it to be used in many aspects of our lives. From car parts to space shuttle, from food packaging to kitchenware, plastics made our lives easier and better. Some attributes of plastic material made plastics so commonly used
1. Plastics can be very resistance to chemicals.
2. Plastics can be both thermal and chemical insulators
3. Plastics are light weight with different degree of strength
4. Plastics can be processed in many ways to produce intricate parts

PETE
Name: Polyethylene Terephthalate (PET or PETE)
Properties: Clear, high use temperature, good moisture barrier, heat resistance, tough, microwave transparency
Comes as: Plastics wrap and dinner trays; peanut butter, beverage, and mouthwash bottles
Recycled to make: Furniture, carpet, clothing fibers, beverage containers

HDPE
Name: High Density Polyethylene (HDPE)
Properties: Good moisture barrier, good chemical resistance
Comes as: Milk and juice bottles, detergent containers, trash and shopping bags
Recycled to make: Drain pipes, recycling bins, detergent bottles, plastics lumber

PVC
Name: Polyvinyl Chloride (PVC)
Properties: Good long term stability, good strength, good transparency, stable electrical properties, good chemical resistance, good weatherability
Comes as: Shampoo bottles, clear food packages, medicine tubes and toiletry
Recycled to make: Speed bumps, mats, decks, packaging, paneling, binders

LDPE
Name: Low Density Polyethylene (LDPE)
Properties: Good flexibility, good transparency, good toughness, easy to melt
Comes as: Squeezable bottles, frozen food or bread bags
Recycled to make: trash liners, furniture, trash cans, lumber, floor tiles, mailing envelopes

PP
Name: Polypropylene (PP)
Properties: High melting point, good chemical resistance
Comes as: Ketchup, medicine, and dairy product containers
Recycled to make: storage bins or trays, ice scrapers, bike racks, brooms, brushes, car battery components, signal lights

PS
Name: Polystyrene (PS)
Properties: Rigid: hard, brittle, clear. Foam: good thermal insulation, lightweight
Comes as: meat trays, egg cartons, plates, CD jackets, food service items, packing foam
Recycled to make: egg cartons, vents, office supplies, foam packing and containers, insulation, thermometers

Other
Nylon, ABS copolymer, Polymethyl Methacrylate (PMMA)

Plastic recycling

Most plastics can be recycled. Thermoplastics can be collected and remolded into other things while thermosets decompose when reheated and thus unrecycleable. Due to varying chemical and physical properties of different plastics, they generally can not be mixed when recycling. Today, most plastics can not be economically retrieved in sufficient quantities to support recycling. Two kinds of plastics, PET and HDPE have the largest and most steady supply.

Plastic is considered to be an extremely effective material to recycle for two reasons:
· The constantly increasing in demand of more plastics in our everyday products. Therefore the supply of recycling plastics and demand of recycled plastics will increase.
· Most plastics do now break down with recycling. With the recycling process, the strands do not shorten and consequently does not reduce the strength.