What is Plastic
and how it made of
Photo: Internet
Plastic is derived from natural, organic materials
such as cellulose, coal, natural gas, salt and of course crude oil. Crude oil
is a complex blend of thousands of compounds and must be processed before it
can be used. The production of plastic begins with the distillation of crude
oil in an oil refinery. This separates the heavy crude oil into groups of
lighter components, called fractions. Each fraction is a mixture of hydrocarbon
chains (chemical compounds consisting of carbon and hydrogen) that differ in
the size and structure of their molecules. One of these fractions, naphtha, is
the essential compound for the production of plastics.
Two
main processes are used to produce plastics - polymerization and
polycondensation - and they both require specific catalysts. In a
polymerization reactor, monomers such as ethylene and propylene are bonded
together to form long polymer chains. Each polymer has its own properties,
structure and size depending on the different types of basic monomers used.
There
are many different types of plastics and they can be grouped into two main
polymer families:
Thermoplastic
(which is softened by heating and then hardens again by cooling).
Thermosetting
substances (which are never softened once cast).
Examples of thermoplastic
Acrylonitrile
butadiene styrene (ABS)
Polycarbonate
(PC)
Polyethylene
(PE)
Polyethylene
terephthalate (PET)
Polytetrafluoroethylene
(PTFE)
Polyvinyl
chloride (PVC)
Polymethyl
methacrylate (PMMA)
Polypropylene
(PP)
Polystyrene
(PS)
Expanded
polystyrene (EPS)
Examples of thermosets
Epoxide
(EP)
Phenol-formaldehyde
(PF)
Polyurethane
(PUR)
Unsaturated
polyester resins (UP)
The composition, structure and
properties of the plastic
Many
of the chemical names of the polymers used as plastics have become familiar to
consumers, although some are better known by their abbreviations or trade
names. Thus, polyethylene terephthalate and polyvinyl chloride are commonly
referred to as PET and PVC, while foamed polystyrene and polymethyl
methacrylate are known under their trademarked names, Styrofoam and Plexiglas
(or Perspex).
Industrial
manufacturers of plastic products tend to think of plastics as either
"raw" resin or "special" resin. (The term resin originates
from the early years of the plastics industry; it originally referred to
naturally occurring amorphous solids such as shellac and rosin.) Raw materials
are high-volume, low-cost plastics for the most common disposable items and durable
goods. They are mainly represented by polyethylene, polypropylene, polyvinyl
chloride and polystyrene. Special resins are plastics whose properties are
tailored to specific applications and which are produced with low volume and
higher cost. Among this group are the so-called engineering plastics or
engineering resins, which are plastics that can compete with die-cast metals in
the plumbing, hardware and automotive industries. Important technical plastics,
less known to consumers than the above-mentioned commercial plastics, are
polyacetal, polyamide (especially those known under the trade name nylon),
polytetrafluoroethylene (trademark Teflon), polycarbonate, polyphenylene
sulfide, epoxy and polyetheretherketone. Another member of the special resins are
thermoplastic elastomers, polymers which nevertheless have the elastic
properties of rubber can be molded repeatedly after heating. Thermoplastic
elastomers are described in the article elastomer.
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