Many of the containers you use are made from plastic, a synthetic organic polymer. |
Plastics
What Is Plastic?
Definition in Chemistry
Plastic Chemical Composition
QUESTION: WHAT IS
PLASTIC?
Have
you ever wondered about the chemical composition of plastic or what it is made
of?
Here's a look a what plastic
is and how it is formed.
Answer: Plastic is any synthetic or
semi-synthetic organic polymer.
While plastics may be made
from just about any organic polymer, most industrial are made from
petrochemicals.
Thermoplastics and
thermosetting polymers are the two types of plastic.
The name "plastic" refers to the
property of plasticity, which is the ability to deform without breaking.
The polymer used to make a
plastic is almost always mixed with additives, including colorants,
plasticizers, stabilizers, fillers, and reinforcements.
These additives affect the
chemical composition, chemical properties, and mechanical properties of a
plastic and also affect its cost.
THERMOSETS AND THERMOPLASTICS
Thermosetting
polymers, also known as thermosets,
solidify into a permanent shape.
They are amorphous and
considered to have infinite molecular weight.
Thermoplastics, on the other
hand, can be heated and remolded over and over again.
Some thermoplastics are
amorphous, while some have a partially crystalline structure. Thermoplastics
typically have a molecular weight between 20,000 to 500,000 amu.*
EXAMPLES OF PLASTICS
polyethylene
terephtalate - PET or PETE
high-density polyethylene - HDPE
polyvinyl chloride - PVC
polypropylene - PP
polystyrene - PS
low-density polyethylene - LDPE
high-density polyethylene - HDPE
polyvinyl chloride - PVC
polypropylene - PP
polystyrene - PS
low-density polyethylene - LDPE
PROPERTIES OF PLASTICS
The
properties of plastics depend on the chemical composition of the subunits, the
arrangement of these subunits, and the processing method.
All plastics are polymers,
but not all polymers are plastic.
Plastic polymers consist of
chains of linked subunits, called monomers. If identical monomers are joined,
it forms a homopolymer.
Difference monomers
link to form copolymers.
Homopolymers and
copolymers may be either straight chains or branched chains.
· Plastics are usually solids. They may be amorphous solids,
crystalline solids, or semicrystalline solids (crystallites).
· Plastics are usually poor conductors of heat and electricity.
Most are insulators with a high dielectric strength.
· Glassy polymers tend to be stiff (e.g. polystyrene). However,
thin sheets of these polymers may be used as films (e.g., polyethylene).
· Nearly all plastics display elongation when they are stressed
that is not recovered after the stress is removed. This is called
"creep".
· Plastics tend to be durable with a slow rate of degradation.
INTERESTING PLASTIC FACTS
· The first completely synthetic plastic was bakelite, which was
made in 1907 by Leo Baekeland. Baekeland also coined the word "plastics."
· The word plastic comes from the Greek word plastikos, which means able to
be shaped or molded.
· Approximately a third of plastic that is produced is used to
make packaging. Another third is used for siding and piping.
· Pure plastics are generally insoluble in water and non-toxic.
However, many of the additives in plastics are toxic and may leach into the
environmental. Examples of toxic additives include phthalates. Nontoxic
polymers may also degrade into chemicals when they are heated.
* An atomic mass unit (symbolized AMU or amu) is defined as
precisely 1/12 the mass of an atom of carbon-12. The carbon-12 (C-12) atom has
six protons and six neutrons in its nucleus. In imprecise terms, one AMU is the average of the proton rest
mass and the neutron rest mass.
.
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