Q. What is a "Polymer"?
Ans. The word Polymer comes from
the Greek "poly" meaning many, and "meros",
parts or units. A polymer is a group of many units. You combine
many monomers (one unit) to create a polymer.
Polymer is often used as a synonym for "plastic", but
many biological and inorganic molecules are also polymeric. All
plastics are polymers, but not all polymers are plastics. Plastic
actually refers to the way a material melts and flows.
Commercial polymers are formed through
chemical reactions in large vessels under heat and pressure. Other
ingredients are added to control how the polymer is formed and
to produce the proper molecular length and desired properties.
This chemical process is called "polymerization".
A homopolymer results from polymerizing
only one kind of monomer. A copolymer results from using different
monomers. Homopolymers have the same repeating unit while copolymers
(which can be random, block, or graft) can vary have different
numbers of repeating units. A terpolymer results from using three
for Common Polymers?
Q. Different Properties of Polymers?
Ans. Polymers are characterized in many ways -
by chemical or physical structure, by strength or thermal performance,
by optical or electrical properties, etc.
Most textbooks will give qualitative and some quantitative data
on polymer properties. Properties can vary widely however, between
manufacturers, for different performance grades, due to additives
and reinforcements, or other reasons. For more precise data, contact
a representative from a polymer producer, compounder, or distributor
for a spec sheet on a particular material and grade. Often grades
are offered to suit the needs of specific types of applications.
Properties of interest typically include:
Strength (Tensile and Flexural)
Modulus (Tensile and Flexural)
Heat Deflection Temperature
VICAT Softening Temperature
Glass Transition Temp
Melt Flow Index
Melting Point, No-flow Temp
Shear Rate/Viscosity Relation
Compressibility (Pressure/Volume/Temperature Relation)
Surface and Volume Resistivity
Flame Resistance (UL Rating)
Composition (Neat, Blended, Filled)
Q. What is the difference between
Polymers and Plastics?
Ans.Most Polymers need some additives
before they can be used as plastics. The proportion of additives
can vary from as low as 300 ppm (0.03%) (Oleamide in LDPE) to
as high as 75% (Plasticisers in PVC).
Some other materials when
compounded with polymers change their properties substantially.
In fact, at times they have properties markedly different from
those of either the polymer or additives e.g. Carbon fibre reinforced
nylon/polyurethane fibre reinforced polyester resins. Talc in
the thermoplastic polyester.
Q. How Plastics
are formed into useful items?
Ans. The single most important property
of plastics is the change that they undergo on heating.
Some plastics can be softened by
heating and will then harden again on cooling. This cycle of softening
and hardening can be repeated many times without any appreciable
change in the properties. Such plastics are termed THERMOPLASTICS.
There is the other class of Plastics
which soften on heating and if kept at that temperature for some
time, harden irreversibly. That is, such products cannot be softened
by further heating. This type is called THERMOSETTING. In thermosetting
materials, chemical reaction takes place during heating and crosslinks
are formed between adjoining chains.
Heat causes the polymer molecules
to turn flexible and if the crosslinks were not formed, the process
could be repeated any number of times.
On the above thermal property depends
the processing of plastics i.e., formation of useful articles.
The various processing techniques include:
Q. Are plastics
Ans. Yes, certain biodegradable
plastics are available. Only trials have been made in India. No
commercial quantities are available as yet.
To carry this topic further,
it may be said that biodegradable plastics will not on their own
solve plastics refuse problem. For example, 20 year old rubbish
dumps when opened up showed half eaten hamburgers and pastries
which could be recognised in that shape.
Q. Are plastics recycleable?
Ans. Yes, almost all thermoplastics
can be recycled. Thermosets are not recycled in the conventional
sense. These can be ground and used as fillers in other plastics.
Q. What are composites?
Ans. These materials consist of
two descreet phases. A fibrous phase surrounded by polymeric resin.
The resin matrix allows stress to be transferred from one fibre
to another. Thus a consolidated structure results which has the
properties of a uniaxially drawn fibres.
Typical reinforcing fibres are
- glass, carbon or organic fibres.
The matrix may be thermoset or thermoplastics,
e.g., unsaturated polyester resin, epoxies (Araldite), nylon,
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