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 different monomers.

Q. Abbreviations for Common Polymers?

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:

Extrusion
Blow-moulding
Injection moulding
Calendering
Thermoforming
Rotational moulding
Compression moulding
Casting.

Q. Are plastics biodegradable?

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, polycarbonate, etc.

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