Question

What are the additives mixed with plastics for its compounding? Explain their functions.

Answer 1

By using different types of additives the properties of the base polymer may be modified in very many different ways so that the range of use of the polymer is extended.
The main compounding ingredients are:
1. RESINS.
2. PLASTICIZERS.
3. FILLERS or EXTENDERS.
4. LUBRICANTS.
5. PIGMENTS.
6. CATALYSTS.
7 STABILIZERS.

There functions are as follows:
• RESINS.
1. It is the binder which holds the various constituents together.
2. It determines which method of moulding is to be used. Resin part of the finished product
may be 30-100 %.

• PLASTICIZERS.
1. Increases the flexibility of the plastics.
2. Imparts flame proofness.
3. Reduces resistance towards chemicals, solvents etc.
4. Examples:- vegetables oils, esters of fatty acids.

• FILLERS or EXTENDERS.
1. Reducing the cost of plastics.
2. Increases the tensile strength and hardness.
3. Reduces the flexibility.
4. Examples:- mica, saw dust, chalk etc.

• LUBRICANTS.
1. Imparts glossy finish.
2. Prevent sticking to plastic to the mould
3. Example:- waxes, soaps.

• PIGMENT
1. They provide colour to the final plastic material.
2. Dyes give transparent colours and pigment gives opaque ones.
3. Examples :-organic and inorganic dyes stuffs.

• CATALYST
1. They are added to only thermosetting plastic. They accelerates the rate of polymerisation.
2. Examples:- H₂O₂
, Zn, ammonia and its salts.

• STABILIZERS.
1. In order to prevent the decomposition and discolouration of the plastic at the moulding
temperature , stabilizers can be used
2. Examples:- stearates of Pb, Ca , Ba, Pb silicates etc, PbCr O₄