Answer:

Compounding of Plastics

In order to impart certain definite properties to the finished product, plastic is compounded with other ingredients. These ingredients are known as additives. The selection of additives and the operation of mixing them with the polymer constituent is known as compounding.

The various additives added are as follows:-

1. RESIN (Binders)

• The main purpose of a binder or a resin is to hold the different constituents of plastic together.
• The binder used maybe natural or synthetic or cellulose derivatives.
• They determine the type of treatment required for fabrication of plastic.
• Binders are of two types: Thermoplastics and thermosetting.

• Eg: Thermoplastic: PE, PP, PVC; Thermosetting: Urea and phenol formaldehyde.

   

        2. FILLERS

• Fillers are added to plastics in order to reduce the cost of plastics, improve hardness, improve shrinkage on setting and brittleness, improve solvent resistance.

• The most common fillers are carbon black, calcium carbonate, calcium sulphate.

   

        3. REINFORCEMENTS

• They are added mainly to improve the tensile and flexural strength properties of the plastic material. Most of them are in the fibrous form.

• Typical reinforcing materials available as fibers are glass, asbestos, boron, carbon, ceramic.

• Recently, synthetic fibres of nylon, polyehtylene and acrylonitrile have also been used.

   

        4. FIRE RETARDANTS

• Plastic compounds may also contain components that improve the fie resistance of the end product.

• The most commonly used are compounds containing halogen, derivatives of antimony, boron, nitrogen and phosphorous.

   

        5. COLORANTS

• Colorants are added to give color to the plastic material.

• They improve the appearance of the plastic material.
• Usually dyes are employed for brilliant transparent effects in clear plastics such as polystyrene.
• Carbon blacks are an important group of pigments that also function as fillers and are good UV light stabilizers.