Thursday, 21 January 2016

Constituents of plastics

The principal constituents of plastics are:
  1. Resins or Binders
  2. Plasticizers
  3. Fillers
  4. Lubricants
  5. Stabilisers
  6. Catalysts or Accelerators
  7. Pigments or Dyes

(i) Resins or Binders: The resins are the basic binding materials in plastics, which holds the other constituents of the plastics. The resign determines the moulding method. Cellulose material or synthetic polymers are used as resigns. These are of two types they are thermo plastics and thermo setting. These two types of resigns differ in thermal nature so they require different treatment methods.

(ii) Plasticizers: The chemical compound that improves the plasticity and flexibility of resign is called as plastisizers. Camphor increases the surface hardness, trybutyl phathalate increases the toughness. Plastcizer should be chemically inert, non-volatile and non-toxic.
Commonly used plasticizers include non-drying vegetable oils, camphor, esters of oliec, aluminium stearates, and trybutyl phathalate.

(iii) Fillers: These material added to resin to enhance performance, mechanical properties and reduce manufacturing costs. These additives are used to make polyester resin more chemical and corrosion resistant, act as a fire retardant, enhance shrink-resistance and be thermally stable, as well as capable of withstanding weather conditions. These are powder, fibrous and laminated fillers.

(iv) Lubricants: Lubricants makes the moulding of the plastic easier giving a flawless and glossy finished product. Lubricants also prevent the plastic material from sticking to the moulding equipment.
Common lubricants are Mosallic soaps, Stearates, oils and waxes.

(v) Stabilizers: The thermal stability of the resin is enhanced by the addition of a stabilizer.
Transparent moulding components such as stearic acid salts of lead, Cadmium and Barium also used as stabilizers.

(vi) Catalysts: Catalyst accelerates the chemical reaction. These compounds also act as hardeners and accelerators. These are required only in the case of thermo setting resigns in order to accelerate the polymerization reaction and form highly cross linked finished product. Hydrogen peroxide, copper, lead and zink is used as catalyst.

(vii) Pigments: Colourants such as pigments and organic dyes are added to give required color to the finished product.

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