Explain in brief Compounding of plastics

Mumbai University > First Year Engineering > Sem1 > Applied Chemistry 1

Marks: 5M

Year: Dec 12, May 2015

1 Answer

Plastic are manufactured synthetically using raw materials mostly from natural gas and petroleum, or from coal mines, forest coal mines, forests, farms, and paper textile mills.

Compounding of plastics include –

Binders, Fillers, Pigments or dyes, Catalysts, Lubricants,Stabilizers

  1. Binders- binders hold other constituents together during manufacturing. Usually natural or synthetic resins are used as binders, which are high molecular weight substances. Binders influence the properties of plastics. The type of the treatment during moulding operation also depends upon binders. If binders used has comparatively low molecular weight, then plastic article gets moulded easily and vice versa.

  2. Fillers- fillers impart better tensile strength, hardness, finish, workability, opacity etc. to the plastic material. The percentage of filler varies with types of plastic. The highest percentage can be up to 50% of the total moulding mixture. The fillers which are added only to improve the mechanical strength of the plastic are known as reinforcing fillers. They reduce shrinkage and brittleness. They also cost of the plastic per unit weight. The fillers May be of organic or inorganic origin.

  3. Pigments/Dyes – these impart desired color to plastic. Organic dyestuffs and inorganic pigments are used for this purpose in small proportion.

  4. Catalysts- these are used to increase the rate of polymerization of fusible resin binder to form cross linked infusible form during moulding operations. Generally thermosetting plastics involve use of catalyst, normally an acids or basic catalyst depending upon the type of thermosets. They are added in small quantities. Commonly used catalysts are hydrogen peroxide, benzoyl peroxide, metallic oxides etc.

  5. Plasticizers- these help to increase the plasticity of the plastics. Plasticizers are essentially used in thermosoftening plastics. They are added to the extent of 8-10% of the total bulk of plastic. Plasticizers are not used in thermosets; they are added in thermosoftening resins only. It increases flexibility. The plasticizers used are normally liquids and hence only disadvantage is, if they are not consistent, they ooze out in finished product.

  6. Lubricants and stabilizers - lubricants help during moulding operations, especially during low or room temperature moulding. The use of lubricants imparts flawlessness, and glossy finish to the plastic products. Commonly used lubricants are soaps, or esters of fatty acids such as oleic and stearic acids or waxes. Stabilizers help improve stability of the plastic besides impart rigidity.

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