Processing of Plastics And Materials used for plastic processing

Most plastic resins have to be combined, compounded or otherwise chemically treated with processing materials before they are ready for processing. Thorough mixing of ingredients is vital for all classes of polymers and special equipment has been developed for the purpose. One of the following additions are usually employed.

1. Plasticizers :

Organic Solvents, resin and even water are used as plasticizers. These substances act as internal lubricants improving flow of and giving toughness and flexibility to the material. Plasticizers are also used to prevent crystallization by keeping the chains separated from one another. For example vinyl are generally hard and brittle materials. By adding a plasticizers they can be made soft and flexible.

2. Fillers :

Typical fillers which include wood flour, asbestos fiber, glass fiber, cloth fiber, mica, slate powders, may be added in high proportions to many plastics essentially to improve strength, dimensional stability and heat resistance.

3. Catalyst :

These are usually added to promote faster and more complete polymerization. As such they are also called accelerators and hardeners.

4. Initiators :

As the name indicates , the initiators are used to initiate the reaction, i.e., to allow polymerization to begin. They stabilize the ends or reaction sites of the molecular chains. H2O2 is a common initiator.

5. Dyes and Pigments :

Pigments and dyes, when added, give plastics their brilliant colors. The coloring is important as it provides sales appeal. The colorants must be able to disperse evenly throughout the molten plastics and must have heat stability.

6. Blowing agents :

A plastic resin such as polystyrene is foamed by injecting a inert gas (nitrogen/argon) before the molten material is forced into the mold. The process creates a porous interiors. The familiar disposable cups are examples.

7. Modifiers :

The modifiers are added to improve mechanical properties / characteristics of the base resin.

8. Antioxidants :

Anti oxidants added to plastics provide resistance to ultraviolet rays. They also impart melt-flow retention for easy molding.

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Mechinopedia For Mechanical Engineers

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