Chapter 6: Plastics and Plastics Composites A Perspective on their Chemistry and Mechanics

6.1 Chemistry of Plastics

It can be considered that the mid 20th century into the 21st century will be known as the age of synthetics; these are plastics, man-made fibres, synthetic rubbers, sealants, caulking compounds, composite materials and synthetic adhesives. In general, the properties of plastics are intermediate between those of fibres and elastomers with many overlapping properties, so, typical plastics may have cohesive energies higher than those of elastomers but lower than those of fibres. Thus plastics exhibit some flexibility and hardness with varying degrees of crystallinity.

Completely synthetic polymers, such as Bakelite, were first produced in 1909. Chemically Bakelite is phenol formaldehyde resin produced when phenol and the gas formaldehyde are combined in the presence of a catalyst. This product is used today in certain engineering applications. Now it is possible to adapt polymers and to create new ones which can be designed for specific functions. Polymers, together with metals and ceramics represent the essential engineering materials in the construction of buildings, household articles of all kinds, vehicles, engines, etc. The main factors responsible for the rapid growth of these engineering materials are [1]:

1. The availability of basic raw materials: the sources of production are coal, oil, wood, agriculture and forest wastes

2. The ensemble of technical properties specific for polymers: lightweight, chemical stability, elasticity, etc.

3. Easy processing using techniques such as extrusion, thermoforming, injection moulding, calendering, casting, etc.