ABSTRACT
The development of composites has been driven by the need for materials with a specific combination of properties beyond those obtainable from a single material. These aims can be achieved in polymers through the use of copolymers or blends, but the specific aspect that characterizes composite materials is that they are made up of distinct phases with very different physical properties. They are often, but not exclusively, found to consist of a relatively soft flexible matrix reinforced by a stiffer, often fibrous component. Sometimes, however, a softer phase is used to improve properties such as when rubber particles are added to a rigid polymer as in the case of a rubber-toughened polymer (Section 23.5). In practice, a large number of materials can be classified as being composites and nature, in particular, provides a number of celebrated examples. Wood is made up of polymeric cellulose fibres reinforcing a continuous organic lignin matrix and bone consists of collagen, a natural polymer, reinforced with a mineral phase of hydroxyapatite. The most widely studied synthetic composites are based upon polymers reinforced with stiff fibres and their use currently is increasing at the rate of 5%–10% per year across a range of different applications.
