ABSTRACT

Composite materials are most often thought of consisting of fibres embedded in a polymer matrix. The attraction of polymers for the role of the matrix is that they are light in weight, often with a density little more than that of water and they can be used, either in solution or molten, to impregnate the fibres at pressures and temperatures which are much lower than those which would be necessary for other materials, for example metals. A disadvantage of polymers as matrix materials are that they do not provide high-performance mechanical properties at right angles to the fibre directions which makes unidirectional composite materials inherently anisotropic. A group of resins, which can be both thermosetting or thermoplastic, are known as thermostable resins. Elastomers can be seen as a lightly crosslinked thermosetting type material operating above its glass transition temperature. Polyimides can be thermoplastic but are more usually used as thermosetting resins.