5 Physical properties of polymers
5.1 The behaviour of polymers
The manufacture of polymer products is controlled by two often conflicting demands: the quality of the finished article in terms of its response to its environment and the ease or difficulty of processing it to shape. Both factors are controlled by what is termed viscoelasticity, namely, the behaviour of the polymer in response to applied stress or strain, and temperature. It is important to appreciate the duality in terms of the elastic and viscous responses of polymer solids and polymer melts, especially for thermoplastics used in engineering applications. For thermosets, the problems of creep and stress relaxation may be less critical (although still important), but their viscous behaviour during processing is vital for an appreciation of the limitations of moulding them to shape.