ABSTRACT
Mechanical degradation of polymers, in its broader sense, comprises a large field, covering fracture phenomena as well as chemical changes
0·5 1·0 Mn/Mn,o
Fie· 8..22. Ultrasonic degradation of PS in toluene solution at ambient temperature. Average MW versus time of irradiation. Polymer concentration
induced by mechanical stress. Because of their macromolecular structure, plastics possess in many respects rather unique physical properties that account for their utilization as raw engineering materials for various purposes. Nevertheless, there exist load limits, i.e. the plastics engineer has to be aware of the loading capacity and of the fact that under permanent mechanical stress plastic materials might exhibit a behaviour quite different from that encountered with metals and other mineral raw materials [8.1). Some data obtained during the study of mechanical degradation of a few polymers are given in Table 8.16 and Figs 8.19-8.22.
