23 – Mechanochemical Degradation

Degradation caused by mechanical actions such as rolling and calendering have been well known in rubber technology for a long time and much work has been done in this area. Most of the research carried out has been for practical purposes and phenomenological in approach. Not only rubbers but most commercial polymers are subjected to violent mechanical actions, such as extruding and pressing, during processing, so degraded polymer molecules may be present in the final products when in use. No particular attention is paid to the damage which might be induced in polymers during mechanical processing. Polymeric materials used for practical purposes experience various types of mechanical destruction: one extreme of mechanical action results in fracture of the material as a whole; at the other extreme are friction or surface scratches, which represent mechanical destruction from a molecular point of view. Although mechanical fracture of polymeric materials has been one of the major research subjects studied from both academic and practical viewpoints, most work has ignored chemical considerations and adopted a purely physical approach, for example estimation of tensile strength or trials to increase the strength of materials. Only a little work has been done for the purpose of obtaining an insight into the molecular mechanisms of mechanical fracture.