Polymer degradation by crazing and its study by small angle scattering techniques

Abstract

Craze formation and breakdown in polymers is reviewed with particular emphasis on the study of crazes by small angle scattering techniques. Small angle scattering, particularly when combined with information obtainable from transmission electron microscopy, has proved to be a powerful technique for the study of crazes. The existence of the three different radiations, X-rays, neutrons and electrons, has helped both in the interpretation of the basic form of craze scattering patterns and in permitting the study of a broad range of problems. X-ray scattering is particularly useful for the acquisition of information on crazes in bulk samples, this information being valuable to test and refine the models of craze formation and growth. The intensity of X-rays from synchrotron sources has permitted the study of such failure processes as mechanical fatigue and impact in real-time. Neutron radiation has proved useful in the study of environmentally-induced crazes while electron radiation is used for the examination of crazes in thin films. The majority of the work on crazing has been done in single phase amorphous polymers, particularly polystyrene and polycarbonate, but the rubber toughened styrenics, in which crazing is an important toughening mechanism, offer a fruitful field of study. It is in these latter systems, where intense crazing is seen, that impact processes can be studied by small angle scattering. Crazing and microcracking in semicrystalline polymers has also been examined by this technique but the lack of a clear picture of the morphology of the scattering entities has made small angle scattering less fruitful here than in amorphous polymers.