Microscope investigations of extension and fracture in crystalline polymers

Thin films of polyethylene, polyhexamethyleneadipamide, polypropylene, and polyoxymethylene have been examined under the microscope during the application of a tensile stress. The response to stress in each case varies with the thermal history of the sample, and indeed this variation correlates closely with the size and type of spherulites formed during sample preparation. The particular behavior of each polymer has been described. In general, it is found that extension of the polymer under stress is usually possible if the spherulites are sufficiently small. In these four cases, long annealing brings about spherulitic growth and a brittle structure which fractures without extension when tension is applied.