X-ray diffraction studies of the crystallinity in polyethylene terephthalate

An x-ray diffraction method is described for the determination of per cent crystallinity in oriented films and fibers of polyethylene terephthalate by using an x-ray diffractometer in association with a scaler counter. Results are presented to show that sample rotation approximately averages out the crystallite orientation effects. Results are presented on per cent crystallinity and specific volume of a number of films and fibers of polyethylene terephthalate possessing different degrees of crystallinity. A linear specific volume-x-ray crystallinity correlation is found. Extrapolation to zero and 100% crystallinity gives values of specific volume for amorphous and crystalline polyethylene terephthalate in good agreement with the measured specific volume of amorphous polymer and the specific volume calculated from the x-ray crystal structure analysis made by Bunn2 for crystalline polyethylene terephthalate.