Reversible long-period change during the annealing of crystalline polymers

Abstract

Abstract A large reversible change in small-angle X-ray diffraction spacing and intensity in both bulk and drawn polyoxymethylene is found for samples carried through a heating and cooling cycle. The diffraction measurements were made at the annealing temperatures. The reversible changes are in addition to the more usual irreversible changes found during annealing experiments in which the scattering is measured at room temperature. Upon recycling the same sample, the changes can be almost completely reversible. Similar reversible changes are not observed for polyoxymethylene single crystals but are observed for drawn polyethylene terephthalate and nylon 6.