Abstract
The morphological changes of polymer crystals during isothermal annealing are usually observed in the medium of air. Single crystal mats of polyetylene (unfractionated) used here were annealed isothermally in xylene for various times. The treated samples were quenched in 0°C methanol and dried in vacuo at room temperature.
The observations of weight loss, long period, molecular orientation and melting point for dried samples were compared with those of the mats annealed directly in air, as a function of treating temperature aT and time-interval ta. The main results obtained are as follows;
(1) At the temperature below Ta=90°C, the weight losses of dried samples were not detectable, where the long spacings of the samples also remained unchanged on the small-angle X-ray pattern like that of untreated original one. It was assumed that xylene acted only as swelling agent for polyethylene at considerably low temperatures.
(2) Upon increasing the temperature higher than Ta=92°C, the weight losses of dried samples became more noticeable, at the approach of Ta=100°C loss-isotherms levelled off after few minutes. In these stages the dissolved polymers recrystallized rapidly at the surfaces of the remaining crystals. It was interesting to note that the small-angle diffraction patterns of the samples treated at Ta=92°C (ta=10min.) or Ta=95°C (ta=1min.) showed coexisting of two long periods corresponding to the initial and the increased new thicknesses.
(3) At the temperature between Ta=92°C (ta<600min.) and 100°C (<10min.), the characteristic phenomena on WAXS patterns for the dried samples were that the orientations remained unchanged, and those on DSC thermograms were that the single sharp melting peaks were preserved during the fusion of samples.
