Morphological changes in annealed ultrahigh molecular weight polyethylene (UHMWPE) gel‐films

X‐ray diffraction of the UHMWPE gel‐films has shown that high heating rate annealing of the films causes deformation of the crystallites. The apparent crystal sizes change with the annealing temperature (Ta). With Ta below 110°C, the dimensions of the crystallites in c‐axis (Lc) increase associated with the decreasing in a‐axis (La) and b‐axis (Lb), but the changes are small because of the higher energy barrier. When Ta is raised to 138°C, Lc is nearly doubled its value at 60°C whereas Lb increases and La remains unchanged. IR spectral subtraction was applied to reveal the morphological changes of the gel‐films upon annealing. It has been found that bands of the same type of conformation have different sensitivities subject to the thermal treatment at different annealing temperatures. The results can be understood by assuming the changing process being completed through chain segments sliding along the (020) sectors.