RADIATION-INDUCED CROSS-LINKING .3. EFFECT ON THE CRYSTALLINE AND AMORPHOUS DENSITY-FLUCTUATIONS OF POLYETHYLENE

Small-angle x-ray scattering (SAXS) was used to determine density fluctuation in radiation-induced crosslinked polyethylene of varying degrees of crystallinity. Density fluctuation FL decreases with increasing crystallinity, while it increases linearly with increasing radiation dose or degree of crosslinking. By means of extrapolation, density fluctuations in the crystalline and the amorphous phases FL(c) and FL(a) were obtained. At a given dose, FL(a) is greater than FL(c). The increase in FL(a) with radiation is found to be much greater than that of FL(c) compared with the initial values at 0 Mrad, FL(c) showing only a negligible increase even at 312 Mrad. The present findings suggest that crosslinks are not introduced within the crystalline phase; they take place primarily in the noncrystalline phase, in agreement with the conclusions reached previously on the basis of changes in crystalline and amorphous densities in irradiated polyethylene.