RADIATION-INDUCED CROSS-LINKING .2. EFFECT ON THE CRYSTALLINE AND AMORPHOUS DENSITIES OF POLYETHYLENE

Small-angle x-ray scattering (SAXS) was used to determine the structural changes in polyethylene induced by radiation. The changes in densities of the crystalline and amorphous phases, rho-c and rho-a, were calculated after direct determination of the mean square density fluctuation < eta-2 >. rho-a increases with increasing radiation dose for both linear and branched polyethylene. This accounts for the serious discrepancy between crystallinities determined from wide-angle x-ray scattering and density measurements. This study confirms our previous proposal that crosslinks occur primarily in the noncrystalline phase, most likely at the defects in the lateral grain boundary regions.