THE TEXTURE OF POLYETHYLENE PRODUCED BY γ-RAY IRRADIATION POLYMERIZATION WITH STIRRING

Abstract

The effect of stirring on the polymerization of ethylene induced by γ-irradiation in a gaseous phase was studied with regard to the morphological features and the physical properties of resultant polymer. The melting temperature, the heat of fusion, the density and the content of CH₃ groups of the polymers formed were independent of the stirring speed, but the specific surface area of the material showed a minimum in the range of 200-500 rpm. Similarly, the viscosity-average molecular weight showed a minimum at a speed of ca. 200 rpm. GPC molecular weight distributions showed double peaks which is characteristic of low-temperature polymerization product. The higher molecular weight species increased with increased stirring speed. The fibrillar morphologies observed under a scanning type electron microscope increased drastically with increased stirring speed. Close inspection of these fibrils revealed that many nodese fibers were produced by a partial unfolding of molecules in the lamellar crystals. It is likely that the increase of fiber-like structures leads to the increase in the specific surface area of the resultant polymers, so that the number of contact of long-lived radicals in the resultant polymeric solid with monomers increases, giving rise to the chain growth and the grafting, which produces long chain branches, and consequently the polymerization rate is accelerated.