004 Improving Processability of Linear Polyethylenes by Radiation-Induced Long Chain Branching
Lewis Parks, Song Cheng, and Ed Phillips: Sterigenics Advanced Applications, 7695 Formula Place, San Diego, CA 92121-2418
E-Mail: lparks@sterigenics.com
Abstract
Long chain branching (LCB) was induced on carefully selected grades of high density and linear low density polyethylenes by electron beam irradiation under ambient conditions at controlled, relatively low radiation doses. Although there was little or no crosslinking, the molecular weight distribution became wider after irradiation. The melt flow index of these polymers decreased significantly with increasing radiation dose. However, differences in melt flow index changes were observed with other irradiated polyethylenes, most likely because of differences in the polyethylene base resins, including additives, manufacturing processes, and types of copolymers. The melt strength of the irradiated polymers from selected grades as measured by the Rheotens method was greatly enhanced. Meanwhile, the melt viscosity at low shear rate was higher after irradiation. Because of LCB, these rheological properties in the irradiated polymers provide both strain hardening at high extensibility and sag resistance at low shear rate to bring about significant improvement of processability for certain polymer converting processes, such as film blowing. Preliminary film blowing trials confirmed the processability improvement.
Keywords: polyethylene, radiation, long chain branching, melt strength, processability