THE EFFECT OF MULTIPLE EXTRUSION PASSES DURING RECYCLING OF HIGH-DENSITY POLYETHYLENE

High density polyethylene blow modling resins have been identified as a primary material for solid waste minimization and recycling. An expe rimental study into the effect of multiple extrusion cycles on the pro perties of a virgin homopolymer, virgin copolymer, natural post consum er, and mixed color post consumer blow molding resin was conducted. Rh eological properties such as shear and elongational viscosity and elas tic modulus were studied in the context of changes experienced during recycling. The G'-G '' (elastic storage and loss modulus) crossover po int was used to measure relative changes in the polydispersity index a nd molecular weight distribution (MWD). It is also shown that extrudat e swell and sag change after multiple extrusion passes. Environmental stress crack resistance was also measured. A rationale for the signifi cant decrease in the environmental stress crack resistance of the virg in copolymer resin is presented. The results are analyzed in terms of known degradation mechanisms such as chain scission and crosslinking, and their relationship to the molecular structure. (C) 1997 John Wiley & Sons, Inc.