Trace levels of mechanochemical effects in pulverized polyolefins

This research investigated the structural changes that occur on different p olyethylene polymer systems as a result of a novel pulverization process ca lled solid-state shear pulverization ((SP)-P-3). High-density polyethylene, low-density polyethylene, and two forms of linear low-density polyethylene were run through a pulverizer under high shear conditions as well as low s hear conditions. The physical properties were examined before and after the pulverization via melt index, melt rheology, GPC, and DSC, techniques. The low shear pulverization did not noticeably alter the physical properties o f the polymers. In contrast, high shear pulverization did result in an incr ease in viscosity as observed by melt index and oscillatory shear experimen ts, although solid-state and bulk properties as observed by DSC and GPC wer e not affected. These results indicate that a small amount of mechanochemic ally induced changes occur as a result of the pulverization process, includ ing incorporation of a small amount of long-chain branches randomly placed on a few of the polymer chains. No evidence of short-chain branching result ing from (SP)-P-3 processing was found in these systems. (C) 2001 John Wile y & Sons, Inc.