REACTIVE PROCESSING OF LLDPES IN COUNTERROTATING NONINTERMESHING TWIN-SCREW EXTRUDER .3. METHODS OF PEROXIDE ADDITION

An ethylene-octene linear low-density polyethylene (LLDPE) was treated with peroxide in a reactive extrusion system. A counterrotating nonin termeshing twin-screw extruder (System 2) was contrasted with a corota ting intermeshing twin-screw machine (System 1). In System 2, the pero xide solution was pumped into the melted polymer, while it entered wit h the polymer pellets in the feed section of System 1. Molecular struc ture changes and the theological behavior of peroxide-modified resins are similar in both operations but System 2 is much more effective. Mu ch lower peroxide levels were needed in System 2. However, reactions i n this setup were also more difficult to control. The presence of micr ogel was clearly evident in System 2 products but not in those made in System 1. The results of such reactive extrusion processes depend cri tically on the method of the peroxide feed and mixing conditions. Reac tion conditions that favor optimum economy and peroxide efficiency are those which may compromise product homogeneity. (C) 1996 John Wiley & Sons, Inc.