BREAKTHROUGH CHEMISTRY FOR PROCESSING STABILIZATION OF POLYPROPYLENE

Abstract

Traditional stabilization systems for polypropylene are typically based on a binary combination of a phenolic antioxidant and a phosphorus based melt processing stabilizer. The phenolic antioxidant provides melt processing stability as a hydrogen atom donor and free radical scavenger; it also provides the polymer with some desired level of short-term or long-term thermal stability, simply for storage or throughout the lifetime of the final article. The phosphorus based melt processing stabilizer, usually a phosphite or phosphonite, functions as a hydroperoxide decomposer above the melting point of the polymer, during melt compounding and processing. Both chemistries work together synergistically to help maintain the original molecular architecture of the polymer. Recently, a new class of additives, 3-aryl-benzofuranones (lactones) has been introduced and adopted commercially. Lactones are highly efficient at scavenging both carbon and oxygen centered radicals during melt processing of polyolefins. Investigations have been underway to examine the impact of low concentrations of lactone in regard to enhancing the performance of traditional stabilization systems. The presumed stabilization mechanism of a lactone and the optimum composition of ternary stabilizer blends for polypropylene are discussed.