Effect of polymerization catalyst technology on the melt processing stability of polyethylenes, Part 3: Additives blends performance

Abstract

This article considers the interaction between additives that occur during the stabilization process. The simultaneous effects of the additives and associated interactions on melt processing stability and processing discoloration were of particular interest. Melt stability is an important factor to consider because physical changes in the processed polymer can occur during the compounding and fabrication steps. Furthermore, discoloration is one of the most important problems affecting commercial polymers. Most discoloration manifests itself as yellowing, especially in the case of polyolefins. Although yellowing can often be associated with degradation processes caused by various agents, such as light or heat, this is not always the case; yellowing can also be due to the interaction of additives in the stabilizer packages. Blends of primary antioxidants (AOs), secondary AOs, and hindered amine light stabilizers have been studied with the intention of further improving stabilization performance together with cost reduction of the stabilized polymer. Although synergism between AOs and a stabilizer is fairly common, antagonism was also observed in terms of melt flow protection and in color stability in some of the AOs tested. The effects of a range of thermal and light stabilizers on the melt stability (investigated via multiple pass extrusion) and color stability of three different polyethylenes (PEs) were examined. The PEs varied in terms of the catalyst system used to synthesize the polymers and included a high‐density polyethylene (HDPE) produced by using a chromium‐based Phillips catalyst and two linear low‐density polyethylenes (LLDPEs) produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The apparent lack of influence of polymerization catalyst system on the mode of stabilizer interaction should lead to the reassessment of stabilizer formulation strategies in relation to PE type/catalyst system and associated commercial/economic considerations. J. VINYL ADDIT. TECHNOL., 22:117–127, 2016. © 2014 Society of Plastics Engineers