Effect of metal stearate antacid on the melt stabilization performance of phenolic/phosphite antioxidants in metallocene LLDPE. Part 1: Melt processing stability

The influence of metal stearates on the melt stabilization performance of combinations of phenolic and phosphite antioxidants in a metallocene LLDPE (mLLDPE) has been investigated. This study focused on the effect of both the origin of the stearine blend (i.e., vegetable or animal) used in the formation of the metal stearates and the type of metal stearate (i.e., calcium and zinc stearate). A multiple extrusion experiment was carried out and melt stabilization performance was monitored by melt flow rate (MFR) measurements. The level of consumption of antioxidants was evaluated by HPLC analysis of solvent extracts. Although antagonism was observed with all formulations containing metal stearates, a noticeably greater detrimental effect was apparent with metal stearates based on the vegetable derived stearine blend. Furthermore, it was apparent that the vegetable zinc stearate had a greater detrimental effect than the calcium stearate equivalent. The presence of impurities such as peroxides and metal oxides in the metal stearates investigated was believed to account for the antagonism observed. J. Vinyl Addit. Technol. 10:137–143, 2004. © 2004 Society of Plastics Engineers.