Effect of metal stearate antacid on the melt stabilization performance of phenolic/phosphite antioxidants in metallocene LLDPE. Part 2: Discoloration

The first part of this series of papers indicated that the melt stabilization performance of phenol/phosphite/metal stearate combinations in metallocene LLDPE (mLLDPE) was influenced by the purity of the fatty acid salt. In this second part, it is shown that the quality of the metal stearate has a direct influence on the discoloration of the aforementioned formulations in the melt state. On the basis of the peroxide and oxide impurity levels in the metal stearates (Part 1), it is suggested that discoloration is directly related to the formation of oxidative transformation products of the phenolic antioxidant. Furthermore, it was observed that the calcium stearates discolored upon aging in air at processing temperatures, while zinc stearates did not. Such discoloration is believed to be partly due to the combination of high levels of conjugated systems consisting of unsaturation and carbonyl groups formed during aging. J. Vinyl Addit. Technol. 10:144–148, 2004. © 2004 Society of Plastics Engineers.