Melt flow hinder with additive

Processing stabilization of polyethylene is usually done by a combination of phenolic and phosphorous antioxidants. A phosphate stabilizer used in the absence of a phenolic antioxidant imparts very low oxidative stability to polyethylene. When hindered phenols are used in combination with phosphites or phosphonites, the melt flow behavior during processing and the thermo-oxidative stability of the polymer improve significantly. Fearon et al. [17] attributed the positive effect of phenolic antioxidants to their interaction with peroxides. The trivalent phosphorous additives often help to improve the color of polymers [18-21]. 

Alkyl and aryl phosphite esters are also effective melt stabilizers. They are often used in combination with hindered phenols to give highly efficient melt stabilizing systems and to reduce discoloration of the polymer because of the oxidation products of the phenols present. Phosphites (particularly those derived from aliphatic alcohols and unhindered phenols) are, however, generally susceptible to hydrolysis. Consequently, moisture-sensitive phosphites affect adversely the handling characteristics (i.e., flow properties) of the additive package and are a source of other problems corrosion of metal surfaces, formation of dark colored spots, and gel formation. In practice, hydrolysis-resistant phosphites based on sterically hindered phenols are used, e.g., AOs 17 and 18, Table 1. 

---