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Additive interactions in the stabilization of film grade high‐density polyethylene. Part I: Stabilization and influence of zinc stearate during melt processing
Author(s) -
Parrondo Aitor,
Allen Norman S.,
Edge Michele,
Liauw Christopher M.,
Fontán Eusebio,
Corrales Teresa
Publication year - 2002
Publication title -
journal of vinyl and additive technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.295
H-Index - 35
eISSN - 1548-0585
pISSN - 1083-5601
DOI - 10.1002/vnl.10349
Subject(s) - zinc stearate , stearate , zinc , chemistry , extrusion , melt flow index , polyethylene , polymer , high density polyethylene , antioxidant , low density polyethylene , organic chemistry , decomposition , chemical engineering , polymer chemistry , materials science , copolymer , composite material , raw material , engineering
The melt stabilization activity of some of the most commercially significant phenolic antioxidants and phosphites (alone and in combination), without and with zinc stearate, was studied in high‐density polyethylene (HDPE) produced by Phillips catalyst technology. Multiple pass extrusion experiments were used to degrade the polymer melt progressively. The effect of stabilizers was assessed via melt flow rate (MFR) and yellowness index (YI) measurements conducted as a function of the number of passes. The level of the phenolic antioxidant remaining after each extrusion was determined by high‐performance liquid chromatography (HPLC). Phenolic antioxidants and phosphites both improved the melt stability of the polymer in terms of elt viscosity retention; the influence of zinc stearate was found to be almost insignificant. However, phosphites and zinc stearate decreased the discoloration caused by the phenolic antioxidants. A correlation was found between the melt stabilization performance of phosphites and their hydroperoxide decomposition efficiency determind via a model hydroperoxide compound. Steric and electronic effects associated with the phosphorus atom influenced the reactivity towards hydroperoxides. Furthermore, high hydrolytic stability did not automatically result in lower efficiency. Besides phosphite molecular structure, stabilization activity was also influenced by the structure of the primary phenolic antioxidant and the presence of zinc stearate.