Influence of carboxylic acid additives on the flow behavior of molten thermoplastics

Following the suggestions of the behavior of carboxylic acid lubricants between steel surfaces and the wide usage of such acids in polymer compounds, we have considered their influence as an additive in polymer melts. An experimental study of the influence of carboxylic acid additives in various thermoplastics in rheometers is described. Capillary and cone-plate experiments are reported. A series of polymers of varying polarity, including polyethylene, poly(propylene), polystyrene, poly(methyl methacrylate), and polyamide-12, are compared. Both aliphatic fatty acids and aromatic carboxylic acids were used as additives. The aliphatic fatty acids include propionic acid, octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, commercial stearic acid (mixture of tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, and octadecanoic acid). The aromatic carboxylic acids include benzoic acid, p-toluic acid, and 3-phenylpropionic acid. The greatest effects were found with polyethylene and poly(propylene). Little or no effects were found with the other polymers. Aliphatic fatty acids were more effective than aromatic carboxylic acids. Mechanisms for this behavior are discussed. (C) 2003 Wiley Periodicals, Inc.