Degradation of Oil-Extended Polymers in Presence of Metal Salts

Abstract

ability of heavy metals such as copper, manganese, and iron to catalyze the breakdown of natural rubber during storage and processing is well known (ß, 8). Use is made of this effect in certain peptizing agents like ferrous naphthenate and in rubber reclaiming agents (6). In the early days of the "cold rubber" development it was feared that the ferrous pyrophosphate, present as an activator for peroxide-catalyzed polymerization recipes, would have a deleterious effect on the aging of these polymers. Synthetic polymers were proved, however, to be more resistant to degradation during aging (4, 7), and production has been successful for almost 7 years.These polymer types, when produced to high viscosity and extended with oil, are much more susceptible to raw polymer breakdown during processing in the copolymer plant and in storage than the normal unextended cold rubbers (9). This undesirable degradation has occurred mainly where relatively highiron, sugar-free recipes are used for the polymerization of the parent polymer. When the polymerization recipe is a sulfoxylateactivated type of very low iron content, deterioration of Sundex 53-extended product during drying and subsequent storage, for as long as 12 months, is negligible. The effect of heavy metals, especially iron, in promoting the breakdown of polymer-oil masterbatches was studied in the pilot plant. EXPERIMENTAL of latex solids. This masterbatch was heated to 100°to 120°F. and stirred continuously during the coagulation process. For several experiments, ferrous sulfate heptahydrate and/or complexing agents were added to the latex before masterbatching.Coagulation was effected at 110°F. by adding the oil-latex masterbatch with agitation to 4% sodium chloride serum at pH 5 to 6. The pH was maintained at 5 to 6 during the coagulation by the addition of 0.5% sulfuric acid. After the precipitation was essentially completed, the pH of the slurry was reduced to 4.0 by the addition of more acid, and leaching was continued for 30 minutes at, 100°to 110°F. for soap conversion. Various metal salts were added to the dilute coagulating acid to determine their relative effects on the heat softening of the crumb during the drying cycle. After the leaching, the serum was decanted, replaced with water at 100°to 110°F ., and stirred for 20 to 30 minutes. The water was then decanted and the washing repeated, using fresh water. Finally, the crumb was spread on a tray and loaded into a circulating air oven dryer. LITERATURE CITED