Rubber Compound Modifications To Minimize the in-Rubber Chemical Degradation of Polyester Cord in Truck Tires

Abstract

Chemical degradation of polyester cord becomes a significant factor in truck tire performance at the high operating temperatures gener ated in severe test conditions. Many rubber chemicals needed to achieve good physical properties in the skim compound play a major role in poly ester degradation. A heat aging test to simulate high temperature tire test ing was developed. The alkyl amines produced by many common acceler ators have been identified as the main polyester degradants. The rate of polyester degradation is dependent upon the activity of the accelerator, which are ranked in decreasing order thiurams, some dithiocarbamates, guanidines, sulfenamides, thiazoles and phosphoryl disulfides, the latter two being essentially innocuous. While adequate rubber physical properties cannot be achieved with a thiazole cure, addition of zinc dibutyl dithio carbamate as a secondary accelerator essentially produced the physical properties of a sulfenamide cure, but without the reactivity to polyester. In another approach, in-rubber filler and amine scavengers have been used to reduce polyester chemical degradation. The rubber polymer blend deter mines the rate of water and amine migration out of the tire influencing their concentrations and reactivity with polyester.