Standardization Program on Shelf Aging of Natural and Synthetic Rubber Materials

摘要

Test specimens made from butadiene-styrene, buna N, natural rubber and neoprene were subjected to shelf aging and low temperature conditioning for periods up to 7 years while in packaged and unpackaged states. Following the aging period, the tensile strength, elongation, tensile product, modulus at 300% elongation, swelling ratio, compression set and stress relaxation of the specimens were determined. Tensile product, modulus at 300% elongation and swelling ratio were found to be the parameters which best indicated the trend in the deterioration of the elastomers. The results of shelf aging in a packaged condition were compared with the results obtained in accelerated heat aging tests, reported previously, and it was found that accelerated heat aging for 10 weeks at 140 F would cause a greater deterioration in the physical properties of butadiene-styrene and buna N specimens than shelf aging for a period of 5 years and a greater deterioration in the physical properties of natural rubber and neoprene specimens than shelf-aging for a period of 6 years. There was comparatively little additional deterioration in the physical properties of butadiene-styrene and buna N specimens despite an increase in the period of shelf aging from 1 1/2 years to 3 1/2 years and even to 5 years, and for the natural rubber and neoprene specimens despite an increase in the period of shelf aging from 2 1/2 years to 4 years and even to 6 years. Recommendations were made to increase the shelf life of end-items made from butadiene-styrene and buna N to 5 years, to reduce the shelf life to end-items made from natural rubber to 1/2 year and to increase the shelf life of end-items from neoprene to 6 years. (Author)