Some Low Temperature Properties of Elastomers

Abstract

A modification of the apparatus employed in measuring the Young's modulus of elastomers at low temperatures is described. The changes made in the apparatus permit the use of a simplified technique which can be adapted to routine testing procedure. The effects of various softeners on the low temperature bending moduli and the brittle point temperatures of stocks based on four butadiene‐acrylonitrile (B/A) type copolymers are given. It is shown that the softeners tested have the same relative effects in all four types and that a wide variation in low temperature properties is imparted to the stocks by the different softeners. Bending modulus curves and brittle point temperatures are given for typical test stocks based on Thiokol FA, and ``mass'' and ``emulsion'' polymerized polybutadiene. It is shown that continued exposure to low temperature affects the Young's modulus of some but not all typical vulcanizates. Data are presented showing this effect on an uncured Hevea gum stock held at 0°C. Certain softeners have been found to induce time effects in one of the B/A type stocks, which exhibits no crystallization, and hence no progressive stiffening in the absence of the given softeners. A method for measuring and evaluating creep under dead load at low temperatures is presented. Accompanying data indicate that in the case of those stocks tested, the creep constant defined reaches a maximum at a definite temperature which is a characteristic of the given stock.