Torsional braid analysis of antioxidant activity in elastomer systems. I. Initial studies

Abstract

AbstractThe torsional braid apparatus as originally described by Lewis and Gillham has been explored as a means of providing a quantitative measure of antioxidant activity of selected compounds when formulated with certain elastomer systems prone to oxidative crosslinking on heat aging. With this technique the time dependence of the sharp torsional modulus increase, corresponding to a change from a rubbery to a highly crosslinked state, is determined. This time dependence is taken as a measure of the rate of oxidative crosslinking in heat‐aged elastomer films coated on a fiber‐glass braid. In this manner an assessment of the activity of antioxidants can be made. To illustrate the application of this technique, two initial studies will be cited. In one study the relative protective effect on a carboxylated styrene‐butadiene latex system of a series of antioxidants was found to be in the following order: α, α′‐2,6‐bis(2‐hydroxy‐3‐tert‐butyl‐5‐methylphenyl)xylenol > the reaction product of nonylated paraethylphenol and formaldehyde > crude 2,2′‐methylene bis(6‐nonylparacresol). In another study, with cis‐polybutadiene as the elastomer, the effectiveness of a series of antioxidants was found to be in the following order: 2,2′‐methylene bis(6‐tert‐butyl paracresol) > 1,3,3,5‐tetramethyl‐1‐m‐tolylindane‐4′,6‐diol > 4,4′‐methylene bis(2,6‐di‐tert‐butylphenol). In addition, the effect of concentration and temperature was studied with the most efficient antioxidant in this last series.