A Study of Thiol Based Bound Antioxidants in Acrylonitrile-Butadiene Rubbers

Abstract

Thiol containing antioxidants, 3,5-di-tertiary-buty1-4-hydroxybenzyl
mercaptan (BHBM), 4-anilinophenylthioglycollamide (PAPT) and 4-anilinophenylthiopropionamide (PPPT) have been successfully bound
to acrylonitrile-butadiene rubber (NBR) by a free radical process
in the latex and during processing.

Under optimum conditions, latex masterbatches and solid masterbatches of the bound thiol antioxidants were prepared and were used as additives for unstabilised NBR latex and normal solid NBR. The concentrations of bound antioxidants have been estimated by infra-red spectrophotometry.

The effect of bound antioxidants on the behaviour of vulcanisates
has been investigated using the Monsanto oscillating disc rheometer.
PAPT and PPPT increased the rate of cure and cross-link density while
BHBM reduced the latter.

Conventional oxygen absorption, oven ageing and stress relaxation
measurements and in addition a cyclic oil/air test specifically
designed for nitrile rubber, in which the mechanical properties were
measured, have been used to evaluate the effectiveness of the bound antioxidants before and after extraction with an organic azeotrope. For comparison the effectiveness of commercially available copolymerised antioxidant, N-(4-anilinophenyl) methacrylamide and a high molecular weight partially polymerised antioxidant, 2,2,4-trimethy1-1, 2-dihydroquinoline, were also investigated. The result
showed that, although the bound antioxidants retained much of their
activity after extraction, the antioxidants behaved differently in
different tests. The performance of the thiol based bound antioxidants
particularly PAPT, is better in the cyclic oil/air test.

Mechanistic studies showed that the antioxidant activity of thiolamides, PAPT and PPPT, involves synergistic chain breaking catalytic peroxide decomposition mechanisms

Date of Award	1981
Original language	English
Awarding Institution	Aston University