A Study of Polymer Bound Sulphur Based Antioxidants in Rubber

Abstract

A commercially available hindered phenolic antioxidant,
2,6-Ditert-butyl phenol has been converted into a mercaptan
derivative, viz. 3,5-Ditert-butyl-4-hydroxy benzyl mercaptan
and the latter has been successfully bound to natural rubber
by a free radical process. Reaction parameters such as
mode of initiation, initiator concentration, mercaptan
concentration, time, temperature etc., have been investigated
in rubber solution, in natural rubber latex, and in
the polymer melt. A masterbatch technique has been developed
to saturate a small quantity of rubber with a large
amount of mercaptan and to use this concentrate to dilute
untreated latex to obtain a desired level of stability.
Infra-red spectroscopy has been used to estimate the concentration
of adduct phenol, and accelerated ageing tests, viz.
oxygen absorption and continuous stress relaxation were
carried out to evaluate ageing behaviour. The effects of
the presence of 3,5-Ditert-butyl-4-hydroxy benzyl mercaptan
on the vulcanization characteristics have been investigated
in detail using a Monsanto Rheometer.
To investigate the mechanism of addition, a number
of mercaptans and simple unsaturated model compounds have
been used and the products have been analysed. The effect
of the presence of antioxidant bound rubber on the oxidation
of polypropylene was studied by a rapid flowing air oven
test.
An attempt to add 3,5-Ditert-butyl-4—-hydroxy benzyl
mercaptan to a saturated polymer, polythelene, was unsuccessful
as theoretically expected.
Oxidation of an unsaturated compound, tetralin, was
studied in the presence of monosulphides which are similar
to those obtained by adding mercaptans to olefins.

Date of Award	1976
Original language	English
Awarding Institution	Aston University