Network degradation accompanying the vulcanization of natural rubber with a sulfur–diphenylguanidine system

Sol fraction and swelling values have been determined for a series of natural rubber–sulfur–diphenylguanidine vulcanizates. These data have been analyzed in terms of the Charlesby and Pinner gel network formation theory with a view to estimating the amount of permanent molecular chain scission accompanying the vulcanization. It is concluded that negligible chain scission occurs before the point of modulus reversion of these curves. In the region of cure reversion, permanent molecular chain scission does occur to a small extent. The principal factor responsible for cure reversion in this vulcanizate is crosslink scission. Chain scission is responsible for only about 3–8% of the observed cure reversion.