Solution

Vulcanisation of Rubber - Natural rubber becomes soft at high temperature (>$$335$$ K) and brittle at low temperature (<$$283$$ K) and shows high water absorption capacity.
The process of vulcanisation includes heating of raw rubber with sulphur and an appropriate additive at temperature range between $$373$$ K to $$415$$ K. Sulphur foms crosslinks at reactive sites of double bonds and thus, rubber gets stiffened.