The changes in network structure and fracture mode of unfilled and filled natural rubber vulcanizates, during ageing at 100°C have been studied by chemical analyses and scanning electron microscopy. The fall in properties during ageing is caused mainly by chain scission. The increase in crosslink density during the initial periods of ageing causes an increase in modulus and tensile strength. Carbon black accelerates ageing, probably by surface catalysis. The simple network structure of efficiently vulcanized rubber results in better retention of properties during ageing. Antioxidant retards ageing. The extent of degradation of vulcanizates is reflected in the nature of the fracture surfaces. The roughness of the tensile fracture surface is affected to varying degrees depending upon the ageing resistance of the vulcanizates. However, in tear, the mode of fracture propagation is affected by ageing. © 1983.
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