Influence of Crosslinking Method on the Properties of Natural Rubber Mixtures

The most important stage in the rubber processing technology is vulcanization / crosslinking, which confers mechanical and thermal stability to rubbers. During crosslinking, rubber molecules with chain configuration are linked by chemical bridges / bonds, and the rubber mass turns from its plastic mass into an elastic one. This is normally done by sulphur and accelerator for general purpose rubbers. The chemistry of vulcanization is complex and the resulting crosslinks may be mono-, di-, tri- or higher poly-sulphides, with a proportion which is among others largely determined by the vulcanization system, the cure time and the temperature. These compounds and their reaction products could be responsible for cytotoxicity and allergy-causing compounds, such as nitrosamines and nitrosatable materials. For these reasons, the aim was to eliminate or reduce toxic ingredients in elaborating and developing crosslinking technologies for natural rubber mixtures, so that the resulting materials may be used in the pharmaceutical or food industry, as well as in manufacturing other rubber goods (toys, various components for footwear, rubber plates, seals and hoses for various purposes, etc.). This paper presents a study on the influence of the vulcanization method on the characteristics of a natural rubber blend. The tested methods have been: (1) with sulphur and vulcanization accelerators, (2) with benzoyl peroxide in the presence of a polyfunctional monomer. Modification of characteristics was analysed depending on the crosslinking method.