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    Abstract

Changes in the Micro-Structure and Tensile Properties of Peroxide Prevulcanised Natural Rubber Latex Films during Thermal Oxidative Ageing
D. Dazylah, M.S. Ma'zam and M.Y. Amir Hashim

The effect of ageing on tensile properties and micro-structure of peroxide prevulcanised natural rubber latex (PPVL) films (with and without antioxidant Irganox 1520®) was studied. The modulus of peroxide prevulcanisates containing Irganox 1520® generally decreased with increasing ageing time at 100ºC. However, there appeared a cyclical increase and decrease of modulus at about one hour intervals over the 0-12 hours ageing time studied. FTIR analysis of films showed evidence of oxidative reaction in aged films whereby the relevant FTIR peaks of natural rubber, C=CH2 at 845 cm-1 and polyisoprene peak at 2958 cm-1, 1576 cm-1, 1470 cm-1, 1126 cm-1 and 845 cm-1, weakened gradually with ageing time. The observation was supported by an NMR study which showed appearance of extra peaks in the spectra, identified as belonging to the relevant degradation products. As the ageing process progressed, the NMR analysis showed a film with a minimum line broadening measure the hydrogen percentage calculated from NMR (H%), indicating a high polymer chain mobility, corresponding to high tensile strength with a modulus at 300 (M300) value of about 0.85 MPa. Transmission Electron Micrographs (TEMs) of unaged peroxide prevulcanised natural rubber latex films showed a mesh of stained network surrounding white domains, whilst aged films tended to show a more distinct staining over the entire surface of the particles. However, this phenomenon was not observed in films protected by Irganox 1520® antioxidant.

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