Photodegradation of natural rubber latex by singlet oxygen generated from methylene blue

Methylene blue undergoes decomposition upon the exposure to ultraviolet (UV) light and oxygen to release reactive species such as singlet and triplet oxygen. These reactive species have adequate energy to oxidise and degrade organic materials including natural rubber (NR). In this work, NR latex was exposed to UV in the presence of methylene blue and hydrogen peroxide to produce low molecular weight NR latex. The Mn of NR was reduced from 544 × 103 g/mol to about 6 × 103 g/mol with low gel content. During the photodegradation, the NR chain was cleaved at both C = C and C-C bonds. The molecular structure of LNR was similar to that of the NR but with new functional groups of hydroxyl and carbonyl, resulting from oxidation and chain cleavage. The rubber particles were originally pear-shaped but changed to spherical after the degradation reaction, although their size remained largely similar.