Effect of smoking on lipids content, macromolecular structure and rheological properties of Hevea brasiliensis sheet rubber

Natural rubber ribbed smoked sheet (RSS) production process involves a drying step in a wood smoke dryer. The purpose of this work was to know whether this smoke drying step affected the lipid composition and the properties of sheet rubber. This study consisted of a comparative study between unsmoked sheets (USS) and ribbed smoked sheets (RSS) obtained from monoclonal latices from RRIM600, BPM24 and PB235 clones. The rubber was sampled in Chantaburi province, Thailand. It was found that the smoking process increased significantly the amount of lipid extract but decreased significantly the free fatty acid content. No significant effect of smoking was detected on macromolecular parameters such as gel content or molar mass distribution and on rheological parameters such as initial plasticity (P0) and Mooney viscosity (ML(1+4)100). In terms of resistance to thermal oxydation estimated by Plasticity retention index (PRI), smoked sheets displayed a tendency to have lower PRI than unsmoked sheets. This difference was significant for PB235 clone. A clonal effect was detected for most of the measured parameters. Indeed, PB235 clone displayed a higher lipid extract, higher P0, higher ML(1+4)100, higher molar mass than those of the other studied clones while its PRI was lower. (Résumé d'auteur