Effect of microorganisms during the initial coagulum maturation of Hevea natural rubber

The involvement of microorganisms in the initial stage of maturation of natural rubber coagula was assessed with five latex treatments that varied in the initial quantity of microorganisms; the treatments ranged from latex added with an antimicrobial agent (3.4 _ 104 CFU/mL) to strongly inoculated latex (2.4 _ 107 CFU/ mL). After 0-6 days of maturation, the obtained rubber was characterized with respect to its physical and structural properties. The Wallace plasticity (P0) and plasticity retention index (PRI) remained constant during maturation with the antibiotic-added treatment. PRI decreased with the maturation time, and the rate was proportional to the initial microorganism concentration. P0 of all inoculated rubber increased for the first 2 days of maturation and decreased after 6 days of maturation. With respect to structural parameters, a higher initial microorganism content corresponded to a higher gel content and a lower weight-average molar mass after maturation, drying, and storage. The inoculated rubber showed a stable value for the number-average molar mass (Mn), in contrast to the noninoculated samples, for which an increase in Mn during maturation was observed. The quantity of microorganisms significantly affected the physical properties and structure of the processed dry rubber. The mechanisms occurring during the initial stage of maturation are complex, and microorganisms are involved not only in the increase in sensitivity to thermooxidation but also in the crosslinking phenomenon between isoprene chains. (Résumé d'auteur