This study was carried out with five rubber clones planted in Cô te d'Ivoire from the first tapping up to the 18th month of tree tapping (1 tapping/4 days). Changes in the natural rubber native mesostructure (macromolecular structure, macrogel, and microgel) of films prepared from fresh field latex were monitored. At the same time, the evolution of the thermooxidation sensitivity of raw rubber samples [grade 10 technically specified rubber (TSR10)] was also monitored with the plasticity retention index (PRI). The substantial initial macrogel rate (70 -86%, depending on the clone) fell during the first 18 months of tree tapping to reach a few percent. However, during the same period, the initially low microgel rate (5-15%) increased and then remain stabilized around 55% rubber. The macromolecular structure [weight-average molecular weight (M w ) and molar mass distribution (MMD)] also changed after tree opening. M w increased and stabilized after 7.5 months of tapping. The bimodal MMD primarily involved short chains (molar mass Ͻ 400 kg/mol) at the opening of the trees. The TSR10 samples, prepared with latex from virgin trees, showed high PRIs and, therefore, low sensitivity to thermooxidation.

The mineral composition of the insoluble (macrogel) and soluble fractions of two natural rubber (NR) samples made from the latex of two different clones (RRIM600 from Thailand and GT1 from Côte d'Ivoire) was determined using inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS results showed that mineral elements were concentrated in the macrogel. The major mineral elements found in macrogel were phosphorus, magnesium, potassium, and sulfur. Some mineral elements were mostly concentrated in micron-sized mineral aggregates, visible at the surface of the samples using scanning electron microscopy coupled with an energy dispersive X-ray microanalyzer (SEM/EDX). The nature of these mineral aggregates was found to be highly variable. Their inhomogeneous distribution in the macrogel indicates that these aggregates do not have a major influence on macrogel structure. (Résumé d'auteur

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