Quality improvement and quality control of African natural rubber : Study on African natural rubber variability, additional rheological analyses with the RPA 2000

Palu Serge, Bonfils Frédéric. 2003. Quality improvement and quality control of African natural rubber : Study on African natural rubber variability, additional rheological analyses with the RPA 2000. Montpellier : CIRAD-CP, 31 p. N° de rapport : CP_SIC 1584

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Résumé : The second set of variability tests on African natural rubber (NR) revealed differences in properties between SAR 10 bales from 4 factories (in Ivory Coast and Cameroon). These differences were revealed by the conventional criteria for NR characterization (SAR standard: Wallace plasticity and Mooney viscosity) and by physico-chemical measurements ("new criteria") not specified by SAR (average molar masses, breakdown index or gel rate). The criteria used in specification standards for TSR grades (IS02000, SMR, SIR, TTR, SAR) are used to guarantee the quality of exported natural rubber batches. The criteria supplied to manufacturers to help them foresee processability are Wallace plasticity (P0), sometimes Mooney viscosity (MV) and the Plasticity Retention Index (PRI). P0, and MV depend on the structure of the raw material on different scales. PRI indicates product susceptibility to thermo-oxidation. Today, however, these criteria are not enough to predict the behaviour of natural rubber during processing, which leads to numerous problems on the production line, hence to additional costs. In order to alleviate this problem, some manufacturers add a pre-mixing stage. Using different natural rubber batches with the same P0 sometimes avoids processing problems, but cannot overcome certain incidents linked to the variability of this agricultural commodity. This is why a new approach has been proposed under the project on quality control of African natural rubber. The aim was to distinguish between SAR 10 batches from 4 African factories using new criteria: molar mass distribution (MMD), free fatty acid rates, etc. MMD is already used to characterize synthetic elastomers such as EPDMs. We have added a rheological aspect, by analysing samples with an RPA 2000 type oscillating die rheometer (Alpha Technologies company). This equipment is already widely used by numerous synthetic elastomer producers and manufacturers to more effectively predict the processability of a compound or raw rubber. The aims of the rheological study with the RPA 2000 were to: - detect correlations between the conventional technological criteria of the SAR standard and the rheological parameters obtained with the RPA 2000, - detect correlations between the "new" physico-chemical criteria and the rheological parameters obtained with the RPA 2000, - measure and assess the ability of the RPA 2000 to distinguish between natural rubbers of different origins. Before recommending the rheological approach for characterizing natural rubber with the RPA 2000, it was therefore necessary to check that it provided additional batch characterization information when compared to currently recommended instruments. This report contains the results found by the Alpha Technologies company (Mr. BURHIN) on the samples supplied, and the interpretation made by the CIRAD laboratory in Montpellier.

Mots-clés Agrovoc : caoutchouc, propriété rhéologique, mesure (activité), qualité, Viscosité, instrument de mesure, poids moléculaire

Mots-clés géographiques Agrovoc : Cameroun, Côte d'Ivoire

Mots-clés complémentaires : Caoutchouc naturel, Plasticité Wallace, Indice de rétention de plasticité

Classification Agris : Q60 - Traitement des produits agricoles non alimentaires

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