Estudo da influência da composição química nas propriedades da borracha natural dos novos clones de seringueira RRIM 711, RRIM 926 e RRIM 937

Abstract

Brazil, that already was the largest producer of natural rubber in the world, faces a deficit in its production, what has resulted in the necessity to research of clonal varieties of rubber trees with high quality and productivity adapted to different areas. In view of this scenario, this study sought to evaluate the chemical composition and as properties from natural rubber of the new clones the effect of the coagulation method on the latex clones RRIM 600 and RRIMM 937 and the influence of the non-rubber constituents soluble in acetone in properties of plasticity Wallace (P0) and plasticity retention index (PRI). The samples were evaluated by physical-chemical, thermal and rheological tests of: DRC, TSC, particle size distribution and Zeta potential, FTIR, NMR, determination of macro and micronutrients by ICP-OES, acetone extract content, ash, nitrogen content, Wallace plasticity, plasticity retention index, Mooney viscosity, thermogravimetry, DSC and rheological behavior. From the obtained results a variance analysis with repeated measures and tests of multiple comparisons was made to evaluate the behavior of the clones in relation to the plots and the collections. Pearson's correlation was used to evaluate the correlations of the variables. The results showed that there were more variations between the clones and the collections in the composition than in the properties. The rubber produced by the new clones presented good performance considering the standards established by the norms, except the clone RRIM 711 that presented the greatest variations in properties and lower values than the others. All clones showed uniformity in the thermal evaluation, and in the inert atmosphere the decomposition occurred in a single stage with a temperature of beginning of degradation varying between 275–280 °C and in oxidative atmosphere occurred in three stages with the temperature of beginning of degradation varying between 210–220 °C. The NMR and FTIR spectra have shown that the natural rubber structure for all the clones studied has mostly the cis-1,4-polyisoprene form. The coagulation method altered the properties of the natural rubber and the extraction of the non-rubber constituents soluble in acetone directly affected the PRI values.