|GALIANI, PATRINI - Federal University - Brazil|
|MARTINS, MARIA - Embrapa|
|DE SOUZA GONCALVES, PAULO - Agronomical Institute Of Campinas (IAC)|
|MATTOSO, LUIZ HENRIQUE - Embrapa|
Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2011
Publication Date: 8/8/2011
Citation: Galiani, P.D., Martins, M.A., De Souza Goncalves, P., Mcmahan, C.M., Mattoso, L.C. 2011. Seasonal and clonal variations in technological and thermal properties of raw Hevea natural rubber. Journal of Applied Polymer Science. 122(4): 2749-2755.
Interpretive Summary: The USDA’s Domestic Natural Rubber project studies the biochemistry of rubber biosynthesis in different rubber-producing species with a focus on those crops suitable for cultivation in the United States. However, interspecific comparisons have been invaluable in the elucidation of the molecular biology, biochemistry, and botany of natural rubber biosynthesis. Our Brazilian collaborators at Embrapa, at the Agronomy Institute (IAC), Campinas - SP State/Brazil (location of experimental Hevea plantations), and at the Federal University of Rio de Janeiro bring expertise in many aspects of rubber production by the Brazilian rubber tree, Hevea brasiliensis, the primary source of natural rubber in the world today. In the example presented here we have learned that oxidative stability of rubber varies by clone and seasonally in Hevea, and that while both thermal and oxidative degradation can occur, mainly oxidative processes influenced by non-rubber constituents are probably responsible for the differences between clones. One specific clone, PR 255 produces natural rubber of higher molecular weight and less seasonal variation than others studied.
Technical Abstract: This study was undertaken over a ten-month period, under the environmental conditions within the state of Mato Grosso, Brazil, to evaluate the causes of variation in technological and thermal properties of raw natural rubber from different clones of Hevea brasiliensis (GT 1, PR 255, FX 3864 and RRIM 600). The technological properties of raw natural rubber (NR) were evaluated by: dry rubber content (DRC), Wallace plasticity (P0), plasticity retention index (PRI) and Mooney viscosity (VR). The thermal performance was evaluated using DSC and TG/DTG techniques. There were significant variations (P<0.01 and P<0.05) between clones and tappings for all technological properties, except for the %DRC among clones (not significant). PRI tests evaluated the thermo-oxidation sensitivity of raw rubber samples. Among all samples, clone PR 255 presented the highest PRI value. Clone PR 255 had a higher (4-5%) Mw, compared with GT 1, suggesting that the higher molecular weight of natural rubber leads to excellent material performance. Clone type and period of the year did not significantly influence the Tg values or thermal behavior (TG/DTG under nitrogen atmosphere) among the four clones evaluated.