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Element distribution maps from Hevea brasiliensis natural rubber latex thin films were obtained, by electron energy-loss spectroscopic imaging in a low-energy (80 kV) transmission electron microscope. C, N, O, P, Na, Ca, Mg, Al, Si, and S maps are presented for latex fractionated by centrifugation, either followed by dialysis or not. Most elements forming non-carbon compounds are concentrated in small, electron-dense spots surrounded by a carbon-rich matrix of polymer, thus showing that the rubber is filled with small particles compatible with the polyisoprene matrix. Ca distribution is unique, since it closely parallels the C distribution, evidencing an important role for -COO(-)-Ca2+-COO- ionic bridges in the structure of natural rubber.

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A borracha natural é obtida da Hevea brasiliensis, uma árvore nativa da floresta amazônica. Ela tem tido grande importância econômica há mais de 150 anos, sendo uma rica fonte de aprendizagem sobre polímeros e materiais poliméricos. Suas notáveis propriedades e vantagens sobre borrachas sintéticas atraíram a atenção de muitos pesquisadores que identificaram várias singularidades estruturais. Hoje, está claro que a borracha natural é um complexo material nanoestruturado, formado por poli(cis-1,4-isopreno), proteínas, fosfolipídios e vários componentes minerais minoritários. A contribuição dos autores para esta aprendizagem está resenhada neste artigo e abriu o caminho para o desenvolvimento de novos nanocompósitos, usando processos suaves e "verdes", dentro de um novo paradigma para a fabricação de materiais derivados de fontes renováveis. Natural rubber is obtained from Hevea brasiliensis, a tree that is native from the Amazon forest. It has been economically important for the past 150 years and it has also been a rich source of learning on polymers and polymeric materials. Its outstanding properties and advantages over synthetic rubbers have attracted the attention of many researchers that unraveled many contributing factors. Now, it is clear that natural rubber is a complex nanostructured material formed by poly(cis-1,4-isoprene), protein, phospholipids and a host of mineral minor components. Contribution of the authors to knowledge on natural rubber is reviewed in this paper and it opened the way to develop a host of new nanocomposites, using mild, "green" processes, within a new paradigm for the fabrication of materials derived from renewable sources.

Recebido em 15/1/09; aceito em 12/3/09; publicado na web em 2/4/09 NATURAL RUBBER AND NANOCOMPOSITES WITH CLAY. The natural rubber is a strategic material which can not be replaced by synthetic rubber in many technological applications. Brazil is a rubber importer, but new techniques of cultivation, breeding and diversification of producing species can reverse this situation. One of the best ways to add value to this commodity is nanotechnology. The production of nanocomposites is already a reality and shows that the sustainable use of this natural resource can lead to new products and boost the national agribusiness setting labor-qualified in the field.Keywords: natural rubber; nanocomposites; sustainability. Borracha naturalA borracha natural (NR) é um polímero de poli(cis-1,4-isopreno) e apresenta propriedades únicas devido a sua estrutura intrínseca, alta massa molar e presença de outros componentes minoritários como proteínas, carboidratos, lipídios e minerais presentes no látex. Cerca de 2500 plantas produzem látex, mas o látex da Hevea brasiliensis se constitui na única fonte comercial importante de látex de borracha natural.