NATURAL RUBBER AND NANOCOMPOSITES WITH CLAY.

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.32381882

Elemental mapping in natural rubber latex films by electron energy loss spectroscopy associated with transmission. electron microscopy

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.74112541254

Natural rubber latex modification by sodium polyphosphate: a SPM study on the improved latex adhesion to glass sheet

Addition of sodium polyphosphate (NaPP) to natural rubber latex at 0.4 weight ratio improves the adhesion of cast latex dry films to flat glass surfaces. Rubber-polyphosphate dispersions were analyzed by turbidimetric titration, PCS and ultramicroscopy, and the results indicate the formation of two domains within the latex-polyphosphate dispersions: one domain has higher rubber particle content than the other. Thick rubber films were examined by AFM, scanning electric potential and modulated force microscopy. The images show that rubber film morphology is completely altered by NaPP addition. Two types of domains are observed in the dry latex film: one type carries excess positive charges and is harder than the other, negative domains. Both domains are compatible, as shown by the extensive interfaces observed in all images observed. In the latex-glass joints, the positive domains concentrate in the vicinity of the negative glass surface, thus making an electrostatic contribution to glass-latex adhesion. (C) 2004 Elsevier Ltd. All rights reserved.45103367337

Formation of calcium crystallites in dry natural rubber particles

In this paper, the effects of drying and aging of natural rubber particles of Hevea brasiliensis are Studied. The evolutions of the particle morphology and of the elemental distribution are investigated using electron-energy-loss spectroscopy imaging in a low-energy transmission electron microscope (ESI-TEM). It is found that when the sample is aged, calcium salt crystallites are formed around the particles. Fusion of these crystallites with time to form larger crystals shows evidence of ion mobility in the dry rubber matrix. Electron diffraction patterns and elemental mapping analysis indicate the crystals to be calcium sulfate. These crystallites are closely associated with membrane materials of the rubber particle and are surprisingly compatible with the hydrocarbon matrix of the rubber particle. It is proposed that polar sites on the membrane materials provide nucleation sites for the crystallization of calcium and sulfate ions from the latex serum. (c) 2005 Elsevier Inc. All rights reserved.288244945

Study on the formation of mesoporous molecular sieves in the presence of various anions

This work describes the mesophases obtained when mesoporous silicates are synthesized in the presence of hydrofluoric, hydrochloric, hydroiodic, acetic or nitric acids. The results show that when the silicate precursor is varied different phases or mixture of phases can be obtained. Thus pure-silica MCM-41 is obtained from sodium silicate or [(TMA)SiO2.5](8) and cetyltrimethylammonium bromide in the presence of acetic, hydrofluoric and hydrochloric acids. Hydroiodic acid affords a mixture of phases from both sources of silica after either mild thermal (347-349 K) or hydrothermal (423 K) treatments. Upon removal of the organic counterpart, MCM-41 is formed from tetramethylammonium silicate and magadiite from sodium silicate. The presence of nitric acid yields MCM-41, for sodium silicate and when HNO3 is used, for tetramethylammonium silicate, after mild thermal treatment. Upon hydrothermal treatment, MCM-41 converts to magadiife. The presence of aluminosilicate anions causes the appearance of phases mixture for nitric and hydrofluoric acids in high surfactant:silicon molar ratios. These results show that the mesophase formation might be the product of competition reactions involving the surfactant, silicate anions and the acid anions present in the reaction mixture. There seems to be a compromise between silicate and aluminosilicate charge density and basicity on the process of assembling and polymerizing (alumino)silicates species on CTA(+) arrangements. Charge density is likely to direct the choice of species that are drawn to the organo-inorganic interface: the highly charged silicate species or the aluminosilicate ones are the first assembled. The polymerization process affects the basicity of species, turning them more or less capable of competing with acid anions for the CTA(+) molecules. When acid anions bind more effectively with CTA(+), they displace silicate or aluminosilicate species and might remain in the solid as contaminating phases. (C) 1999 Elsevier Science B.V. All rights reserved.324167121122

Electrostatic Interactions: An Effective Mechanism for Rubber Adhesion and Blending

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Deryagin introduced electrostatic adhesion many years ago but it was later considered unimportant, largely due to the difficulties in making reproducible electrostatic measurements and to the lack of clear understanding about the mechanisms for insulator electrostatic charging. More recently, electric force microscopy results on latex, polymer latex blends, and nanocomposites have shown the ubiquity of domains with excess charge, in every polymer material. In some cases, excess charge was identified by analytical transmission electron microscopy as the result of excess ions (positive or negative) concentration distributed throughout the coexisting phases and interfaces. Interaction between charged domains within nanostructured rubber blends and composites prepared from aqueous dispersions may thus contribute to their stability and mechanical properties. This article shows charge distribution patterns in one natural rubber blend, together with elemental and electric potential maps for rubber latex films from two commercial sources, evidencing large differences that were not previously reported. Electrostatic adhesion effectiveness in the making of a multicomponent system is demonstrated by casting films from a natural rubber-starch-clay nanocomposite, from aqueous dispersions and without using any sort of chemical modification or compatibilizing agent. Microscopy examination of these films show parallel clay lamellae finely interspersed within polymer, which accounts for the singular macroscopic tensile behavior of this material, with modulus in the 70 MPa range together with 500% elongation. (C) Koninklijke Brill NV, Leiden, 2012266SI767782Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq