Amidos termoplásticos plastificados com glicerol (TPS), e reforçados com bentonita cálcica, foram preparados por extrusão. A morfologia dos materiais extrusados foi analisada por microscopia eletrônica de varredura. Foram avaliados os efeitos do teor de argila e do teor de glicerol sobre as propriedades físicas dos materiais. Os resultados de difração de raios X mostraram que o aumento no teor de glicerol contribuiu para o aumento da cristalinidade do tipo B. A adição da argila levou a materiais híbridos com propriedades melhoradas em relação ao TPS sozinho, mesmo após o envelhecimento sob condições de umidade relativa do ar de 80% durante 90 dias. A difração de raios X também permitiu a avaliação da intercalação da argila na matriz de amido, antes e após o condicionamento. Resultados de testes mecânicos sob tensão uniaxial sugeriram um alto grau de exfoliação.Glycerol-plasticized corn starch materials (TPS), reinforced with calcium bentonite, were prepared by melt extrusion. Scanning electron microscopy was used to visualize extrudates morphology. The effects of clay content and of glycerol content on physical properties of extrudates were evaluated. As determined by X-ray diffraction, the increase in glycerol content led to materials with higher B-type crystallinity. Addition of clay resulted in hybrid materials with improved properties in relation to TPS alone, even after conditioning at a high relative humidity for 90 days. X-Ray diffraction was also used to evaluate clay intercalation within the polymeric matrix, before and after conditioning. Results from tensile tests suggested a high degree of exfoliation.Keywords: thermoplastic starch, calcium bentonite, hybrids, aging, mechanical properties
IntroductionHybrid materials, such as organic polymer/inorganic filler composites, have been developed for decades. Addition of filler was shown to improve the stiffness and strength of polymeric materials. Recently, silicate type clays like montmorillonite (the major constituent of bentonites) have received much attention as non-conventional reinforcing fillers. The reason for this interest is related to their potential ability to be exfoliated, at least partially, into nanometric high aspect ratio platelets, which can be dispersed within polymer matrices, and thus favorably modify polymer properties. In general, thermal, mechanical, flammability and barrier properties of the matrix polymer are improved by addition of clay nanofillers.The most commonly used routes to achieve exfoliation and dispersion of clays are in situ polymerization, intercalation from solution, and melt-processing. Melt processing has advantages because it does not require the use of solvents. However, intrinsic incompatibility of hydrophilic layered silicates and hydrophobic synthetic plastics usually causes a loss in mechanical properties. Modification of natural clay surfaces by cation exchange reactions is frequently carried out to expand the distance between clay galleries, reduce the surface energy, and improve adhesion. Exchangeable cat...
