Estudo de composições de amido termoplástico: extrusão reativa e nanocompósitos com microfibrilas de celulose

Abstract

A resistência à tração, módulo de elasticidade e alongamento das amostras de TPS com o diisocianato, na presença ou ausência de ácido cítrico, e poli(isocianato) bloqueado na ausência de ácido cítrico, aumentaram em comparação ao TPS. Todos os materiais modificados quimicamente apresentaram redução na absorção de água após a modificação química. Observou-se um aumento na massa molar das amostras com quantidades menores de incorporação do diisocianato e poli(isocianato) sem ácido cítrico, resultado da formação de grupos uretana no material. As propriedades mecânicas dos nanocompósitos sofreram um significativo aumento na resistência e módulo de elasticidade se comparada ao TPS original. A adição de microfibrilas ocasionou um aumento da resistência mecânica dos nanocompósitos. The nanocomposites were prepared with nom modified thermoplastic starch reinforced with cellulose microfibrils obtained by alkaline treatment of eucalyptus pulp, followed by cryogenic grinding. The materials were characterized by infrared spectroscopy (FT), X-ray diffraction, dynamic mechanical analysis (DMA), liquid chromatography size exclusion high-efficiency (HPSEC), atomic force microscopy (AFM) microscopy, transmission and scanning (MTV-EGF), water absorption and mechanical tests. The use of single-screw extruder for the chemical modification of thermoplastic starch proved to be efficient because it promoted the reaction of diisocyanates in the presence or absence of citric acid. The process was also effective in decreasing the crystallinity of the TPS, which can increase its stability after processing. The tensile strength, modulus and elongation of TPS samples with the diisocyanate in the presence or absence of citric acid, and blocked polyisocyanate in the absence of citric acid increased after chemical modification by REX. For all chemically modified materials it was observed a decreased in the water absorption compared to the TPS. There was an increase in molar mass of the samples with smaller amounts of diisocyanate and polyisocyanate without citric acid, as a result of the formation of urethane groups in the material. The mechanical properties of nanocomposites underwent a significant increase in strength and elastic modulus when compared to the pristine TPS. The microfibrils addition causes an increase in the mechanical properties of the nanocomposites.