Síntese de nanowiskers de fibra de mandioca: formação de nanocompósitos com álcool polivinílico

Abstract

The nanowhiskers are crystalline domains of cellulosic sources and have been used in the preparation of nanocomposites due to the abundance of available raw material derived from several renewable and biodegradable sources. In addition, they show modification feature facility of surface by means of chemical treatments, and also have large superficial area and differentiated morphology, showing excellent mechanical and thermal characteristics, as well as of barrier. In this study nanowhiskers were extracted from cassava bagasse generated in starch separation step. The cellulose nanowhiskers obtained by acid hydrolysis were characterized by thermal analysis (TG and DSC), infrared spectroscopy (FTIR) and x-ray diffraction (DRX). In the FTIR spectra differences were observed between nonowhiskers (NWM), crude cassava fiber (FBM) and purified cassava fiber (FPM), indicating favoring in the formation of stable nonowhiskers. The crystallinity of FPM and of NWMs was also observed in DRX, with increase of crystallinity of 254.87% and 165.62%, respectively when compared to FBM. The thermal stability increased with chemical treatments performed on FBM, and the NWM degradation occurred basically in only one step, indicating chemical and dimensional homogeneity of the sample. Nanocomposites formed by polymeric matrix of polyvinyl alcohol (PVA) and reinforcements of 2.5, 5 and 10% of NWM were compared to the PVA through thermal analysis (TG and DSC), infrared spectroscopy (FTIR), x-ray diffraction (DRX) and traction analysis. The thermal stability of nanocomposite with reinforcement of 5% of NWM increased. In FTIR analysis, the occurred bands are features of PVA. The diffractogram of DRX has shown an increase of nanocomposite crystallinity with less reinforcement of NWM, in a 38% -increase range. The mechanical properties have shown significant improvements in nanocomposites with NWM reinforcement. The nanocomposite formed with smaller amount of reinforcement has shown the highest modulus of elasticity and the nanocomposite formed with reinforcement of 5% of NWM has shown higher level of resistance and tensile breakdown. The present study has found that the use of the residual mass of potato starch manufacturers becomes a promising use in the production of nanowhiskers and incorporation of them in nanocomposites as reinforcement.