Tratamentos químicos das fibras do mesocarpo de açaí para a produção de filmes de nanocelulose e nanocompósitos de quitosana

Abstract

The açaí depulping generates great amounts of wastes composed of seeds involved by mesocarp fibers that can be modified for the production of sustainable biomaterials. This work aimed to chemically modify the açaí mesocarp fibers for the production of cellulose nanofibrils chitosan based nanocomposites. The fibers were submitted to pre-treatments with reaction time variation (1, 2 and 3 h) and number of reaction times (1 and 2 x). The alkaline pre-treatments were carried out with sodium hydroxide (NaOH) at 5% at 80°C in the proportion of 1 g fibers/100 mL of solution. For bleaching, subsequent to alkaline pretreatments, it was used a 24% hydrogen peroxide (H2O2) and 4% NaOH (1v:1v) solution at 60°C in the proportion of 1 g fibers/80 mL of solution. Nafibrils from bleached fibers with three (NC_3P) and twenty-one (NC_21P) passages in the grinder and nanocellulose films were produced by the casting method (FNC_3P and FNC_21P). Chitosan based nanocomposites were produced with different concentrations of cellulose nanofibrils reinforcement (5%, 10%, 15% and 20%). The characterization was performed by optical microscopy (fibers); X-ray diffraction (fibers and nanocellulose films) filmes de nanocellulose); scanning electron microscopy (nanocellulose films); and physical properties (nanocellulose and nanocomposites). The bleached fibers were selected for the production of nanofibrils based on morphology, cristallinity, and more efficient removal of non-cellulosic components from the fibers (diameter = 1.79 μm; length = 216.86 μm; aspect ratio = 121; crystalline index = 68.78%; and yield = 64%). For the nanocellulose films it was determined density of 1.21 g/cm³ and 1.26 g/cm³, water absorption of 60.42% and 21.42%, water solubility of 30.85% and 6.63%, and permeability to water vapor of 74.49% and 44.38% for FNC_3P and FNC_21P, respectively. Chitosan based nanocomposites produced with nanofibrils NC_21P showed better physical resistance than those produced with nanofibrils. Higher nanofibril levels in the nanocomposites substantially improved the water absorption, but not the other physical properties. It was concluded that the alkaline pretreatment of açaí mesocarp fibers must be carried out 1 X for 2 h, followed by bleaching 2x by 2 and 3 h. Nanofibrils with better quality were obtained with 21 passages in grinder. The best nanofibril level as chitosan based nanocomposites reinforcement was 20%.