Filmes de nanofibrilas de celulose e microssílica do resíduo do açaí com alta reatividade superficial.

Abstract

The açaí production chain generates large amounts of waste composed of lignocellulosic fibers and seeds that are wasted and pollute the environment. The objective of this work was to develop highly reactive biodegradable films from the combination of two materials derived from açaí pulping waste: cellulose nanofibrils and microsssilica. The fibers were submitted to alkaline treatments with sodium hydroxide (NaOH) and bleaching with hydrogen peroxide (H2O2). Cellulose nanofibrils were produced with five passes in the Supermasscolloider grinder. Three residue compositions were subjected to microssilica production: (a) seeds + lignocellulosic fibers; (b) lignocellulosic fibers; and (c) seeds. The samples were sequentially submitted to the following procedures: treatment with (2N) HCl; heat treatment at 650 °C for 3 h; treatment with (6N) HCl to form sodium silicate (Na2SiO3) using magnetic stirring in 2.5N NaOH solution, forming the gel with the addition of sulfuric acid (H2SO4); and oven drying. Cellulose nanofibril films were produced with different concentrations of microssilica (2.5%, 5%, and 10%) by the casting method. The following characterizations were performed: scanning electron microscopy (SEM) for the fibers; transmission electron microscopy for nanofibrils; Fourier transform infrared spectroscopy, thermogravimetry, SEM with energy dispersive spectroscopy and X-ray diffraction for microssilicas; and contact angle and physical properties of the films. Chemical treatments individualized the fibers and removed organic and inorganic extractives from their surfaces. Cellulose nanofibrils with approximately 30 nm in diameter were obtained. The proposed methodology for obtaining silica structures, with chemical treatments and combustion at 650°C, from the three fractions of açaí waste, was efficient for the isolated fibers, as it resulted in a mineral fraction in a more significant proportion (≈ 96%), with a predominance of microstructures composed of crystalline silica, with high thermal resistance and without evidence of primary organic chemical components of the biomass. The seeds containing or not fibers submitted to the same process resulted in organic residue in greater proportion and lesser proportion of silica microparticles. The addition of high purity silica microparticles resulted in films of high surface reactivity, wettability, water absorption, and permeability. These features are advantageous for applications such as sustainable electronic devices and printing papers.