Obtenção e caracterização de nanocristais de celulose por hidrólise ácida a partir do bagaço de cana-de-açúcar

Abstract

The present work aimed at the obtaining and characterization of cellulose nanocrystals from sugarcane bagasse. Initially, chemical pre-treatments of the bagasse were carried out with sodium hydroxide, hydrogen peroxide and sodium hypochlorite to remove lignin, hemicellulose and other impurities. Later, the fibers were subjected to acid hydrolysis with 60% (m/m) sulfuric acid for 75 minutes in three temperature conditions (25 oC, 40 oC and 55oC) to obtain the cellulose crystals. The hydrolysis was also performed on a microcrystalline cellulose (MCC) for comparison purposes. The resulting material from each procedure was centrifuged and dialyzed in water to remove acid excess and subsequently lyophilized to obtain the material in powder form. Untreated, treated and hydrolyzed fibers were characterized by the techniques of thermogravimetry (TGA-DTG), X-ray diffraction (DR-X) and optical microscopy, in order to verify the effect of chemical pre-treatments and hydrolysis conditions applied. The increase of hydrolysis temperature provided darker crystals, caused by cellulose degradation reactions, reducing its crystallinity index of 77.89% for hydrolysis at 25°C to 74.23% at 55°C. A higher sulphonation of the crystals was obtained at higher hydrolysis temperatures, however, reducing their thermal stability, with initial degradation temperature of 204°C for hydrolysis at 25°C and 115°C for hydrolysis at 55°C. The hydrolysis conditions applied were efficient for obtaining cellulose crystals in this work, but a high agglomeration of the fibers made it difficult to determine their dimensions. In order to obtain higher nanocrystals yields, some remediations could be applied in future attempts, such as performing different chemical pre-treatments prior to hydrolysis to increase the removal of amorphous constituents from the fibers, which was not very significant between treatments. Associating mechanical treatments with hydrolysis would also become interesting to increase the separation of agglomerated fibers and facilitate acid attack, as well as a longer hydrolysis time.