Estudo do efeito do ph e da adsorção de surfactante catiônico na redispersão de nanocristais de celulose em água

Abstract

The use of environmentally friendly materials from renewable sources, as well as cellulose, has been presented as a subject of interest to many researchers. In this work the cellulose nanocrystals (CNC) were extracted from commercial microcrystalline cellulose (CMC) with subsequent pH adjustment and surface modification with the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), aiming to dry the CNC and rehydrate them in water. The influence of dialysis procedure, pH range, surface modification and drying technique on colloidal stability and particle size distribution were studied. Three drying techniques were studied: (1) oven drying, (2) drying by lyophilization and (3) spray drying. The oven drying process showed the formation of indissoluble agglomerates preventing the redispersion of CNC, in this technique the effect of the pH adjustment was evaluated, and it was observed that for acidic pH conditions the degradation of CNC occurs. On drying by lyophilization it was possible to redisperse the CNC in water, but it was not possible to obtain a stable dry material, as water desorption occurred. It was also observed that for larger additions of the counterion 𝑁𝑎+, better particle size distribution results were obtained for the redispersed suspensions. The influence of the surfactant on redispersion was tested in the spray drying drying technique. The adsorption of the cationic surfactant to the surface of the CNC was confirmed by the Fourier transform infrared spectroscopy (FTIR) technique. It has been shown that with the addition of 1% surfactant to the CNC suspensions it is possible to redisperse them obtaining characteristics very close to those of the suspensions prior to the drying process, however, loss of colloidal stability has been observed for some samples after redispersion. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and rheological analysis were used to characterize the material obtained by spray drying, which was determined as the most suitable drying technique. The particles were presented with a spherical morphology and with the formation of agglomerates. High crystallinity indexes were obtained for samples with adsorption of CTAB surfactant, but with low thermal stability. The kinematic viscosity assessment indicated a pseudoplastic behavior for the CNC suspensions and an increase in the viscosity of the samples after drying and redispersion indicated the formation of agglomerates.