Síntese e caracterização de membranas assimétricas de acetato de celulose obtido a partir da celulose do caroço de manga e do jornal

Abstract

This thesis presents the study of the utilization of alternative sources of cellulose, mango seed and newspaper (parts without ink), to produce cellulose acetate (CA) and investigation of the morphological characteristics and transport properties of membranes produced of these materials. The margins of the newspaper was delignified and mango seed was treated in NaOH 1 mol L-1 to produce of the cellulose acetates that were characterized. The materials showed distinct values of the viscosity average molecular weight and lignin content that has influence on the characteristics of the materials produced. The formulations of the membranes cellulose triacetate (CTA)/dichloromethane/water and CTA/dichloromethane/water/magnesium perchlorate lead to asymmetric membranes that were characterized by transport properties and morphology. The results showed that the remaining lignin content in cellulose acetate after the acetylation procedure has influence on the characteristics of their membranes. Magnesium perchlorate used on the formulation has an important role on the stability of the membrane solution. The membrane produced from newspaper has presented an ion diffusion coefficient of 8.47 x 10-8 cm2 s-1, which is similar to the value presented in the literature for a commercial cellulose acetate. In an attempt to improve final characteristics of the membranes, it was carried out a study of the production parameters of cellulose acetate production, delignification process and acetylation. This study lead to the production of new materials with lower lignin content and reduced reaction time (2 h for newspaper and 14 h for mango seed). Using these new cellulose acetate samples it was possible to produce much more resistant membranes, which reached 35 bar in operation at a separation system. In order to reach selectivity in a salt rejection experiments, was used new conditions of membrane preparation, such as changing the solvent to the system dioxane/acetone, increasing evaporation time and using acetic acid as admixture. With these new conditions it was possible to obtain selectivity and increase the salt rejection of the membrane produced from CAmango seed from 77,8% to 91,3% (best result) with the use of acetic acid as admixture and increase in evaporation time from 30 to 90 seconds. The highest salt rejection value obtained for a membrane produced from CA-newspaper was 69.4% using evaporation time of 120 seconds and without using an admixture.