Microwave-assisted pretreatment of eucalyptus waste to obtain cellulose fibers

Abstract

This work aims to evaluate the impact of microwave-assisted methodology in the pretreatments of the eucalyptus waste (Eucalyptus citriodora), to remove non-cellulosic components. Two pretreatments, without and with microwave, were used: (a) mercerization using sodium hydroxide, and (b) bleaching using hydrogen peroxide. The times (15 and 30 min) and power (100 W, 400 W, and 800 W) of microwave varied in order to find out the best conditions to obtain cellulose fibers. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, thermogravimetric analysis (TGA), lignocellulosic contents (TAPPI), and statistical analysis (bivariate analysis) were used to evaluate the delignification of the obtained cellulose fibers. Life Cycle Impact Assessment (LCIA) analyses were used to evaluate environmental impacts [Cumulative Energy Demand (CED), Agricultural Land Occupation, and Climate Changes (CC)] from two processes: non-microwave and microwave-assisted pretreatment. FTIR results show an increase in the intensity of the cellulose bands and a decrease in bands of non-cellulosic components, corroborating with photomicrographs, which show the fiber opening. FTIR, TGA, TAPPI, and statistical analysis results show that the best condition for mercerization was 30 min, with 400 W and 800 W and the bleaching process with 400 W, the last condition presenting 99.1% of cellulose purity. From LCIA analyses, it was observed a decrease of environmental impacts as CED and CC for microwave-assisted pretreatment compared to non-microwave, being more intensified for CED, both at the laboratory scale and industrial scale. Therefore, the use of microwave promoted an increase in the removal of non-cellulosic compounds of the eucalyptus waste, which reduced reaction time, energetic expenditure, and reagent quantities.