Fiber disruption of betung bamboo (Dendrocalamus asper) by combined fungal and microwave pretreatment

Abstract

Combined fungal andmicrowave pretreatment is an attractivemethod to alter carbohydrate and lignin structure of lignocellulosicmaterials for improving hydrolysis process to convert these lignocellulosicmaterials to bioethanol. This study was conducted to obtain information on the carbohydrate and lignin characteristic changes after combined biological and microwave pretreatment of betung bamboo. Based on our previous research, incubation for 30 days using 5 and 10% (w/v) inoculum loading of white rot fungi, Trametes versicolor which has better delignification selectivity compared to the other incubation time, was chosen as the fungal pretreatment prior to microwave pretreatment for 5, 10 and 12.5 minutes at 330 W. The evaluation of characteristic changes after pretreatment was performed using the analysis of FTIR spectroscopy,X-Ray diffraction and SEM. FTIR spectra demonstrated that the combined pretreatment only affected the change of intensity bands of FTIR spectra, without any changes in the functional groups. This band intensity decrease occurred on unconjugated bonds of carbohydrate peaked at 1,736 cm-1 (C =0 in xylan), 1,373 cm-1(C-Hdeformation in cellulose and hemicellulose), 1,165 cm-1(C-O-C vibration in cellulose -1 -1 and hemicellulose) and 895 cm-1(C-H deformation or C-O-C stretching at β-glicosidic linkage characteristic in -1 cellulose). The pretreatment decreased the hydrogen bond stretching of cellulose and the linkage between lignin and carbohydrate. This decrease of hydrogen bond was associated with crystallinity of bamboo cellulose, illustrated by occurring structural changes. The crystallinity index tended to increase slightly due to the cleavage of the amorphous fraction. SEMimages illustrated that the pretreatment disrupted the fiber structure. The longer duration of microwave irradiation, the greater the degradation level of fiber.