Fiber Disruption of Betung Bamboo (Dendrocalamus asper) by Combined Fungal and Microwave Pretreatment

Abstract

Combined fungal and microwave pretreatment is an attractive method to alter carbohydrate and lignin structure of lignocellulosic materials for improving hydrolysis process in order to convert these lignocellulosic materials to bioethanol. This study was conducted to obtain the information on the characteristic changes of cellulose and lignin after combined biologicaland microwave pretreatment of Betung Bamboo. Based on our previous research, incubation for 30 days both for 5 and 10% liquid-inoculum loading of white rot fungi, Trametes versicolor, was chosen as the fungal pretreatment prior to microwave pretreatment at 30% power level for 5, 10 and 12.5 minutes. The evaluation of characteristic changes after combined pretreatment was performed using the analysis of FT-IR spectroscopy, X-Ray diffraction and SEM.FTIR spectra demonstrated that the combined pretreatment only affected the decrease of intensity bands of FTIR spectra with increasing microwave irradiation time, without any changes in the functional groups.This band intensity decrease occured on unconjugated bonds of carbohydrate peaked at 1736 (C=0 in xylan), 1373 (C-H deformation in cellulose and hemicellulose), 1165 (C-O-C vibration in cellulose and hemicellulose), and 895 (C-H deformation or C-O-C stretching at β-glicosidic linkage characteristic in cellulose) cm-1. 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,ilustrated by occurring structural changes. Syringil propane units were more soluble than guiacyl moieties. The crystallinity of cellulose tended to increase slightly due to the cleavage of the amorphous fraction. SEM images illustrated that the pretreatment disrupted the fiber structure while the longer microwave irradiation, the greater fiber degradation level. Prolonging microwave irradiation on 5% inoculum loading decreased lignin degrading ability. Crystalline allomorph of 5% inoculum loading for 10 minutes showed that Iβ (triclinic) structure of cellulose has transformed into monoclinic (Iα) structure.Key words: betung bamboo, combined biological andmicrowave pretreatment, cellulose and lignin changes, FTIR, SEM, XRD