Source: SEAMEO BIOTROP's Research Grant | 2013
Abstract:Combined biological-microwave pretreatment was attractive method to alter carbohydrate and lignin structure of lignocellulosic materials for improving hydrolysis process to convert them to bioethanol. This study was conducted to obtain the information on characteristic changes of cellulose and lignin after biological-microwave pretreatment of bamboo. Based on our previous research, incubation for 30 days both 5 and 10% of liquid inoculum loading of the white rot fungi, Trametes versicolor was chosen as biological pretreatment prior to microwave pretreatment at 30% of power level for 5, 10 and 12.5 minutes. To evaluate the characteristic changes after combined pretreatment were utilized analysis by FT-IR spectroscopy, X-Ray diffraction and SEM. Pretreatment with 10% of inoculum loading showed better delignification selectivity (up to 2) compared to 5% of inoculum loading. FTIR spectra demonstrated that the biological-microwave pretreatment only affected decreasing of intensity bands of FTIR spectra a long with increasing microwave irradiation time without any changes in the functional groups. Band intensity of unconjugated bonds of carbohydrate peaks at 1736 (C=0 in xylan), 1373 (C-H deformation in cellulose and hemicellulose), 1165 (C-O-C vibration in cellulose and hemicellulose), 895 (C-H deformation or C-O-C stretching at β-glicosidic linkage characteristics in cellulose) cm-1 reduced. The pretreatment decreased the hydrogen bond stretching of cellulose and the linkage between lignin and carbohydrate associated with crystallinity of bamboo cellulose illustrated occuring the structural changes. Syringil propane units were more solubilized than guiacyl moties. The crystallinity of cellulose tended to slight increase due to cleavage of the amorphous fraction. SEM image ilustrated that the pretreatment disrupted the fiber structure and the longer microwave irradiation, the greater degradation fiber level. Prolonging microwave irradiation on 5% of inoculum loading decrease lignin degrading ability. Crystalline allomorph of 5% of inoculum loading for 10 minutes showed that Iβ (triclinic) structure of cellulose has transformed into monoclinic (Iα) structure.
Key words: betung bamboo, biological-microwave pretreatment, cellulose and lignin changes, FTIR, SEM, XRD
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