COMPARATIVE ANALYSIS OF MORPHOLOGICAL AND STRUCTURAL CHANGES IN GAMMA AND ELECTRON BEAM IRRADIATED SUGARCANE BAGASSE

Abstract

"Sugarcane bagasse is an abundant source of cellulose and hemicelluloses that could be hydrolyzed to yield fermentable sugars, which can be utilized for the production of biofuel and other high-value bio-chemicals. To do so, it has to be made accessible for hydrolyzing chemicals and enzymes, and radiation exposure is one of the most effective and green techniques, among other physico-chemical processes. The present study investigated the effects of gamma and electron beam (e-beam) irradiation on sugarcane bagasse, with respect to changes in its physical, chemical, thermal and morphological characteristics. Sugarcane bagasse was irradiated with gamma radiation, using Co60 at a dose rate of 2.5 kGy/h, and electron beam at a dose rate of 2.5 kGy/pass. The maximum dose was varied up to 1000 kGy and changes in the physico-chemical characteristics of bagasse were observed at 500 kGy dose exposure. The physical appearance of bagasse (after gamma and e-beam treatments) changed from off-white to yellow in colour, while beyond 500 kGy, the samples became fluffy. With an increase in the radiation dose, the cellulose content reduced from 48% to 36%, following Co60 gamma exposure, and to 16% after e-beam exposure at 1000 kGy. The hemicellulose content was found to reduce from 31% to 16% after 1000 kGy of Co60 gamma exposure, but after e-beam radiation, it increased to 39%. The lignin fraction did not change much after any of the treatments, and was found to be in the range of 19-20% and 17-23%, after gamma and e-beam radiation exposure, respectively. In most of the irradiated samples, X-ray diffraction (XRD) confirmed a significant increase in crystallinity index with the increase in the radiation dose up to 1000 kGy. However, a decrease in the crystallinity index of bagasse was observed after e-beam irradiation. Scanning electron microscopy (SEM) analysis showed remarkable disruption of the structure, caused by high energy irradiations (gamma and e-beam). The particle size analysis indicated fragmented particles on increasing irradiation doses, but the distribution is more prominent in the case of the e-beam treatment. A lowering of the derivative thermogravimetric (DTG) peak from 339 °C in raw bagasse to 295 °C and 303 °C, for the samples subjected to gamma and e-beam radiation, respectively, was observed, in the thermal study of the biomass. The physico-chemical changes observed during the study clearly indicated that ionizing radiation exposure of lignocellulosic biomass led to the disintegration of its matrix, which may give easy access to hydrolytic chemicals or enzymes. Thus, it can be concluded that, although both ionizing radiations investigated here can fulfill the objective of disintegrating the biomass structure, gamma is more effective than e-beam radiation."