Pretreatment step is one of the pivotal processes in the exploitation of lignocellulosic biomass for bioethanol production. An ecofriendly system only allows mild pretreatment strategies for industrial bioethanol production. The steam explosion pretreatment process is reported to be efficient in arranging rice husk for these procedures with the use of mild acids or bases. In the current work, pretreatment method like steam explosion pretreatment method was used with NaOH and HNO3 to degrade the complex structures and release the sugars entrapped within lignin. The pretreatment effect on the matrix of husk cell-wall and its constituents are characterized microscopically (scanning electron microscopy) and spectroscopically (Fourier Transform Infrared Spectroscopy) in order to comprehend the future possibility of its digestion by cellulase. The crystallinity index of native substrate is very high (0.94 cm-1), which reduced significantly to -0.277 and -0.34 cm-1 when pretreated with 2% HNO3 and 10% HNO3 respectively. The steam explosion pretreatment does not support degradation of the cellulosic fibrillar arrangement, but causes intense re-localization of lignin. The images of scanning electron microscopy were in agreement with the findings of Fourier Transform Infrared Spectroscopy; the ordered structure generally found in native rice husk was missing, suggesting that the structure of the 2% HNO3 treated rice husk was more amorphous. Partial removal of hemicelluloses and complete removal of wax is the outcome of this research work. Results revealed that steam explosion pretreatment increases the possibility of digestion by enhancing cellulose accessibility through lignin re-localization and a partial elimination of hemicelluloses rather than by cell wall disruption.
Keywords: Bioethanol; rice husk; steam explosion; FTIR; SEM and crystallinity index.