The pretreated biomass felt softer than the untreated material. For this reason, physical changes in the untreated and pretreated rice straw were observed by scanning electron microscopy (Supplementary material). The change in surface morphology after pretreatment was clearly evident from the images. The micro fibrils were loosened from the initial rigid structure, thus increasing the external surface area and porosity of the rice straw. Similar obserobservations
were reported for rice straw pretreated with aqueous ammonia