Topochemical characterization of sugar cane pretreated with alkaline sulfite

Biomass pretreatments and subsequent conversion to fuels and materials involve a multitude of topochemical interactions. Detailed knowledge about changes in surface composition of biomass caused by pretreatments allows tailoring of biomass processing steps to advance hydrolysis of polysaccharides to monomers. In this work, sugar cane internodes selected from experimental hybrid plants with varied chemical composition were treated with the alkali-sulfite process (ASP). A combination of Xray photoelectron spectroscopy (XPS), time-of-flight-secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FE-SEM) were used to evaluate the topochemical changes occurring during the pretreatment step. The chemical treatment caused intense delignification and morphological changes on the sugar cane fiber surfaces. FE-SEM indicated that the fibers from rind regions and especially from the pith-rind interface showed collapsed cell walls with grooved appearance after partial delignification. The surface coverage of carbohydrates and lignin increased and decreased after ASP, respectively, as showed by XPS and ToF-SIMS. Inorganic components such as calcium and magnesium were washed out and partially redistributed over the fiber surfaces. Our results indicated that surface lignin was dissolved during the pretreatment while surface hemicelluloses were exposed or relocated. This information can be useful to design of different mixtures of enzymes to be used after pretreatments to hydrolyse polysaccharides to monomers.