EFFECT OF DELIGNIFYING PRETREATMENTS ON THE CRISTALLINITY, ENZYMATIC HYDROLYSIS AND ULTRASTRUCTURE OF SUGAR CANE CROP RESIDUES

Lignocellulosic materials account for about 71% of the total biomass in the planet. Given their abundance, they are being considered as a potential feedstock for bioethanol production which can reduce the use of fossil fuel consumption. An alternative is the use of leaves and buds which are crop residues from sugar cane, and can be converted into ethanol by pretreatment, hydrolysis and fermentation. In this study, we evaluated the effect of two delignification pretreatments, enzymatic and organosolv of four substrates (S1: untreated, S2: enzymatic treatment, S3: organosolv and S4: organosolv followed by alkaline bleaching) on the crystallinity and sugars production by enzymatic hydrolysis measured as crystallinity index (CrI), relative intensity number (Ir), global hydrolysis rate (IGS) and ultrastructural changes, by means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction and scanning electron microscopy (SEM). The results showed that substrates with the lowest residual lignin content and Kappa number, have the highest CrI and IGS values, showing that changes in the crystalline structure of cellulose as well as delignification enhance enzymatic hydrolysis. SEM micrographs of substrates S2 and S3 show slight surface modifications with respect to S1, while destruction of the substrate cell walls and great defibrillation, typical of a large delignification, validated by the FTIR spectra, are observed in S4.