Chemithermomechanical (CTM) processing was used to pretreat sugarcane bagasse with the aim of increasing cell wall accessibility to hydrolytic enzymes. Yields of the pretreated samples were in the range of 75-94%. Disk refining and alkaline-CTM and alkaline/sulfite-CTM pretreatments yielded pretreated materials with 21.7, 17.8, and 15.3% of lignin, respectively. Hemicellulose content was also decreased to some extent. Fibers of the pretreated materials presented some external fibrillation, fiber curling, increased swelling, and high water retention capacity. Cellulose conversion of the alkaline-CTM- and alkaline/sulfite-CTM-pretreated samples reached 50 and 85%, respectively, after 96 h of enzymatic hydrolysis. Two samples with low initial lignin content were also evaluated after the mildest alkaline-CTM pretreatment. One sample was a partially delignified mill-processed bagasse. The other was a sugarcane hybrid selected in a breeding program. Samples with lower initial lignin content were hydrolyzed considerably faster in the first 24 h of enzymatic digestion. For example, enzymatic hydrolysis of the sample with the lowest initial lignin content (14.2%) reached 64% cellulose conversion after only 24 h of hydrolysis when compared with the 30% observed for the mill-processed bagasse containing an initial lignin content of 24.4%.

Dynamic vapor sorption and thermoporometry probe complementary dimensions of water interaction with cellulose. While sorption is primarily sensitive to the first hydration layers, thermoporometry is primarily sensitive to the nanometric water-filled pores. In this article, these analytical techniques are detailed and applied to model mesoporous materials and to a wide spectrum of celluloses. Correlations between techniques are explored. In dynamic vapor sorption, celluloses present a general characteristic time of desorption. On the other hand, they present highly variable characteristic times of sorption, indicating that material-specific properties may be inferred from sorption kinetics. Regarding thermoporometry, the thermodynamics of ice melting in irregular pore shapes is introduced. Moreover, in our thermoporometry analysis with differential scanning calorimeter, freezing temperature is extended to -70°C, allowing pores smaller than a few nanometers to be measured. Nevertheless, several data corrections are required for accurate thermoporometry at this condition. Comparisons between techniques show that sorption hysteresis is positively correlated with wet porosity. The presented developments and results will guide future application of these techniques to probe water in celluloses.

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Sugar cane bagasse is recalcitrant to enzymatic digestion, which hinders the efficient conversion of its polysaccharides into fermentable sugars. Alkaline-sulfite pretreatment was used to overcome the sugar cane bagasse recalcitrance. Chemical and structural changes that occurred during the pretreatment were correlated with the efficiency of the enzymatic digestion of the polysaccharides. The first 30 min of pretreatment, which removed approximately half of the initial lignin and 30% of hemicellulose seemed responsible for a significant enhancement of the cellulose conversion level, which reached 64%. After the first 30 min of pretreatment, delignification increased slightly, and hemicellulose removal was not enhanced; however, acid groups continued to be introduced into the residual lignin. Water retention values were 145% to the untreated bagasse and 210% to the bagasse pretreated for 120 min and fiber widths increased from 10.4 to 30 μm, respectively. These changes were responsible for an additional increase in the efficiency of enzymatic hydrolysis of the cellulose, which reached 92% with the 120 min pretreated sample.

Lateral dimensions of cellulose crystallites have been widely reported to increase as plant biomasses are submitted to a variety of high-temperature chemical treatments. Cellulose co-crystallization is often indicated to be the phenomenon underlying crystallite dimensional change, but precise mechanisms and relationships with concurrent phenomena are not well understood. This work investigates cellulose structural evolution in sugarcane bagasse submitted to wide range (160-190°C, up to &50 % solubilization) of hydrothermal treatments, performed in pressurized liquid hot water. Cellulose structural characterization combines fiber and powder X-ray diffraction with analysis of two-dimensional diffraction patterns employing the Cellulose Rietveld Analysis for Fine Structure (CRAFS) model. We observe that increases in lateral dimensions of cellulose crystallites closely follow changes in bagasse chemical composition. For a given composition, treatment temperature per se seems to be secondary for changes in crystallites. Partial cellulose de-crystallization and decreasing distortion of crystallite unit cell are found to co-occur with increasing crystallite lateral dimensions. Our interpretation of results emphasizes the importance of removing hemicelluloses acting as intercrystallite spacers, which seems to be the limiting factor for cellulose cocrystallization.