Thermochemical pretreatment of biomass results in structural reorganization of cell wall polymers that help in breaking down the cell wall. However, the impact of pretreatment on biomass is not fully understood due to the variable cell wall composition and multifaceted interaction between polymers and solvents. Model systems that mimic cell wall polymers potentially can help in understanding polymer-polymer interactions. In this study, model hemicellulose-cellulose composites were prepared by synthesizing bacterial cellulose in presence of glucomannan or xyloglucan dissolved in the growth media. Small-angle neutron scattering (SANS) was used to study structural changes in the composites as a result of dilute acid pretreatment (DAP). By growing deuterium labeled cellulose in the presence of hydrogenated hemicellulose it was possible to deconvolute the scattering signatures of the two components. No significant change in the crystallinity and glucan chain packing was observed in the DAP cellulose by X-ray diffraction (XRD). However, at the nanoscale, DAP cellulose showed a collapse in structure as indicated by a decrease in Rg from 250Å to 130 Å and a change of power law exponent (α) from 2.77 to 3.13. This was interpreted as expulsion of water from the space between microfibrils resulting in formation of a tightly packed macrofibril. In addition, the cellulose network after DAP show less entanglement than in the untreated cellulose. Addition of xyloglucan (XG) decreased cellulose crystallinity in the composite material and altered the glucan chain packing in the microfibrils as determined by analysis of the XRD pattern. After removal of the XG by DAP, the nanoscale cellulose structure showed minimal change but the crystallinity increased. On the other hand, in composites formed using glucomannan (GM) the structural changes that occurred due to DAP were similar to the cellulose only samples. However, the cellulose network of the pretreated composite was more entangled (α= 2.82) than the cellulose only counterpart (α=2.2). Our results show that XG and GM interact with the cellulose network differently. XG directly interacts with the microfibrils that comprise the macrofibrils, while GM only interacts at the surface of the macrofibrils. This study provides insight into cellulose-hemicellulose interactions and may help in developing better extraction processes for cell wall polymers.

Insights into hemicellulose-cellulose interactions from thermochemical pretreatment of model composite materials

255th National Meeting (2018)

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