Impacts of Diverse Pretreatments on Cell Wall Porosity, Swelling, and Enzymatic Hydrolysis Yields

A key obstacle in the utilization of lignocellulosic biomass as a bioenergy feedstock lies in the recalcitrant secondary cell wall structure. An examination of key characteristics of cell walls may provide a fundamental understanding of factors affecting enzymatic digestibility. In this work, cornstover, switchgrass, and hydrid poplar feedstocks were subjected to combinations of alkaline, liquid hot water, and/or oxidative delignifying pretreatments. Cell wall-water interaction within pores and surfaces of these materials are examined using both ¹H-NMR cryoporisemetry and differential scanning calorimetry to characterize pore structure. In addition, polymer probe sets are employed using both charged and uncharged polymer probes through solute exclusion chromatography to quantify water volume accessible within cell wall pores to these probes. Water retention, an indirect metric for water swelling capacity, is utilized to quantify swelling of biomass samples in response to different extents of pretreatment. Enzymatic digestibility is conducted to compare digestibility effectiveness to cell wall pore and swelling characteristics. Correlations are developed between water retention, pore size distributions determined from thermoporosimetry and differential scanning calorimetry experiments, and enzymatic hydrolysis yields.