Agricultural feedstocks, like cotton stalk and sorghum stover, are a relatively inexpensive and renewable source of valuable fibers and platform chemicals. However, the cost-effective extraction of these bio-products remains elusive. Amongst the various lignocellulosic biomass fractionation methods, the microwave technology has gained increasing attention due to its rapid heating efficiency, reduced energy consumption, and operational simplicity. Hence, in this study, we have evaluated the mechanism of biomass disintegration by microwave via particle size, surface area, surface chemistry, and cellulose crystallinity analyses. Additionally, the microwave conditions, namely temperature (150 – 190 °C) and retention time (10 – 30 min), were optimized following the response surface methodology to maximize oligosaccharide yields from the liquid effluents. For the baseline scenario, we compared the physico-chemical changes in microwave-treated biomass to that of pressurized hot water extracted samples. The results indicate that microwave extraction significantly reduces the particle size (cotton – 26%, sorghum – 13%), cavitates secondary cell wall, depolymerizes and condenses lignin, and decreases cellulose crystallinity (8%) when compared to pressurized hot water treatment. The highest hemicellulose extraction efficiencies for cotton stalk and sorghum stover biomass were achieved at the microwave conditions of 190 °C /30 min and 170 °C/30 min, respectively. The corresponding xylooligosaccharide yields were between 51% (cotton) and 67% (sorghum). Thus, this study elucidates how microwave extraction could be a highly effective strategy for oligosaccharide extraction by virtue of accelerated physical and chemical disintegration of lignocellulosic feedstocks.
