Microwave expansion pretreatment for enhancing microwave-assisted alkaline extraction of hemicellulose from bagasse

Microwave expansion pretreatment (MEP) is a promising approach to effectively disrupt the intricate network structure of bagasse for enhanced hemicellulose extraction. A synergistic strategy combined MEP and microwave-assisted alkaline extraction (MAAE) of hemicellulose with the aim of maximizing the hemicellulose extraction yield. The effect of microwave expansion pretreatment on the structural characteristics of the bagasse hemicellulose was studied with optical microscope, scanning electron microscopy, and the Brunauer–Emmett–Teller (BET) method. The results showed that the pressure generated from the gases after radiation is quickly released, disrupts the highly organized structure of the cell wall, and increases the specific surface area, making more “pathways” for alkaline solution diffusion. In the comparison of the raw material, the microwave-assisted alkaline extraction of MEP treated the sample for 50 min, utilizing 4% NaOH solution as an extraction agent, resulting in a distinct enhancement in the yield of the hemicellulose, increasing from 62.59 to 82.75%. Additionally, the MEP also presented a favorable contribution to decreasing sodium hydroxide consumption; the yield obtained by the 50-min synergistic process (employing 4% NaOH solution as extraction agent) is 82.75%, which was much higher than by the 50-min MAAE process (employing 8% NaOH solution as extraction agent). Meanwhile, the higher yield of hemicellulose (more than 85%) with higher molecular weight indicated the potential advantages of MEP strategy for hemicellulose extraction. In general, MEP was beneficial for the extraction of hemicellulose from bagasse using MAAE. Graphical abstract