Hydrothermal treatment of sorghum (Sorghum bicolor (L.) Moench) stalks for enhanced microfibrillated cellulose production

Abstract

Microfibrillated cellulose (MFC) derived from natural fibers has gained significant interest as an environmentally friendly material for economic and ecological reasons. Sorghum (Sorghum bicolor (L.) Moench), a widely cultivated crop that generates waste during bioethanol production, holds the potential for producing MFC and can be used for enhancing polymer’s performance, particularly in terms of crystallinity. The hydrothermal treatments aimed to unbundle lignocellulose networks into MFC with reduced amorphous content and enhanced crystallinity The hydrothermal treatments, necessitating specialized apparatuses and exhibiting limited scalability, can be effectively replaced by the domestic pressure cooker, an alternative intriguing vessel for the simple, cheap, and economical hydrothermal reactor. Hydrothermal treatments using pressurized steaming methods were performed at different durations (5, 25, and 60 min), in which the fibers were positioned above the water level to enable targeted interaction with the steam. Characterization of the treated fibers namely chemical composition, morphology, crystallinity index, and thermal stability were analyzed using FTIR spectroscopy, FE-SEM, XRD, and TGA. The results demonstrate the removal of binding materials, such as amorphous hemicellulose and lignin, from the sorghum fibers, leading to fiber defibrillation and producing MFC size range from 12.2 to 19.4 μm. Hydrothermal treated fiber started to decompose at Tinitial around 275 °C-282 °C higher than fiber untreated Tinitial = 229 °C. The 5 min treatment has generated the highest crystallinity index (52%) and the highest maximum peak temperature (365.26 °C). Additionally, the treatments have increased the fibers’ crystallinity index and thermal stability, highlighting the potential use of sorghum fiber as a reinforcement candidate in natural fiber polymer composites.