Effect of Glycolic Acid and Ethanolamine on Preparation of Hemp Fibers in a Cascade Organosolv Degumming Process

In an attempt to implement eco-friendly degumming for preparation of hemp fibers, this study developed a cascade organosolv degumming method employing the advantages of both organic acids and organic bases without using any inorganic alkaline reagents. The cascade degumming improved the hemicellulose and lignin removal rates by 20.1% and 139.8%, respectively, under low temperature (≤ 110 °C) and short reaction time (≤ 3 h). The different mechanism of lignin removal by GA and ETA was verified. The FTIR result showed that GA mainly acted on removal of G-type lignin, while ETA mostly removed S-type lignin. In addition, the FTIR and solid-state ¹³C NMR results revealed that the esterification induced by GA was eliminated by ETA in the cascade degumming process. The HSQC NMR result confirmed that the cascade degumming process mainly acted on β-β bond, while β-O-4 bond was relatively preserved. Although the hemp fibers of the cascade degumming exhibited slightly lower tensile strength, the cascade degumming contributed to finer hemp fiber diameter (10.09 dtex) than the alkaline degummed fibers (12.66 dtex). Thus, the cascade degumming has favorable effects in removing gum components and achieving better fiber separation.