Deep eutectic solvent degumming of hemp fiber: Key factors influencing fiber property and its mechanism

In order to remove non-cellulosic materials from the surface of hemp fiber for potential application in textile industry, a DES (choline chloride: urea, 1:2)- alkali H2O2 (DES- alkali H2O2, DAHD) hemp fiber degumming method was established. The changing regularity of DES treatment on the degumming effect of hemp fiber under different operational conditions (temperature, time and bath ratio) were fully investigated. The properties of purified fibers and the mechanism of degumming were systematically analyzed using several test methods. Chemical composition showed that treated fibers have higher cellulose content than alkaline treated ones, whereas removal rate of non-cellulose components reached 53%. The tenacity, length and degree of polymerization (DP) of the treated fiber was increased by 25%, 30% and 20%, respectively compared with traditional alkali degumming. Analysis by Py-GC/MS indicated the major pyrolysis product (LG) of cellulose was increased by 27.77% after DAHD treatment, and the major ester and ketones content was decreased by 1.07% and 11.13% due the removal of hemicellulose, respectively. Results from 2D NMR revealed that cleavage of β-O-4′ linkages significantly occurred and β-5′ linkages were all removed. The G-type lignin was further degraded than the S-type in DES-alkali H2O2 degumming system. Besides, DES still has enough degumming effect after repeated utilization. This study provides an potential practical method for hemp fiber extraction, which is characterized by high fiber quality, low energy consumption, eco-friendly and high efficiency.