Degumming of hemp fibers using combined microwave energy and deep eutectic solvent treatment

Hemp bast fibers were degummed using combined microwave energy (MWE) and deep eutectic solvent (DES) to generate pure hemp cellulose fibers for potential textile applications. The properties of the degummed fibers were investigated and compared with those of the alkali-treated fibers using several analytical techniques. Results revealed that hemp fiber surface underwent dramatic structural disruption during the pretreatment, due to the removal of "gummy" compounds (i.e., pectin, oil, wax, etc.), lignin, and amorphous cellulose. The treated fibers had much enhanced thermal stability due to the removal of the gummy materials. The reduced enthalpy (171.34 J/g) of MWE-DES treated fibers at 1:20 fiber-DES ratio as compared to that of raw hemp fibers (272.09 J/g) also confirmed the higher thermal stability of MWE-DES treated fibers. Chemical composition analysis showed that the holocellulose content in the treated fiber samples at 1:20 fiber-DES ratio increased to 98.63% which was comparable with the holocellulose content (98.87%) of the alkali-treated fibers. The Ultraviolet (UV) protection factor (UPF) of MWE-DES treated fibers at 1:10 and 1:20 fiber-DES ratio was, respectively, 118.11 and 114.19, meeting the requirement of UV resistant textile fibers. The study demonstrates a potentially effective, less time-consuming, and environmentally sustainable protocol for manufacturing purified hemp cellulose fibers using combined MWE-DES treatment.