Synergetic ultrasound-swollen treatment modulates the impact of molecular structure and dissolution performance of cellulose in NMMO solution

Considering the environmental requirements and economic sustainable development, it is crucial to adopt an environmentally friendly and effective pre-treatment to improve the dissolution efficiency of cellulose in aqueous N-methyl-morpholine-N-oxide (NMMO) solution by disrupting the intra- and inter-molecular hydrogen bonds of cellulose for the development of the lyocell fiber industry. Herein, a facile strategy of synergetic ultrasound-swollen treatment was developed to shorten the swelling and dissolution time to make a homogeneous cellulose solution. The novelty of this work lies in that the synergetic ultrasound-swollen treatment could effectively disrupt the molecular chains of cellulose, increase the pore volume and specific surface area, and accelerate the dissolution of cellulose in aqueous NMMO solution. The substantial decrease (55.76%) of number-average molecular weight implied the cleavage of molecular chains. The remarkable increase of specific surface area (about 5 times) and short dissolution time proved the effective synergetic effect of ultrasonic cavitation and swelling of NMMO solution. Therefore, the synergetic ultrasound-swollen treatment not only accelerated the diffusion of the NMMO solution into the crystalline regions of cellulose to disrupt molecular chains, but also enlarged the specific surface area and improved the dissolution efficiency.

Graphical abstract