Molecular dynamics simulations of performance degradation of cellulose nanofibers (CNFs) under hygrothermal environments

Abstract

ABSTRACT Cellulose nanofibers (CNFs) have received wide attention in recent years. However, the performance degradation of CNFs has become a serious problem restricting their development when exposed to hygrothermal environments. While most studies have attributed the degradation behaviour to the water susceptibility of CNFs, the internal mechanism and detailed performance evolution are seldom reported at the molecular level. This paper used molecular dynamics simulation to study the effects of moisture on the diffusion, structure, mechanical strength, and chemical stability of CNFs. Simulation results indicated that the water diffusivity in amorphous cellulosewas10 times higher than in crystalline cellulose, demonstrating the preferential water uptake in amorphous cellulose. Meanwhile, the diffusion coefficient of water was found to be almost constant in the amorphous cellulose with less than 5% moisture. This behaviour was related to the amount and size of pores in amorphous cellulose. Furthermore, under high humidity, there was a significant decrease in mechanical strength and chemical stability of amorphous cellulose. However, in the range 0–5.0% of water absorption, the mechanical performance showed a slight increase, and chemical stability was also relatively high. These results provide a crucial point (<5 wt% moisture) for CNFs to remain stable under hygrothermal environments.