Elucidating the impact of density, alignment, and moisture content on the mechanical properties of cellulose nano-assemblies using multiscale molecular dynamics simulations

Cellulose nanomaterials are promising to a range of applications as they are bio-based and host impressive mechanical properties, such as high tensile modulus, while maintaining low density. However, nanoscale interactions between cellulose nanocrystals and their environment modulate bulk mechanical properties: increasing moisture content, decreasing density, and nanocrystal disorder have all been shown to decrease the tensile modulus. Atomic-scale molecular dynamics (MD) simulations provide useful information about such nanoscale interactions but are limited in length and timescales, which presents challenges when applying models to bulk materials. Bottom-up coarse-grained models increase the length and time-scales accessible to MD by systematically mapping atomic information to lower resolution models. The current study leverages multiscale MD simulations to study the impact of moisture content, density, and cellulose nanocrystal alignment on the tensile modulus of simulated cellulose nano-assemblies. The results reveal the experimentally suggested trends are due in large part to anisotropic inter-crystal interactions, mediated by both hydrophilic and hydrophobic driving forces, and provide actionable insights for engineering high performance cellulosic materials.