Component size dependent lignin-carbohydrate complex adsorption at crystalline cellulose surfaces

The materials characteristics of natural wood but also the properties of artificial cellulose/hemicellulose-based wood-inspired composite materials result from the molecular level organization and interactions between cellulose, hemicellulose, and lignin. Here, we use atomistic detail molecular dynamics simulations to examine the adsorption of model lignin-carbohydrate complexes (LCCs) consisting of a glucomannan polysaccharide chain with differing lignin fragment linkages to the crystalline facets of cellulose nanocrystals. The findings show that on crystalline cellulose surfaces exceeding in surface dimensions the length of the adsorbed hemicellulose chain, the LCCs can adopt orientations both parallel and perpendicular to the surface chains with response depending on the crystalline facet. The observation of perpendicular orientations is unexpected, as previous molecular level modelling studies systematically report parallel LCC adsorption orientation, however on cellulose interfaces modelling the narrow natural wood cellulose fibrils. Here, the perpendicular adsorption orientation is stabilized by extensive hydrogen bonding and adsorption of the hemicellulose chain with negligible chain bending. Overall, the results show that component dimensions (hemicellulose chain length vs cellulose crystalline surface dimensions) combined with understanding the differences of adsorption response at the difference crystal facets are crucial in understanding wood-inspired materials.