Xyloglucan Structure Impacts the Mechanical Properties of Xyloglucan-Cellulose Nanocrystal Layered Films-A Buckling-Based Study.

Interactions between polysaccharides, specifically between cellulose and hemicelluloses like xyloglucan (XG), govern the mechanical properties of the plant cell wall. This work aims to understand how XG molecular weight (MW) and the removal of saccharide residues impact the elastic modulus of XG-cellulose materials. Layered sub-micrometer-thick films of cellulose nanocrystals (CNCs) and XG were employed to mimic the structure of the plant cell wall and contained either (1) unmodified XG, (2) low MW XG produced by ultrasonication (USXG), or (3) XG with a reduced degree of galactosylation (DGXG). Their mechanical properties were characterized through thermal shrinking-induced buckling. Elastic moduli of 19 ± 2, 27 ± 1, and 75 ± 6 GPa were determined for XG-CNC, USXG-CNC, and DGXG-CNC films, respectively. The conformation of XG adsorbed on CNCs is influenced by MW, which impacts mechanical properties. To a greater degree, partial degalactosylation, which is known to increase XG self-association and binding capacity of XG to cellulose, increases the modulus by fourfold for DGXG-CNC films compared to XG-CNC. Films were also buckled while fully hydrated by using the thermal shrinking method but applying the heat using an autoclave; the results implied that hydrated films are thicker and softer, exhibiting a lower elastic modulus compared to dry films. This work contributes to the understanding of structure-function relationships in the plant cell wall and may aid in the design of tunable biobased materials for applications in biosensing, packaging, drug delivery, and tissue engineering.