Xyloglucan is the major hemicellulose occurring in plants. Its structure consists of a β-(1-4)-D-glucan backbone decorated with α-D-xylosyl and β-D-galactosyl units. In nature, xyloglucan coats cellulose forming a network that regulates structural rigidity and strength of cell wall. Inspired in these biosystems, we took advantage of the interaction between cellulose and xyloglucan to fabricate stimuli responsive films containing cellulosic polysaccharides. Cellulose nanocrystals (CNC) and chitin nanocrystals (ChiNC) were isolated by acid hydrolysis of cellulose cotton linters and chitin flakes from crab shells, respectively. (CNC-XG) and (ChiNC-XG) multilayer films were fabricated by spin-coating assisted layer-by-layer technique. Films were prepared from CNC (3 g L-1), ChiNC (1 g L-1) and XG (0.5 g L-1) to obtain similar thickness. The swelling behavior of films was evaluated by the H2O/D2O solvent exchange method monitored by quartz crystal microbalance with dissipation (QCM-D). Increase of thickness during swelling was determined by the coupling of QCM-D and ellipsometry. For four-bilayer films, results showed lower water uptake (93%) for (CNC-XG)4 compared to 135% of (ChiNC-XG)4. Thickness increased from 32 to 133 nm for (CNC-XG)4, and from 40 to 294 nm for (ChiNC-XG)4 when films were exposed to water. The difference suggests that XG adsorbs onto CNC via a specific coupling, in which flexible XG chains adopt a flat conformation to fit the surface morphology such that swelling is low. Differently, XG deposition onto ChiNC seems less specific and the steric hindrance caused by the acetyl groups may result in the formation of loops and tails stretched out along the surface, which favor water uptake by XG. This work demonstrates that the swelling behavior of xyloglucan-containing films can be easily modulated by xyloglucan arrangement onto nanocrystal surface so that responsive materials can be fabricated from polysaccharide building blocks.

Bioinspired xyloglucan-containing films as responsive smart materials

249th National Meeting (2015)

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