The coefficients of hygroscopic swelling (CHS) of self-organized and shear-oriented cellulose nanocrystal (CNC) films were determined by capturing hygroscopic strains, which was produced by isothermal water vapor intake in equilibrium. The characterization of dimensional changes induced by the hygroscopic swelling of the films is enabled by contrast-enhanced microscopy digital image correlation. The distinct microstructure and birefringence of CNC films helped in exploring the in-plane swelling at relative humidity values ranging from 0% to 97%. Water vapor intake in the films was measured using dynamic vapor sorption at constant temperature. The experimental moisture sorption and kinetic profiles were analyzed by fitting with Guggenheim, Anderson, and DeBoer (GAB) and parallel exponential kinetics (PEK) models, respectively. Self-organized CNC films showed isotropic swelling, CHS ~ 0.040 %strain/% C whereas, shear-oriented CNC films exhibited an anisotropic swelling, resulting in CHS ~ 0.02 and ~ 0.30 %strain/%C, parallel and perpendicular to CNC alignment, respectively. Finite element analysis (FEA) predicted moisture diffusion as the predominant mechanism for swelling in CNC films.

Hygroscopic swelling determination of cellulose nanocrystal (CNC) films by polarized light microscopy digital image correlation

256th National Meeting (2018)

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