Water transport properties of bio-nanocomposites reinforced by Luffa cylindrica cellulose nanocrystals

Poly(ε-caprolactone) (PCL) based nanocomposite films reinforced by cellulose nanocrystals isolated from Luffa cylindrica were prepared by film casting/evaporation technique in nonaqueous media. The contribution of nanofiller content on the transport properties of PCL matrix was investigated through water sorption and water permeation processes. Besides, the recently-developed long-chain isocyanate grafting on cellulose was applied to L. cylindrica nanocrystals. Its impact on the water transport properties was specifically investigated at a nanoparticle loading higher than percolation threshold. A peculiar behavior against water vapor molecules was exhibited as functions of content, of water activity, and of surface-chemical modification. This behavior was related to the establishment of hydrogen-bonding interactions between nanocrystals during the formation of the three-dimensional cellulose network which contributed to a restriction of matrix chain mobility. For simulating the water sorption measurements, the Park and GAB models were applied to the experimental data. The mathematical parameters were found to agree well with the measured ones. The water content predicted as well as the nanocomposite behavior described by both models were discussed. Regarding water permeation, a barrier effect to water is highlighted by the reduction of the permeability: the nanoscale rod-like morphology of nanocrystals made longer the diffusion path of diffusing molecules by tortuosity effect. Moreover, a dependence between penetrated water concentration and water diffusivity is evidenced.