Mechanical, thermal and barrier properties of nano-biocomposite based on gluten and carboxylated cellulose nanocrystals

• Carboxylated cellulose nanocrystals significantly improved several properties.
• Mechanical properties improved significantly with low loadings of nanocrystals.
• Barrier properties against water vapor were enhanced significantly.
• At a concentration of 10 wt.% C.CNC, melting point increased significantly.

Bio-based polymers and biocomposites are a relatively new and growing market in light of recent societal concerns including dwindling petroleum reserves, environmental and end-of-live disposal issues. Developing sustainable and environmentally friendly alternatives to current packaging films, such as polyethylene is neither easy nor simple. We report here on our effort to develop a novel nanocomposite-based packaging film comprised of gluten filled with carboxylated cellulose nanocrystals (C.CNCs). We observed the effect of different C.CNC loadings on the mechanical, thermal, sorption and barrier properties of the resulting composite films. The results of differential scanning calorimetry (DSC) indicated that increasing the C.CNC amount from 0 to 10 wt.% showed a minimum at 5 wt.% for the glass transition temperature (Tg). The mechanical properties showed that the breaking elongation (ɛb) decreased by 26%, but tensile strength (TS) increased (60%) in the presence of C.CNC, with a maximum at 7.5 wt.%. The reinforcing effect of C.CNCs was also confirmed by dynamic mechanical analysis (DMA) where, by adding C.CNC, an increase in storage modulus was detected. As compared to film without C.CNC, the water vapor permeability (WVP) decreased from 7.74 × 10−11 to 4.96 × 10−11 mol/m.s. Pa for the film containing 7.5 wt.% C.CNC; with increasing nanocellulose content, water uptake of the nanocomposites increased but water solubility decreased. These results indicate that the nanocellulose is promising as a reinforcing agent in gluten polymers.