Enhancement of thermal and mechanical properties of waterborne polyurethane-urea via chitin nanocrystal reinforcement

Chitin nanocrystals (ChNC) have attracted significant interest as reinforcement due to their exceptional mechanical properties such as Young's modulus, surface functional groups that promote hydrogen-bonding interactions with specific matrices, and high length/diameter aspect ratio. Therefore, this study investigated the incorporation of chitin nanocrystals into a waterborne polyurethane urea dispersion (WBPUU) at concentrations ranging from 0.5 to 7 wt%. Nanocomposite films were prepared using an ultra-sonication assisted solvent casting method, and their properties were thoroughly analysed. The results demonstrate that the addition of ChNC significantly enhances thermomechanical stability, Young's modulus and stress at break, achieving the percolation threshold at a theoretical concentration of 3 wt% of ChNC. Notably, beyond the percolation threshold, these properties have increased significantly up to WBPUU7, with thermomechanical stability improving by more than 500 % and both Young's modulus and stress at break increasing by over 100 % when compared to values obtained at WBPUU. The study revealed that the addition of ChNC significantly influences water absorption, resulting in a fourfold increase in uptake in a basic medium. Furthermore, the abrasion resistance of the nanocomposites improves with ChNC content due to stable and interconnected network forms.