Toughening of Poly(hydroxyurethane)–Epoxy Hybrid Networks by High-Aspect-Ratio Cellulose Nanocrystals

High Resolution Image Download MS PowerPoint Slide Nonisocyanate polyurethanes are sustainable alternatives to conventional polyurethanes but often exhibit limited mechanical performance. Here, poly(hydroxyurethane) (PHU)–epoxy hybrid networks were prepared to tune matrix stiffness through covalent cross-linking and reinforced with wood- and tunicate-derived cellulose nanocrystals (CNCs). Increasing epoxy content enhanced Young’s modulus and tensile strength while reducing strain at break. In contrast, incorporation of CNCs into an intermediate PHU–epoxy matrix produced substantial mechanical enhancement at low loadings. Tunicate-derived CNCs, characterized by higher aspect ratios, provided greater reinforcement than wood-derived CNCs and achieved a maximum toughness of ∼27 MJ m –3 at 2 wt %, exceeding both wood-derived CNC nanocomposites (≤17 MJ m –3 ) and neat PHU–epoxy hybrids (≤16.5 MJ m –3 ). Scanning electron microscopy confirmed homogeneous CNC dispersion, while Fourier transform infrared spectroscopy indicated extensive hydrogen-bonding interactions. These results demonstrate that epoxy hybridization and high-aspect-ratio CNC reinforcement provide complementary routes to enhance the mechanical performance of biobased PHU materials.