Synthesis, Thermal and Mechanical Properties of Nonisocyanate Thermoplastic Polyhydroxyurethane Nanocomposites with Cellulose Nanocrystals and Chitin Nanocrystals

Incorporating biobased nanofillers including cellulose nanocrystals (CNCs) and chitin nanocrystals (ChNCs) into nonisocyanate polyurethane (NIPU) offers a multifunctional approach to improving mechanical and thermal properties while promoting sustainability and green chemistry. Nanocomposites of segmented thermoplastic polyhydroxyurethane (PHU) from vanillyl alcohol bis(cyclocarbonate) (VABC), poly(tetramethylene oxide) diamine (PTMODA), and bis(aminomethyl) norbornane (NORB) reinforced with a low amount of CNCs and partially deacetylated ChNCs were prepared and characterized. Fourier transform infrared spectroscopy, atomic force microscopy, and small-angle X-ray scattering revealed that partially deacetylated ChNCs were covalently grafted to the PHU through aminolysis of carbonate end groups in the hard segment, while CNCs were mixed with the PHU without interfacial covalent bonding. Consequently, the PHU/ChNC nanocomposites showed nanophase separation with smaller hard domains compared to neat PHU, while the PHU/CNC nanocomposites exhibited a phase-mixed system with broader interface regions. Dynamic mechanical analysis and tensile tests further revealed that the PHU/ChNC nanocomposites demonstrated a 49-fold increase in Young's modulus, a 20-fold increase in ultimate tensile strength, and a three-order-of-magnitude enhancement in storage modulus in the rubbery state compared to the PHU/CNC nanocomposites, highlighting the profound influence of interfacial covalent linkages in enhancing the thermal mechanical performance of segmented PHU.