The preparation and characterization of polyurethane reinforced with a low fraction of cellulose nanocrystals

Cellulose nanocrystals (CNC) produced from renewable cellulosic feedstocks have been used in polymer reinforcement, resulting in significant enhancements to mechanical properties. In this study, a series of CNC reinforced polyurethane (PU) nanocomposites were manufactured and tested for their rheological, thermo-mechanical, mechanical and abrasion properties. First, stable polyol-CNC suspensions were prepared using a combination of water and 1,3-propanediol as dispersing solvent. These suspensions were then combined with isocyanates to produce CNC reinforced PU samples. Rheological testing of the uncured polyol-CNC-isocyanate liquid suspension indicated the formation of a pervading network between CNC particles. The thermo-mechanical properties of the CNC reinforced nanocomposites were significantly improved compared to unreinforced PU, as measured by differential scanning calorimetry and dynamic mechanical analysis. With the addition of 0.5% CNC by weight to the PU resin, the glass transition temperature increased 10 degrees C. Furthermore, this CNC reinforcement of the PU resin yielded an increase in the tensile strength, Young's modulus, elongation at break, and abrasion resistance of approximately 30%, 55%, 70%, and 40%, respectively. These increases are likely due to a combination of increased cross-linking density within the PU network, arising from PU-CNC molecular interactions, and the reinforcing effect of the CNC.