Bio-based waterborne polyurethanes reinforced with cellulose nanocrystals as coating films

In this study, two different bio-based waterborne polyurethanes (WBPUs) that use castor oil and tartaric acid in their formulations were modified by the incorporation of a renewable reinforcement, cellulose nanocrystals (CNC), to be further applied as metal coatings of tailored properties. Different mixed suspensions were prepared by blending aqueous suspensions of CNC with the WBPU dispersions to achieve CNC concentrations of 5 wt. % and 10 wt. % (dry basis). The viscosities of the mixed suspensions were adjusted, so that they could be used in dip-coating of aluminum plates, used as substrates. The coatings were tested using macroscopic methods such as knife and tape tests and contact angle. Microscopic techniques such as nanoindentation, nanoscratch and nanowear were carried out. The results showed the feasibility of using these nanocomposite WBPUs as coatings and the utility of the microscopic techniques in the characterization of the resulting surfaces.