Tailoring the Performance of Vegetable Oil-Based Waterborne Polyurethanes through Incorporation of Rigid Cyclic Rings into Soft Polymer Networks

Vegetable oil-based polymeric materials always suffer from relatively poor performance, such as lower tensile strength and glass transition temperatures, than petroleum-based polymeric materials, which greatly limit their practical applications. In this study, octahydro-2,5-pentalenediol (OPD) was synthesized from naturally occurring citric acid and used together with castor oil as the polyol blends for the production of bio-based waterborne polyurethane (PU) dispersions (PUDs). The effects of the OPD contents on the particle size and zeta potential of the resulting polyurethane dispersion, and the thermal stability, mechanical properties, and hydrophilicity of the resulting polyurethane films were systematically investigated. Taking advantage of the rigid cyclic structures of the OPD and the flexible fatty acid chain of castor oil, waterborne polyurethane (WPU) films with tailorable mechanical performance ranging from elastomeric polymers to rigid plastics were successfully prepared and characterized. The tensile strength of the samples increases from 9.5 to 22.3 MPa with the ratio between OPD and castor oil increasing from 0:10 to 5:5, whereas their elongation at break decreases from 192 to 12%. A significant increase in the glass transition temperature, transparency, and anticorrosive properties was observed for the resulting polyurethane films with increasing the OPD content. However, the thermal stability of the PU films exhibited a slight decrease as the OPD content increased. Moreover, the water contact angle exhibited a slight increase for the polyurethane films prepared from polyol blends compared to the WPU film prepared from pure castor oil. This work provides a novel route to tailor the performance of vegetable oil-based waterborne polyurethanes through the incorporation of rigid cyclic rings into soft polymer networks.