Low volume shrinkage, high bio-based, and UV-curable coatings from castor oil-based reactive diluent via a one-step reaction

UV-curing technology possesses the advantages of fast curing, and cured at room temperature, which has been developed rapidly in recent years. However, the volume shrinkage usually occurs during the UV-curing polymerization process, seriously hindering its application. In this paper, a low volume shrinkage, high bio-based contents, and UV-curable resins was fabricated from the raw materials of castor oil, and cardanol. A three functional castor oil-based reactive diluent (COSH) was synthesized using a one-step method of thio-ene click reaction, and the COSH was blended with cardanol-based PUA (CNPUA) oligomer with different content, and prepare bio-based UV-curable materials. The comparative investigation were conducted on the thermal, and mechanical properties with petroleum-based diluents of trimethylolpropane triacrylate (TM), and trimethylolpropane tris (3-mercaptopropionate) (TMSH), respectively. As the content of COSH increased to 40%, the bio-based content of the CNPUA/COSH reached to the highest value of 60.0%, and the viscosity and volume shrinkage of CNPUA/COSH exhibited the lowest data of 1651 mPa·s, and 13.3%, respectively. The COSH not only had good dilution ability, but also possessed excellent anti volume shrinkage ability, and the mechanism of the anti shrinkage COSH was also explored. In addition, the three long carbon chain structures of the COSH endowed the cured coating excellent adhesion of 1 level, and pencil hardness of 3 H-4 H, as well as the flexibility of 2 mm. Lastly, the kinetics of the resulting resins were studied using real-time infrared spectroscopy (RT-IR). This study provides a feasible method for preparation of oil-based reactive diluents, and a new strategy for constructing the sustainable UV-curable materials with high performance.