Use of tung oil as a reactive toughening agent in dicyclopentadiene-terminated unsaturated polyester resins

Unsaturated polyester resin terminated with dicyclopentadiene (DCPD-UPR) was modified by tung oil (TO) via intermolecular Diels–Alder reaction occurring at the later stage of melt polycondensation. These TO-modified DCPD-UPR (DCPD-UPR-TO) polymers were characterized by FT-IR, 1 H NMR, and gel permeation chromatography. The DCPD-UPR-TO polymers were further blended with styrene comonomer and cured via free-radical polymerization to give crosslinked thermosetting polymers. Scanning electron microscopy was employed to produce surface morphology and dynamic mechanical analysis was conducted to study the thermo-mechanical properties. Thermal and mechanical properties of these biomaterials were also investigated and the results show that toughness of them increases obviously as the increase of TO content. Compared with the neat DCPD-UPR matrix, the matrix obtained from DCPD-UPR-TO with a TO content of 20% has maximum increase of 373% and 875% in impact strength and tensile failure strain due to the synergistic effects of phase separation and crosslink density. However, the optimum amount of tung oil is 10% because its polymer matrix gives a best stiffness–toughness balance. These oil-based polymer materials show promise as an alternative to replace petroleum-based materials.