Phase-separation dominating mechanical properties of a novel tung-oil-based thermosetting polymer

Abstract This paper focuses on the structure–property relationship of a tung-oil-based thermosetting polymer, which was obtained by curing a newly developed tung-oil-based monomer (TOPERMA) with different styrene contents. Phase separation was first observed from transparency of the polymer matrixes and further studied by scanning electron microscopy (SEM). The separation resulted from the incompatibility of maleinated oil-based resins and styrene, and might be influenced by curing temperature and reactivity ratios of the reactive monomers. By dynamic mechanical analysis (DMA) storage modulus, glass transition temperature, and crosslink density of the bio-based polymer materials were investigated. The two effects of phase separation and crosslink density were used to correlate the microstructure factors with the obtained thermo-mechanical and mechanical properties of the tung-oil-based resins. It was found that the phase-separation effect was the dominating factor affecting the mechanical properties rather than other factors. The matrix of TOPERMA with 33% styrene exhibited good stiffness–toughness balance due to the minimum extent of phase separation it had. This developed eco-friendly bio-based polymer shows potential structural application as sheeting molding compounds.