Vinyl Ester Resin Modified with Acrylated Epoxidised Soybean (AESO) and Linseed (AELO) Oils: Effect of Additional Urethane Crosslinking

Bisphenol A-based vinyl ester resin (VE) was modified with acrylated epoxidised soybean and linseed oils (AESO and AELO, respectively) in 10 wt.%. The double bond/epoxy ratio in these functionalised vegetable oils was practically the same, i.e. 30/70%, allowing us to deduce effects caused by the different unsaturations in the parent oils. The crosslink density of the resins was enhanced by adding polyisocyanate. The glass transition temperature (T_g) of the hybrids was determined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Resistance to thermal degradation was assessed by thermogravimetric analysis (TGA). The fracture toughness and energy (K_c and G_c, respectively) were determined on compact tension specimens at room temperature. Incorporation of AESO and AELO reduced the T_g of VE along with slight reductions in the K_c and G_c data. The T_g reduction was less for AELO than AESO which was attributed to the higher functionality of AELO compared to AESO. Urethane crosslinking of VE (VEUH) prominently enhanced the T_g. Modification of VEUH with AES(L)O enhanced the T_g due to additional crosslinks. Urethane hybridisation was associated with a strong decrease in both K_c and G_c compared to those of the parent VE. K_c and G_c of VEUH did not change practically as a function of blending with AES(L)O. Incorporation of AES(L)O reduced the resistance to thermal degradation of both VE and VEUH.