Additive toughening effects on new bio-based thermosetting resins from plant oils

The aim of this work was to find a suitable toughening agent for triglyceride-based thermosetting resins suited for high performance composite applications. Rigid polymers with high stiffness have been developed from triglyceride oils. The highly cross-linked structure gives these polymers high yield and fracture stress, but the reduced molecular mobility makes these polymers very brittle with poor resistance to crack initiation and propagation. Three methods have been used to increase toughness of triglyceride-based thermoset resins: (1) liquid rubber, (2) plasticizer, and (3) inorganic nano-filler. The following results were obtained: (1) The liquid rubbers, carboxyl terminated poly(butadiene-co-acrylonitrile) (CTBN) and vinyl terminated poly(butadiene-co-acrylonitrile) (VTBN), form a secondary elastomeric phase dispersed in the continuous polymer matrix but only provide a small increase in toughness. (2) Epoxidized soybean liquid rubber (ESR), a prepolymer of epoxidized soybean oil with triethylene tetramine, forms a one phase structure when added to the triglyceride-based resins. The K1C value of the resulting materials doubled at 15 wt% ESR content, and the G1C value increased more than four times. (3) Organo-treated clay was added as a nano-filler. The G1C value is doubled at 2.6 vol% clay loading. Among these three toughening methods, the nano-filler was the best as there is no trade off with other mechanical or thermal properties.