Ph15ase separation morphology and mode II interlaminar fracture toughness of bismaleimide laminates toughened by thermoplastics with triphenylphosphine oxide group

Toughness improvement of bismaleimide (BMI) resin is very important for its application in composite materials. Blending with thermoplastic polymer is usually used to increase the toughness of BMI matrix. In this work we prepared two thermoplastic polymers with polar triphenylphosphine oxide group in the polymer backbone. The synthesized thermoplastics with different polarities were investigated by several physicochemical methods. Then through scanning electronic microscopy we observed the phase separation morphology of BMI blends at different doping concentrations of thermoplastics. Additionally mode II interlaminar fracture toughness G_IIC of BMI laminates toughened with thermoplastics by ex-situ method was examined. The results showed that thermoplastic with strong polarity would bind tightly with BMI during curing and the phase-separation structure might be fixed at the primary stage; while secondary phase separation could happen in a relatively weak polarity system. It indicates that by regulating the polarity of thermoplastic, we may control the phase separation morphologies of blending system and the mechanical properties of composite.