Toughening of benzoxazine structural adhesives and surface films

In this paper, acrylic triblock copolymer (BMG) was used to toughen the benzoxazine/epoxy (BZ/EP) resin system and prepare a BZ/EP/DDS/BMG resin. BZ/EP/DDS/BMG resin curing characteristics, viscosity-temperature characteristics, heat resistance, toughness, morphology, and bonding performance were studied. The results show that the curing agent 4,4-diamino diphenyl sulfone (DDS) can lower the curing temperature of the BZ/EP/DDS system, making it suitable for co-curing of benzoxazine prepreg. The BMG did not affect the curing temperature of the BZ/EP resin. When 15 phr BMG was added, the viscosity of the BZ/EP/BMG resin at 139–189 °C was lower than 5.0 Pa·s, showing a minimum viscosity of 2.0 Pa·s. BMG significantly increased the toughness of the BZ/EP/DDS/BMG system while barely decreasing its heat resistance. The impact strength of the BZ/EP/BMG resin increased by 71% when 20% BMG was added. Furthermore, theBZ/EP/DDS/BMG resin demonstrated excellent bonding performance, with lap shear strength and peel strength at room temperature reaching 30.6 MPa, and 37.2 N/cm, respectively. Therefore, the prepared BZ/EP/DDS/BMG resin is suitable as a matrix for BZ structural adhesives and composite surface films.