Modification on phthalonitrile containing benzoxazine with cyaniding diamine-type benzoxazine: Curing reaction and properties of their glass fiber-reinforced composites

Phthalonitrile resin is a kind of high-performance thermosetting resins . Decreasing the curing temperature and accelerating the curing reaction rate have become the focus of research on phthalonitrile modification. Based on the reactivity, thermal and mechanical properties of diamine-type benzoxazine , a monocyano-functionalized diamine-type benzoxazine (MD-cn) was synthesized and applied to modify bisphthalonitrile resin containing bisphenol-type benzoxazine/nitrile phenylenediamine (BA-ph/BAB). Curing reaction properties and curing mechanism of BA-ph/BAB/MD-cn were studied by gelation time, DSC, DRA and in-situ IR. Results showed that MD-cn could significantly boost the curing reaction rate and reduce its curing temperature of BA-ph/BAB. Meanwhile, glass fiber reinforced composites (BA-ph/BAB/MD-cn/GF) was prepared and their properties were studied. Results showed that MD-cn improved the crosslinking density and curing degree of BA-ph/BAB could make the BA-ph/BAB/MD-cn resin matrix possess higher stiffness. Therefore, BA-ph/BAB/MD-cn/GF composites exhibited higher flexural strength (494 MPa, increased 40%) and flexural modulus (26 GPa, increased 13%) as well as good dimensional stability. Compatibility between MD-cn and BA-ph/BAB was investigated by DMA and SEM. Moreover, with the increase of MD-cn content, the good thermal stabilities ( T 5% >404.5 °C, Y c, 800 °C >66%) of cured BA-ph/BAB/MD-cn were obtained. Besides, interfacial adhesion properties of BA-ph/BAB/MD-cn/GF composite laminates were also studied.