Thermal behaviour of benzoxazine blends based on epoxy and cyanate ester

In the present work, an attempt has been made to develop high-performance polymeric hybrid binary blends of epoxy/ benzoxazine and benzoxazine/cyanate ester with varying weight percentages (25/75, 50/50 and 75/25 wt%) of resins, namely, bisphenol-F epoxy resin (DGEBF), benzoxazines [bisphenol-F/aniline (BF-a) and imidazole core-based bisphenol/aniline (IBP-a)] and cyanate ester [bisphenol-F bifunctional cyanate ester (BF-CE)]. The molecular structure, polymerisation temperature/ cure behaviour, glass transition temperature (T-g) and thermal stability of the neat polymeric matrices and binary hybrid blends of polymeric matrices were characterised using different analytical techniques, viz. Fourier Transform infra-red spectroscopy (FTIR), Nuclear Magnetic Resonance spectroscopy (NMR), Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA). Among the binary hybrid blends, the lowest polymerisation temperatures (T-p) were noticed in the case of blends of epoxy/benzoxazine were 219 degrees C for DGEBF/BF-a (25/75 wt%) and 170 degrees C for DGEBF/IBP-a (25/75 wt%). Similarly, in the case of blends of benzoxazine/cyanate ester, the lowest values of T-p observed were 155 degrees C and 153 degrees C for BF-a/BF-CE (75/ 25 wt%) and IBP-a/BF-CE (75/25 wt%), respectively. The highest values of T-g observed for the blends of epoxy/benzoxazine were 175 degrees C and 254 degrees C for DGEBF/BF-a (25/75 wt%) and DGEBF/IBP-a (25/75 wt%), respectively. Whereas, the highest values of T-g observed in the case of blends of benzoxazine/cyanate ester were 234 degrees C and 278 degrees C for BF-a/BF-CE (25/75 wt%) and IBP-a/BF-CE (75/25 wt%), respectively. From the TGA results of blends, the maximum degradation temperature (T-m(ax)) and limiting oxygen index (LOI) value calculated from the char yield, which ascertain that almost all the binary hybrid blends of epoxy/benzoxazine and benzoxazine/cyanate ester possess good flame retardant behaviour.