Non-isothermal Cure Kinetics of Polybenzoxazine/Carbon Fiber Composites by Phase Change Theory

The cure of benzoxazines (BA-a) and benzoxazine/carbon fiber (BA-a/CF) composites was monitored by non-isothermal differential scanning calorimetry (DSC) at various heating rates. The characteristic temperatures of BA-a and BA-a/CF were analysed. The results showed that the initial cure temperature of BA-a/CF was lower than that of BA-a at the same heating rate. Various kinetic parameters and apparent activation energies for both curing systems were obtained by using a modified version of the Avrami equation. For BA-a, the apparent activation energy was 116.8 kJ/mol, which agreed well with the published data. For BA-a/CF, the results showed that the plot of Avrami rate constant vs. 1/T was not a straight line for the whole curing temperature range, but it displayed a marked change in slope at around 220 ^o C. The apparent activation energies at primary and second section were 105.6 kJ/mol and 224.8 kJ/mol respectively. The cure reaction of benzoxazines was not only catalysed by carbon fiber, but also was retarded by it.