Research On Curing Process And Mechanical Properties Of BMI And BMI Matrix Composites Cured By Microwave Radiation

In order to generalize the application of microwave curing technique in the field of bismaleimide(BMI) resin matrix composite materials, some fundamental researches on curing process and performance were carried out. A certain BMI resin system that could be cured relatively fast under microwave was developed by resin system selection and further optimization. The microwave curing process of BMI resin was studied, and the resin casting and BMI resin matrix composite with comparable thermal and mechanical properties were successfully prepared by microwave. Thus, some practical experience and theoretical guidance was provided for the application of microwave curing technique in BMI resin matrix composite.The influence of parameters of BDM/DABPA/DCP resin system on its microwave curing efficiency was studied by “Latin Square Design”. The results showed that the pre-polymerization of BDM/DABPA led to a sharper exothermic pick of the resin DSC curve, which could enhance the curing reaction greatly. The recipe of BMI resin system was BDM/DABPA= 0.8:1 mole ratio, pre-polymerization time=60 minutes, and the amount of DCP was 1.5 wt% of the whole mass of BDM+DABPA. Besides, the curing process of BMI resin under microwave was studied. It could be concluded that the chemical crosslinking reaction was only activated under a certain high level of microwave power(450W). Besides, the curing speed of resin under microwave increased with time in the beginning and then decreased.In order to compare the microwave and thermal curing process, the BMI resin castings were cured in two ways. Above all, the microwave curing had a great advantage in saving time, as the time was reduced by 87% under microwave. The glass transition temperature(Tg) of the resin castings was nearly same, indicating that microwave curing could maintain the thermal performance of resin. Investigation on mechanical properties of resin castings showed slightly higher modulus and lower strength in both flexural and tensile test. The main reason was that the speed of curing reaction was faster under microwave and the crosslinking density was higher, which added to the stiffness, fragility and then reduced the strength of resin casting.To explore the mechanical properties of BMI/GF composite, the composite laminate was prepared under microwave and thermal conditions using BMI/GF prepreg. The BMI/GF prepreg was obtained through a self-made drum-winding system. A series of mechanical test was applied to the cured laminate in order to give a general evaluation of microwave curing technique. Compared to thermal cured [0/90]3s laminate, the flexural and tensile strength of microwave cured laminate had a decrease less than 7.7%, while the tensile modulus had an increase of 7.6%. The short beam shear strength of [0/0]3s laminate also decreased by 10% It was mainly due to the mechanical property change of resin matrix as mentioned before. When cracks occurred within composite, the fragile resin matrix could not stop the growth of the cracks, thus reducing the strength of laminate.