Study On Heat-resistant Structural Adhesives Of Bismaleimide

With the urgently demanding of heat-resistant structural adhesive in aeronautics and astronautics, the type of bismaleimide has been the focus in research. In this article, we firstly researched the raw materials, recipes and technics. Nano-SiO_x and whisker SiO₂ were used to modify the systems of adhesives, and we got the curing technics excellent, and the cohesive strength high, at the same time the heat-resistance and toughness assorted with each other well.In recipes and technics, according to tensile shear strength, we assured the optimal proportions were: bismaleimide (BMI)/ diamine diphenyl sulfone (DDS) =1:1.5(mol), prepolymer/epoxy (EP) =60/40(quality). Viscosity and the time to gel indicated that the adhesives had fine technics;Fourier transform infrared(FTIR) and differential scanning calorimetry (DSC) were used to analyze the reaction mechanisms, and confirm the best curing technics of 150℃/2h+200℃/2h+220℃ /1.5h. Finally the curing kinetics of BMI/ DDS / EP was studied. The apparent activation energy ΔE, pre-exponential factor A and the curing reaction order n were calculated.Merely the BMI/DDS/EP adhesives were very brittle;the next step was to enhance the toughness. In practice, we added nano-SiO_x and whisker SiO₂ to the system, and necessary silane coupling agent gamma-chloropropyltriethoxy silane (KH-550) improved the performances of fillings' surfaces. The test of laser granularity instrument and transmission electron microscope (TEM) pictures showed that coupling agent exerted modification effect, and nano-SiOx dispersed well in matrix. FTIR spectrums approved that the molecule of KH-550 effectively grafted to the surfaces of nano-SiO_x and whisker SiO₂. The dosages of fillings and coupling agent were examined via their affection on dispersion.For nano-SiO_x and whisker SiO₂ were organic, their additions played important roles in heat-resistance and mechanical properties. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) charactered the heat-resistance of modified adhesives. Nano- SiO_x made glass transition temperature (T_g) and heat decomposition temperature separately improve to 208℃ and 295℃;Whisker SiO₂ made heat decomposition temperature reached 275℃。 Nano- SiO_x made bendingstrength and impacting strength increased 36.8% and 6.2% to the greatest extent;The addition of whisker Si(>2 also made contributions to mechanical properties in a certain degree.Combined with scanning electron microscope (SEM) pictures of sections after bending and impacting, the mechanisms of nano-SiOx and whisker SiO2 modifying the adhesives were discussed primarily. Several theories together acted on the last results, but the dispersion was the most important factor at all the time.