| Composites of hollow glass microspheres (HGM) filled epoxy resin were manufactured, which has lower density, higher strength and less saturated water absorption. The density of the composite is 0.682 g/cm3. Its compressive strength and modulus are 70 MPa and 1.540 GPa, respectively. The water gain at saturation is less than 3%.The mechanical properties of composites were investigated as a function of the volume fraction (Vf) and particles size of HGM, and the effects of HGM modified by coupling agent, content of curing agent (2-ethyl-4-methylimidazole, 2,4-EMI) and reactive diluent (n-butyl glycidyl ether, BGE) on the mechanical properties of epoxy resin and composites were studied. Further more, the morphology, fractography and failure features of composites were analyzed by SEM, and mathematic equation was modeled to predict the compressive strength and modulus. The experimental results indicated that with the increasing of Vf, the compressive strength decreased, and compressive, flexural modulus increased. When Vf<0.20, little effect of Vf on the flexural and impact strength was observed. But when Vf>0.20, as Vf increased, the flexural and impact strength decreased greatly. Through the SEM photographs of the fracture surfaces, it was found that when Vf >0.30, fracture of the composites was resulted from the break of HGM, thus in this condition HGM modified by coupling agent had little effect on the mechanical properties of composites. In addition, with the increasing content of 2,4-EMI, the toughness and impact strength of composites and resin improved, but its modulus reduced. Similarly, adding BGE also conduced to the improvement of impact strength and slight decrease in compressive strength and modulus.Moisture absorption of the composites in deionized (DI) water and salt water at different temperature were studied, respectively. Moisture absorption kinetics and effect of water absorption on mechanic properties were also investigated. It was found that the composites absorbed little water in saturation at room temperature, but when water temperature increasing, the saturated water absorption, absorbing rate and water diffusion coefficient at the beginning stage increased greatly. In salt water the composites had less water absorption, absorption rate and diffusion coefficient than that in DI water. No significant difference was observed in the compressive and flexural strength of the specimens at room temperature compared to the dryspecimens. However, specimens showed much decrease in strength compared to the dry samples at 60℃. The modulus of the wet samples was lower than that of dry ones, especially at high temperature. In addition, water absorption affected severely to the mechanical properties of composites in ID water compared to that in the salt water.Curing kinetics of 2,4-EMI cured bisphenol-A diglycidyl ether type epoxy resin (DGEBA) system was analyzed by DSC. When 2,4-EMI concentration and curing temperature increasing, curing reaction rate increased. From the results of DSC, the optimized curing condition was decided. Based on the curing mechanism, the differential equations of curing reaction rate were listed and curing reaction model was established. The model can predict part of experimental results, but some deviations were observed at the higher value of curing degree because of the effect of diffusion. Thus the critical curing degree and diffusion factor were introduced to the former model, the curing kinetic model with the control of diffusion was developed. This model can well predict the curing kinetics.In order to overcome the brittleness of epoxy resin, some toughening agents, such as, reactive liquid rubbers (CTBN), polysulphide rubber (PSR) and polyurethane (PU), were blended to this system. After addition of CTBN, PSR and PU, the impact strength of pure resin and composites were improved, but strength and modulus was reduced. It was found with SEM that in curing process tiny spheres of CTBN were separated from epoxy resin, and in high CTBN concentration, double continuous phases were... |
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