| Epoxy resins are a series of important thermosetting resins. They become widely used in aeronautics and astronautics, architecture and machinery, insulation materials, the field of matrix resins of advanced composite materials because of their advantages of excellent mechanical properties, electrical insulation properties, chemical stability, heat resistence, low shrinkage rate, high binding strength and easy processing. However, there are some disadvantages of cured epoxy resins such as brittleness, poor crack and impact resistence, as well as fracture toughness because of the relatively high crosslinked density. As a consequence of above, it is of necessity to research on the toughening modification of epoxy resins because of the very outstanding theoretical significance and practical value. The main research content and the conclusions are as follows:Phenolphthalin (PPL) and2,6-difluorobenzonitrile were taken as the reactants to prepare poly(aryl ether nitrile) which bears pendant carboxyl groups (PEN-L) by solution polycondensation and nucleophilic substitute. FTIR,1HNMR, DSC, TGA and GPC were adopted to characterize the structure and properties of synthesized polymer. The glass transition temperature (Tg) was248℃, the temperature at5%weight loss was427℃and the residual carbon rate at700℃was60.25%.Non-isothermal differential scanning calorimetry (DSC) and Fourier transform infrared spectrometer (FTIR) were applied to test and analyze the cured modified DGEBA/MeHHPA/PEN-L systems. Curing feasibility was explored and verified while the curing process of the mixture was established as follows:105℃/2h+155℃/3h+205℃/2h.The neat and modified epoxy resin systems were completely cured according to the curing technics system:105℃/2h+155℃/3h+205℃/2h and it could be verified that the polymer thoroughly inserts into the networks of epoxy resins through chemical bonds by FTIR, DSC, DMA test and analysis. Research on the thermal and mechanical properties of the cured PEN-L modified epoxy resin systems with different PEN-L mass fraction while the detailed analysis and comparison of the corresponding properties between the cured DGEBA/MeHHPA/PEN-L systems and the cured neat epoxy resin system which only used ordinary curing agent-4-methyl-hexahydrophthalic anhydride (MeHHPA) was taken into consideration. Heat resistence and thermal stability of the cured modified epoxy resin systems were well improved with the addition of different mass fraction of PEN-L which was demonstrated by DSC and TGA test. Moreover, the glass transition temperatures, the thermal decomposition temperatures and the residual carbon rate of cured modified epoxy resin systems gradually enhanced to varying degrees with the increase of the mass fraction of PEN-L. The flexural strength and moduli of the cured modified epoxy resin systems decreased considerablely after the increasing PEN-L was added into the mixture.The maximum decline rate when compared with the cured neat epoxy resin system was43%and42%, respectively. Nevertheless, the flexural strain at break was tremendously improved and the maximum is5.11%and increases by89%than the corresponding value of cured neat epoxy resin system. It revealed that the fracture toughness which contains the critical stress intensity factor (KIC) and the critical strain energy release rate (GIC) was obviously enhanced by the continuous increase of mass fraction of PEN-L. When the cured modified epoxy resin system contained the PEN-L of15%mass fraction, fracuture toughness KIC achieved the maximum of5.43MN/m3/2and increased by98%, the maximum of the critical strain energy release rate was7.755kJ/m2and increased by215%when compared with the cured neat epoxy resin system, respectively. The notched impact strength expressed the similar trend to fracture toughness. |
PDF Full Text Request