| Epoxy resin is one of the most important thermosetting resins.High-performance fiber-reinforced epoxy resin composites are widely used in aerospace,land transportation,machinery and other fields due to their high specific strength and specific modulus.However,the rather poor toughness seems to be a bottleneck of development.Therefore,design and preparations of high toughness epoxy resin matrix has always been the focus of researches on advanced composites.At present,several common toughening methods have been developed such as introducing rubber elastomers or flexible segment in cross-linking network.Nevertheless,these methods will lead to a reduction of strength,modulus and heat resistance of the resin matrix.It might be a new effective way that apply thermoplastic polymers of high modulus,high toughness and good heat resistance,such as polyether sulfone(PES),to modify epoxy resin as tougheners.In this paper,the dissolution and curing behavior of epoxy resin modified by PES(PES/E51 system)were investigated,the mechanical properties and phase structures of the castings and carbon fiber composites based on the modified epoxy resin were also studied.Firstly,the dissolution properties of PES/E51 systems were studied.In observations with a polarized opticalmicroscope,results showed that without any assistance of organic solvent,PES could be thoroughly dissolved in E51 within 30 minat 120℃.Further with addition of curing agent,DETD,solution systems of PES/E51/DETD were prepared.Based on isothermal and non isothermal DSC analysis,the curing conditions of PES/E51/DETD systems was determined to be under 120 ℃ and for 2 h.The apparent activation energy of PES/E51/DETD systems during curing was effected by the addition of PES.A minimum apparent activation energy appeared as50.96 k J/mol when concentration of PES was 10 wt.%.Secondly,castings were prepared with PES/E51/DETD systems containing different content of PES,and mechanical properties,thermal performance and phase structures were tested or characterized.The result showed that with the increase of PES,the mechanical properties of the castings showed a tendency to increase first and then decrease.The PES/E51/DETD system casting containing 15 wt.% PES exhibited a tensile strength of 48.06 MPa and an impact strength of 25.8 k J/m2,which were 2.3 folds and 3 folds of those for non-modified epoxy resin casting respectively.This indicated great improvements on the strength and toughness of the resin.In observations of microstructures for the castings,bicontinuous structures were found in phases of PES and E51.Phase inversion occurred when the amount of PES was above 15 wt.%.By analyzing the variation trend of curing exothermic peak temperature,it was found that the addition of PES promoted the curing of PES/E51/DETD resin system before phase inversion,but it played a hindering role after reversal of phases.Finally,the carbon fiber reinforced PES/E51/DETD system composites were prepared by compression molding and VARI processing.Results of study on rheological properties showed that viscosities of PES/E51/DETD systems containing PES of 0 wt.and 15 wt.% both meet the requirements of compression molding and VARI processing.Both of the two resin systems exhibited good stability of viscosity at 80℃,the temperature required for the operation of coating or filling.Results of mechanical properties tests on composites showed that there was an obvious boosting in the toughness for compression molding processed carbon fiber reinforced PES/E51/DETD composites containing 15 wt.% PES.The fracture absorption energy increased by 43.3% when compared with that of the composites without modifications of resin.However,viscosity of the resin system increased with addition of PES.Because the composites processed via VARI molding were strongly influenced by viscosity of resin systems,the PES/E51/DETD systems of high viscosity brought decreases of the interlayer adhesion thus finally lead to reduction of comprehensive mechanical properties. |
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