The Study Of Epoxy Resins Modified By Poly (Aryl Ether)s Containing Phthalazinone Moiety

Thermosetting epoxies possess many desirable properties,such as high tensile strength and modulus,excellent chemical and solvent resistance,high dimensional and thermal stability,good adhesive properties and processability.These characteristics make them ideal candidates for many important applications,especially matrix for high-performance fiber-reinforced composites in aerospace.However,the epoxy resins are generally brittle due to their high cross-link density,which limits their further proliferation into other applications that requires more impact resistant or tougher materials.This drawback has prompted many studies devoted to increasing their fracture toughness without compromising their desirable attributes.Poly(aryl ether) s containing phthalazinone moiety(PPAEs),are a kind of novel high performance polymer.Their special structure endows them with excellent comprehensive properties,including outstanding thermal properties and good solubility.It is expected to toughen epoxy resins without decreaseing their thermal properties.Therefore,the research on the epoxy resins modification by PPAEs is proposed on the summarization of early study of thermoplastic modified epoxy resins.A series of DGEBA / PPAEs blends were prepared by mechanical mixing without any solvent.In order to produce the mixtures with toughness and thermal resistance,we focused on the effects of the kinds and content of PPEAs on the structure and properties of DGEBA/ PPAEs mixtures in different curing conditions.The main studies and results are in the following:First,the curing kinetics of different blends was measured by differential scanning calorimetry(DSC).All the curing reactions of the blends began at 150℃and the activation energy was about 60 KJ/mol,which suggested that the additions of PPAEs didn't changt the curing conditions of epoxy resins.The structure and properties of DGEBA/PPEK blendings were investigated.The glass transition temperatures(T_g) increased but the thermal stabilities decreased lightly by the measurement of DSC and thermalgravimetry(TG) respectively.The impact strength and fracture toughness has not significantly increased in different curing conditions.The scanning electron microscope(SEM) proved that DGEBA/PPEK blends formed homogeneous phase, and the interface bonding was weak.Therefore,there was lack of the process of energy absorption to enhance the toughness of the blends. In order to increase the interface bonding of the thermoplastics with epoxy resins, PPENK,with the polar cyano pendant group,was used to modify DGEBA epoxy resins.The T_g of the blends increased by the addition of PPENK and the thermal stabilities were maintained.All the blends did not degrade under 390℃.Moreover,the toughness was enhanced to some degree.Although the DGEBA/PPENK blends form homogeneous phase, the dipole-dipole interaction between cyano pendant groups increased the interface bonding with epoxy resins to increase the toughness.On the foundation of those two studies,PPESK was choosen to toughen epoxy resins. There were two glass transitions in the DSC traces of DGEBA/PPESK blends.One was the epoxy rich phase,and the other was the PPESK rich phase.These two T_gs were all enhanced greatly,which perhaps because of the two phase interpenetrating to restrain the deformation of each other.Meanwhile,the thermal stabilities of the blends were maintained.None of the blends degrade under 390℃.The toughness obtained the maximum(3.42 KJ/m~2) by the addition of 15 phr PPESK.The fracture surfaces were rough and the cracks deviated their original ways to initiate deflection and disproportionation.So the toughness of DGEBA/PPESK blends was improved.Finally,PPBES,containing biphenyl in the chain,was used to modify DGEBA epoxy resins.There were also two glass transitions with 20 phr PPBES and the two T_gs were close to each other.The T_g of the epoxy resin increased and the DGEBA/PPBES blends did not degrade under 395℃.The toughness obtained the most significant enhancement in the PPAEs systems.The maximum of impact strength was 3.76 KJ/m~2 by the addition of 15 phr PPBES after cured in thel50℃/3h +180℃/3h + 200℃/2h conditions.The increment was 65%.From the above results,we can summarize that the PPAEs play the leading role in the toughness enhancement in the DGEBA/PPAEs blends.The toughness mechanisms of PPAEs modified epoxy resins are summarized in the following:(1) Crack deflection.The cracks deviated from their original plane to splite into some branches and initiate more ductile microcracks,which resulted the increasing surface area of the cracks,thereby increasing the toughness.(2) Local plastic deformation of the matrix.PPAEs,which diffused into epoxy resin,improved the plasticity of epoxy resin around the PPAEs dispersed phase.Thererfore, the fracture mechanisms such as crack deflection and branches,ductile microcracks,ductile tearing of the thermoplastics and local plastic deformation of the matrix are responsible for the increase in the fracture toughness of the DGEBA/PPAEs blends.