Research On Latent Fast Curing Epoxy Resin For Prepreg

The prepreg is the basis of fiber reinforced polymer matrix composites,and the final performance of the composite material is closely related to the performance of the raw material prepreg.It is usually required that the prepreg has a long storage life,which can reduce the cost of storage and transportation;and in order to improve the production efficiency of composite parts,the development of latent fast-curing epoxy systems suitable for prepreg preparation has become a current research hotspot.The main contents of this article are as follows:(1)Dicyandiamide(DICY)was used as curing agent to cure bisphenol A epoxy resin(DGEBA).The effect of 2-ethyl-4-methylimidazole(2E4MI)content on the properties of DGEBA-DICY system was studied.The curing kinetics of DICY was characterized by Non-isothermal differential scanning calorimetry(DSC),and the activation energy was calculated.The results showed that the addition of 2E4MI accelerator changed the curing mechanism of DICY,maked it easier to dissolve in the resin,thereby increasing the curing reaction rate.The mechanical properties of resin castables were tested,and the ratio with the best mechanical properties was selected to carry out isothermal DSC and latent test.Finally,the curing time of the system was only 20 min at 160?,and the curing degree after 15,30 and 60 days stored at room temperature were 0.146,0.276 and 0.339,respectively,which proves that the system had great latent properties.(2)Using diaminodiphenyl sulfone(DDS)as the main curing agent to cure the epoxy resin diluted by polypropylene glycol diglycidyl ether(PPGDGE).The effects of different dosage of2E4MI on curing kinetic parameters and mechanical properties of DGEBA-PPGDGE-DDS system were researched.The results showed that with the increase of 2E4MI addition,the low temperature exothermic peak increased and the high temperature exothermic peak decreased.On the one hand,it may be because the increase in imidazole content leads to an increase in the resin cured by imidazole.On the other hand,it may be because the pre-curing exotherm increases and the positive and negative ion-containing adducts generated in the first step of the imidazole reaction increase,which will attack the hydrogen on the primary amine of DDS,accelerate the reaction of the DDS with epoxy resin,thus leading to the partial DDS reaction advance.The addition of 2E4MI could reduce the energy barrier and improve the overall reaction activity.Finally,the resin system with the best mechanical properties could be cured within 80 min at 180?,and the curing degree after 15,30 and 60 days storaged at room temperature were 0.176,0.253 and 0.406 respectively,which meets the preparation requirements of latent fast curing prepreg.(3)Using DDS as the main curing agent to cure the epoxy resin diluted by PPGDGE.The effects of different contents of 1-benzyl-2-methylimidazole(1B2MZ)on the curing kinetics and mechanical properties of DGEBA-PPGDGE-DDS system were researched.The results of non-isothermal DSC showed that the initial temperature of the system decreased about 40?after adding 1B2MZ,and the reaction termination temperature also decreased significantly.The results showed 1B2MZ can improve the reactivity of DDS curing system at medium temperature.The curve of E_?and?calculated by Ozawa-Flynn-Wall method was closely related to the content of 1B2MZ.Among them,the degree of curing when DDS starts to react increased with the increase of the content of imidazole.This was because there is a temperature-rising transition period between the beginning of reaction exotherm of 1B2MZ and the reaction of DDS,and the degree of curing reached by the system during this transition period increased with the increase of imidazole content.Finally,the resin system with the best mechanical properties could be cured at 180?for 90 min,and the curing degree after 15,30 and 60 days storaged at room temperature were 0.144,0.227 and 0.304,respectively.It proves that the system has the best latency during the test period.(4)The three latent fast curing systems were selected as the research objects,the gel time and Isothermal,heating up viscosity were also tested to explore their technological properties.Then the three resin systems were coated on the fiber to make prepreg,and the glass fiber reinforced composites were formed by molding process.The fiber volume content,flexural strength,short beam shear strength,tensile strength and moisture absorption resistance were tested.The results showed that the composites prepared by the optimal resin system of 2E4MI and DDS had the best mechanical properties,with the flexural strength of 779.46 MPa,the shear strength of 42.22 MPa,the tensile strength(modulus)of 543.34 MPa(18.12 GPa),and the flexural strength after moisture absorption was still the largest,which was 574.54 MPa.Therefore,the best resin formulation system of 2E4MI and DDS could be used to prepare latent fast curing prepreg.