| Epoxy resin not only has the advantages of good adhesion,high mechanical strength and good heat resistance,but also has the advantages of large adjustable formula and wide application range.It has been widely used in the field of vehicle,ship,aircraft and other composite materials.Epoxy resin itself does not exist mechanical properties,only through appropriate curing agent and curing process can make epoxy resin have excellent properties,but cured epoxy resin shows the characteristics of high strength and brittleness.Therefore,epoxy resin toughening is always a hot issue.In practical applications,we hope that epoxy resin has good mechanical properties and toughness in the process of application.How to solve this problem is the key to expand the application range of epoxy resin materials.According to the toughening mechanism of crack branching induced craze and rivet effect in phase separation system,the mixed curing system of DPSEP/E51/DDM was designed in this paper,and the difference of solubility parameters in curing process was used to tough the cured resin.As a result,the phase separation structure was induced in the reaction process,and the toughening effect was realized.The main work and results of this paper are as follows:1?Using NaOH/TMAB as catalyst,DPSEP,was prepared by one-step reaction.The structure of the synthesized resin was characterized by FT-IR,1H-NMR and GPC.The epoxy value of the epoxy resin was titrated by hydrochloric acid-acetone method.The epoxy value of DPSEP was 0.5174g/mol,which was 85%of the theoretical epoxy value.The preparation of DPSEP was successful.2?The curing behavior of two curing systems,DPSEP/DDM and E51/DDM,was studied by non-isothermal curing kinetics(DSC).The results show that the initial curing temperature of DPSEP/DDM and E51/DDM is 91.04? and 88.13? respectively,the curing peak temperature is 172.96?and 173.59? respectively,and the heating rate is 15?/min-1.The activation energies of DPSEP and E51 resin were 58.5kJ·mol-1 and 53.1kJ·mol-1,respectively,so DPSEP was lower active than E51.3?The cured compounds of DPSEP/E51/DDM blend were characterized by AFM,SEM and tensile test.It was found by AFM that when the content of DPSEP was 2.5%,5%,7.5%and 10%respectively,the size of the phase separation increased gradually,which were 80-180 nm,100?256nm,138?217nm,100-3 80nm,respectively.It can be seen from SEM that with the increase of DPSEP content,the fracture section is rougher and.the crack branching is more serious.When the addition of DSPEP is 2.5%,its tensile strength,modulus and the elongation at break was 87MPA,2.12GPa and 6.7%respectively,which was 11.4%,2.42%and 53.67%higher than that of pure E51.By comparing the micro-morphology and mechanical properties of different DPSEP addition systems,we found that the toughness and mechanical properties of the system with nano and sub-micron phase separation were the best.The blends of DPSEP/E51/DDM were studied by DMA,DSC and TGA.The cured compound has a glass transition temperature similar to that of the pure E51 epoxy resin,and all of the cured compounds are found to be in the same glass transition temperature as the pure E51 epoxy resin which is 147?.By means of thermal stability test,we found that the weight loss temperature of 5%and residual carbon ratio of 800? with different addition of DPSEP did not change much,so it had the same thermal stability as that of pure E51 cured compound. |
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