Preparation And Properties Of Rare Earth Cation-Indole Dynamic Crosslinking Epoxy Resin

Owing to the excellent mechanical properties and chemical stability,epoxy resins are widely used in aerospace,mechanical and electronic equipments.The epoxy resins usually need to be cured to develope crosslinking structure,although the increase of crosslinking density helps to improve its mechanical strength,it will sacrifice its maximum elongation and toughness.Therefore,it has become a key problem in the field of polymer materials to maintain the toughness of epoxy resin while realizing their high strength.The design of new epoxy resin with high strength and toughness is also of far-reaching significance to promote the development of polymer industry.In this paper,a new type of high strength and toughness epoxy resin?IN-EP-Eu?driven by cation(Eu³⁺)-?is designed to avoid the contradiction between rigidity and ductility in epoxy resin.Compared with the traditional non-covalent bond,the Eu³⁺-?interaction can be formed and released in time through the point-to-face interaction,which can better dissipate energy and improve the strength and toughness of epoxy resin.In addition,the IN-EP-Eu film has fluorescent color change characteristics due to the presence of rare earth Eu³⁺,thus realizing the high-strength and toughness of epoxy resin with high efficiency of multiple anti-counterfeiting.The specific research conclusions are as follows:?1?A new type of indole based epoxy film?IN-EP?was designed and synthesized.The effect of different indole contents on the mechanical properties of the system was investigated.When the indole content increased gradually,the tensile strength of the film increased at first and then decreased,with the same regularity of its elongation at break.Therefore,the optimum addition content of indole?the equivalent ratio of indole to bisphenol A diglycidyl ether?was 0.5.Its tensile strength is 100.89 MPa and elongation at break is 2.96%.This best content is selected as the basis of the subsequent experiments.?2?The existence of Eu³⁺-?effect in IN-EP-Eu polymer network was proved by EDX,fluorescence,UV absorption and radial distribution functions.Secondly,by testing the mechanical properties of IN-EP-Eu with different Eu³⁺content(the mole ratio of indole to Eu³⁺),we found that when the content of Eu³⁺was 1/8,the strength was 112 MPa,which is11.1%higher than IN-EP,and the elongation at break was 5.54%,which is about 1.87 times of IN-EP.The Young's modulus and fracture energy of IN-EP and IN-EP-Eu are calculated by using the stress-strain curve.The results show that IN-EP-Eu has high modulus?3.25 GPa?and fracture energy?9.50 J/cm²?,and its fracture energy is about 2.44 times of IN-EP?3.89J/cm²?.Futhermore,the application of cation-?interaction in commercial epoxy was studied.With the change of Eu³⁺content,C-IN-EP-Eu showed a similar change rule with IN-EP-Eu,C-IN-EP-1/8Eu had higher mechanical strength?51 MPa?and toughness?7.17%?.Therefore,the existence of Eu³⁺-?interaction can enhance and toughen the epoxy resin,solving the contradiction between them.?3?To explore the fluorescent properties of IN-EP-Eu film under different acid conditions,the two variables of immersion time and pH value were adjusted,the fluorescence of Eu³⁺in the system decreases with the increase of immersion time,and decreases with the decrease of immersion pH,the fluorescent color of the film changes from red to blue,indicating that the increase of H⁺concentration causes the decrease of Eu³⁺concentration and fluorescent intensity,indicating the change of acidity will influernce the fluorescent performance.At the same time,the combination of barcode and QR code successfully endows IN-EP-Eu with multiple anti-counterfeiting performance.The epoxy resin with high strength,toughness and effective anti-counterfeiting performance driven by Eu³⁺-?interaction has a broad prospect in the field of aerospace and electronic equipment.