Preparation And Application Of Metal-organic Frame Composites Based On Epoxy Polymer Material

Metal-Organic Frameworks(MOFs)materials have attracted great attention in different research fields due to their special structure,high crystallinity,high specific surface area,and design flexibility.However,MOF particles are usually difficult to process due to their brittleness,insolubility,difficulty in molding,and low compatibility with other materials.Therefore,it is urgent to develop effective preparation methods to further expand the application of MOFs.In recent years,hybridization with polymer materials to prepare MOFs-based polymer composites is a new trend in MOFs research.Due to the various unique properties of polymers,such as flexibility,thermal stability,chemical stability,and good compatibility,these properties can be well combined with MOFs materials to prepare composites that have both the inherent properties of MOFs and polymer properties.MOF composites have some new characteristics that are difficult to achieve with individual components.It can greatly improve the functions of MOFs such as luminescence,sensing,catalysis,environmental purification,gas selective adsorption,hydrolytic stability,and biocompatibility,and expand its practical application range.What's more,the thermal stability and mechanical properties of polymer materials can also be further improved.Although more and more MOF composites and their different applications have been explored,this field is still in the emerging stage and faces many challenging problems.This thesis is based on the rare earth MOF compounds[Ln-BTC(Ln=Eu,Tb and La)]and the ZIF-8 compound with zeolite structure,respectively,combined with an epoxy compound curing agent 1,3,5-triglycidyl isocyanurate(TGIC)or epoxy resin(EP),prepared rare earth MOF luminescent composite materials and flame-retardant EP composites,and made a detailed study on the application of synthetic materials.The specific research content is as follows:(1)The preparation of polymer composites based on Ln-MOFs can be used as an effective strategy to improve the stability and processing ability of their powders.To explore a more simple and novel strategy to develop new types of Ln-MOFs polymer composite materials with significant luminescent properties,Ln-MOFs(Ln=Eu,Tb and Eu_0.05Tb_0.95)were combined with TGIC in a covalent bonding way by grinding and heating curing,a series of new functional luminescent materials have been prepared,and the structure and luminescence properties of the composites have been comprehensively and systematically explored using a series of characterizations.In Ln-MOF@TGIC composites,the uncoordinated carboxyl group(-COO^-)in Ln-MOFs is chemically bonded with the epoxy group in TGIC,and the composites have excellent fluorescence properties.Among them,Eu_0.05Tb_0.95-BTC showed excellent yellow light properties,but the color of Eu_0.05Tb_0.95-BTC@TGIC changed to tangerine after curing.By comparing the solid-state fluorescence spectra,it is found that the emission intensity of Eu³⁺in the Eu_0.05Tb_0.95-BTC@TGIC composite is significantly increased.Compared with Ln-MOFs(Ln=Eu and Tb),the fluorescence lifetime(?)and quantum yield(?)of Ln-BTC@TGIC(Ln=Eu and Tb)composites are relatively increased.Given the above changes,we use DFT calculation to further analyze the energy transfer mechanism.The results show that the reason for the change in the fluorescence efficiency of Eu_0.05Tb_0.95-BTC@TGIC may be part of the energy transfer from Tb³⁺to Eu³⁺ions,and then part of the energy transfer may come from covalently bonded TGIC molecules,so its luminous efficiency has changed.Therefore,the covalent bond combination of TGIC and Ln-MOFs promotes the improvement of the luminescence performance of the composites.We further used the Ln-BTC@TGIC composites as a fluorescent coating by a simple spraying method to prepare a flexible polyimide(PI)composite film(Ln-BTC@TGIC@PI)with fluorescence characteristics,which further expanded the application of rare earth MOFs and polymer materials.(2)To improve the flame-retardant properties of EP,we combined it with ZIF-8with a zeolite structure to prepare epoxy composites and study its flame-retardant properties.We prepared ZIF-8@DMMP composite flame retardant additive by loading dimethyl methylphosphonate(DMMP)in the ZIF-8 channel by immersion,then it was added into the EP to obtain composites with good flame retardant and smoke suppression properties.The feasibility of this strategy was proved by cone calorimetry and smoke density test.Further analysis of carbon residue shows that ZIF-8@DMMP as a flame retardant for EP is different from the previous single flame retardant additive:the ZIF-8 framework could absorb the decomposition products of composites,reduce the generation of smoke particles.What's more,its thermal decomposition product Zn O could also promote the formation of carbon residue,and the catalytic effect of Zn O could catalytically oxidize CO to CO₂,effectively reduce the generation of harmful gases.In addition,the DMMP in the ZIF-8 pores is gradually released during the combustion process and inhibits the free radical chain reaction and the production of combustible alkanes in the gas phase,further reducing the release of heat,making the carbon layer denser,and covering the surface of the composites.Thereby forming a stronger physical barrier effect.Therefore,the synergistic flame-retardant effect of ZIF-8 and DMMP effectively improves the thermal stability of polymer materials.(3)Compared with transition metal Zn²⁺,rare earth ion La³⁺has a higher electron energy level,larger ionic radius,higher charge,and stronger coordination ability,so it is also widely used in the preparation of flame retardant polymer systems.Therefore,based on selecting ZIF-8 as the EP flame retardant,we further combined the rare earth La-MOF(La-BTC)with DMMP and studied its flame retardant properties for polymer materials.We combine DMMP and La-BTC to prepare La-BTC@DMMP composite flame retardant additive by immersion and then add it to EP to prepare flame retardant polymer composites.Through a series of characterizations,it is proved that there is a coordination effect between the DMMP molecule and La-BTC.In addition,in the characterization of the flame retardant properties of the EP composites,we used the Limiting Oxygen Index(LOI)test and found out that when the addition amount of La-BTC@DMMP was 5%,the LOI value of the EP composites increased to 27.7%,which makes it achieve a better flame retardant effect.