Preparation And Properties Of Acrylate Block Copolymer/PDA-MOF-5/epoxy Resin Composites

Epoxy resin is widely used as a coating or substrate in composite materials in various fields due to its excellent thermomechanical properties,good chemical and heat resistance.However,there are some problems with epoxy resin that the brittleness and crack propagation resistance are poor.How to improve the toughness of epoxy resin has been one of the research hotspots,and the introduction of block copolymers(BCPs)in epoxy resin to improve toughness is one of the novel approaches at pesent.The Acrylate BCP epoxy alloys were prepared by using polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate block copolymer(PMMA-Pn BA-PMMA,abbreviation Acrylate BCP)as the toughening modifier of epoxy resin in this paper.The strength and stiffness of Acrylate BCP epoxy alloys are slightly reduced compared to pure epoxy resins.In order to improve the strength and stiffness of the epoxy alloys,a second modifier,MOF-5 with mechanical responsiveness,was added to prepare MOF-5/epoxy resin composites and Acrylate BCP/PDA-MOF-5(Polydopamine(PDA)modified MOF-5)/epoxy resin ternary composites.The changes of mechanical properties and thermodynamic properties of three composites were explored,and the toughening and strengthening mechanism of Acrylate BCP and MOF-5 were revealed.The main research contents and results of this thesis are as follows:The first part,the preparation and properties of Acrylate BCP epoxy alloys.Epoxy alloys with different contents of Acrylate BCP were prepared by solution method,and then the thermodynamic properties of the epoxy alloys were analyzed by DSC,DMTA and TG.The glass transition temperature(T_g)and storage modulus(E?)of the epoxy alloys decreased with the increase of Acrylate BCP contents,and the thermal stability did not change.The fracture toughness,tensile and flexural properties of epoxy alloys were systematically studied and analyzed.Compared with pure epoxy resin,the epoxy alloy containing 5wt%Acrylate BCP had an increase in the critical stress intensity factor(K_IC)of more than 1.2 times and a critical energy release rate(G_IC)increase of more than 3 times at room temperature;modulus decreased with the increasing contents of Acrylate BCP.The dispersion of Acrylate BCP in epoxy resin and the different fracture failure surfaces of epoxy alloy were observed by SEM and AFM.When the content of Acrylate BCP exceeded 15wt%,it agglomerated inside of the epoxy resin,and a large amount of Pn BA block precipitates to cause macroscopic phase separation,resulting in the increased roughness;an uniform nano-sized spherical structure appeared on the surface of the epoxy alloy containing 5wt%Acrylate BCP,and the main toughening mechanism of Acrylate BCP was determined to be"crack deflection".The second part,the preparation and properties of MOF-5/epoxy composites.MOF-5powders were synthesized by hot solvent method,and MOF-5/epoxy composites with different MOF-5 contents were prepared by blending method.The structure of MOF-5 and MOF-5 in MOF-5/epoxy composites were characterized by XRD,FTIR and SEM.The successful synthesis of MOF-5 was approved,and mechanical agitation did not destroy the structure of MOF-5.And then the mechanical properties of composites with different MOF-5contents were systematically studied.The results showed that the tensile strength,Young?s modulus and elongation at break of the composites containing 0.5wt%MOF-5 were increased by 32.8%,29.5%and 6.2%,respectively,compared with pure epoxy resin;the flexural strength and flexural modulus of the composites containing 0.3wt%MOF-5 increased by25.2%and 20.4%,respectively.The thermodynamic properties of the composites were analyzed by DSC,DMTA and TG.The T_gof all composites increased,showing a higher E?and the damping curve of the loss factor(Tan?)decreased significantly with the increase of MOF-5 content which means MOF-5 can absorb part of the mechanical energy and exhibits the ability to block load transfer.By analyzing the fracture toughness of the composites,the K_ICof the composites containing 0.3wt%MOF-5 increased by 48.51%and the G_ICincreased by 72.4%.It was determined that MOF-5 can toughen epoxy resin through the mechanism of"particle bridge"or"crack pinning".The third part,the preparation and properties of Acrylate BCP/PDA-MOF-5/epoxy ternary composites.A layer of PDA was polymerized on the surface of MOF-5 by dopamine(DA)self-polymerization method to improve the dispersibility of MOF-5 in epoxy resin,and Acrylate BCP/PDA-MOF-5/epoxy ternary composites were prepared by blending method.The structure of PDA-MOF-5,the adhesion mechanism of PDA and MOF-5 and the dispersibility of MOF-5 and PDA-MOF-5 in epoxy resin were characterized and observed by XRD,FTIR and SEM,and the tensile and flexural properties of different contents of PDA-MOF-5 ternary composites were systematically analyzed.The results showed that PDA successfully polymerizes on the surface of MOF-5 without destroying the structure of MOF-5;the tensile strength,Young?s modulus,elongation at break,flexural strength and flexural modulus of the ternary composites containing 0.4wt%PDA-MOF-5 were increased by 14%,3.4%,8.7%,21.2%and 6.1%,respectively;there was a chemical interaction between PDA and MOF-5,and the dispersion of PDA-MOF-5 was more uniform than MOF-5.The thermodynamic properties of the ternary composites were analyzed by DSC,DMTA and TG.The T_gand E?of all ternary composites increased and both showed good thermal stability.By analyzing the fracture toughness of ternary composites,K_ICand G_ICof ternary composites containing 0.6wt%PDA-MOF-5 were increased by 17.83%and 6.6%,respectively,and both PDA-MOF-5 and Acrylate BCP had a toughening effect on the epoxy.