Research and development of modification of the ho

Research and development of modification of epoxy resin

research and development of modification of epoxy resin

May 6, 2020

01 preface

in recent years, scientific researchers have carried out a lot of modification research on epoxy resin to overcome its brittleness, impact, poor heat resistance and other shortcomings, and have achieved fruitful results. In the past, the modification of epoxy resin has been limited to rubber, such as carboxyl terminated butadiene rubber, hydroxyl terminated butadiene rubber, polyimide rubber and so on. In recent years, the modification of epoxy resin is deepening, and the modification methods are changing with each passing day, such as interpenetrating method, chemical copolymerization method, etc., especially the liquid crystal toughening method and nano particle toughening method are the hot coatings studied in recent years. The research progress of epoxy resin modification at home and abroad in recent years was reviewed

02 acrylic acid toughened modified epoxy resin

at present, there is no specific regulation on the depth of the tooth path in China. Toughening epoxy resin with acrylic substances can introduce active groups into the acrylate copolymer, and use the active groups to react with the epoxy groups or active groups of the epoxy resin to form a continuous copolymer to increase the compatibility between the two phases. Another method is to use acrylate elastic particles as toughening agent to reduce the internal stress of epoxy resin. Acrylate can also be crosslinked into a complex structure and then form an interpenetrating complex (IPN) structure with epoxy resin to achieve the purpose of toughening

Zhang Haiyan and others used the addition polymerization of epoxy resin and methacrylic acid to obtain epoxy methacrylic acid resin (EAM). Its processibility is similar to that of unsaturated polyester, and its chemical structure is similar to that of epoxy resin. The modified resin system after curing not only has excellent adhesion and chemical stability, but also has the advantages of good heat resistance, high elongation, simple curing process, etc. At the same time, due to the introduction of copolymer segment methacrylate, the crosslinking density of the system during curing is reduced, and the introduction of side groups provides more free volume for the movement of main chain molecules, so the impact performance of the modified system is improved

Wei yabing used IPN method to study the toughening modification of polyacrylate on epoxy resin. He crosslinked the linear polypropylene butyl ester into a shaped structure and cured it with epoxy resin and curing agent to form an interpenetrating structure. This method increases the compatibility between butyl acrylate and epoxy resin. The interpenetrating system has high bonding strength and excellent resistance to damp heat aging

Li Jiming first prepared butyl acrylate (PBA) seed lotion by lotion polymerization, synthesized a core lotion under the action of initiator, and then introduced polymethyl methacrylate shell on the seed to obtain core-shell particles. When using this particle to toughen epoxy resin, because the solubility parameters of polymethylmethacrylate are similar to those of epoxy resin, the interfacial compatibility between them is very good. When observed by SEM, it can be found that the shell of core-shell particles is dissolved with epoxy resin, while the core PBA is a granular dispersed phase in the epoxy matrix. UT carried out dynamic mechanical analysis on the epoxy matrix system toughened by pba/pmma core-shell particles. In the dynamic mechanical diagram, it can be found that there is no glass transition peak corresponding to PMMA in the high temperature region, but only the glass transition peak corresponding to epoxy resin, which also proves the compatibility between epoxy resin and PMMA. For the lack of modified system, we must ensure that the impact strength of each process port is significantly improved, and the fracture characteristics are transformed from brittle fracture of epoxy resin to ductile fracture

03 polyurethane toughening modification

the main purpose of using polyurethane to modify epoxy resin is to improve its brittleness, improve its flexibility and increase its peel strength. Polyurethane has good adhesion, flexible molecular chain and high elasticity at room temperature. Using the idea of polymer alloy, Shi Liyi and others prepared PU/EP blend system by melt blending method. He used isocyanate terminated polyurethane prepolymer and epoxy resin to add curing agent to cure under melting conditions to obtain a blend modification system: because isocyanate itself can react with epoxy groups, the two phases of the modified system have good compatibility. Using DMA analysis, it can be found that there is only a single wide glass transition change in its spectrum when m (PU):m (EP) = 20:80, which further proves the compatibility of the two phases. Compared with epoxy resin, the impact strength of the modified system has been greatly improved

at present, the most studied polyurethane toughening epoxy resin system is to form sipn and IPN structures with polyurethane and epoxy resin. These two structures can play the role of "forced compatibility" and "synergistic effect", so that the high elasticity of polyurethane is organically combined with the good heat resistance and adhesion of epoxy resin, and a satisfactory toughening effect is achieved

y.li et al. Modified and grafted bisphenol A epoxy resin with polyether polyurethane oligomer with isocyanate at the end. They formed a homogeneous solution in tetrahydrofuran solution, and then formed a semi interpenetrating structure of linear polyurethane penetrating the epoxy complex under the action of DDM curing agent. The two have good synergistic performance when the dosage ratio is 70/30. The shear strength, peel strength and impact strength of the system are greatly improved. The fracture elongation of the system is increased from 2.09% of epoxy matrix to 211.9%, and the fracture strength is increased by 18.56mpa. At the same time, the system also has good damping characteristics. Guan Yunlin et al. Discussed the relationship between the phase behavior of pu/ep and the bonding shear properties. Through infrared spectrum analysis, it was found that there was not only the crosslinking reaction between EP and Pu, but also the copolymerization reaction between them. DSC analysis shows that the system has a single wide glass transition temperature at high temperature. At the same time, it is also found that the glass transition temperature of the system increases with the increase of the amount of epoxy resin, even higher than the Tg of EP matrix. The reason is that after the amount of EP increases, the connection reaction between Pu and EP increases, and the force between molecules increases. From the dynamic mechanical spectrum, it can also be seen that the loss peak moves towards high temperature. Through TEM observation, it is found that the interface between the two phases of the system is fuzzy, which further proves the compatibility of the two phases. The connecting copolymer of polyurethane and epoxy resin in the system greatly increases the interpenetrating effect of the two, thus improving the overall performance of the system

04 bismaleimide (PI) modified

bismaleimide has good heat resistance, and its modified epoxy resin can greatly improve the bonding strength of epoxy resin at high temperature. Guan Changshen and others prepared a new toughening system of epoxy resin with bismaleimide, epoxy resin and aromatic diamine as raw materials. The system has good heat resistance and excellent adhesion. Its shear strength (45# steel/45# steel) has little change at room temperature and 200 ℃. Xu Ziren added allyl bisphenol A to increase the compatibility between epoxy resin and BMI. Through infrared spectrum analysis, it is found that allyl bisphenol A can be grafted with bismaleimide to form bismaleimide resin with epoxy group. When adding curing agent, it can be cured and crosslinked with epoxy resin, so that the two phases in the system have good compatibility. A tough epoxy modified resin with high temperature resistance was obtained

Liang Guozheng synthesized epoxy bismaleimide (EB) based on epoxy resin. The system is formed by the reaction of functional bismaleimide and epoxy resin, and the curing mechanism of Bismaleimide is used. The system not only has the characteristics of good adhesion of epoxy resin and low straight limit rate of curing shrinkage lithium titanate in large-scale commercial use, but also has high heat resistance similar to bismaleimide resin. At the same time, the impact property of this system is also 2. 5% higher than that of bismaleimide When focusing, be careful not to make the objective lens touch the sample greatly

05 polyamide acid (PAA) modification

polyamide acid (PAA) is the reaction intermediate of polyimide (PI). Compared with PI, PAA can be prepared in low boiling solvent. Compared with PI modified epoxy resin system, PAA modified epoxy resin system has better peeling performance. When using PAA to modify epoxy resin, it is equivalent to the curing agent of epoxy resin and can form ester like structure with epoxy group. At the same time, PAA itself has certain activity and can amidate to form PI long chain, so that the curing system shows high bonding shear strength and heat resistance. Zhao Shilin et al. Synthesized PAA with PMDA and ODA in thf/ch3oh mixed solvent and successfully used it as curing agent and modifier of epoxy resin. The modified system has good comprehensive properties due to the synergy between PAA and EP. At the same time, the low boiling point solvent is easy to volatilize when the system is cured, and will not cause large internal stress. Kevin et al. Discussed the influence of curing temperature on the performance of PAA modified EP system. The internal stress in materials is usually the reason for the decline of comprehensive properties of materials. They used a two-stage curing process to fully eliminate the residual solvents and bubbles in the curing system to further improve the overall performance of the system

06 conclusion

in the future, epoxy resin will develop in the direction of "large-scale, high purification, refinement, specialization, serialization and functionalization". With the continuous efforts of scientific researchers, the research on the modification of epoxy resin will also change with each passing day. Epoxy resin will be more and more widely used in people's life