Study on Toughening Modification of Epoxy Resin

2004-04-29 08:55:38
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Abstract : The toughening modification technology of epoxy resin is reviewed. The toughening mechanism and development status of rubber elastomer and thermoplastic resin toughened epoxy resin are discussed. The thermotropic liquid crystal polymer and flexible segment curing are briefly introduced. New epoxy resin toughening modification technologies such as agents and interpenetrating network structures.
Keywords: purple epoxy resin; toughening; modification.
Epoxy resins are products obtained by the polycondensation reaction of a compound having an epoxy group with a polyhydric hydroxy compound (bisphenol A, a polyhydric alcohol, a polybasic acid, a polyamine). Epoxy resin has high strength and excellent adhesive properties and can be used as coatings, electrical insulation materials, reinforcing materials and adhesives. However, due to its brittle material, low cracking resistance and impact resistance, and poor heat resistance, its application has been limited. To this end, domestic and foreign scholars have conducted a large number of modification studies on epoxy resins to improve the toughness of epoxy resins. At present, the toughening research of epoxy resin has achieved remarkable results. There are mainly three toughening methods: (1) Toughening is performed by adding a dispersed phase such as a rubber elastomer, a thermoplastic resin, or a liquid crystal polymer to an epoxy matrix. 2 The thermosetting resin is continuously toughened through the epoxy resin network to form an interpenetrating and semi-interpenetrating network structure. 3 Curing the epoxy with a curing agent containing "soft segment", introducing a flexible segment in the cross-linked network, and improving the flexibility of the network chain molecules to achieve the purpose of toughening.
l Rubber Elastomer Toughening Epoxy rubber elastomers form blocks by reacting reactive end groups (eg, carboxyl, hydroxyl, and amino groups) with reactive groups in the epoxy resin (eg, epoxy groups, hydroxyl groups, etc.); The phase separation process of the reactive rubber in the epoxy resin system is the key to the success of the toughening. Many decades of research have been conducted in this area since Mc Garry discovered that carboxylated nitrile rubber (CTBN) can significantly increase the fracture toughness of epoxy resins. According to reports in the literature, rubbers that have been studied or applied for toughening modified epoxy resins include carboxyl-terminated polyethers, polyurethane liquid rubbers, polysulfide rubbers, fluoroelastomers, neoprene rubber, nitrile rubber, and acrylic butadiene. Ester rubber and so on. By adjusting the solubility parameters of rubber and epoxy resin, the sea-island structure formed by phase separation during the gelation process is controlled, and rubber particles existing in the dispersed phase stop the cracks, branch cracks, and induced shear deformation, thereby improving the fracture of the epoxy resin. toughness. There are two trends in the study of toughening epoxy resins with liquid rubber. One is to continue to use CTBN toughening epoxy resin system, focusing on the in-depth discussion of the toughening mechanism; the other is to use other suitable {liquid rubber, such as silicone rubber, polybutadiene rubber and so on.
D. Verchere[1] studied the toughening effect of epoxy-terminated nitrile rubber (ETBN) on bisphenol A epoxy resin. When the content of ETBN was 20wt%, the fracture toughness GIC of the resin increased from 0.163kJ/m2 to 0.588. kJ/m2 is more than 3 times higher than before toughening. Han Xiaozu [2] used tough hydroxyl-terminated nitrile rubber (HTBN) to toughen the epoxy/hexahydrophthalic anhydride system. When the HTBN content reached 20phr, the toughening resin had an impact strength of 900kJ/cm2. Pre-sexuality (340kJ/cm2) increased more than 2 times. Sun Jun [3] used polymer design methods and controlled reaction processes to prepare modified silicone rubbers with amino-terminated materials, analyzed their infrared spectra, and confirmed that their products had the expected structure, ie, the modified silicone rubber was an amino-based seal. end. The modified epoxy resin was used to toughen and modify the epoxy resin. Through the impact strength test of the toughened body, it was found that the impact strength of the toughened body was within the range of 0 to 15 parts of the modified silicone rubber. After a significant increase, the impact strength of the toughened body increases slowly after adding more than 15 parts. Experiments show that the modified silicone rubber has a good toughening effect on the epoxy resin. In addition, there have been significant advances in the research of active end group-based liquid rubber toughening epoxy resins and polysulfide rubber modified epoxy resins. Such as Wang Dewu [4], who developed polysulfide rubber modified epoxy waterproof anti-corrosion anti-mold coating, is a polysulfide rubber modified epoxy solution as a film material, adding metal oxide filler, organic amine curing agent added Two-component coating. The coating has strong adhesion to metals and non-metals (3 to 4 MPa for steel adhesion and 4 to 5 MPa for concrete adhesion). The coating film is hard, smooth and plump, does not absorb dirt and algae, and has good toughness and high strength. Elasticity, weather resistance, mold resistance, abrasion resistance, acid and alkali resistance, and resistance to various solvents.
In recent years, the application of core-shell emulsion polymer compatibilization technology has made new progress in rubber elastomer modified epoxy resin. Core-shell particle size and the interfacial properties of epoxy resins can be designed and altered using emulsion polymerization techniques. Lin KF[5] studied the toughening of bisphenol A epoxy resin system using butyl acrylate as the core, methyl methacrylate and glycidyl ether methyl acrylate copolymer as the shell core-shell particles, and discussed Toughening mechanism.
Ashida Tadashi [6] studied the addition of poly(butyl acrylate) rubber particles and PBA/PMMA (poly(butyl acrylate/poly(methyl methacrylate)) core-shell particles to epoxy resin, using dicyandiamide as a curing agent. Structure and properties of the resulting cured product. The results show that the use of acrylic rubber particles can improve the fracture toughness of epoxy resin, but far less than the toughening effect of core shell particles (PBA/PMMA); in the epoxy resin curing process, due to the phase of PMMA and epoxy resin The capacitance is good, and the epoxy resin penetrates into the surface layer of the shell to bond with the colloidal particles, and the energy absorption level of the epoxy matrix around the core-shell particles is increased due to plastic deformation, and the fracture toughness is greatly improved.
Fan Hong [7] synthesized a series of PBA/PMMA core-shell composite elastic particles and used it to toughen the bisphenol A epoxy resin DEG-MA/DDM system. Studies have shown that the appropriate PBA/PM MA core-shell ratio is a prerequisite for toughening epoxy resin with core-shell composite elastomer particles; adding suitable core-shell ratio composite particles can improve the impact strength, shear strength, and reduction of the modified system. The internal stress of the curing system. With the decrease of the size of the core-shell particle rubber phase, the impact strength of the modified system increases gradually and the internal stress decreases, but the shear strength of the system is not significantly affected. The cavitation of core-shell particles caused shear toughening under the action of external force.
2 Addition of resin-alloyed modified epoxy rubber elastomers significantly increases the toughness of epoxy resins at the expense of heat resistance and rigidity, and for high cross-link density epoxy resins, rubber elasticity The toughening effect of the body is very small; and the research work of forming a polymer alloy with a thermoplastic resin and an epoxy resin to toughen and remodel makes up for the insufficiency of the rubber elastomer modified epoxy resin. Thermoplastic resins commonly used in toughening epoxy resins include polysulfone, polyimide, polyphenylene oxide, and liquid crystal polymers.
Liu Jingchao [8] studied the preparation of rigid polyurethane macromolecules by in-situ polymerization to modify epoxy resins. When the content of rigid polyurethane in the curing system is small, the rigid molecules can be uniformly dispersed in the epoxy matrix at the molecular level to form a molecular composite material. The entire system is similar to a semi-interpenetrating network. These rigid molecules can enhance the matrix. Improve the matrix tensile strength, while preventing cracks and increase the toughness of the matrix. Wang Huiming [9] and other polyether sulfone (PES) toughened DDS cured epoxy resin. Adding 12.5 parts of PES to 100 parts of epoxy, the impact strength of the system increased by nearly 3.34 times, and GIC increased by 1.2 times.
James L. Hedrick [10] and other end-hydroxy-terminated aryl ether phenols (PSF) for toughening agent modified epoxy Epon828. The toughening effect of PSF on the molecular weight and content of epoxy was investigated. Studies have shown that an appropriate increase in the molecular weight of PSF and an increase in the content contribute to the improvement of the toughness of the epoxy resin, containing 15wt% of molecular weight of 8200g/mol PSF can make the epoxy KIC as high as 1.3 × 106N/m3/2, The pre-toughening KIC (0.6×10 6 N/m 3 /2) increased nearly 2 times.
Polyetherimides were used to increase the fracture toughness of bisphenol A cyanate/phenolic epoxy resin blends. The experimental results show that polyetherimide is an effective toughening agent for cyanate ester/phenolic epoxy resin blends. The addition of 15% polyetherimide can increase the fracture toughness to 1.45 MPa, and the bending strength is also improved. . The microstructures of the modified blends were studied by scanning electron microscopy and dynamic viscoelastic spectra. A double continuous structure was found. The toughness and solvent resistance of the blends were mainly related to the phase behaviors. The curing process contained 10% polyetherimide. The fracture toughness and morphology of the blend have no apparent effect.
Douglas J. Hourston et al. [10] investigated the toughening effect of different content of polyimide ether (PEI) on TGDDM/DDS system. When the PEI content is 15 wt%, the GIC of the resin is as high as 0.54 kJ/m2, which is about 2 times higher than that before the toughening. Studying the effect of PEI content on the two-phase morphology of epoxy and PEI, it was found that when PEI content is less than 15wt%, PEI is dispersed into the epoxy continuous phase in the form of particles; after the PEI content is higher than 15wt%, the system undergoes phase transformation. The PEI forms a continuous phase. As the PEI content continues to increase, the PEI becomes a continuous phase (30 wt%), and the epoxy becomes a granular dispersed phase, and the toughness of the resin is significantly improved.
The aminated polycarbonate (a-PC) and the epoxy resin (EP) are mixed in a certain proportion, heated to 120-160°C, and the molten diaminodiphenylmethane is added to prepare a cured aminated polycarbonate toughened. Epoxy resin. The results show that EP and a-PC form a network structure, and when the mass fraction of a-PC is 10%, the fracture toughness of the specimen is maximum.
3 New Technology for Toughening and Modification of Epoxy Resins 3.1 Study of Toughened Epoxy Resins by Thermotropic Liquid Crystalline Polymers (TLCP) TLCP has higher physical and mechanical properties and heat resistance than other polymers. It is sheared to form a fibrous structure with a high degree of self-reinforcement. After the TLCP modified epoxy resin is cured, the system is a two-phase structure. The TLCP exists in the form of fibrils in the system, which can prevent cracks and improve the toughness of the matrix. The heat resistance and stiffness of the material are not reduced or increased.
Wei Chun [12] synthesized a thermotropic liquid crystal polymer (LCPU) with terminal groups containing reactive groups and modified epoxy resin CYD. 128/4,4'-diaminodiphenyl sulfone (DDS) curing system, the relationship between impact properties, tensile properties, elastic modulus, elongation at break, glass transition temperature Tg and LCPU content of the modified system The effects of different types of liquid crystal compounds CYD-128/DDS were compared. The morphological structure of the material was investigated by scanning electron microscopy (SEM). The results showed that the addition of LCPU can increase the impact strength of the cured system by 2 to 3.5 times, the tensile strength by 1.6 to 1.8 times, the elastic modulus by 1.1 to 1.5 times, the elongation at break by 2 to 2.6 times, and the Tg by 36%. At ~60°C, the morphology of the fractured surface of the modified material gradually exhibits ductile fracture characteristics.
Zhang Hongyuan [13] designed and synthesized a side chain type liquid crystal polymer (SLCP). When T31 is used as a curing agent, SLCP has a good toughening effect on epoxy resin. When the strength and glass transition temperature were not decreased, the elongation at break was 2.6 times higher than that of the unmodified cured product. However, when the triethanolamine was used as the curing agent, the modification effect of SLCP on the epoxy resin was not obvious.
Chang Pengshan [14] etc. Toughened E-51 epoxy with liquid-crystalline epoxy 4,4-diglycidyl ether diphenyl-acyloxy (PHBHQ) containing aryl ester mesogenic units, choosing the melting point and PHBHQ mesogenic phase. The mixed aromatic amines with consistent temperature and lower reactivity are curing agents. When the amount of PHBHQ is up to 50wt%, the impact strength of the cured resin is up to 40.2kJ/m2, compared with 23.0 kJ/m2 when the PHBHQ is not added. Increased nearly 2 times. In addition, the glass transition temperature also has a certain increase.
3.2 Study on Toughening of Epoxy Resin with Flexible Segment Curing Agent The increase of macromolecular curing agent containing soft segment