Epoxy Adhesives: Reinforcement Modification and Formulations
2026-04-29
In general, epoxy adhesives possess good mechanical properties, particularly in terms of adhesion and mechanical strength; however, to further enhance these properties in practical applications, the adhesives must undergo reinforcement and modification. 
Reinforcement with Specialty Epoxy Resins
Special epoxy resin epoxy, such as AG-80, AFG-90, phenolic epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, liquid crystal epoxy resin TDE-85, 731, etc. These resins can achieve good reinforcement effects when used alone or in combination with other epoxy resins. Like liquid crystal epoxy resin, it is a thermosetting liquid crystal polymer with easily oriented mesomorphic units and reactive epoxy groups in its molecular structure. It combines the characteristics of ordered liquid crystals and network cross-linking, and its cured product has excellent mechanical properties, which have important potential applications in aerospace, military defense, and other fields.
Toughening Modification
There are many methods for toughening epoxy adhesives, such as toughening with rubber elastomers, thermoplastic resins, interpenetrating network structures, the introduction of flexible chains, and nanoparticles. These methods enhance the adhesive’s toughness while simultaneously improving its bond strength.
Fiber Reinforcement
Whiskers are short fibers at the micro/nano level grown from high-purity single crystals, and their mechanical strength is equal to the strength generated by the forces between adjacent atoms. The highly oriented structure of whiskers gives them high strength, high modulus, and high elongation, which can be used for reinforcing epoxy resins. Whiskers can be divided into two categories: organic whiskers and inorganic whiskers. Among them, organic whiskers mainly include cellulose whiskers, butyl polyacrylate styrene whiskers, poly (4-hydroxybenzoate) whiskers (PHB whiskers), and other types, which are widely used in polymers. Inorganic crystal whiskers mainly include ceramic crystal whiskers (SiC, potassium titanate, aluminum borate, etc.), inorganic salt crystal whiskers (calcium sulfate, calcium carbonate, etc.), and metal crystal whiskers (aluminum oxide, zinc oxide, etc.).
In addition, chopped fibers and fiber pulp made from glass fiber, carbon fiber, aromatic polyamide fiber, stainless steel fiber, basalt fiber, and mullite fiber can all be used to reinforce epoxy adhesives.
Silane Coupling Agent Modification
The addition of an appropriate silane coupling agent can improve the affinity between the adhesive resin and the substrate, effectively enhancing the bond strength and heat aging resistance of epoxy adhesives. The typical dosage ranges from 1% to 5%, and most of these agents are organosilicon coupling agents.
Filler Reinforcement
Fillers can reduce the shrinkage rate of the adhesive layer and improve dimensional stability; enhance the mechanical strength of the adhesive, such as shear resistance, compression resistance, and bending resistance; improve the operability of the product; reduce costs; and improve the special properties of the product (such as high-temperature resistance, conductivity, thermal conductivity, dielectric properties, insulation properties, flame retardancy, etc.). Common fillers include talc powder, calcium carbonate, silicon micro powder, quartz powder, etc. Functional fillers include conductive metal powder, thermally conductive metal powder or boron nitride, electrical mica powder, flame-retardant aluminum hydroxide, etc.
Formulation Examples of Reinforced and Modified Epoxy Adhesives
Nano-Filler Modified Epoxy Adhesive Formulation
Component | Raw Material | Formula 1 | Formula 2 |
Component A | Epoxy resin (E-44 or E-51) | 100 | 100 |
Nano SiO₂ powder | 7.0 | 10 | |
Nano SiC fiber | — | 10~20 | |
Component B | Toughening agent CBP | 10~20 | 10~30 |
Curing agent T-31 | 10~30 | 10~30 | |
Other additives | Appropriate amount | Appropriate amount |
Performance characteristics: Adding nano SiO ₂ and one-dimensional SiC whiskers significantly improves the strength of epoxy resin adhesives, but simply adding one of the fillers has a similar improvement in strength. Adding 7% nano SiO ₂ and 10% one-dimensional nano SiC whisker fiber composite filler to the epoxy adhesive coating can produce a synergistic effect, and the tensile strength, shear strength, and impact strength of the adhesive are superior to those of a single filler.
Nano-Rubber Powder Modified Epoxy Adhesive Formulation
Component | Raw Material | Parts by Mass Range |
Component A | Bisphenol A epoxy resin | 60~85 |
Nano crosslinked rubber powder | 10~30 | |
Diluent | 1~10 | |
Component B | Modified amine curing agent | 92~95 |
Curing accelerator | 2~5 | |
Coupling agent | 1~3 |
Performance and Application: The particle size of nano crosslinked rubber micropowder is small and can be uniformly dispersed in the continuous phase of epoxy resin. The enormous surface energy of particles enhances the binding force between epoxy adhesive molecules and the adhesive force between epoxy adhesive and substrate surface, greatly improving the adhesive strength and heat resistance of the adhesive.
This adhesive can be used for bonding metal to metal and metal to other materials, mainly as a structural adhesive.
Related Post: Epoxy Adhesives: Toughening Modification and Formulas
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