How Polymers Toughen Epoxy Resins

The polymers used for toughening epoxy resins are mainly high molecular weight rubbers and thermoplastic resins, especially high heat-resistant thermoplastic resins such as nitrile rubber, nylon, polyphenols, polysulfones, polyether ketones, Polyether ether ketone and so on. Polymer toughened epoxy structural adhesive is an important way to modify epoxy structural adhesives. How can the polymer achieve toughened epoxy structural adhesives? China Epoxy Resin Industry Association specifically explained this.

The polymer used to toughen epoxy structural adhesives has high toughness, high strength, high heat resistance, compatibility with epoxy resins, and phase separation during curing. In the formation of island structure or interpenetrating network structure, so that the cured material has high strength and high toughness. It is mainly used for the preparation of medium-temperature or high-temperature curing epoxy structural adhesives with high strength, high toughness and high heat resistance. For the main force structure of the glue, such as metal honeycomb structure and sheet metal structure of the glue, aircraft, rockets, ships, vehicles, heavy machinery and other mechanical structure of the glue.

Epoxy-NBR structural adhesives are epoxy structural adhesives toughened with high-molecular solid nitrile rubber, and most use nitrile 40 with a high nitrile content. Epoxy-NBR structural adhesives are usually supplied in two forms: glue and film. When the glue solution is used, a low molecular weight liquid bisphenol-A epoxy resin is used. When the film is prepared, a high molecular weight solid double is used. Phenolic type A epoxy resin, or in combination with liquid epoxy resin. The use temperature is about -55 ~ 80 °C. The introduction of multifunctional epoxy resins such as phenolic epoxy, amino polyfunctional epoxy, TDE-85, etc. can improve the high temperature resistance. Dicyandiamide or dicyandiamide-accelerator systems are often used as hardeners. Low active aromatic polyamines can also be used to increase heat resistance. Addition of nitrile rubber (such as *******, **, etc.), * accelerants (such as ZnO, MgO, etc.), and fillers (such as fumed SiO2) into the adhesive can further increase the toughness. effect. The nitrile toughened epoxy adhesives have significantly improved shear, peel, and fatigue resistance. The hygrothermal aging resistance is slightly inferior to the phenolic-nitrile adhesive, but much better than the epoxy-nylon adhesive. Such domestic adhesives are self-powered No. 2, No. 3, J-23, J-30, etc.

Epoxy-nylon structural adhesives are important polymers how to toughen epoxy structural adhesives. Experts from the China Epoxy Resin Industry Association said that the polymer solid nylon (polyamide) is a polymer with excellent toughness. There are a large number of polar amide groups in the molecule, which can react with epoxy groups. Increase adhesion and improve toughening effect. Due to its large polarity, high melting point, poor compatibility with epoxy resins, and the inability of nylon to dissolve common solvents can not be used to prepare a glue solution. The nylon used for the toughened epoxy adhesive is a modified alcohol-soluble nylon such as hydroxymethyl nylon, nylon 6/nylon 66/nylon 610 terpolymer, etc. In addition, after the structurally different crystalline nylon is melted, a low-melting-point mixed melt can also be obtained. For example, the melting point of nylon 610 and nylon 11 is 162° C., and the melting point of nylon 66 and nylon 11 is 121° C. Epoxy-nylon structural adhesives have high shear strength and peel strength, as well as good fatigue and impact resistance. The disadvantages are the poor heat resistance and water resistance, especially the poor resistance to moisture and heat aging, which limits its application. Increasing the heat resistance and heat and humidity resistance of epoxy-nylon adhesives is one of the current research topics and some progress has been made.

Another class of toughened epoxy structural adhesives with polymers is an epoxy-polysulfone structural adhesive. Epoxy - nitrile rubber and epoxy - nylon rubber use temperature is not high, the former, such as self-adhesive - No. 2 glue temperature is only -60 ~ 60 °C, while the latter, such as 402 glue but also -60 ~ 120 °C. To prepare a high temperature resistant epoxy structural adhesive must handle the relationship between heat resistance and toughness. The two are often contradictory. The use of a thermoplastic resin with high heat resistance and good toughness to toughen the epoxy resin is an effective way to properly handle this contradiction. Polysulfone has been used in adhesives, and polyphenylene ether, polyether ketone, polyether ether ketone, etc. are being studied. And very tough thermoplastic polymers. The diphenylsulfone group in the polysulfone molecular structure is a highly conjugated aromatic ring system, and its compound bond is stronger than the non-conjugated bond structure, and can absorb a large amount of heat energy without causing breakage of the main chain and the branch chain, thus having a relatively high High thermal stability. The diphenylsulfone group in the conjugated system is in a solid position in space, while the * atom is in the highest oxidation state and has a high antioxidant capacity. So polysulfone can maintain fairly good stiffness and strength at high temperatures, with high heat resistance and thermal oxygen stability. The isopropyl group and the ether bond give the molecular chain a certain flexibility, so that the polysulfone has a large toughness and is easily melt processable. Polysulfone is very resistant to creep, and its creep is one of the smallest of thermoplastic resins.