Cyanoacrylate adhesives bond strength

The cyanoacrylate adhesives are more rigid and less resistant to moisture than acrylate acid diester adhesives. They are available only as low-viscosity liquids that cure in seconds at room temperature without the need of a primer. The cyanoacrylate adhesives bond well to a variety of substrates, as shown in Table 7.25, but have relatively poor thermal resistance. Modifications of the original cyanoacrylate resins have been introduced to provide faster cures, higher strengths with some plastics, and greater thermal resistance. 

Anhydrides of polyfunctional carboxylic acids, as well as the acids themselves, have been reported to improve the thermal resistance as well as impact toughness of cyanoacrylate adhesives.Bond hot strengths are improved substantially, even though the thermal decomposition temperatures of the polymer remain unchanged. 

Cyanoacrylates and Light-Curing Acrylic Adhesives - These types of adhesives have achieved widespread acceptance in high-speed manufacturing because they cure rapidly, offer high bond strength to many substrates and are easy to dispense 9. (See Reference 189 for the structure of these chemicals.)... 

Parts molded from polyetherimide can be assembled with all common thermoplastic assembly methods. Adhesives that are recommended include epoxy, urethane, and cyanoacrylate. However, service temperature must be taken into consideration in choosing an adhesive because PEI parts are generally used for high-temperature applications. Good adhesion can be effected by simple solvent wipe, but surface treatment by corona discharge, flame treatment, or chromic acid etch will provide the highest bond strengths. 

For adhesive bonding of PES to itself or to other materials, epoxy adhesives are generally used. Cyanoacrylates provide good bond strength if environmental resistance is not a factor. Parts made from PES can be cleaned using ethanol, methanol, isopropanol, or low-boiling petroleum ether. Solvents that should not be used are acetone, MEK, perchloroeth-ylene, tetrahydrofuran, toluene, and methylene chloride. 

The viscous isoamyl cyanoacrylate shows the least deterioration of bond strength to bone in an aqueous environment. This material has the further advantage that (1) it may be more suitable for applications where some filling of a gap by the adhesive is required and (2) it is considered to be less toxic than the lower homologues of the 2-cyanoacrylate series. 

In many cases, glass and even porcelain bondings are carried out as repairs in households. In such cases, it has to be pointed out that, compared to the two-component reactive adhesives, in particular epoxides, cyanoacrylates show only a limited bond strength in the face of high temperature and humidity stress in connection with rinsing agents in the cleaning equipment. 

Assemblies joined with cyanoacrylate adhesives exhibit good long-term durability, particularly when the materials are somewhat flexible, such as rubbers and most plastics (see Fig. 7). Bonded lap shear specimens have been aged outdoors for 7 years with good retention of strength (see Table 8). 

The most important step in the successful application of a cyanoacrylate adhesive is the application of a thin adhesive film between two well-mated surfaces. The thiimer the film is, the faster the rate of bond formation, and the higher the bond strength. Bond strength is dependent on proper surface preparation. 

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