Cyanoacrylates adhesive shear strengths

Whilst some adhesive shear strengths are given in Table 4.6 fluorosilicones can often be recommended for high-temperature applications and so if the operating temperature is >100 C, it is unlikely that cyanoacrylates could be used as suitable adhesives. 

On some grades of Santoprene (e.g., 103-50), adhesive shear strengths up to 8 N/mm can be achieved with an ethyl-based cyanoacrylate and primer but with other grades (e.g., Santoprene 201-55), only 1.5 N/mm is achieved. 

Woodward et al. 20) also investigated the shear strength of animal skin sections glued with a cyanoacrylate adhesive and cut off by a dermatome. Unfortunately, their method is complicated and it is impossible to perform a comparative estimation of the strength of glueing with different cyanoacrylates. 

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). 

Epoxies, isocyanate cured polyester, and cyanoacrylates are used to bond acetal copolymer. Generally, the surface is treated with a sulfuric-chromic acid treatment. Epoxies have shown 150 to 500 psi shear strength on sanded surfaces and 500 to 1000 psi on chemically treated surfaces. Plasma treatment has also been shown to be effective on acetal substrates. Acetal homopolymer surfaces should be chemically treated prior to bonding. This is accomplished with a sulfuric-chromic acid treatment followed by a solvent wipe. Epoxies, nitrile, and nitrile-phenolics can be used as adhesives. 

Tbe lower esters of alkyl 2-cyanoacrylates (eg, methyl, ethyl esters) provide adhesives with excellent lap-shear strengths to a variety of different substrates (3). They are, however, brittle materials and generally require the addition of a rubber-toughening agent to improve peel strength and impact resistance (4). The low esters have pungent odors whereas the higher esters, in particular the alkoxyalkyl esters, are virtually odorless (3). 

Electron Spectroscopy for Chemical Analysis. Bond strength in Newton (N) using lap shear test (see Fig. 14.2). An epoxide adhesive was used for PVF, PTFE, and ECTFE, a cyanoacrylate adhesive for PVDF. 

The lower esters of the alkyl cyanoacrylates cure to clear, hard resins which exhibit good adhesion and tensile shear strengths to a wide variety of substrate combinations. They are, however, brittle and exhibit low peel and impact strengths. Higher viscosity versions of the lower esters filled with 5-10% of poly(methylmethacrylate) resins are somewhat less brittle and can offer double the impact strength of low viscosity monomeric adhesives, as well as significantly better peel strengths. 

Adhesives recommended include epoxies, vinyl alcohol—vinyl acetate copolymer, polyvinyl alkyl ether, polyacrylate (carboxylic), polyurethane (two-part), epoxy-phenolics, silicones, and cyanoacrylates. The high-strength thermoset and alloy adhesives are rarely justified for bonding lead. Even when other properties recommend these adhesives, the designer should check to see whether some low-cost or easier-to-use adhesive is also suitable. An exception is teme (lead-coated steel). This is a much stronger metal than lead, and lap-shear strengths exceeding 2.1 MPa are reported for adhesive joints with teme.° ... 

After a dwell time of five seconds under the device, it can be seen in Figure 7.10 that the shear strength of the bond between the LPDE sample and cyanoacrylate adhesive increased 10-fold, and the shear strength of the bond between the LPDE sample and the light cure acrylic adhesive increased 40-fold. Subsequently, MIL-STD-883 Method 2011.7 was applied as a destructive bond pull test to evaluate bond strength and bond strength distribution of various surface contaminations after CO2 treatment. The apparatus used had an accuracy of 5% and performed at a 90° peel angle. 

Cyanoacrylates form strong thermosetting bonds between many materials without heat or an added catalyst. They are particularly useful in bonding metal to nonmetal. Lap-shear strengths of 13.7 MPa have been reported. However, the resistance of these adhesives to moisture is still somewhat low [3]. These materials set very quickly when squeezed out to thin films between many types of adherends. 

Structural adhesive types recommended are epoxy (up to 71°C), polyester with isocyanate-curing agent (up to 121°C), and cyanoacrylate (up to 82°C). Structural adhesives for bonding acetal copolymer to itself have yielded shear strengths of 4.1—5.5 MPa. Nonstructural adhesives are usually... 

Epoxy adhesives such as Huntman s Araldite AW 134 with HY 994 hardener (cured for 15 min at 120°C) and Araldite AV 1566 GB (cured for 1 h at 230°C) give the best results with this engineering resin. Other adhesives that can be used are cyanoacrylate (Loctite 414 with AC primer), anaerobics (Loctite 638 with N primer), and silicone sealant (Loctite Superflex). The highest lap-shear strength was obtained with Araldite AW 134. This adhesive has balanced properties, good resistance to mechanical shock, thermal resistance to 100°C, and reasonable stability in the presence of aliphatic and aromatic solvents. Some solvents, particularly chlorinated hydrocarbons, will cause deterioration of the bond [30]. 

Low surface energy substrates, such as polyethylene or polypropylene, are generally difficult to bond with adhesives. However, cyanoacrylate-based adhesives can be effectively utilized to bond polyolefins with the use of the proper primer/activa-tor on the surface. Primer materials include tertiary aliphatic and aromatic amines, trialkyl ammonium carboxylate salts, tetraalkyl ammonium salts, phosphines, and organometallic compounds, which are initiators for alkyl cyanoacrylate polymerization [33-36]. The primer is applied as a dilute solution to the polyolefin surface, solvent is allowed to evaporate, and the specimens are assembled with a small amount of the adhesive. With the use of primers, adhesive strength can be so strong that substrate failure occurs during the course of the shear tests, as shown in Fig. 11. 

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