Nitrile phenolic adhesives

Not only is low tensile shear strength noticed on moisture aging, but also the mode of failure changes from one of cohesion to adhesion. Table 7.6 shows the effect of humidity and water immersion on an epoxy-nylon adhesive compared to a nitrile-phenolic adhesive. Substrate primers have been used with epoxy-nylon adhesives to provide improved moisture... 

TABLE 7.6 Effect of Humidity and Water Immersion on the Tensile Shear Strength of Epoxy-Nylon and Nitrile-Phenolic Adhesives 10... 

Exposure time, months Epoxy-nylon adhesive Nitrile-phenolic adhesive ... 

Certain adhesive systems are more resistant to interfacial degradation by moist environments than are other adhesives. Table 15.16 illustrates that a nitrile-phenolic adhesive does not succumb to failure through the mechanism of preferential displacement at the interface. Failures occurred cohesively within the adhesive even when tested after 24 months of immersion in water. A nylon-epoxy adhesive bond, however, degraded rapidly under the same conditioning owing to its permeability and preferential displacement by moisture. 

Nylon-epoxy adhesive, psi Nitrile/phenolic adhesive, psi... 

Epoxy and nitrile-phenolic adhesives have been used to bond polyolefin plastics after plasma surface preparation. Shear strengths in excess of 3000 psi have been reported on... 

Structural adhesives that are commonly used for composites are supplied in two basic forms semisolid B-stage film and thixotropic pastes. The film adhesives are cast or extruded onto carrier fabrics or films and partially cured to a semisolid. They can easily be handled, cut, and applied to the joint area. There is no need for mixing, metering, or dispensing of liquid components. In use, these adhesive systems are activated by heat and pressure. The semisolid B-stage film liquefies briefly on application of heat and then cures to an insoluble state. Epoxy, polyimides, epoxy-nylons, epoxy-phenolic, and nitrile-phenolic adhesives are available as B-stage film. 

Polyvinylchloride, polyvinylidene chloride, polyvinyl fluoride Trichloroethylene, methyl ethyl ketone 1. Abrasion grit or vapor blast or 100-grit emery cloth followed by solvent degreasing. 2. Solvent wipe with ketone. Suitable for rigid plastic. For maximum strength, prime with nitrile phenolic adhesive Suitable for plasticized material... 

According to one author, epoxy-phenolic adhesives for high-temperature applications were developed during World War II at Forest Product Laboratories in Madison, Wisconsin, and nitrile phenolic adhesives shortly after World War II [9, pp. 153, 156]. A patent for epoxy resins was applied for in Germany in 1934, and the inventor disclosed that it could be hardened with equivalent amounts of amines, diamines, or polyamines and that it showed strong adhesion [14, p. 8]. Epoxy resins are believed to have been commercialized in the United States first by the former Jones Dabney Company sometime after 1942. 

The liquid nitrile-phenolic adhesives are dried at 80°C and cured for 15-30 minutes at 90°C at contact to 0.70 MPa pressure. ... 

Nylon-epoxy film adhesives have the tendency of picking up substantial amounts of water before use. They also tend to lose bond strength rapidly after use on exposure to water or moist air. After 18 months of exposure to 95% RH, conventional nitrile-phenolic adhesive loses only a fraction of its initial strength, going from 21 to 18 MPa in tensile shear. On the other hand, one of the best nylon-epoxy adhesives available degraded from about 34 to 6.8 MPa in just two months under the same test conditions. A considerable effort has been made to solve this moisture problem, but nitrile-epoxy or acetal-toughened epoxy film adhesives are still superior in durability. "" ... 

Nitrile-phenolic adhesives are more resistant to radiation damage than epoxy-based adhesives. 

Epoxy and nitrile-phenolic adhesives have been used to bond these plastics after surface preparation. The surface can be etched with a sodirim sulfiiric-dichromate add solution at an elevated temperature. Flame treatment and corona discharge have also been used. However, plasma treatment has proven to be the optimum siuface process for these materi2ds. Shear strengths in excess of 3000 Ib/in have been reported on polyethylene treated for 10 min in an oxygen plasma and bonded with an epoxy adhesive. Polyolefin materials can also be thermally welded, but they cannot be solvent cemented. 

These materials may be bonded with epoxy, thermosetting acrylic, urethane, and nitrile-phenolic adhesives. Special surface treatment is not necessary for adequate bonds. However, plasma treatment has been reported to provide enhanced adhesion. Solvent cementing and certain thermal welding methods can also he used with thermoplastic polyester. 

Epoxy-phenolic adhesives are exceptional in that they have good adhesive properties at both elevated and low temperatures. Vinyl-phenolic adhesives maintain fair shear and peel strength at -423 °F, but strength decreases with decreasing temperature. Nitrile-phenolic adhesives do not have high strength at low service temperatures, because of rigidity. 

Nitrile rubber/phenolic adhesives are also quite useful in adhering rubber to various met-als, " e.g., in the manufacture of rubber covered metal rollers. Huber reported that a nitrile/phenolic adhesive composition provided excellent bonding of rubber to a magnesium roll (Table 20). Other metal bonding applications with nitrile rubber/phenolic adhesives include laminating aluminum foil to paper and then to wood, bonding abrasives to metal, and bonding polyamide to metal. 

Supported films of nitrile phenolic adhesives are formulated with excess phenolic resin which gives a more brittle polymer with resin on its surface. This surface excess obviates the need for priming the metal substrate with nitrile-phenolic before bonding. The brittleness of the adhesive is offset by the presence of fabric as the carrier. Solvent based nitrile phenolics contain an excess of nitrile rubber. Materials which are used as the support comprise cotton nylon polyester glass tissue paper. The support may be either woven or non-woven. 

The last two items of the earlier list involve the behaviour of primers, in part chemical, in part physical, as forms of adhesives sticking the bulk adhesive to the actual metal, wood or other adherend. When dissimilar materials are to be joined, an adhesive suitable for one may not be so for the other. In these circumstances a primer for one of the substrates is chosen to be both suitable for it and compatible with the adhesive. Phenol-formaldehyde condensation products are often thus used particularly when the adhesive itself contains such material dispersed in another polymer, e.g. Redux775 (Bonded Structures, Ltd) or various epoxy-phenolic or nitrile-phenolic adhesives. Most important members of the class of coupling agents are the reactive silanes (siloxanes) and titanates. These materials have achieved their main use in the treatment of glass fibres for the manufacture of glass reinforced plastics. 

Fig. 123. Behaviour of a nitrile-phenolic adhesive on extended exposure trial (data from Hockney, 1973).

Strength of joints in aluminium alloy bonded with a nitrile-phenolic adhesive on exposure to wet air at 50°C. o 50% r.h. 100%r.h. A Joints which have been exposed at 100%r.h. for 5000h and then stored for a further SOOOh at 50% r.h. After Comyn, Brewis and Tredwell (1987). Crown copyright... 

---