Nylon-epoxy durability

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. "" ... 

In a review of previous work, DeLollis concluded that the nitrile-phenolic is the most durable adhesive, surviving all environmental exposures. The nylon-epoxy adhesive performed well on exposure to medium-humidity environments, but was susceptible to high humidities. The nitrile-epoxies showed good resistance to most outdoor exposures except the seacoast environment, where bonds failed after four years. Epoxy/polyamide bonds gave good results after four years exposure to an industrial environment and joints exposed to a tropical climate had retained about 33% of their initial strength after three years. This performance should be compared with that of some heat-cured adhesives, for which the bonds are completely degraded by tropical exposure. 

Nylon-epoxy is typically used in film and tape adhesive applications and has maximum service temperature of 138°C, compared with 177°C for unmodified epoxies. The addition of nylon provides increased flexibility and peel strength compared to unmodified epoxies. Nylon-epoxy is a tough material with excellent tensile lap shear strength and good fatigue and impact resistance. However, the addition of nylon results in deterioration in creep resistance and poor peel strength at low temperatures. Furthermore, the hydrophilic nature of nylon imparts poor moisture resistance in both uncured and cured forms of the resin. Consequently, nylon-epoxies are not as durable as elastomer-epoxies or other thermoplastic modified epoxies. 

Elastomer-epoxies are prepared mostly by nitrile rubber addition as the elastomeric component and are usually called modified or toughened epoxy. The bond strengths of elastomer-epoxies are lower in comparison to those of nylon epoxies. Their durability with respect to moisture resistance is better, but not as good as those of vinyl phenolics or nitrile-phenolics. A wide application is in films and tapes. Elastomer-epoxies typically cure at low pressures and temperatures, and over short cure periods, by adding a catalyst to the adhesive formulation. 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

The results for the 120 C-curing epoxy film adhesives are shown in Fig. 9. Marked differences are noted here. The AF-44 nylon-toughened epoxy has very poor durability at any load and adhesion failure predominates. AF-126-2, the first-generation nitr ile-r ubber-f lexibilized epojiy has somewhat better durability and the failure mode is at least partially cohesive. AF-163 and AF-163-2, the second-generation-toughened epoxies, show a substantial... 

Uses. Applied as a powder coating, nylon provides a high degree of toughness and mechanical durability to office furniture. Other polyamide resins are used as curing agents in two-component epoxy resin-based primers and topcoats, adhesives, and sealants. 

Polyamides (nylon) can be bonded well with cyanoacrylates, epoxies, and acrylics. Careful durability testing of joints is recommended because of the tendency of the plastic to absorb atmospheric moisture. 

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