Epoxy-nylons

The basic RIM process is illustrated in Fig. 4.47. A range of plastics lend themselves to the type of fast polymerisation reaction which is required in this process - polyesters, epoxies, nylons and vinyl monomers. However, by far the most commonly used material is polyurethane. The components A and B are an isocyanate and a polyol and these are kept circulating in their separate systems until an injection shot is required. At this point the two reactants are brought together in the mixing head and injected into the mould. 

There are numerous bifunctional monomers used in condensation polymerization. Some of the more popular signature groups that turn up frequently are shown in Figure 22-3. Important copolymers made by condensation include epoxies, nylon, polyesters, polycarbonate, and polyimides. As always, there are exceptions, and one is Nylon 6 made by a ring opening reaction of caprolactam. All of these will be covered in the next two chapters. 

Delamination Carbon-epoxy Nylon films 270 25 Charpy impact... 

Expandable PS Thermoplastic urethane Abietic acid derivatives Polyester fiber Chlorinated polyether resins Butadiene-acrylonitrile copolymers Melamine resin Polyurethane filament Cast epoxy Nylon-6... 

The early aerospace adhesives were primarily based on epoxy resin chemistry. However, unique applications requiring high temperatures and fatigue resistance have forced the development of epoxy-phenolic, epoxy-nitrile, epoxy-nylon, and epoxy-vinyl adhesives specifically for this industry. The aerospace industry has led in the development and utilization of these epoxy-hybrid adhesives. 

Vinyl-phenolic Nitrile-phenolic Epoxy-phenolic Epoxy-nylon Epoxy-nitrile 3000-4500 15-35 3000-4500 15-60 2000-3200 6-12 5500-7200 80-130 3700-6000 22-90... 

Alloyed blends consisting of epoxy-phenolic, epoxy-nylon, and epoxy-polysulfide adhesives... 

Epoxy-nylon adhesives are limited to a maximum service temperature of 85°C, and they exhibit poor creep resistance. Possibly their most serious limitation is poor moisture resistance because of the hydrophilic nylon (polyamide) constituent.9 The degradation by exposure to moisture occurs with both the cured and uncured 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 ... 

A pressure of 25 psi and temperature of 175°C are required for 1 h to cure the epoxynylon adhesive. Because of their excellent filleting properties and high peel strength, epoxy-nylon adhesives are often used to bond aluminum skins to honeycomb core in aircraft structures. In these applications, climbing drum peel strengths in excess of 150 lb/in have been achieved. 

Another common method of flexibilizing epoxy adhesives is by blending the primary epoxy resin with other, more elastic polymers. Epoxy-nylon, epoxy-polysulfide, and to a certain extent epoxy-urethane hybrids use such a mechanism to provide flexibility. These flexibilizers are important additives for epoxy adhesives even though they may reduce certain... 

Soluble thermoplastic polymer additions (e.g., epoxy-nylon and epoxy-vinyl) provide very tough and somewhat flexible systems, but they are limited because of their high viscosity and high raw materials costs. Almost all these systems need to be handled at elevated temperatures or as solvent solutions. They require elevated temperature to achieve wetting and cure. 

Borates Zinc borate, barium metaborates, ammonium fluoroborate, boric acid Flexible PVC, polyolefins, unsaturated polyesters, thermoplastic polyesters, epoxies, nylons, urethanes, and phenolics Alcan, Amspec Chemical, Asahi Denka Kogyo, Borax, Buckman Laboratories, Great Lakes... 

A significant advantage of tape and film adhesives is the greater toughness that is available compared to other adhesive types. This is primarily due to the ease with which resinous modifiers can be added to the formulation via solvent solution. Thus, hybrid epoxy adhesives such as epoxy-nylon, epoxy-phenolic, etc., are often found in tape or film form. 

Typically tape or film epoxy adhesives are modified with synthetic thermoplastic polymers to improve flexibility in the uncured film and toughness in the cured adhesive. Epoxy resins can also be blended with phenolic resins for higher heat resistance. The most common hybrid systems include epoxy-phenolics, epoxy-nylon, epoxy-nitrile, and epoxy-vinyl hybrids. These hybrid film adhesives are summarized in Table 13.2, and structural properties are shown in Table 13.3. 

Epoxy-nylon adhesives were developed in the 1960s for high-peel-strength applications. The key to their development is the use of noncrystalline nylons that are soluble in alcohols and other epoxy-compatible solvents. A commercial example of adhesive-grade nylon includes DuPont s Zytel 61. Standard nylons are not practical because of their incompatibility with most other resins. 

Epoxy-nylon film adhesive can be manufactured by solution casting processes. However, a more efficient and environmentally acceptable method is to calender dry blends of powdered nylon with a bquid epoxy resin with accelerators and other modifying resins directly... 

Epoxy-nylon adhesives show exceptionally high tensile shear and peel strengths however, they have poor resistance to moisture and elevated temperatures. These adhesives can absorb significant amounts of water from the ambient environment before and after cure. Table 7.5 gives tensile shear and peel strengths for a series of adhesives made by dissolving various ratios of nylon and epoxy resins in a alcohol-water mixtures. 

The toughness of an epoxy-nitrile adhesive is nearly equivalent to that of an epoxynylon adhesive. However, the epoxy-nitrile system has much better hydrolytic stability. Also, the low-temperature properties of an epoxy-nitrile adhesive are superior to those of epoxy-nylon adhesive. Table 7.3 illustrates the effect of nitrile addition on tensile shear and peel strength. 

Environment Epoxy + polyamine Epoxy + anhydride Epoxy + polyamide Epoxy- phenolic Epoxy- polysulfide Epoxy-nylon Phenoxy (thermoplastic)... 

Epoxy-nylon Epoxy-phenolic Epoxy-polyamide Filled epoxy... 

Next to the epoxy-nylons and epoxy-urethanes, the epoxy-polysulfide adhesives show the greatest lap shear tensile strength at temperatures below 0°C. Bonded etched steel substrates show a tensile shear strength of 2900 psi at room temperature, and this increases to 3400 psi when the temperature is reduced to -156°C. Epoxy-nylon and epoxy-polysulfide are the only adhesives that show an increase in strength as the temperature is significantly reduced. 

C cured film (nitrile-phenolic, vinyl-phenolic, novolac-epoxy) 120°C cured film (modified epoxy, nitrile-epoxy, nylon-epoxy)... 

Heat cured paste (nitrile-epoxy, nylon-epoxy, vinyl-epoxy)... 

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. 

Common adhesives for sandwich construction include nitrile phenolic films, modified epoxy pastes and films, epoxy-nylon films, polyimide films, and modified urethane liquid... 

Epoxy-phenolic adhesive compositions of commercially available types Epoxy-nylon adhesive composition... 

Polysulfone A number of adhesives have been found useful for joining polysufone to itself or to other materials. These include 3M Company s EC 880 solvent-base adhesive, EC 2216 room-temperaturecuring epoxy two-part paste, Bloomingdale Division, American Cyana-mid Company BR-92 modified epoxy with DICY curing agent, or curing agent "Z" (both spreadable pastes), vinyl-phenolics, epoxy-nylons, epoxies, polyimide, rubber-based adhesives, styrene polyesters, resorcinol-formaldehyde, polyurethanes, and cyanoacrylates. The EC 880, EC 2216, and the two BR-92 adhesives are recommended by the polysulfone manufacturer. Union Carbide (16) (17). 

The plastics industry and all the products made from plastics are almost entirely dependent on chemicals extracted or produced from hydrocarbons. This includes not only the familiar materials such as polyethylene, polypropylene, polyvinyl chloride (PVC), epoxies, nylon, polyesters, polycarbonate. Teflon and Plexiglas, but also includes a large portion of materials made from rubber and a diverse group of other materials formulated from polymers such as tape, glue, ink, waterproofing, wax, and polishes. Virtually all the synthetic fibers used in textile products, Orion , Dacron , Nylon and polyesters are made from polymers based on hydrocarbons. 

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