Epoxies recommended adhesives

Extended exposure of the uncured material to temperatures or conditions outside those recommended by the manufacturer will cause change in physical properties of the uncured material and will likely reduce its resulting cohesive and adhesive strength. The reactions that occur due to ambient storage conditions are described in Chap. 3. Figure 17.5 shows the effect of aging conditions on the tensile shear strength of an epoxy film adhesive. 

There are frequent reports about non-occupational cases of epoxy-resin sensitivity too. Contact dermatitis due to the epoxy resin in textile label patches has been attributed to the epoxy containing adhesive (Fregert and Orsmark 1984). We recommend limiting patch tests with epoxy chemicals to the standardised test series because of the danger of active sensitisation. Once proven, epoxy resins should not be re-tested, in our opinion. When testing epoxy-exposed individuals, never forget to include chemical additives such as the broad range of hardeners. 

Cementing the cover slip. After the sample has been lapped down to the desired thin-section thickness, the cover slip is applied. To this end, the sample is washed thoroughly in water and then dried. A drop of cold-setting adhesive is then applied to the section and spread across the section surface with a cover slip. The thickness of the cover slip is 0.15 mm. Recommended adhesives include Canada balsam thinned with xylene, or a suitable epoxy resin. It is important for the indices of refraction to correspond. 

Surface treatment prior to adhesive bonding typically consists of surface roughening and may be followed by acid etching or plasma, corona, ultraviolet or laser treatments. These increase surface functionality and improve bond strength. There are a number of recommended adhesives which are often based on epoxy resin chemistry. However, it should be remembered that many adhesives do not offer the very high-temperature performance of PAEK. 

Two-Component Conductive Adhesives Two-component electrically conductive adhesives include products that provide high peel and tensile lap shear strength over a broad temperature range, and silver-filled epoxies recommended for electronic bonding and sealing applications. 

The thickness of the coating also affects permeability, and in general, there is a correlation between thickness and life. However, with relatively thick coatings as obtained with some modern materials such as epoxies the relationship is not so well established. There may be a limiting thickness above which either little additional protection is obtained or the increase in cohesive strength reduces its adhesive strength. Coatings should always be applied as closely as possible to the manufacturer s recommended thickness. 

Compatibility of ethanol with tank and piping materials such as carbon steel, stainless steel, and Fiberglas is good. Zinc linings and epoxy linings are not stable in ethanol systems and are not recommended for use. Also, epoxy adhesives and resins are dissolved by ethanol. Teflon and nylon are compatible elastomers. In... 

Since slower-curing epoxy adhesives systems flow over and wet high-energy surfaces very well, there is little chance for air to become trapped at the interface. As a result, mechanical abrasion is often recommended as a substrate surface treatment prior to application of the epoxy adhesive. The added surface area and the mechanical bonding provided by the additional peaks and valleys on the surface will enhance adhesive strength. If the adhesive does not wet the substrate surface well, such as in the case of epoxy resin on polyethylene, mechanical abrasion is not recommended since it will only encourage the probability of gas voids being trapped at the interface. 

TABLE 16.7 Starting Formulations for Several Epoxy Adhesives Recommended for Bonding Plastic Substrates52... 

Cellulosics are normally solvent-cemented unless they are to be joined to another substrate. In these cases, conventional adhesive bonding is employed. Polyurethane, epoxy, and cyanoacrylate adhesives are commonly used to bond cellulosics. Surface treatment generally consists of solvent cleaning and abrasion. Cellulosics can be stress-cracked by uncured cyanoacrylate adhesives and some components of acrylic adhesives. A recommended surface cleaner is isopropyl alcohol. 

Commonly used adhesives for both PET and PBT substrates are isocyanate cured polyesters, epoxies, and urethanes. Surface treatments recommended specifically for PBT include mechanical abrasion and solvent cleaning with toluene. Gas plasma surface treatments and chemical etch have been used where maximum strength is necessary. 

Polyethylene terephthalate cannot be solvent-cemented or heat-welded. Adhesives are the prime way of joining PET to itself and to other substrates. Only solvent cleaning of PET surfaces is recommended as a surface treatment. The linear film of polyethylene terephthalate (Mylar) provides a surface that can be pretreated by alkaline etching or plasma for maximum adhesion, but often a special treatment such as this is not necessary. An adhesive for linear polyester has been developed from a partially amidized acid from a secondary amine, reacted at less than stoichiometric with a DGEB A epoxy resin, and cured with a dihydrazide.72... 

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. 

Adhesives recommended for polyphenylene sulfide include epoxies, and urethanes. Joint strengths in excess of 1000 psi have been reported for abraded and solvent-cleaned surfaces. Somewhat better adhesion has been reported for machined surfaces. The high heat and chemical resistance of polyphenylene sulfide plastics makes them inappropriate for either solvent cementing or heat welding. 

Certain adhesive materials are hazardous when mixed together. Epoxy and polyester catalysts, especially, must be well understood, and the user should not depart from the manufacturers recommended procedure for handling and mixing. Certain unstabilized solvents, such as trichloroethylene and perchloroethylene, are subject to chemical reaction on contact with oxygen or moisture. Only stabilized grades of solvents should be used. 

Starting formulations for several epoxy adhesives recommended for bonding plastic substrates... 

The so called "flexiblized" epoxy is most commonly used for filling such joints. Sponge rod is not used in food plants due to possible subsurface contamination and bacterial growth. Several years ago, a series of tests were made and it was found that silicones are better for strong oxidizing chemical resistance, such as nitric acid. Unfortunately they lose adhesion in wet or submerged exposures. They require very dry clean surfaces and a silicone primer. A test installation is recommended before you use silicone in a project. 

Polycarbonate Conventional adhesives recommended include epoxies, modified epoxies, polyurethanes, acrylics, RTV silicones, cyanoacrylates, one-part elastomers, some epoxy-polyamides, and hot melts (13). 

Modified Polyphenylene Oxide (NORYL ) Conventional adhesives recommended include epoxies, polysulfide-epoxies, silicone, synthetic rubber, acrylics, cyanoacrylates, and hot melts (14). 

Polystyrene Although polystyrene is usually bonded by solvent cementing, it can be bonded with vinyl acetate/vinyl chloride solution adhesives, acrylics, polyurethanes, unsaturated polyesters, epoxies, urea-formaldehyde, rubber-base adhesives, polyamide (Versamid-base), polymethylmethacrylate, and cyanoacrylates. The adhesives should be medium-to-heavy viscosity and room-temperature and contact-pressure curing. An excellent source is a Monsanto Company technical information bulletin which recommends particular commercial adhesives for bonding polystyrene to a number of different surfaces. Adhesives are recommended in the fast-, medium-, and slow-setting ranges (10). 

Polyethylene and Polypropylene Acceptable bonds have been obtained between treated polyolefin surfaces with polar adhesives, such as epoxies, or solvent cements containing synthetic rubber or phenolic resin. The solvent adhesives are applied to both surfaces and the solvents allowed to evaporate before the parts are joined. Recommended epoxies are the anhydride-cured and amine-cured types. Also suitable is a two-component, polyamide-modified epoxy compound. Other adhesives that provide adequate bond strength to treated polyolefins include styrene-unsatmated polyester and solvent-type nitrile-phenolic (15). 

Poly butylene Terephthalate (PBT) Commercial adhesives recommended include modified epoxies, cyanoacrylates, acrylics, polyurethanes, silicone, and polyesters. 

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). 

Phenolic Adhesives recommended are neoprene and urethane elastomer, epoxy and modified epoxy, phenolic-polyvinyl butyral, nitrile-phenolic, polyester, cyanoacrylates, polyurethanes, resorcinols, modified acrylics, polyvinyl acetate, and urea-formaldehyde (1). 

The method of adhesion of the plates to the foam surfaces and the type of adhesive used are all-important in this test and, depending on the nature of the polymer, epoxy- or polyester-based adhesives are recommended. 

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