Cures room-temperature

Resorcinol is to phenol as melamine is to urea. Resorcinol—formaldehyde (RF) is very expensive, produces dark and waterproof gluelines, but will cure at room temperature. As with melamine and urea, resorcinol is often combined with phenol to produce phenol—resorcinol—formaldehyde (PRF) adhesives, thus producing an exceUent adhesive with some of the economy of phenol. These adhesives are the mainstay of the laminated timber industry which generally requites a room-temperature cure with durable, waterproof gluelines. 

A.dhesives, Cjanoac late, Eapid Room Temperature Curing, Solventless, Army Materials and Mechanics Research Center, Watertown, Mass. 

Epoxy stmctural adhesives are used in an extraordinarily wide range of appHcations. They are available in essentially all of the forms discussed above, except for primer—Hquid combinations or as room temperature curing Hquids. The highest technology appHcation for epoxies is in aerospace stmctural... 

For many moderate-duty films for operating temperatures below 80 to 120°C, M0S2 is used in combination with acryflcs, alkyds, vinyls, and acetate room temperature curing resins. For improved wear life and temperatures up to 150—300°C, baked coatings are commonly used with thermosetting resins, eg, phenohcs, epoxies, alkyds, siUcones, polyimides, and urethanes. Of these, the MlL-L-8937 phenoHc type is being appHed most extensively. 

Urea resin adhesives, by the use of the proper hardener, may be set either by heat or at room temperature. For room temperature curing, the hardener may be ammonium chloride, together with basic materials like calcium phosphate to neutralize excess acid that might damage the wood. Cold set or room temperature set adhesives are those that set satisfactorily at 20 —30°C, whereas a hot set adhesive generally means one that is set above 99 °C. 

Cobalt salts are used as activators for catalysts, fuel cells (qv), and batteries. Thermal decomposition of cobalt oxalate is used in the production of cobalt powder. Cobalt compounds have been used as selective absorbers for oxygen, in electrostatographic toners, as fluoridating agents, and in molecular sieves. Cobalt ethyUiexanoate and cobalt naphthenate are used as accelerators with methyl ethyl ketone peroxide for the room temperature cure of polyester resins. 

Adhesives. Because of exceUent adhesion to many substrates, epoxy resins are extensively used for high performance adhesives. These can be categorized into high temperature curing systems (soHds and Hquids) and room temperature curing systems (Hquids). 

Since cross-linking occurs via an addition mechanism across the double bonds in the polyesters and the reactive diluent there are no volatiles given off during cure (c.f. phenolic and amino-resins) and it is thus possible to cure without pressure (see Figure 25.1). Since room temperature cures are also possible the resins are most useful in the manufacture of large structures such as boats and car bodies. 

In the presence of certain aromatic tertiary amines such as dimethylaniline, benzoyl peroxide will bring about the room temperature cure of general purpose polyester resins. 

More frequently either methyl ethyl ketone peroxide or cyclohexanone peroxide is used for room temperature curing in conjunction with a cobalt compound such as a naphthenate, octoate or other organic solvent-soluble soap. The peroxides (strictly speaking polymerisation initiators) are referred to as catalysts and the cobalt compound as an accelerator . Other curing systems have been devised but are seldom used. 

When cured with room temperature curing system these resins have similar thermal stability to ordinary bis-phenol A type epoxides. However, when they are cured with high-temperature hardeners such as methyl nadic anhydride both thermal degradation stability and heat deflection temperatures are considerably improved. Chemical resistance is also markedly improved. Perhaps the most serious limitation of these materials is their high viscosity. 

Rather similar are the 5.5-dimethylhydantoin derivatives shown in Figure 26.18 (b, e). These resins are said to eonfer improved weathering resistance but also exhibit higher water absorption. Another trifunctional material is p-glycidyl-oxy-A,A/-diglycidylaniline. This has been recommended for adhesive systems in conjunction with benzophenonetetracarboxylic acid dianhydride, which is a room temperature curing agent in this case. 

In 1975 Wacker-Chemie introduced silicones under the name of m-polymers. These are also room temperature curing liquid polymers which give rubbery materials on cross-linking and are available both as one- and two-component systems. Their particular feature is that they contain dispersions of copolymers such as those of styrene and n-butyl acrylate in the shape of rods or rice grains in the fluid silicone polymer. A small amount of the organic copolymer is also grafted onto the silicone backbone. 

An interesting blocked room-temperature curing urethane windshield adhesive is described by Barrons [63] ... 

Fig. 7. Room-temperature curing concept for a phenol-blocked isocyanate-terminated prepolymer.

In other studies [115], the bond strengths of joints made from steel substrates coated with a variety of oils and waxes ( 6 mg/cm ) and Joined with acrylic adhesive were investigated. Lap-shear strengths up to 15 MPa were obtained with room temperature curing. Very little degradation was seen after 1000 h of... 

An additional activating hydroxyl group on the phenolic ring allows resorcinol to react rapidly widi formaldehyde even in die absence of catalysts.8 Hiis provides a method for room temperature cure of resorcinol-formaldehyde resins or mixed phenol-formaldehyde/resorcinol-formaldehyde resins. Trihydric phenols have not achieved commercial importance, probably due to tiieir higher costs. 

The corrosion resistance and polymer-bonding compatibilities of the lonizable organophosphonates and the neutral organo-silanes are directly related to their inherent chemical properties. Specifically, NTMP inhibits the hydration of AI2O2 and maintains or Improves bond durability with a nitrile-modified epoxy adhesive which is cured at an elevated temperature. The mercaptopropyl silane, in addition to these properties, is compatible with a room temperature-cured epoxy-polyamide primer and also exhibits resistance to localized environmental corrosion. These results, in conjunction with the adsorbed Inhibitor films and the metal substrate surfaces, are subsequently discussed. 

The binder should preferably be capable of room temperature curing so that manufacturing of propellant is not too time consuming and also, at the same time, production is cost-effective due to the saving of energy. 

This structure has superior water-resistant properties in comparison to conventional polyols used for PU synthesis. Room temperature cures are easily obtained with typical urethane catalysts. Short chain diols, fillers and plasticizers may also be used in their formulations in order to vary physical properties. Formulations usually with NCO/OH ratio of 1.05 are used for this purpose. Such urethanes are reported to be flexible down to about -70 °C. HTPB is regarded as a work horse binder for composite propellants and PBXs. HTPB also successfully competes with widely used room temperature vulcanizing (RTV) silicones and special epoxy resins for the encapsulation of electronic components. HTPB-based PUs are superior in this respect as epoxy resins change their mechanical properties widely with temperature. 

Room temperature curing characteristics resulting in energy savings specially in the case of larger propellant grains [96]. 

Room-temperature-cured epoxy films on glass (hours in 70°C water to adhesion loss)... 

The specimen used for ITS testing can be any section of the composite, provided that after mounting and polishing, fibers normal to the polished surface can be found. A section of composite approximately 1 cm x 1 cm was cut from the laminates previously prepared. The sections were embedded in 1 in. diameter phenolic ring mounts with room temperature-cured epoxy mounting media. The sections were oriented so that the fiber ends were normal to the face of mount to be polished. The initial steps of the polishing were accomplished on a Struers Abramin polisher and the final step was a on Beuhler Vibromet I vibrating lap polisher. The steps used are listed in Table 2. 

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