Heat reactivation

Heat-reactive resins are more compatible than oil-soluble resins with other polar-coating resins, such as amino, epoxy, and poly(vinyl butyral). They are used in interior-can and dmm linings, metal primers, and pipe coatings. The coatings have excellent resistance to solvents, acids, and salts. They can be used over a wide range of temperatures, up to 370°C for short periods of dry heat, and continuously at 150°C. Strong alkaUes should be avoided. 

Substituted heat-reactive resins are most widely used in contact-adhesive appHcations and, to a lesser extent, in coatings (77,78) -butylphenol, cresol, and nonylphenol are most frequendy used. The alkyl group increases compatibiHty with oleoresinous varnishes and alkyds. In combination with these resins, phenoHcs reduce water sensitivity. Common appHcations include baked-on and electrical insulation varnishes, and as modifiers for baking alkyds, rosin, and ester gum systems. Substituted heat-reactive resins are not used for air-dry coatings because of theh soft, tacky nature in the uncured state substituted nonheat-reactive phenoHcs are the modifying resin of choice in this case. 

PhenoHcs that are not heat-reactive may be incorporated into both air-dried and baked oleoresinous coatings. AppHcations vary widely and include clear and pigmented exterior varnishes, aluminum-maintenance paints, 2inc-rich primers, can coatings, insulation varnishes, and concrete paints. As modifiers in a great variety of appHcations, they enhance the performance of oleoresinous and alkyd coatings. 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

Neoprene—phenohc contact adhesives, known for thein high green strength and peel values, contain a resole-type resin prepared from 4-/-butylphenol. The alkyl group increases compatibiHty and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenoHcs in the formulation. 

Waterborne contact adhesives contain an elastomer in latex form, usually an acryflc or neoprene-based latex, and a heat-reactive, cross-linkable phenohc resin in the form of an aqueous dispersion. The phenoHc resin improves metal adhesion, green strength, and peel strength at elevated temperature. A typical formulation contains three parts latex and one part phenohc dispersion (dry weight bases). Although metal oxides may be added, reaction of the oxide with the phenohc resin does not occur readily. 

Neoprene 750A. It is a medium-gel, slow-crystallizing polymer. It combines flexibility, dry tack, heat-reactivity and cohesive strength. 

Chlorinated rubber is also used to promote the adhesion of solvent-borne CR adhesives to metals and plasticized PVC. Addition of a low molecular weight chlorinated rubber (containing about 65 wt% chlorine) improves the shear strength and creep resistance of polychloroprene adhesives [75] but a reduction in open time is also produced. A heat reactivation (process in which the surface of the adhesive film is raised to 90-100°C to destroy the crystallinity of the film and allowing diffusion to produce polymer chain interlocking more rapidly) restores tack to the polychloroprene adhesives. 

Chemical Reactivity - Reactivity with Water. Reacts violently with water, liberating hydrogen chloride gas and heat Reactivity with Common Materials None if dry. If wet it attacks metals because of hydrochloric acid formed flammable hydrogen is formed Stability During Transport Stable if kept dry and protected from atmospheric moisture Neutralizing Agents for Acids and Caustics Hydrochloric acid formed by reaction with water can be flushed away with water. Rinse with sodium bicarbonate or lime solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water Anhydrous grade dissolves with evolution of some heat Reactivity with Common Materials Metals slowly corrode in aqueous solutions Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Srinivas, B. K., and El-Halwagi, M. M. (1994b). Synthesis of combined heat reactive mass-exchange networks. Chem. Eng. Sci. 49(13), 2059-2074. 

Substituted heat-reactive resins, 18 782 Substituted isoquinolines, 21 208 Substituted nickel carbonyl complexes, 17 114... 

Protective coatings are the fourth major user of rosin, either directly or in a modified or derivative form. Varnishes and alkyds are the most common types of protective coatings using rosin. Rosin is combined with a heat-reactive phenol-formaldehyde resin to produce a widely used varnish. Printing inks also use substantial amounts of rosin. 

Phenolic resins are well known for their contribution in improving hardness, gloss, and water and chemical resistance in oleoresinous varnishes. Those based on p-alkyl-substituted phenols and with heat-reactive methylol groups have also been incorporated into alkyd resins. The reaction has not been well smdied. Presumably, the methylol group would react with the unsaturation functionality on the fatty acid chain to form the chroman stmcture, similar to what is believed to have occurred in the varnish. Etherification between the methylol group and free hydroxyl of the alkyd resin, catalyzed by the residual acidity in the resin, would be another possible reaction. 

LX-685 [Neville]. TM for a heat-reactive resin used in the manufacture of ready-mixed aluminum paints, grease- and gasoline-resistant coatings, floor and deck enamels, and concrete curing compounds. 

One very important niche application for calcium aluminate (cements) is as refractory castables. Key to the success of calcium aluminates in this application are their refractory properties that contrast with those of Portland cements. Although Portland cement maintains good strength when heated, reactive components (CaO) are liberated and can absorb moisture from the atmosphere when cooled, causing expansion and deterioration of, for example, kiln linings. CACs are not much susceptible and can be used to form monolithic castables and refractory cements [28, 29],... 

The fluid dimer polyamides and fatty amido amines also react with phenolic resins (23). These reactions are significantly different from those of epoxy resins. With the heat-reactive phenolic resins, the aminopolyamide portions react with methylol groups. A carbon-nitrogen bond or cross-link is formed and a volatile byproduct, water, is produced. This reaction requires external heat to remove water. At temperatures near 150 °C the reaction proceeds smoothly. Since curing at elevated temperatures is required, the pot life or shelf life at room temperature is relatively long. The liquid dimer polyamide and fatty amido amines also react with alpha, beta unsaturated acids and esters (29) and with polyesters (30). The unsaturated esters reduce viscosity, lengthen useful pot life, and reduce heat of reaction. Thus, they are useful diluents when low viscosity is desired. 

Raw Materials Base-Catalyzed Reactions Acid-Catalyzed Reactions Classification of Phenolic Resins Unsubstituted and Heat Reactive Unsubstituted and Nonheat Reactive Substituted and Heat Reactive Substituted and Nonheat Reactive Applications... 

Phenolic resins can be divided between heat-reactive and nonheat-reactive resins and between resins made by using unsubstituted or substituted phenols. A review of the four resulting classifications follows. 

Unsubstituted and Heat Reactive. The first class, the unsubstituted, heat-reactive resins, are made by using phenol, cresols, and xylenols. They are multifunctional and thus can be cross-linked to form films. They are soluble in alcohols, ketones, esters, and glycol ethers and insoluble in aromatic and aliphatic hydrocarbons. They will tolerate some water in their solvents and, in some cases, are completely water soluble. They are compatible with polar resins such as amino resins, epoxies, polyamides, and poly(vinyl butyral), though compatibility on curing is dependent on reaction between the two resins. Less polar resins such as alkyds and drying oils are incompatible. 

Unsubstituted, heat-reactive phenolic resins are commercially available as 100% viscous liquids, as water and alcohol solutions, and as solid resins. The viscous liquids are mixtures of monomers and dimers of varying raethylolation. The water solutions contain resins of monomers and dimers with the highest degree of raethylolation. Alcohol solutions contain resins that are higher in molecular weight and are too reactive to isolate as solids. 

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