Epoxy diluents

The viscosity of a resin system can be reduced by the addition of a diluent, which can be non-reactive (e.g. dibutyl phthalate, benzyl alcohol and furfuryl alcohol) or reactive (a low molecular weight epoxide, triphenyl phosphite or x-butyrolactone). The x-butyrolactone can, for example, act as a solvent for a catalyst system used in a solventless system and take part in the reaction. Diluents tend to be rather volatile and could be partially lost in cure systems operating under a vacuum. Flexibilizers can impart toughness but at the expense of mechanical properties, chemical resistance and heat resistance. 

Reactive diluents are generally monoglycidyl or diglycidyl ethers. The monoglycidyl ethers have only one epoxide group per molecule and will therefore reduce the functionality and consequently, reduce the crosslink density. 

Dow has a series of diluents (e.g., Dow 736 732) based on the polyglycols of propylene oxide  

Gel permeation chromatograhy (GPQ is used to separate the various eomponents of epoxy resins and these separated components are treated with various ehemieal reagents and resubmitted for GPC or high performance liquid chromatography (HPLQ. Typical reagents used are  

Concentrated HCl to convert epoxy groups to chlorhydrin units. 

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The monofunctional epoxy diluents are essentially chain stoppers since they inhibit crosslinks from forming. The extent to which the cured properties are affected is directly dependent on the concentration of the diluent added to the epoxy resin. The general effect is to reduce viscosity and improve the impact and thermal shock resistance while slightly reducing the thermal resistance. The thermal expansion of the cured resin is increased, as it is also with nonreactive diluents. This can lead to internal stress on the bond line depending on the thermal expansion of the substrate material. 

Monofunctional epoxy diluents are used primarily with DGEBA epoxy blends. The most common monofunctional diluents are butyl glycidyl ether and phenyl glycidyl ether. The effect of butyl glycidyl ether and other reactive diluents on the viscosity of epoxy resin is shown in Fig. 6.3. Because the monofunctional diluents reduce crosslink density, they are used at relatively low levels to avoid degrading heat and chemical resistance or other properties of the adhesive. 

Difunctional epoxy diluents are low-viscosity, low-MW epoxy resins. These diluents may be used at very high concentrations, and they do not greatly affect the properties of the cured resin. In some instances the difunctional epoxy diluents will actually improve properties. These materials include butadiene dioxide, vinyl cyclohexane dioxide, and diglycidyl ether of resorcinol. 

Since many of the difunctional epoxy diluents are added to epoxy adhesive formulations as flexibilizers as well as viscosity reducers, they are discussed in greater detail in Chap. 8 with other flexibilizing additives. 

Monofunctional epoxy diluents are long-chain molecules that have one functional group that can react with the epoxy system. The linkage prevents the diluent from migrating out of the cured epoxy during aging. The long chains force the molecules in the cured structure to... 

TABLE 14.3. Select Examples of Monofunctional Epoxy Diluents... 

The effect of adding a mono-epoxy diluent to reduce the cross-linking density is shown in Figure I, middle curve. The reactive diluent NC-513 has been added to the NC-540-cured system and this allows the cure to proceed to where only 11% unreacted epoxy is present after 7 days of reaction. Surprisingly, the NC-540/NC-513 system has an extended pot life even though the maximum cure is achieved faster. 

The formulations described in this paper were prepared using a dispersion disk and degassed In vacuum. The basic formulation of the resin matrix consisted of 33 parts of cycloaliphatic diepoxid, 33 parts of cresolnovolac epoxide, 33 parts of cycloaliphatic epoxy diluent, 0.5 parts of silane and 0.5 parts of photolnltlator (resin A). In addition fused silica 150 parts (resin B), 186 parts (resin C), 233 parts (resin D) was added. In the toughened mixture (resin E) the cycloaliphatic epoxide of resin D was substituted by 41.7 parts of a dispersion of 20Z silicone elastomer In epoxy resin. In the flexlbilized modification (resin F) 33 parts of epoxldlsed soya bean oil were added to resin D. 

However, it is also known that, DGEBA epoxy resin, amine hardeners, dicarboxylic (phthalic) anhydride hardeners, and reactive epoxy diluents are all common causes of allergic contact dermatitis. And since all are health hazard causing organic pollutants, no remnants should be left in the composite, and must be decreased or avoided completely [73, 74]. 

CAS 2426-08-6 EINECS/ELINCS 219-376-4 Uses Epoxy diluent for tooling, elec, applies., floorings, highly filled coatings... 

Uses Epoxy diluent for exposed aggregates, potting, coatings, floorings... 

CAS 68609-97-2 EINECS/ELINCS 271-846-8 Uses Epoxy diluent for coatings Features Reactive less likely to crystallize than Epodil 748 Properties Gardner 1 liq. sp.gr. 0.890 dens. 7.4 Ih/gal vise. 8 cps flash pt. (Seta) > 200 F... 

CAS 68609-96-1 EINECS/ELINCS 271-845-2 Synonyms Alkyl (C8, CIO) glycidyl ether C8-10 glycidyl ether Octyidecyl glycidyl ether Oxirane, mono ((C8-10-alkyloxy) methyl derivs. Classification Nonaromatic ether Definition Glycidyl ether of C8-10 alcohols Properties Dens. 0.900 ref. index 1.4420 Toxicology Irritant sensitizer possible mutagen TSCA listed Uses Reactive epoxy diluent functional monomer modifier for coatings. 

Classification Nonaromatic ether Definition Glycidyl ether of Cl 2-14 alcohols Properties Dens. 0.890 ref. index 1.4470 Toxicology Skin irritant sensitizer possible mutagen Uses Reactive epoxy diluent modifier for flooring, aggregate bonding, potting, encapsulation, adhesives Manuf./Distrib. Aldrich... 

Uses Reactive epoxy diluent for exposed aggregates, potting, flooring, casting, tooling, laminates, solv.-free coating systems, fiber-reinforced composites stabilizer for chlorinated hydrocarbons adhesion promoter for PVC, acrylic resins, PU Manuf./Distrib. Aldrich Raschig... 

Uses Reactive epoxy diluent for solv.-free coating systems, laminating resins, fiber-reinforced composites, elec, applies. stabilizer for vi-nylidene chloride-vinyl chloride copolymers, chlorinated hydrocarbons chem. intermediate for pharmaceuticals curing system additive for bisphenol A-epichlorohydrin epoxies for food contact Regulatory FDA 21CFR 177.2280... 

Uses Reactive epoxy diluent functional monomer modifier for coatings, tooling applies., adhesives... 

Uses Reactive epoxy diluent, vise, modifier for laminates, tooling, potting, elec, and civil engineering applies. 

Properties M.w. 206.29 dens. 1.038 b.p. 165-170 (14 mm) flash pt. 101 C Toxicology Mutagen TSCA listed Uses Reactive epoxy diluent for tooling, elec, applies., flooring, casting, laminating stabilizer for chloro org. compds. Manuf./Distrib. Aldrich http //www.sigma-aidrich.com... 

Uses Pharmaceuticals personal care prods. flavors fragrances poiyesters acryiates epoxy diluents plastics coatings inks photographic materials textiles leather lubricants polyurethanes agric. solvents modifiers in alkyd resins fine chems. plasticizers Manuf./Distrib. ABCR http //www.abcr.de, Acros Org. http //www.acros.be, Aldrich http //www.sigma-aldrich.com, Alfa Aesar http //www.aifa.com, Fluka http //www.sigma-aidrich.com... 

Uses Personal care prods. flavors fragrances polyesters acrylates epoxy diluents plastics coatings inks photographic materials textiles leather lubricants polyurethanes agric. solvents modifiers in alkyd resins ... 

Allyl glyddyl ether is a monoglycidyl derivative, used as a reactive epoxy diluent for epoxy resins. As an impurity, it was considered as the sensitizing agent in a plastic industry worker allergic to 3-glycidyloxy-propyltrimethoxysilane, an epoxy silane compound used as a fixing additive in silicone and polyurethane. 

Dibutyl phthalate is mainly used as a non-reactive epoxy diluent. 

Phenoxy resins Epoxy diluents 11-17 4-11 Coatings, laminates, glass sizing... 

Low MW epoxy diluents, particularly the aromatic monoepoxides such as phenyl glycidyl ether (PGE) are known to have high toxicity and should be handled with care. They are capable of causing skin and eye irritation and sensitization responses in people. They may also present a significant hazard from inhalation. 

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