Epoxy, Vinyl Ester, and Phenolic Resins

Because of the wide application of these resins to diverse industries and their very different kinetic models and mechanisms of cross-linking and reactions, phenomenological kinetic models for epoxy, vinyl ester, and phenolic resins are presented in the next three subsections. 

Thermoset (epoxy, vinyl ester and phenolic resins) or thermoplastic prepreg can be used, as well as wet resin/dry fiber, to give composites with less than 2% voids. An autoclave is not required and epoxy composites can be produced some 10 times quicker. 

For more corrosive environments, epoxy vinyl esters and phenolic laminating resins [10] are used quite successfully as well, particularly where fire retardancy is an issue, such as in the oil industry. The glass is normally E-glass roving, but some mats are used for more complicated shapes and an external surface veil is incorporated to produce an acceptable degree of outer smoothness. 

In the TsC the filler is also inserted in a resin matrix, typically phenolic although epoxy and vinyl ester are also used. However, there is not a carbonization step like in the CCC. Due to the similarity in composition, CCC is sometimes confused with TsC. Chaimel manufacturing in TsC is done by compression molding. Entegris Inc. commercializes TsC BPs based on vinyl ester and phenolic resin. 

The fracture energy GIc of unsaturated polyesters (UP), vinyl esters (VE), and phenolic resins, is less than 200 Jm 2 at room temperature. Epoxy networks can exhibit higher values but always lower than those of thermoplastics of similar Tg, as polycarbonate, polyetherimide, or polyphenylene ether. 

FRP materials are made up of the polymer and reinforcing fibers. The polymer is typically a thermoset polymer thermoplastics can be used as well. Some typical thermoset polymers used are epoxy resins, unsaturated polyester resins, epoxy vinyl ester resins, phenolic resins, and high performance aerospace resins such as cyanate esters, polyimides, and bismaleimides. These resins... 

For commodity applications, there are four major classes of resins that are used in FRP applications. They are phenolic resin, epoxy resin, unsaturated polyester resin, and epoxy vinyl ester resins. A more complete description of these types of resins and their many variations can be found in Handbook of Thermoset Plastics. This is not a comprehensive list of resins used in composite manufacture, as commodity materials like polyurethanes and isocyanurate resins are sometimes used as well to make FRP parts. However, these materials are not covered in this chapter owing to their limited use, but, the principals of fire safety that apply for the resins described subsequently apply to these materials as well. 

Cold curing unsaturated resin was obtained in the following way. A mixture of BPA, BPA monocyanate and BPA dicyanate was cyclotrimerized and reacted with BMI. The obtained prepolymer with phenolic hydroxyls (cf. Scheme 9) was then treated with epichlorohydrin and alkali. The phenolic hydroxyls were thus transformed into glycidyl ether groups. Then the addition of methacrylic acid to the epoxy groups was carried out. The obtained vinyl ester (epoxyacrylate) type resin was dissolved in styrene and cured with the usual benzoyl peroxide/dimethylaniline system [131],... 

Intrinsically non-flammable polymers are few, but phenolic resins have a good reputation both in Are and smoke performance, which has resulted in their becoming increasingly favoured for reinforced plastics structures, for example, underground transport, where such concerns are greatest. Polyether ether ketone (PEEK) is also a low fire and smoke polymer. Unsaturated polyesters, vinyl esters and epoxy resins bum readily, but modified versions are available with improved behaviour. For example, both bromine and chlorine are used extensively in the form of chlorendic (HET) acid, tetrachlorophthalic anhydride (TCPA) and tetrabromo-phthalic anhydride (TBPA) which can be reacted into the polyester in small quantities and can act as permanent (non-migrating) flame retardants. 

Polymer composites are plastics within which fibres are embedded. The plastic is known as the matrix (resin) and the fibres dispersed witbin it are known as the reinforcement Thermosetting matrix materials include polyester, vinyl ester and epoxy resins. For higher temperature and extreme environments, bismaleimlde, polyimide and phenolic resins are used. Composites can be used to replace metal parts but care must be taken during design. Most engineering materials have similar properties in any direction (called isotropic) where composites have not This can however be offset by arranging the reinforcement layers in varying directions. 

Vinyl esters are thermosetting resins that consist of a polymer backbone with an acrylate or methacrylate termination. The backbone component of vinyl ester resins can be derived from epoxide, polyester or urethane but those based on epoxide resins have most commercial significance. Bisphenol A epoxy formed vinyl esters were designed for chemical resistance and commonly formulated for viscosity for use in filament winding of chemical containers. Typically styrene is used as a reactive dilutent to modify viscosity. Phenolic novolac epoxies are used to produce vinyl esters with higher temperature capability and good solvent resistance, particularly in corrosive environments, and their FRP composites have demonstrated initial economy and better life cycle costs compared with metals. 

TSWB, a flame retardant additive from Avtec, see Section 4.4.1, is a sandy-coloured particulate material that may be mixed into various resins and applied to cured parts or incorporated directly into resin systems. About 20-35 wt% loading is suggested and the additive has been assessed in epoxy, vinyl ester, polyester and phenolic resin compositions. 

Many matrix choices are available, and each type has an impact on the processing techniques, physical and mechanical properties, and enviromnental resistance of the finished part. Thermoplastic and thermoset materials can be resin matrices. Thermoplastic matrices have been developed to increase hot/wet use temperature and the fracture toughness of composites. Thermosetting resins, however, are more common. The common thermoset matrices for composites include polyester and vinyl esters, epoxy, bismaleimide, polyimide, and cyanate ester and phenolic triazine resins. 

While epoxy resins are known for excellent chemical resistance properties, the development and commercialization of epoxy vinyl ester resins in the 1970s by Shell and Dow offered enhanced resistance properties for hard-to-hold, corrosive chemicals such as acids, bases, and organic solvents. In conjimction with the development of the structural composites industry, epoxy vinyl ester resin composites found applications in demanding environments snch as tanks, pipes and ancillary equipment for petrochemical plants and oil refineries, automotive valve covers, and oil pans. More recently, epoxy and vinyl esters are used in the construction of windmill blades for wind energy farms. Increasing requirements in the composite industries for aerospace and defense applications in the 1980s led to the development of new, high performance multifunctional epoxy resins based on complex amine and phenolic structures. Examples of those products are the trisphenol epoxy novolacs developed by Dow Chemical and now marketed by Huntsman (formerly Ciba). 

Phenolic thermoset resins are the oldest thermoset materials. They do not find as wide an application in the corrosion-resistant field as do the epoxies, vinyl esters, polyesters, and furans. As with other thermoset resins, they can be formulated to meet certain properties, but in general they do not have the range of corrosion resistance of the other thermosets. Table 8.6 shows their resistance to atmospheric corrosion and Table 8.7 gives their operating temperature range. 

Similar to all commercial plastics, the traditional and more commonly used thermosetting resins are considered as petrochemicals, having been manufactured from petroleum. Some of the primary distillation products of crude oil, which can be classified either as olefins or aromatics, serve as precursors for the synthesis of thermosets. For example, epoxy resins are manufactured by the reaction of epichlorohydrin, a chloro-oxirane, and a derivative of propylene, with bisphenol A, which is a derivative of cumene. Another example would be the unsaturated polyesters (UPs), which are derivatives ultimately originating from ethylene (ethylene glycol) and benzene (maleic acid) [6]. Epoxies and polyesters constitute more than 95% of the thermoset composite market of the two, polyester-based systems predominate in volume by about 10-fold [6, 7]. Other thermoset resins used in reinforced form are phenolics, vinyl esters, and polyimides. Details of the properties and applications of these thermoset systems will be further discussed in the following section. 

IV CROSSLINKED POSS-CONTAINING RESINS AND MATERIALS 106 A. Vinyl Ester, Epoxy, and Phenolic Resins Containing POSS 108... 

Epoxy vinyl ester, phenolic, methacrylate, styrene-divinylbenzene, cyanafe ester, and dicyclopentadiene (DCPD) resins have been made in Pittman s laboratory in which various POSS macromers have been chemically incorporated. For example, a low-viscosity aliphatic epoxide resin was blended with macromer 32 (Fig. 15) and aliphatic triamine curing agents, and these blends were cured in five stages to both 120°C and 150°C. The incorporation of 5 and 25 wt % of 32 into these epoxy resins gave an increase in the storage modulus versus that of the neat epoxy. " The... 

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