Epoxy-anhydride phenolic resins

Phthalic anhydride (Figure 26.10 I) is an important example of the first class of hardener. It has a molecular weight of 148 and about 0.6-0.9 equivalent is used per epoxy group. For the lower molecular weight bis-phenol resins this works out at about 35-45 phr. The hardener is usually added at elevated temperature of about 120-140°C. It will precipitate out below 60°C but will again dissolve on reheating. 

On the other hand, epoxies cured with acid anhydrides and phenolic resins exhibit little or no reactivity when stored in direct contact with explosives and propellants. 

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). 

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. 

Acceptable bonds have been obtained between polyethylene surfaces with polar adhesives such as epoxies (anhydride- and amine-cured and two-component modified epoxies) and solvent cements containing synthetic rubber or phenolic resin. Other adhesives recommended include styrene-unsaturated polyester and solvent-type nitrile-phenolic. 

Polyvinyl formal and butyral contain -OH groups that are cured by dialdehydes, diisocyanates, anhydrides, epoxy, melamine, and phenolic resins. 

The epoxy/oxirane ring can be opened in the presence, particularly, of active hydrogen atoms. Active hydrogen groups are contained in such materials as aliphatic and aromatic amines, alcohol groups in, for example, solid epoxy resins and phenolic resins, thiols, and aliphatic and aromatic anhydrides. The addition reaction leads to a cross-linked, infusible structure provided both materials contain at least two reactive species one of them must contain greater than two. 

Crosslinking through epoxy groups is done by means of hardeners polyamines, anhydrides of di- and polybasic acids, phenolic resins, polyphenols, poly-mercaptans, and carbon sulfur. 

Su WF, Huang HW, Pan WP (2002b) Thermal properties of rigid rod epoxies cured with diaminodiphenylsulfone and dicyandiamide. Thermochim Acta 392 391-394 Su WF, Lee YC, Pan WP (2002c) Thermal properties of phthalic anhydride- and phenolic resin-cured rigid rod epoxy resins. Thermochim Acta 392 395-398 Su WF, Hsu SH, Tai YY, Chen MH (2012) Liquid crystalline epoxy nanocomposite material and application thereof U.S. Patent 8,309,632... 

Zinc surfaces may be involved either by the use of galvanized steel or of zinc die castings. Again, anhydride-cured epoxies should be avoided as also should adhesives which contain tackifiers based on rosin derivatives. These rosin materials tend to form soaps with zinc and to form them at the interface between metal and adhesive thus creating a weak boundary layer. Polychloroprene adhesives are recommended for use with zinc as the tackifier used is normally a tcrt-butyl phenolic resin which is perfectly safe, although some products may contain other, less satisfactory, tackifier. 

In order to obtain cured products with higher heat distortion temperatures from bis-phenol epoxy resins, hardeners with higher functionality have been used, thus giving a higher degree of cross-linking. These include pyromellitic dianhydride IV, and trimellitic anhydride V. 

Epoxy plastics Group of plastics composed of resins produced by reactions of epoxides or oxiranes with compounds such as amines, phenols, alcohols, carboxylic acids, and anhydrides, and unsaturated compounds. 

Resins used were two types of epoxy resins (EP) and an unsaturated polyester resin (UP) as shown in Figure 1. EP is the bis-phenol-A type resin cured with methyl-tetrahydrophthalic anhydride (MTHPA) or 1,8-p-menthandiamine (MDA). UP is the iso-phthalic type resin which has ester bonds in the main chain and is crosslinked by styrene (10). 

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