Epoxy resin curing epoxide-amine system

There are two options for the other component of an epoxy resin system. Use of mono- or di-anhydrides as curing agents, usually catalyzed by a tertiary amine, causes reactions with the residual secondary hydroxyls in the repeating unit of the prepolymer forming esters and free carboxylic acids. The carboxylic acids formed also react with the epoxide end groups forming cross-links and further free secondary hydroxyl groups. Maleic anhydride, phthalic anhydride, or pyromellitic dianhydride are suitable for this process (Eq. 21.27). 

In order to impart these properties to the final product, very careful selection of the epoxide resin and hardener system, as well as all the other components of the formulation, is vitally important. As the cured material is crosslinked, the structure and properties of the original resin will be completely changed. The material will no longer be soluble without decomposition and its chemical resistance will depend as much upon the hardener selected as upon the epoxy resin. As an illustration of the dependency of the cured system upon the hardener, acid anhydride based hardeners offer excellent resistance to acid environments, whilst amine-type hardeners offer maximum resistance to alkaline environments. 

Epoxy Contain epoxide resin cures by chemical reaction two-part system (hardener and resin) excellent adhesion to most substrates, tough and durable films good resistance to solvents, water, chemicals, and abrasion poor resistance to sunlight (chaUdng breakdown process) which limits outdoor use to primers and intermediate coats most commonly used are polyamide- and amine-cured modified epoxies can be used in steel concrete, flooring and lining applications. 

Resin I contains roughly equal amounts of diglycidyl ether of bisphenol A (DGEBA) and an epoxy cresol novolac. Sufficient dicyandiamide (DICY) as a curing agent is present such that the amine/epoxy ratio is 0.85. Monuron is present as an accelerator. The supplier s recommend standard cure is two hours at 127°C. Previous work (1 ) has shown that this cycle produces a fully cured system, as indicated by the disappearance of the epoxide absorbance band in the infrared spectrum. 

Resin II contains tetraglycidyl methylene dianiline (TGMDA) as the principal epoxide with small amounts of a cresol novolac and DGEBA. DICY as curing agent is present in an amount such that the amine epoxy ratio is 0.25. Diuron is the accelerator. The supplier s recommended standard cure is the same as for SP250. However, in this system approximately 20 percent of the epoxide remains unreacted following the cure cycle (1 ). Selected resin plates were subjected to additional cure at 170°C and 220°C. The samples post cured at 220 C for forty minutes showed no residual epoxide absorbance in the IR spectrum. 

Cured epoxy-anhydride systems exhibit excellent thermal, mechanical, and electrical properties, and are used in filament-wound epoxy pipe, PCB laminates, mineral-filled composites, and electrical casting and encapsidation applications. Anhydride-cin-ed epoxies also have better aqueous acid resistance than similar amine-cured systems. Anhydrides are the principal curing agents for cycloaliphatic and epoxidized olefin resins in electrical casting and potting. Some... 

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