Elastomer-modified epoxy applications

Elastomer-Modified Epoxy Resins in Coatings Applications... 

R.S. Drake, "Elastomer-Modified Epoxy Resins for Structural Applications", SAMPE Quarterly, 6, (4),... 

Elastomer-modified epoxy resins are used in composites and structural adhesives, coatings, and electronic applications. Similar approach to toughen epoxy vinyl esters using other elastomeric materials has been reported (204). Other elastomer-modified epoxies include epoxy-terminated urethane prepolymers, epoxy-terminated polysulfide, epoxy-acrylated urethane, and epoxidized polybutadiene. Preformed dispersions of epoxy-insoluble elastomers have been developed and reported to achieve toughening without Tg reduction (205,206). 

An elastomer modified epoxy vinyl ester that expands the serviceability of thermoset resins in traditional FRP applications. 

Drake, R., and Siebert, A., Elastomer modified epoxy resins for structural applications, SAMPE Quarterly, 6, No. 4, July, 1975. 

The amount of elastomer contained in a rubber-modified epoxy resin is usually dictated by the final application and material properties desired. Knowing that one equivalent of epoxide reacts with one equivalent of carboxylic acid and the final concentration of elastomer that is desired, one can add another term to Equation (2) to account for the equivalents of epoxide consumed during the esterification reaction. The equivalent weight of the CTBN elastomers vary from lot to lot but is typically —1800 g eq . Using this number as an example, the expanded equation now reads,... 

For applications such as swimming pools and water-purification tanks, for which chemical resistance is required, or where resistance to dynamic stress is needed, special epoxy resins are used. Blends of a waterborne synthetic emulsion with a cement compound are suitable for applications with lower requirements. In some cases, e.g. sewage-treatment plants, elastomer-modified bitumen mortars are still used. 

Nylon-epoxy is typically used in film and tape adhesive applications and has maximum service temperature of 138°C, compared with 177°C for unmodified epoxies. The addition of nylon provides increased flexibility and peel strength compared to unmodified epoxies. Nylon-epoxy is a tough material with excellent tensile lap shear strength and good fatigue and impact resistance. However, the addition of nylon results in deterioration in creep resistance and poor peel strength at low temperatures. Furthermore, the hydrophilic nature of nylon imparts poor moisture resistance in both uncured and cured forms of the resin. Consequently, nylon-epoxies are not as durable as elastomer-epoxies or other thermoplastic modified epoxies. 

Commercially available liquid rubber (CTBN, ATBN)-toughened epoxy often shows outstanding fracture properties, and the technology is exploited in engineering adhesives [58]. However, because the butadiene component of the elastomer contains unsaturation, it would appear to be a site for premature thermal and/or oxidative instability, and such modified resins are not suitable for application at high temperature. One would imagine that excessive crosslinking could take place with time which would detract from otherwise desirable improvements accomplished with these structures. Second, there is some limitation in its use due to a possibility of the... 

Recently, impact modifiers have been developed for plastics other than PVC. Polybutylene and other olefinic thermoplastic elastomers, for example, are being used to enhance the processability, toughness, and heat stability of polypropylene film. Hydroxy-terminated polyethers are being used to increase the impact resistance of polystyrene. Other conunon applications are polycarbonate, polyurethane, thermoplastic polyester, epoxy, and polysulfone. 

Elastomer epoxies generally contain nitrile rubber as the elastomeric component. This system is also referred to as a modified or toughened epoxy. One of the applications of widest use is in films and tapes. Elastomer epoxies cure at low pressures and low temperatures over a short time interval. This is achieved by adding a catalyst to the adhesive formulation. Bond strengths of elastomer epoxies are lower than those of nylon epoxies. However, the major advantage of elastomer epoxies is their sub-zero peel strengths, which do not decrease as fast as those of nylon epoxies. In addition, the moisture resistance of elastomer epoxies is better than that of nylon epoxies but not as good as that of vinyl-phenolics or nitrile-phenolics. Limitations to the use of elastomer epoxies include poor water immersion resistance and poor properties when exposed to marine conditions. 

Further toughening of VERs modified with a CTBN elastomer by introducing an epoxy-terminated butadiene-acrylonitrile copolymer diluted with a styrene monomer (Hycar ETBN 1300x40 from BF Goodrich) was presented [69]. The improvement of toughness achieved by the incorporation of the CTBN elastomer (Table 21) extends the range of VER applications from corrosion resistant equipment to automotive, marine and infrastructure markets. 

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