Thermoplastic epoxy, flexibilized

Polyamides containing amino groups are also excellent flexibilizers for epoxies since they co-react with the epoxy resin and introduce their inherent thermoplastic properties. 

Flexibilized epoxy adhesives have moderate strength on flame and corona treated polyolefin substrates. Elevated cure temperature results in better adhesion because of more efficient wetting of the substrate surface. Table 16.13 shows a starting formulation for an epoxy adhesive that develops high peel strength to many difficult-to-bond substrates such as polyethylene, thermoplastic rubber, and polyester film. 

Polyester resins (alkyds) were commercialized for coatings use in 1926, and unsaturated polyesters were used as thermoset fiberglass composite matrix resins in the 1940s, but the early resins made poor adhesives. When flexibilized resins appeared in the 1950s, they were used as adhesives. Today, unsaturated polyesters are widely used as adhesives for thermoset plastics bonding, and even for metal bonding in most countries, but are seldom used as adhesives in the United States, where the more expensive epoxy adhesives are used in similar applications. The saturated polyesters, used as thermoplastic hot-melt adhesives, seem to have appeared in the literature first in the 1954—1957 period. 

Thermoplastic rubber block copolymers, with completely new adhesive performance, were developed in 1965 [21]. The first commercial product was Shell Chemical s Kraton 101, of styrene polybutadiene-styrene composition. This development led to the carboxy-terminated nitrile (CTBN) rubber modifiers used to flexibilize epoxy and other brittle resin adhesives in the late 1960s. Today, the thermoplastic rubber block copolymer adhesives are used in hot melt-, solvent- and water-based adhesives, and as hot melt- and solvent-based sealants. Major applications are as pressure-sensitive adhesives, construction adhesives and sealants, and general assembly adhesives. 

Features Curing agent for maintenance and marine coatings, overprint varnishes, masonry and pool coatings, adhesives, caulks, grouts flexibilizer for thermoplastic polyamides Properties Gardner 9 max. sol n. dens. 7.6 Ib/gal vise. (G-H) W-Y amine no. 51-57 pot life 18 h (250 g) 59-61% solids in IPA/toluene Use Level 100 phr with epoxy resin of EEW=525 Epikure 3100-HX-60 [Resolution Perl. Prods.]... 

Reactive flexibilizers such as polysulfldes, urethanes, polybutadienes, and polyesters are copolymerized with epoxies to increase flexibihty, improve adhesion, modify electrical properties, and improve resistance to chemicals. Nonreactive extenders such as thermoplastics, asphaltums, and waxes are used to modify properties and reduce the cost of the compounds. Polyarylene ether sulfone as an extender in epoxy resins increases the fracture toughness fivefold with only a slight drop in Tg. 

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