Toughened adhesives impact strength

Two-component, room temperature curing epoxy adhesives have evolved over three distinct generations, from brittle to flexible to toughened. The quest for toughening is due to the inherent lack of peel and impact strength properties in brittle epoxy adhesives and... 

Polyamides and saturated polyesters can be toughened with ABS, ethylene-propylene copolymers/terpolymers or EPDM rubbers grafted with maleic anhydride to increase the dispersion and adhesion of the modifier. Styrene-butadiene copolymers are also effective. The notched Izod impact strength of polyamide 6-6 can be increased more than 20-fold by impact modifiers, whereas short glass fibres often reduce the impact strength, even though they increase the modulus. 

Although development of toughened adhesives has been limited to the various acrylic (both anaerobic and non-anaerobic) and epoxy types, overall performance has been improved spectacularly. Both environmental resistance and peel and impact performance have been raised substantially without sacrificing shear strength. 

In the last ten years, a number of improvements in cyanoacrylate adhesive technology have been published. Some of these modifications have been translated into new products. For instance, a series of adhesives is being sold with improved performance in the following areas contaminated surface bonding, hard-to-bond plastics, operating temperatures, moisture durability, impact strength, and chlorosis. A toughened cyanoacrylate based on a methyl acrylate-ethylene copolymer has been marked recently. An allyl cyanoacrylate-based adhesive with improved heat durability has also been introduced. A survey of recently patented modifications and improvements for cyanoacrylate adhesives is outlined in Table XIX. 

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