Epoxy adhesives are generally more resistant to a wide variety of liquid environments than other structural adhesives. However, they are generally considered to be very rigid systems, and as such they do not have exceptionally good impact or peel resistance unless modified with tougheners.
Many one component epoxies contain rubber toughening agents such as carboxylic acid terminated butadiene nitrile rubber (CTBN) or amine terminated butadiene nitrile rubber (ATBN). These elastomers are pre-reacted at the 5-15% level with the epoxy resin at high temperature. During the final cure, the rubber must precipitate out of solution into discrete particles within the epoxy resin matrix.
RESULTING PROPERTIES
The table above shows a comparison of adhesives formulated with and without a CTBN adduct. When compared to the control epoxy, the toughened formulation exhibits significantly higher peel strength and moderately higher tensile shear strength. CTBN modified epoxy adhesives are generally one part systems, cured with dicyandiamide at elevated temperature. However, two part, room or mildly elevated temperature curing systems are also possible and provide similar improvements in properties such as shown above.
