Elastomer modification of epoxy based film adhesives: adhesive and mechanical properties

Abstract

Three approaches were employed to improve the flow and sandwich bonding properties of a nylon-carrier supported film adhesive based on carboxyl terminated butadiene acrylonitrile (CTBN)-modified novolac epoxy resin. These included the addition of a commercial acrylate flow modifier, replacement of novolac epoxy partly with solid diglycidyl ether of bisphenol A (DGEBA) resins, and replacement of CTBN partly with an epoxy functional acrylate terpolymer (EPOBAN). Adhesive properties such as lap shear strength (LSS), T-peel strength (TPS) and flatwise tensile strength (FTS) on honeycomb core bonded sandwich specimens were evaluated using aluminium adherends. The addition of the flow modifier in low concentrations enhanced the flexibility of the system and resulted in a marginal increase in LSS, TPS and FTS. Replacing novolac epoxy partly with solid DGEBA resulted in a less brittle system with enhanced LSS and TPS, but with reduced FTS due to the decreased flow characteristics. A substantial increase in FTS was observed when CTBN was partly replaced with EPOBAN. The introduction of EPOBAN resulted in good flow and fillet properties and the optimum FTS was obtained for the composition based on 25/75 CTBN/EPOBAN ratio. Mechanical properties of selected systems were also studied in addition to adhesive properties.