Delaminations in Resin-EPDM Monomer Bondlines as a Result of Solvent Exposure and Adhesive-Induced Phenolic Resin Disproportionation Reactions

Abstract

Delaminations in aluminum-to-phenolic resin-cured ethylenepropylene-diene monomer (EPDM) rubber bondlines were studied by a variety of techniques, including surface chemical analysis, microscopy, gas chromatography=mass spectrometry (GC=MS), pyrolysis gas chromatography=mass spectrometry (PyGC=MS), and analysis of solvent extracts from the failures by high performance liquid chromatography=mass spectrometry (HPLC=MS). The rubber was bonded to the aluminum using a common, commercially available metal primer and rubber-to-metal adhesive. The locus of failure was cohesive in a thin layer of rubber near the rubber= adhesive interface. Two chemical contributing factors to the debonding were found. One was the use of a cleaning solvent (d-limonene) that reacts with rubber and competes with normal cross-linking. Another was an incompatibility with the rubber-tometal adhesive that causes disproportionation and breakdown of the phenolic resin. Both mechanisms are expected to cause a lowered cross-link density and reduce rubber tensile strength, leading to weakened rubber near the rubber=adhesive interface.