Use of intumescent flame-retardant systems in epoxy adhesives for debonding purpose

This work investigates the use of intumescent flame-retardant additives as a new debonding solution to disassemble bonded aluminum substrates. Melamine polyphosphate (MPP) or ammonium polyphosphate (APP) was incorporated into an epoxy adhesive joint as both an acid source and a swelling agent with this stimulus responsive behavior being triggered by heating. The ability of the system containing intumescent additives to swell and foam under heat radiation was efficiently exploited to provide enough local pressure to induce porosities and cracks at the interface, facilitating the disassembling of bonded aluminum substrates. Several aluminum/intumescent-epoxy/aluminum laminates were assembled and tested to assess the influence of the MPP and APP content on the mechanical strength of the joints. The structural, morphological, mechanical, and thermal properties of these modified epoxy resins and assemblies with aluminum substrates were studied using Scanning Electron Microscopy (SEM), a pull-off test, Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). The ability of the intumescent-modified joints to support temperature-controlled debonding was evaluated using an oven. The lower debonding temperatures found were comparable to laminates with unmodified epoxy joint systems. Our patented debonding on-demand technology, based on an intumescent flame-retardant system, represents a promising treatment for multi-material structures and will enable products to be recycled at the end of their service life.