Microwave-based removal of polyurethane and epoxy floor coatings

Abstract

A new debonding technique based on microwave stimulation is being investigated in epoxy and polyurethane floor coatings by combining specific microwave absorbers with temperature-induced blowing agents. Current methods, including mechanical processes such as grinding, typically produce materials with multiple fractions, impeding recycling and the establishment of a circular economy. The microwave method facilitates mono-fraction materials and enhances accessibility to commonly used recycling techniques, particularly in solvolytic processes such as polyurethane recycling. Consequently, a standard two-layer coating system is used, consisting of an epoxy primer and a polyurethane overlay. Various microwave absorbers, such as carbon black and carbon fibres, as well as blowing agents based on thermally expanding particles are investigated. The influence of the additives on the thermo-mechanical properties is studied to identify suitable combinations. The modified materials are later evaluated for their mechanical properties. Two microwave antennas, operating at a frequency of 2.45 GHz and power of 1 kW, are used and compared to activate the modified coating systems. The technology has been successfully integrated into the formulation to allow mono-fraction recovery of the materials. No significant negative effects on material quality were observed. However, due to the extended processing time required for the debonding, further optimisation is necessary. Nevertheless, the feasibility of utilising a laboratory-based microwave approach has been substantiated.