Background
Around 500,000 tonnes of powder coating waste are generated worldwide every year. Due to its adhesive properties and chemical reactivity, this waste is difficult to recycle and must be disposed of at great expense. In particular, its strong adhesion to metal surfaces during thermal processes prevents economical further processing. Previous recycling methods are either only suitable for certain powder coating systems or lead to caking and equipment wear. The invention closes this gap by chemically inactivating the adhesion-promoting groups.
Technical Description
The process involves the provision of solvent-free powder coating waste, e.g. from thermosetting systems such as epoxy, polyester or hybrid powder coatings. These are mixed with an anionic surfactant as reactants, such as saturated fatty acids or PEGs.
The functional groups are inactivated by chemical reactions such as esterification, ring opening, amide formation or acid hydrolysis. Subsequent heating of the reactant-powder coating mixture (≥ 60 °C) activates the reactions and ensures freedom from adhesion. Pilot tests in extrusion, injection moulding and 3D printing were successfully carried out using industrial parameters, and functionality in various polymer matrices (e.g. PE, PP) was demonstrated.
Possible Applications
• Extrusion of recycled powder coatings for the production of plastic strands and granulates.
• Injection moulding using modified powder coating waste as filler or base material.
• 3D printing process with increased print resolution.
• Additive manufacturing of improved powder coating-based structures through the addition of long-chain fatty alcohols.
• Combination of powder coating waste with thermoplastics such as PP or PE for the production of cost-effective filled composite materials
The image describes the reactions between the catalyst and various polar groups in powder coatings, as well as an example of the detachment of old powder coating residues mixed with the catalyst. (© TU Berlin)
