Low-Pressure Plasma Treatment Applied to Polymeric Materials for a Sustainable Footwear Industry

In this paper INESCOP proposes the improvement of the bonding of footwear soling materials using the low-pressure plasma surface treatment as a non-polluting and resource-efficient technology by means of adhesive bonds, with a reactive hot melt polyurethane adhesive, as a more sustainable alternative to current chemical surface treatments such as halogenation. More precisely, low-pressure plasma is capable of cleaning and removing all impurities, such as oxides, oils and fats on material surface. Then, it is activated by producing new chemicals species on the top layer of the substrate. Thus, the materials' surface acquires new surface functionalities, improving the compatibility adhesive-substrate and, therefore their adhesion properties. Furthermore, in this work the surface modifications produced in these materials of different polymeric nature have been optimised to increase their roughness, wettability, adhesive properties, etc., and have been validated through various experimental characterisation techniques. As a result, the samples treated with plasma meet the adhesion requirements for footwear materials. As a result, low-pressure plasma treatment has desmonstrated to be a green, alternative, and sustainable technology in line with European policies on circular economy, which enhances material surface properties by improving the adhesion bonding process.