Sustainable adhesives and adhesion processes for the footwear industry

Abstract

The key to sustainable development in the footwear industry through the principles of circular economy lies in taking care of the design, as well as the introduction of innovative and more resource efficient materials and processes to reduce or avoid the use of water, energy, hazardous chemicals and to minimise emissions and waste. In fact, the environmental footprint is already being considered as another requirement of the footwear through eco-design. In this sense, previous studies carried out by INESCOP regarding its environmental impact in terms of carbon footprint showed that 15% of it corresponds to the assembly processes, mainly by adhesive joints, due to their content on organic solvents, hazardous chemicals and polymers from fossil origin. Therefore, this paper focuses on recent developments carried out by INESCOP on more sustainable adhesives and adhesion processes for the upper-to-sole assembly in the footwear manufacturing process, through different approaches. Firstly, bio-based reactive polyurethane hot melt adhesives have been synthesised using polyols from different renewable sources. Secondly, the use of the low-pressure plasma surface treatment to improve the adhesion of polymeric materials used as soling materials was assessed in order to reduce volatile organic compounds emissions, as well as the use of hazardous chemicals for total automation of the bonding process.