Temperature-induced switchable adhesion of N-isopropylacrylamide incorporated pressure sensitive ahesives

Abstract

Due to the rise in global population and living standards, waste treatment has become an inevitable and critical issue for a sustainable environment. Reducing the amount of produced waste is important, and likewise, recycling processes are essential for reducing additional environmental pollution and economic costs. For an effective recycling process, disassembly among different types of materials is crucial. The disassembly process typically requires the removal of ‘adhesives’ - which are widely used for packaging, and assembly of products. However, the removal process requires harsh solvents (e.g., acidic, organic) that are unfriendly to nature, and may cause additional pollution. In response to this issue, functional adhesive materials which can be removed without the use of harsh solvents are drawing significant attention. One of the methods is to utilize properties of stimuli-responsive polymers to synthesize pressure sensitive adhesives (PSAs); however, it is technically very difficult to simultaneously satisfy (i) strong initial adhesion (without stimulus), (ii) sufficiently weak adhesion strength but stronger cohesion (with stimulus), and (iii) reversibility. In this work, thermo-switchable PSAs are synthesized by copolymerizing N-isopropylacrylamide (NIPAM) which possesses thermal-responsive properties, acrylic acid (AA) which endows adhesive properties, and 2-ethylhexyl acrylate (EHA) which has a low glass transition temperature (responsible for flexibility). The synthesized thermo-switchable PSA containing NIPAM showed sufficiently high peel strength at room temperature, which showed ~97% decrease upon heating. More importantly, even at high temperatures, no residues are left behind due to the cohesive nature of NIPAM at high temperatures. The reversible adhesion property of thermo-switchable PSA was retained during the heating/cooling cycle repetition. Thus, the developed thermo-switchable PSA can enhance the reusability/recyclability of valuable materials, and also minimize the usage of toxic chemicals for adhesive removal, contributing to a more sustainable future.