NIR Organic Dyes as Innovative Tools for Reprocessing/Recycling of Plastics: Benefits of the Photothermal Activation in the Near-Infrared Range

Photoinduced thermal polymerization upon Near-InfraRed (NIR) light has been recently reported in the literature as an efficient tool for polymer synthesis. In this work, a completely different approach is developed since polymeric materials containing a very low amount of a stimuli-responsive compound are prepared by using a benchmark UV photoinitiator. As the stimuli-responsive compound, an organic dye strongly absorbing in the near-infrared region is selected. The heat released by its irradiation with an inexpensive and highly penetrating NIR light source allows the development of an unprecedented approach for reprocessing, reshaping, recycling, and self-healing. Several parameters have been studied in order to determine their influence on the polymer temperature: the wavelength of the NIR irradiation, the irradiance of the NIR light source, the choice of heater (IR-813 p-toluenesulfonate or a squaraine dye), and the heater concentration. The thermoplastics bonding and debonding has also been studied and showed promising results since two pieces of polymers could be pasted together after a short time of NIR irradiation. Finally, self-healing ability of the thermoplastic is investigated and furnished impressive results even for large scratches.