Laser flash pyrolysis of face mask waste to vinylidene-terminated PP wax and further functionalized as compatibilizer

Abstract

During the COVID-19 pandemic, face masks, as personal protective equipment (PPE) against the coronavirus (SARS-CoV-2), have been widely used worldwide. How to properly dispose of used PPE has brought a huge challenge to the ecosystem and human health. Here we proposed a laser flash pyrolysis (LFP) strategy to upcycle the used polypropylene(PP) face mask to vinylidene-terminated PP wax (PP-VDT) and further functionalized for compatibilizer application. Carbon black (0.2 wt%) was mixed with masks as a light absorbent to improve photothermal conversion efficiency. An infrared laser was adopted as the thermal source to quickly depolymerize the used PP face mask within just several milliseconds. The pyrolysis fragments quickly vaporized out to form PP-VDT with high selectivity (average terminal vinylidene per molecular chain was up to 1.55). The PP-VDT appeared as white solid particles which were clean and high purity. In addition, PP-VDT as polymer precursors could be further functionalized by thiol-ene chemistry to hydroxyl-terminated PP (PP-OH) and isocyanate-terminated PP (PP-HMDI), which could be used as compatibilizer in PLA/PP blends to decrease the size of the dispersed PP phase and to improve tensile strength. Therefore, this LFP technique was an effective upcycling method for PP face masks to obtain value-added products.