Self-charging and long-term face masks leveraging low-cost, biodegradable and sustainable piezoelectric nanofiber membrane

The mass discarding face masks has caused severe environmental problems during and after the COVID-19 pandemic. To reduce waste and minimize environmental impact, we present a new face mask featuring self-charging extended service time and fully biodegradable materials. To extend the effective service time, we need to supplement the lost electric charge of the electret layer of face masks, for which task we propose to use the piezoelectric effect and generate electricity from breathing motions. However, existing piezoelectric materials are either toxic, impermeable, rigid, costly, or non-degradable. We synthesize a fully biodegradable piezoelectric membrane composed of polyvinyl alcohol (PVA) and glycine (GLY) via the electrospinning process. Parameters are accurately controlled to ensure that glycine crystallizes into a highly piezoelectric β phase during electrospinning and enables piezoelectric responses of the filter membrane. Tested with the standard 0.3 μm particles, face masks made of the PVA-GLY membrane show an outstanding filtration efficiency of 97%, which remains stable over at least 10 ​h of high-concentration continuous filtration. Furthermore, we demonstrated the biodegradability of PVA-GLY masks, which can degrade completely within a few weeks, compared to commonly used surgical masks requiring over thirty years to be decomposed.