Valorization of mixed plastics waste for the synthesis of flexible superhydrophobic films

Abstract

Superhydrophobic surfaces are typically created by enhancing nanoscale roughness or incorporating anti-wetting additives like silanes, nanoparticles, or fluorinated compounds. Limited by the availability of nano-structured templates, simple fabrication, flexibility of the material, and cost-effectiveness, the quest to synthesize superhydrophobic films remains challenging. Herein, we report the valorizing of mixed plastic waste for the synthesis of flexible superhydrophobic films via open-loop recycling. We focused on improving the nanoscale surface roughness of the material by using a series of steps including selective dissolution, thermally induced phase separation, controlled spin-casting, and annealing. We synthesized a two-layered superhydrophobic film with high surface roughness and sufficient mechanical strength, making it suitable for use as a free-standing material. The contact and sliding angles were found to be 159° and 4°, respectively, with an RMS (root mean square) surface roughness of 228 nm. This approach is demonstrated with mixtures of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), which are among the most abundant components of post-consumer plastic waste. Life cycle assessments show that synthesized superhydrophobic films have lower carbon dioxide emissions and embodied energy than virgin PE and PP derived from petroleum. Our design strategy not only yields a superhydrophobic product but also provides an alternative to plastic waste recycling by bypassing cost-intensive sorting techniques.