Poly(vinyl alcohol)/nanocellulose film integrated with phenolic waste-based carbon dots for ultraviolet-blocking and flame retardant applications

Recycling of thermosetting plastic waste and development of functional biopolymer-based films have become captivating issues in the worldwide recently. The current work highlights the facile approach to transform the thermosetting phenolic foam (PF) waste to dual-functional carbon dots (CDs) via simple hydrothermal treatment. The obtained CDs have displayed good graphite structure with rich carbon (C), nitrogen (N), sulfur (S), and phosphorus (P) elements. The absorption peak and quantum yield (QY) values of N, S, P-doped CDs (N,S,P-CDPF) were affected by the hydrothermal precursors and reaction. The fluorescent N,S,P-CDPF derived from PF have further been assembled with the poly(vinyl alcohol) (PVA) and oxidized nanofibrillated cellulose (ONFC) to develop ultraviolet (UV) blocking and flame retardant (FR) films via the solution casting approach. The morphology, transparency, UV-visible behavior, and flame retardancy of the composite films were studied. The light-blocking efficiency and flame retardancy of the films were verified by adjusting the loading ratio of N,S,PCDPF in the films. The film with 0.05 wt% N,S,P-CDPF can absorb most of UV and some blue light (similar to 39.6 % at 450 nm), and retain 76.5 % transparency at 800 nm. In addition, the PF-derived N,S,P-CDPF have proved to be good flame retardant owing to the increased limiting oxygen index (LOI) >31.7 %, and reduced heat-release rate (HRR) from 287.4 W/g to 127.2 W/g for the PVA-ONFC@CD(PF)5 film compared to the pristine PVA film. Finally, the current studies provide a promising strategy for recycling of PF waste as a flame retardant UV absorber and create awareness regarding the flame retardant and flexible UV-blocking packaging materials.