Sustainable Flame-retardant and Tough Poly(vinyl alcohol) Films with Phytic Acid and Biochar: A Simple and Effective Approach

Poly(vinyl alcohol) (PVA) is a biodegradable and environmentally friendly material known for its gas barrier characteristics and solvent resistance. However, its flammability and water sensitivity limit its application in specialized fields. In this study, phytic acid (PA) was introduced as a halogen-free flame retardant and biochar (BC) was introduced as a reinforcement to achieve both flame resistance and mechanical robustness. We thoroughly investigated the effects of BC particle sizes (100–3000 mesh) and addition amounts (0 wt%–10 wt%), as well as PA addition amounts (0 wt%–15 wt%), on the properties of PVA composite films. Notably, the PA10/1000BC5 composite containing 10 wt% PA and 5 wt% 1000 mesh BC exhibited optimal properties. The limiting oxygen index increased to 39.2%, and the UL-94 test achieved a V-0 rating. Additionally, the PA10/1000BC5 composite film demonstrated significantly enhanced water resistance, with a swelling ratio reaching 800% without dissolving, unlike that of the control PVA. The water contact angle was 70°, indicating that hydrophilic properties remained essentially unaffected. Most importantly, the tensile modulus and elongation at break were 213 MPa and 281.7%, respectively, nearly double those of the PVA/PA composite film. This study presents an efficient and straightforward method for preparing PVA composite films that are flame-retardant, tough, and waterresistant, expanding their potential applications in various fields.