Flame retardant polyvinyl alcohol film with self-releasing carbon dioxide and ammonia from phytic acid and urea

This paper utilizes the reaction of phytic acid (PA) and urea (UM) in polyvinyl alcohol (PVA) solution to synthesize flame retardant gasses (CO2, NH3) for the preparation of PVA composite films containing flame retardant microbubbles. The flame retardancy of PVA composite films was assessed using methods including limiting oxygen index (LOI), vertical burning (UL 94), and cone calorimetry. The results indicated an increase in the LOI of the PVA composite film containing flame retardant microfoam from 20% to 30% compared with the pure PVA film, and that UL 94 reached VTM-0. Furthermore, its peak exothermic rate and total exothermic amount were reduced by 36.25% and 38.92%, respectively, compared with the pure PVA film. The investigation of the flame-retardant mechanism employed thermogravimetric-infrared (TG-IR), scanning electron microscopy (SEM), Raman spectroscopy, and infrared spectroscopy. The results demonstrate that the CO2 and NH3 flame retardant microbubbles within the composite film render it less ignitable at the initial stage, and that the internal UM of the composite film continues to decompose, releasing CO2 and NH3 upon heating. In addition, the acidic substances decomposed by PA during combustion promote the dehydration, cross-linking, and cyclization of PVA, generating chemical structures such as P-O-C, P-O-P, and PO4 with enhanced thermal stability. This encourages the formation of a continuous, dense charcoal layer and impedes the transfer of oxygen and heat into the interior.