Bio-constructed fireproof poly (vinyl alcohol)/β-cyclodextrin/phytic acid composite films for food preservation

As a biodegradable and non-petrochemical produced polymer, poly (vinyl alcohol) (PVA) films have great potential in packaging fields due to their excellent oil resistance, gas barrier capacity, and mechanical performance. Yet the high flammability of PVA films always draws the fire risks even at an instant contact with fire or voltaic arc, which is demanding the fireproof ability. The traditional method of adding inorganic flame retardants and organic phosphate ester will raise mechanical problems, opacity, and food toxicity that shall not be utilized in the future. Herein, we propose a multiple cross-linking method by introducing bio-based β-cyclodextrin (CD) and phytic acid (PA) to endow PVA composite film (PCP) the fireproof and antibacterial capacity and retain the mechanical properties and transmittance. The results indicated that due to the catalytic charring effect of PA and CD, the peak heat release rate and total heat release of PCP 0.25 decreased by 63.3 % and 38.8 %, respectively. The char residues increased from 6.1 to 32.1 wt% and reached to UL-94 V-0 rating. Thanks to the physically cross-linked network formed by CD and PVA and the chemically cross-linked network formed by PA and PVA, the tensile strength and elongation at break of PCP 0.25 increased from 61.6 MPa and 224.3 % for PVA to 87.6 MPa and 382.0 %, respectively. The transmittance of PCP 0.25 in the visible light range was almost identical to that of pure PVA. While its ultraviolet light transmittance was below 10 %, demonstrating excellent transparency and UV-shielding property. In vitro antibacterial tests, due to the abundant phosphate groups in PCP 0.25 , enzymes on the surface of bacterial cell walls could be deactivated, leading to bacterial lysis and death, thereby exhibiting inhibitory effects against both Escherichia coli and Staphylococcus aureus . Moreover, compared to the commercial food preservation materials, the composite film shows better water vapor barrier ability, which also shows excellent fire resistance, presenting the great prospective in food preservation.