Suppressing diffusion of small molecule flame retardant to construct anti-aging poly(vinyl alcohol) composite films through dynamic hydrogen bond and strong coordination effect

Diffusion or migration of small molecules is not always desirable, and would impose a significantly negative impact on the aging resistance of polymer composites, in particularly when the temperature is above glass transition temperature ( T g ). In this study, an acidic polyimide (PI) was elaborately designed to tie with a base small molecule flame retardant (guanidine phosphate, GP) for suppressing the diffusion of GP in PVA matrix by strong coordinate effect. As expected, PVA/GP composite films with only hydrogen bonding interaction lost UL94 VTM-0 rating, while PVA/PI-GP composite films with dual interactions (hydrogen bond and coordinate bond) still passed UL94 VTM-0 test even they were applied by the same aging treatment (80 °C for 12 h). Meanwhile, the optical transparency and mechanical properties were seriously deteriorated for PVA/GP composite films while these properties were well kept for PVA/PI-GP composite films. To the best of our knowledge, this is the first work to improve the anti-aging performance of flame retardant polymer composites through acid-base coordination between organic small molecules and polymeric materials. Interestingly, this special effect endowed PI with excellent water-soluble, and can be blended with PVA and GP at molecular level. The dynamic hydrogen bonding interaction further enhanced their compatibility, and the stress imposed on PVA chains can be effectively shared with PI (reinforcing agent) and GP (plasticizer). As a result, the tensile strength and elongation at break increased by 84 % and 225 %, respectively. Encouragingly, the unique combination of PI and GP played a synergistic effect on the flame retardant PVA in the terms of gaseous and condensed phase, and the heat release rate (HRR) and total heat release (THR) of PVA/PI-GP composite films decreased by 37.4 % and 31.7 % compared to PVA control films, respectively. More excitingly, the water resistance capability was also significantly improved, and the water swelling degree and water solubility sharply decreased from 450.4 % to 69.8 %, and from 41.5 % to 15.7 % owing to the increased hydrophobicity. Furthermore, the PVA/PI-GP composite films are recyclable and possess self-healing capability, and the mechanical properties and optical transparency of beyond 85 % were reserved when they were treated by corresponding treatments. Interestingly, the UV protection was obviously improved while the optical transparency was well kept, this unique property was used in anti-counterfeiting and food preservation.