Green and Facile Fabrication of α-Zirconium Phosphate-Based Core–Multishell Nanoparticles for Enhancing Fire Retardant Performance of Poly(vinyl alcohol)

At present, most flame retardants, especially halogenated compounds, are banned because of concern for environmental and health issues. In prospect of developing more ecofriendly and effective flame retardants, an alternative solution to develop novel biobased and inorganic flame retardants is addressed. Herein, a nano flame retardant consisting of a lamellar alpha-zirconium phosphate (alpha-ZrP) nanosheet modified with chitosan (CH), phytic acid (PA), and a metal ion (Cu2+) with a core-multishell structure is fabricated in water solution via a green and facile self-assembly method and applied to enhance the fire retardant effect of poly(vinyl alcohol) (PVA). Thermogravimetric analysis (TGA) demonstrated that after the addition of alpha-ZrP@CH@PA@Cu, PVA composites maintained their well-performed ability of char formation. The limit oxygen index (LOI) of pure PVA increased from 18.4 to 29.8% for PVA/alpha-ZrP@CH@PA@Cu and it reached UL-94 V-1 grade. In the microscale combustion calorimeter test (MCC), the peak heat release rate (pHRR) and the total heat release (THR) of PVA/alpha-ZrP@CH@PA@Cu sharply decreased by 82.3 and 62.2% compared with pristine PVA. The results implied that alpha-ZrP@CH@PA@Cu could endow PVA with superior fire retardant properties. Moreover, the research manifested the synergy between alpha-ZrP and CH@PA@Cu and a double barrier flame retardant mechanism in a condensed phase. In the alpha-ZrP@CH@PA@Cu flame retardant system, the inorganic alpha-ZrP nanosheet acted as an insulating core, and the CH@PA@Cu constituted an intumescent shell, where the outer CH@PA@Cu intumescent shell formed an expanded char layer serving as the first barrier to hinder heat and oxygen transfer, and then the inner alpha-ZrP core layer, as the second barrier, would prevent the further exchange of flammable gases and energy between the polymer and fire during combustion. As a result, this ecofriendly nano flame retardant with the core-multishell structure has a potential application value.