Multifunctional polyvinyl alcohol composites via melt blending with a bio-based P-N synergistic flame retardant: Achieving simultaneous enhancement in fire safety, UV shielding, and mechanical properties

Polyvinyl alcohol (PVA) is a promising biodegradable polymer, but its widespread application is critically constrained by inherent flammability, limited UV resistance, and the mechanical compromises often incurred by conventional flame-retardant modifications. To address these challenges, a novel bio-based phosphorus‑nitrogen synergistic flame retardant (DPP) was developed from pyridoxal phosphate via a facile Schiff base condensation and P H addition route. This well-designed DPP was efficiently incorporated into PVA via a green melt blending process, yielding composites that achieved a simultaneous enhancement of multiple properties. With a 10 wt% DPP loading, the composite exhibited exceptional flame retardancy, achieving a limiting oxygen index (LOI) of 30.5%, a UL-94 V-0 rating, along with a 63.2% reduction in its peak heat release rate (PHRR) and a 32.7% decrease in total heat release (THR). Additionally, it provided outstanding UV shielding performance, with an ultraviolet protection factor (UPF) of 362 and over 99.7% blocking of both UVA and UVB radiation. Impressively, its tensile strength was enhanced to 25.2 MPa, thus overcoming the common performance trade-off. This multifunctionality stems from DPP's well-orchestrated molecular design: it operates through a vapor- and condensed-phase synergistic flame-retardant mechanism and intrinsic UV absorption, while its strong interfacial hydrogen bonding with PVA constructs a physical crosslinking network, underpinning the concurrent mechanical enhancement. This work presents a strategy for fabricating sustainable, high-performance, multifunctional PVA materials. The PVA/DPP composites obtained via this strategy show promising potential for advanced applications such as outdoor protection and safe electronics packaging.