Design and development of zinc borate-modified EVA/POE composites with improved flame-retardant and anti-dripping performance

Abstract

Anti-dripping performance is pivotal for suppressing flame propagation and mitigating secondary ignition in polymeric materials. Conventional ethylene-vinyl acetate (EVA) composites filled with aluminum hydroxide (ATH) or magnesium hydroxide (MH) show enhanced flame retardancy but suffer from severe molten dripping, which severely limits their practical applications. Herein, zinc borate (ZB) and organically modified montmorillonite (OMMT) were used as anti-dripping agents for EVA composites, and their effects on the mechanical properties, flame retardancy and anti-dripping performance were systematically investigated. With 2 wt% ZB added, the composite’s elongation at break and melt flow rate (MFR) increased by 12.7% and 70.59% compared with pristine EVA, respectively, due to ZB’s excellent dispersibility that improved filler-matrix interfacial compatibility, thus enhancing mechanical properties and processability. Its limiting oxygen index (LOI) reached 46.4% (11% higher than pristine EVA), outperforming OMMT-modified composites. A self-designed device confirmed ZB-modified EVA remained intact without dripping for 180 s, while pristine EVA (S0) dripped at 80 s. Under simulated fire, ZB-containing EVA composites exhibited superior thermal stability and insulation. After 10 min of ablation, the back surface temperature of 2 wt% ZB composite (S4) was only 293.15°C, 179°C lower than S0, attributed to ZB-induced denser, more graphitized char layers that effectively inhibited heat and mass transfer. This work demonstrates ZB’s great potential as a high-efficiency anti-dripping and flame-retardant additive for EVA composites, and provides a novel feasible strategy for fabricating high-performance flame-retardant polymeric composites with excellent anti-dripping performance.