Nano-architectured magnesium oxysulfate whisker decorated with scaly Fe(OH)3 toward an efficient way to improving flame retardancy and smoke suppression of flexible polyvinyl chloride composites

To enhance the flame-retardant and smoke-suppression efficiency of magnesium oxysulfate whiskers (MOSw) in flexible polyvinyl chloride (fPVC), a hierarchical MOSw@PDA@Fe(OH) 3 nanohybrid with scaly Fe(OH) 3 decoration was designed. With only 0.23 wt % Fe element incorporating, the fPVC/MOSw@PDA@Fe(OH) 3 composite attains a UL-94 V-0 rating with 28.2 % and 57.9 % reductions in peak heat release rate and peak smoke release rates, respectively, compare to the fPVC/MOSw composite. Thermogravimetric analysis (TGA) indicates that both PDA and Fe(OH) 3 accelerate the decomposition of the third degradation step of MOSw, increasing the non-flammable gas, enhancing heat absorption and cooling the matrix. Concurrently, most of the Fe compounds are migrated into the gas phase, scavenging ·H and ·OH radicals and catalyzing the thermal oxidation of soot. TGA results also show that tiny Fe compounds (only 0.05 wt % of Fe element) in the condensed phase effectively catalyze dehydrochlorination of fPVC at lower temperatures, promoting trans-conjugated polyene formation and crosslinking into more and denser char layer. Hydrogen bonding between Cl atoms of PVC and hydroxyl/amino groups of PDA strengthen the interfacial adhesion, leading to increases in tensile strength and modulus. Simultaneously, the whisker morphology of MOSw facilitate crack deflection and energy dissipation, yielding an 85.27 % increase in impact strength. This structural design maximizes filler efficiency with minimal loadings, balancing fire safety and mechanical strength in composites.