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.
The preparation of high-performance epoxy resins (EP) with enhanced mechanical properties and flame retardancy for building materials has long been a significant challenge. In this study, bio-based phytic acid (PA) was intercalated into the layers of layered double hydroxides (LDH) via coprecipitation. Subsequently, ultrafine Fe(OH) 3 was in situ grown on PA-intercalated LDH through tannin-mediated assembly, resulting in the synthesis of the LDH-PA@TA-Fe(OH) 3 hierarchical hybrid flame retardant. Comprehensive characterization of its microstructure, morphology, and chemical composition was performed. The EP composite demonstrated a LOI of 31.3 % and a UL-94 V-1 rating when the additive of 7.5 wt% LDH-PA@TA-Fe(OH) 3 was utilized. Additionally, the EP/LDH-PA@TA-Fe(OH) 3 composite demonstrated a substantial reduction in peak heat release rate (pHRR) and peak smoke production rate (pSPR) with reductions of 48.1 % and 52.7 %, respectively, along with a 62.5 % decrease in peak CO production rate (pCOP), compared to neat EP. These improvements in fire safety are primarily ascribed to the synergistic flame retardancy of LDH and Fe(OH) 3 in condensed and gas phases, along with the efficient catalytic charring performance of PA and Fe 3+ . Furthermore, the incorporation of LDH-PA@TA-Fe(OH) 3 enhanced the mechanical properties of EP, which could be ascribed to the improved dispersibility of the modified LDH and the strengthened interfacial interaction. This study introduces a novel approach for the development of highly effective LDH-based hybrid flame retardant materials, enabling the fabrication of EP composites with superior mechanical performance and fire safety.
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