Nano-enhanced thermo-mechanical properties of ethylene vinyl acetate with intumescent agent and organoclays

Abstract

Ethylene vinyl acetate copolymer (EVA) micro-composites having both anionic and cationic clays were made using a solution-blending technology. Anionic clay (layered double hydroxide; LDH) and Cationic clay (Fluoro-mica; ME) were functionalized with hydrophobic molecules such as stearate (SA) and cetyltrimethylammonium (CTA) for improving the compatibility with hydrophobic EVA. The SA intercalated MgAl-LDH (SA-LDH) and CTA intercalated ME (CTA-ME) were prepared by co-precipitation and ion-exchange methods, then blended into EVA matrix together along with intumescent flame retardant (IFR) by solution blending forming final EVA micro-composite. The impact of organoclays on the flame retardancy of EVA micro-composites were tested by a cone calorimeter test and vertical flammability with UL-94 test method. As per XRD for EVA micro-composites, the (00l) peaks of organoclays vanished, indicating their exfoliation in EVA matrix. The thermo-mechanical characteristics for EVA micro-composites improved further than EVA containing IFR only. EVA composite containing 30 wt% IFR, 1 wt% LDH and 4 wt% ME (L1M4-I30-EVA) passed the UL-94 test with V-0 rating, lowering the peak heat release rate from 2107.7 kW/m² of intact EVA to 213.1 kW/m². The observed char morphology revealed that organoclays were effective in forming rigid tight char layers. The synergy between organoclays and the IFR in the current EVA micro-composite is crucial for improving char formation and enhancing flame-retardant performance.