Effects of Layered Nanoclays on the Cellular Structure, Dynamic–Mechanical–Thermal Properties and Fire Behavior of Flame-Retardant ABS Foams

The present work deals with the preparation and characterization of fire-retardant acrylonitrile–butadiene–styrene (ABS) foams incorporating 25 wt% of a phosphorus flame-retardant (PFR) system formed by 50% of ammonium polyphosphate (APP) and 50% of aluminum diethylphosphinate (AlPi). To further enhance performance, 5 wt% of the PFR was replaced by either montmorillonite (MMT) or layered double hydroxide (LDH) nanoparticles, maintaining the overall FR content constant. The formulations were prepared by melt blending, and foams were produced using a one-step supercritical carbon dioxide (sCO2) dissolution foaming process. The incorporation of the PFR, alone or partially replaced by nanoclays, resulted in foams with smaller cell sizes and higher cell nucleation densities compared to pure ABS, with cell sizes reducing from 60 μm to as low as 40 μm and cell densities reaching values > 107 cells/cm3. The presence of LDH notably modified the thermal decomposition of ABS–PFR, increasing the temperature at 5% mass loss (T5%) by more than 10 °C and the amount of formed residue by more than 15%. The ABS–PFR/LDH foam also showed a higher glass transition temperature (3 °C increase) and a higher specific storage modulus (920 MPa·cm3/g, a more than 40% increase). Cone calorimetry revealed a very significant reduction in the peak of the heat release rate (PHRR) and increased residue formation for ABS–PFR compared to ABS (from 1672 kW·m−2 to as low as 483 kW·m−2). LDH nanoparticles further decreased HRR during the early quasi-static combustion stage of foams, indicating a more effective condensed-phase flame-retardant action than MMT.