Reprogramming the thermal degradation pathway of PVC/PUA foams via In-Situ crosslinking: Toward low smoke and flame-triggered shape memory

PVC/PUA/CPVC nanocomposite foams were fabricated via a plasticizing-foaming-reinforcing strategy. • PUA catalyzes the dehydrogenation of CPVC, forming a rigid preliminary carbonized skeleton and restructuring the pyrolysis pathway. • Condensed-phase trapping of volatile smoke precursors improves simultaneously flame retardancy and smoke suppression. • The optimized PVC/PUA/CPVC nanocomposite foam achieves excellent fire safety. High-performance poly(vinyl chloride)-based ternary nanocomposite foams, incorporating polyurea and chlorinated poly(vinyl chloride) (PVC/PUA/CPVC), were prepared using "plasticizing-foaming-reinforcing" (PFR) strategy. Here PUA strengthened PVC matrix and CPVC endowed excellent flame retardancy. The incorporation of CPVC significantly enhances the fire safety of the foam while well-preserving its original superior mechanical properties and solvent resistance. Specifically, the foam not only achieves a UL-94 V-0 rating, but its limiting oxygen index (LOI) is also increased to 35.7%, while the maximum smoke density (MSD) and smoke density rating (SDR) are decreased to 83% and 75%, respectively. The essence of this superior performance lies in the reconstruction of the pyrolysis pathway in the condensed phase. Catalytically accelerated by PUA during early pyrolysis, CPVC generates abundant highly reactive conjugated polyenes that rapidly undergo self-cyclization and cross-linking to in-situ construct a rigid preliminary char skeleton. This skeleton-building process kinetically outpaces the acid-catalyzed melt-collapse of the matrix. Simultaneously, the crosslinked structure robustly immobilizes the monocyclic aromatic hydrocarbons (MAHs) generated from PVC degradation within the condensed phase within the condensed phase, forcing their in-situ aromatization and transformation into a highly graphitized, dense char layer. Furthermore, leveraging the unique "sea-island" microphase-separated structure within the cell walls and its excellent ablation resistance, the PVC/PUA/CPVC nanocomposite foam exhibits a rapid flame-triggered shape memory behavior, demonstrating broad application prospects in the field of smart fire-alarm sensors.