Supramolecular interface engineering of a hierarchical core-shell flame retardant for smoke-suppressive and fire-safe PVC composites

In this study, a stimuli-responsive microcapsule flame retardant material, MgO@SiO 2 @rGO-β-CD, was successfully designed and prepared, and it was applied to polyvinyl chloride (PVC) to construct high-performance MgO@SiO 2 @rGO-β-CD/PVC composites. Amorphous SiO 2 was coated on the surface of MgO by the sol-gel process to form MgO@SiO 2 core-shell structure. Subsequently, the composite of reduced graphene oxide (rGO) and β-cyclodextrin (β-CD) was anchored on the surface of MgO@SiO 2 by ultrasound-assisted assembly to construct a multifunctional outer layer. The structure achieves stable binding through Si– O –Mg covalent bond and hydrogen bond interaction, and uses π-π stacking and hydrogen bond interaction to form a GO/β-CD dynamic outer layer to achieve controllable loading and release of dispersant polyethylene glycol (PEG). The microcapsule material triggers GO oxidative decomposition and β-CD/PEG inclusion complex dissociation above 250 °C, releasing the inner MgO and forming a carbon layer. When the addition amount was only 6 wt%, MgO@SiO 2 @rGO-β-CD/PVC composites exhibited excellent flame retardant and smoke suppression properties: The peak heat release and total heat release were reduced by 56% and 55%, respectively, compared with pure PVC. The limiting oxygen index of the composite was increased to 30.1% and passed the UL-94 V-1 rating. The microstructure characterization confirmed that the stimuli-responsive microcapsule flame retardant material MgO@SiO 2 @rGO-β-CD was uniformly dispersed in the matrix, and its multi-layer structure could catalyze the formation of a continuous and dense intumescent carbon layer during the combustion process, exerting the synergistic flame retardant mechanism of gas phase quenching, condensed phase barrier, and catalytic carbon formation.