Appropriate surface modification or functionalization is prerequisite for the application of inorganic nanoparticles. And surface control between organic and inorganic interface plays an important role in constructing organic–inorganic composites. In-situ polymerization has been extensively studied to improve the compatibility and dispersibility of inorganic nanoparticles, but the polymerized nanoparticles tend to concatenate and form large composites, restricting further applications. Herein, uniform and dense polyacrylic acid (PAA) membranes have been grafted on layered double hydroxide (LDH) nanosheets via an in-situ initiating and terminating radical graft polymerization method. With initiating and terminating on the same particle, the size, morphology and density of grafted PAA onto the surface of LDHs can be controlled by adjusting the ratio of initiated sites to terminated sites, the amount of redox initiator or monomer. As a result, with only 17.33% organic grafting ratio, PAA@LDHs with largely improved compatibility can be monodispersed in polyethylene (PE) and polyvinyl chloride (PVC) matrices, which is determined by a fluorescence microscope technique.

Considerable smoke and toxic volatiles generation has compromised the application of thermoplastic polyurethane (TPU) and caused a great threat to human life. Here, nano-MgFe layered double hydroxide (MgFe-LDH) with uniform particle size was synthesized to reduce smoke density and toxic gases of TPU composites using ammonium polyphosphate (APP) as a flame retardant agent. The results show that the combination of 16 wt.% APP and 4 wt.% MgFe-LDH greatly decreased the smoke density (D_20min and D_{s, max}), smoke production rate (SPR) and heat release rate (HRR) of TPU composites. Furthermore, the MgFe-LDH synergist demonstrated high efficiency in decreasing total volatiled products and toxic volatiles evolved, such as the CO, HCN and isocyanates. The reason was mainly attributed to the chemical reaction between MgFe-LDH and APP, which can promote the compactness of char layers with fine microstructure formed in the decomposition process of MgFe-LDH/APP/TPU composites. The protective char layers could act as barriers between combustion zone and matrix to protect the unburned substrate and promote smoke suppression effect.