Bio-based polyphenol tannic acid as universal linker between metal oxide nanoparticles and thermoplastic polyurethane to enhance flame retardancy and mechanical properties

It has been well confirmed that metal oxide nanoparticles can simultaneously enhance the flame retardancy and mechanical performance of polymer composites, owning to its catalysis effect and robust characteristic. However, most metal oxide nanoparticles tend to aggregate in polymers due to their high specific surface energy, thus deteriorating their enhancement effect. One simple and effective as well as environmentally friendly functionalization approach is desiderated for the practical application of metal oxide nanoparticles. Tannic acid is a naturally derived polyphenol compound which spontaneously combines with metal ions by coordinate bond. Due to size effect, there are lots of defect situ in the surface of metal oxide nanoparticles which can interact with tannic acid. Therefore, tannic acid was used to modify three kind of representative metal oxide nanoparticles (ZnO, Fe2O3 and Co3O4). The SEM photographs of fracture surface show that the modified metal oxide nanoparticles have a favorite dispersion state in thermoplastic polyurethane (TPU) matrix. As a result, the flame retardancy and mechanical properties of TPU composites have been significantly improved. Specifically, with 4% addition of tannic acid modified metal oxides (MO-TA), the peak HRR value showed a remarkable decrease of 22.7%, 14.1% and 19.3%, compared to pure TPU. Meanwhile, the tensile stress of [email protected] increased to 39.2, 34.0 and 39.8 MPa from 22.1 MPa of pure TPU, suggesting an effective mechanical performance improvement. The universality of polyphenol compounds to enhance the interfacial interaction between metal oxide nanoparticles and polymer resin opens a novel pathway to prepare high performance polymer composite materials.