Modification of halloysite nanotubes with supramolecular self-assembly aggregates for reducing smoke release and fire hazard of polypropylene

A novel nano-clay flame retardant (HNTs@MEL-PA) is prepared by modifying halloysite nanotubes (HNTs) with supramolecular self-assembly technology using melamine (MEL) and bio-based phytic acid (PA) as the building blocks. Transmission electron microscopy images and Fourier transform infrared spectra show that the surface of HNTs is successfully decorated with MEL-PA supramolecular aggregates by hydrogen bonding. The feasibility of using HNTs@MEL-PA as a flame retardant for polypropylene (PP) is explored. Compared with PP/HNTs composites, the dispersion of HNTs@MEL-PA and its interfacial interactions with PP matrix are greatly improved. Heat release of PP is decreased in a certain degree and its smoke release is greatly reduced by HNTs@MEL-PA. With the addition of 15 wt% HNTs@MEL-PA, total smoke production of PP is decreased from 15.7 to 10.2 m(2), indicating the greatly improved fire safety. Flame retardant and smoke suppression mechanisms of HNTs@MEL-PA are proposed based on thermal decomposition results and the analysis on char residue.