Preparation of DOPO Derivative Modified Carbon Nanotubes and Their Effect on Flame Retardancy of Polylactic Acid

Using carboxyl carbon nanotuhes (CNT-COOH) and 9, 10-dihydm-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative DOPO-NH2 as raw materials, a new type of inorganic-organic hybrid flame retardant (CNT-DOPO) was prepared through acid chlorination and condensation reactions. The structure was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, and the grafting rate was quantitatively tested. CNT-COOH, DOPO-NH, and CNT-DOPO were added to polylactic acid (PLA) in the same mass fraction of 5% to prepare flame-retardant PLA composites. The results showed that DOPO-NH, was successfully grafted onto carbon nanotubes with a grafting rate of about 50%. The cone calorimetric test results showed that the peak heat release rate of PLA/5CNT-COOH, PLA/5DOPO-NH2 and PLA/5CNT-DOPO was 46%, 3.4%, 39.8% lower than that of pure PLA, respectively. The morphology and structure, analysis of the char residues showed that the char layer of PLA/5CNT-DOPO had the highest degree of graphitization, and carbon nanotubes and DOPO-NH, had a certain promoting effect on the condensed phase flame retardancy. The theological results showed that the addition of carbon nanotube had a great effect on the viscoelastic transition of PLA composites. PLA/5CNT-COOH and PLA/5CNT-DOPO basically exhibited elastic behavior. The addition of carbon nanotube or modified carbon nanotube increased the viscosity of PLA composites at low frequency, and promoted the formation of consistent and compact char layer in the later stage of combustion, Accordingly, the heat release rate and the smoke production of PLA composites decreased significantly.