Synthesis of a novel intumescent flame retardant based on phosphorus, nitrogen, and silicone, and application in VMQ

Abstract

A novel intumescent flame retardant (DTT) based on silicone, phosphorus, and nitrogen was synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), aminopropyl triethoxy silane (KH550), and 1, 4-phthalaldehyde successfully. The chemical structure of DTT was characterized by Fourier transform infrared spectroscopy (FTIR) and 31P-NMR spectra. DTT was then used to improve the flame retardancy of methyl ethyl silicone rubber (VMQ). The flame retardancy, combustion behavior, and thermal stability of the flame-retarded VMQ composites were quantified by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetry, and thermogravimetric analysis (TGA). With the content of DTT increased, the LOI of VMQ composite increased gradually, which was 29.8% when 25 mass% DTT was added. Meanwhile, the flame-retarded VMQ composite obtained UL-94 V-0 rating. In addition, the combustion time was reduced by 50.96%, which was from 520 to 255 s, and the total heat release was reduced by 26.25%, which was from 53.53 to 39.48 MJ m−2. TGA results indicated that the pure VMQ composite had an excellent thermal stability and DTT decomposed ahead of the VMQ matrix to perform the flame-retarding effect better. The flame-retarding mechanism in condensed phase was discussed based on the digital photographs, SEM images, and FTIR spectra of residue chars. Then the mechanism in the gaseous phase was also discussed. In addition, the mechanical property of flame-retarded VMQ composite was studied.