Analysis of thermal stability and pyrolysis kinetic of dibutyl phosphate-based ionic liquid through thermogravimetry, gas chromatography/mass spectrometry, and Fourier transform infrared spectrometry

Abstract

To analyze the feasibility of phosphorus-containing ionic liquids used as flame retardants on flammable materials, thermal stability and pyrolysis kinetics of 1-butyl-3-methylimdazolium dibutyl phosphate ([Bmim][DBP]) were investigated using nonisothermal thermogravimetry. The apparent onset decomposition temperature (T0) and mass fraction of residual carbon were 275.2–297.3 °C (± 0.5 °C) and 8.6–10.2% (± 0.1%), respectively. The apparent activation energy (Ea), pre-exponential factor (A), and most probable kinetic function [G(α)] were calculated using thermokinetic methods as Ea = 152–164 kJ mol−1 (± 2 kJ mol−1), ln A = 27.7 ± 0.4 s−1, and G(α) = − ln(1 − α). The maximum operation temperature was estimated as 166.0 ± 0.2 °C, which was considerably lower than T0. The pyrolysis products were identified through gas chromatograph/mass and Fourier transform infrared spectrometers. As a novel finding, the main flame-retarding mechanism of [Bmim][DBP] occurred primarily in condensed phase. Complementally, [Bmim][DBP] was testified to have the flame-retardant effect on epoxy resin by limited oxygen index and vertical burning tests.