Recent applications of X-ray grating interferometry imaging to evaluate flame retardancy performance of brominated flame retardant

In this work, fire inhibition performance of four flame retardant formulations of brominated flame retardant (BFR: GreenArmor®), antimony(III) oxide (Sb2O3) and high impact polystyrene (HIPS) is reported. The standard Underwriters Laboratory (UL 94) vertical burn test was applied for assessing the flame retardancy of a variety of polymer blends. A formulation having 13.3 wt% GreenArmor®, 4 wt% Sb2O3 and 82.7 wt% HIPS, named sample D, successfully passed the flame test and was rated V-0. The other formulations with deficient composition exhibited low flame retardancy, as expected. The X-ray grating interferometry method is introduced for probing the 3D internal structures across the burnt UL 94 flame retarded polymer blend formulations to present the detailed mechanisms of flame retardancy. The X-ray images revealed several features for the formulation (sample D) that passed the UL 94 test: heat-induced dissolution of BFR and Sb2O3 residual particles, formation of gas bubbles inside the burnt polymer test bar, deflation of gas bubbles in a char layer through a microcrack, and thick char layer development, defined by the Br and Sb concentration profile to a depth of 100–220 μm. Also, the X-ray images show clear differences between formulations that pass and fail the UL 94 test. X-ray grating interferometry imaging is proposed as a novel technique for assessment of new generation flame retardants.