Exploring microencapsulated magnesium tetraborate: A promising flame-retardant additive for polyurethane-based composites

Abstract

Boron compounds exhibit low toxicity and diverse molecular structures, rendering them effective flame-retardant additives in polymer-based materials through various mechanisms of action. Magnesium tetraborate (MTB) and melamine formaldehyde (MF) resin-encapsulated MTB were used to enhance the flame-retardant performance of polyurethane (PU). MTB was synthesized by solid-state synthesis. MF microcapsulated MTB-MF is prepared by in situ polymerization. The synthesized MTB-based materials are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). PU composites containing MTB and MTB-MF with varying amounts were produced by reaction of isocyanate and polyether polyol. The flame-retardant action of MTB and MTB-MF in PU was studied using the limiting oxygen index (LOI), a mass loss calorimeter (MLC), and TGA. In addition to the thermal behaviors of the PU composites, which were characterized by TGA and TGA coupled with FTIR, the morphologies of the residues were investigated using scanning electron microscopy (SEM). Results show that 5PHR-MTB containing a PU composite achieved a 24% LOI value. Besides, the peak heat release rate of 5PHR-MTB containing PU composites was reduced by 8% with respect to the PHRR of neat PU. 5PHR-MTB-MF microcapsule (the mass ratio of MTB:MF-1:3) achieved the maximal LOI value of 27%, and significantly decreased the peak heat release rate from 350 to 70 kW/m2 with respect to neat PU. The present work demonstrates that MF microcapsules, prepared with high efficiency, exhibit remarkable fire-proof performance, making them a promising multifunctional composite for use as a flame retardant in polyurethane applications.