The synergism effect of montmorillonite on the intumescent flame retardant thermoplastic polyurethane composites prepared by selective laser sintering

Selective Laser Sintering (SLS) is a powder-based 3D printing technology. It offers a new means of fabricating complex modules with special properties, such as mechanical, flame retardant, electrical and thermal properties. In this paper, the effect of an intumescent flame retardant (IFR) and montmorillonite (MMT) on the fire resistance of thermoplastic polyurethane (TPU) was investigated. TPU composites powders were prepared by mixing with a two-step method and can be effectively applied to SLS. Morphology characters exhibited that the fillers disperse well in the TPU powder. The structure analysis and hydrophilia analysis of sodium montmorillonite (Na-MMT) and organically modified montmorillonite (OMMT) demonstrates the different compatibility in TPU, which reflects diverse flame retardant behavior. With 22% IFR and 3% OMMT fillers, the LOI of TPU composites increased from 17.2% to 28% and subsequently a UL-94 V-0 ranking was obtained. In the CCT results, the formula of 22% IFR and 3% OMMT showed the lowest heat release and smoke production. The study also explored the effects of flame retardant fillers on the thermal stability of TPU composites and melting and crystallization behaviors in SLS processing. In addition, the char residues after heating were analyzed via scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and laser Raman spectroscopy. The results demonstrate that the composites have favorable flame retardant properties, thermal stability, char forming performance, and SLS process properties. The TPU composites prepared via SLS in this study demonstrated extensive potential in fire protection materials.

Automated summary

This study investigates the effect of intumescent flame retardant and montmorillonite on the fire resistance of thermoplastic polyurethane. It is found that with a certain ratio of fillers, the LOI of TPU can be significantly increased and a better fire rating can be achieved.