Effect of layered double hydroxide on the flame retardancy of intumescent flame retardant thermoplastic polyurethane composites prepared by selective laser sintering

Presently, layered double hydroxides (LDHs) are pervasively adopted as part of flame retardant polymer composite materials due to its favorable synergism effect with certain flame retardants. In addition, it is environmentally friendly. Meanwhile, selective laser sintering (SLS) is a powder-based three-dimensional (3D) printing technology, providing a novel path to manufacturing polymer composite materials with complex shapes. In this research, flame retardancy of thermoplastic polyurethane (TPU) was enhanced based on LDHs and intumescent flame retardant (IFR). Being prepared by SLS technology. First, TPU composite powders based on LDHs and IFR were obtained using a two-stage mixing method. Morphology analysis revealed that IFR and LDHs were dispersed uniformly in TPU powder. Subsequently, flame retardant TPU composites were prepared with TPU composite powders using the SLS process under appropriate 3D printing parameters, thereby enabling flame retardant TPU parts to be obtained. With 23 wt% IFR and 2 wt% LDHs filler, the limiting oxygen index of TPU composite was reached to 31.7%, while passing the UL-94 V-0 level during the vertical burning test. The cone calorimeter test showed that the heat release rate, smoke production rate, as well as production of carbonic oxides, all decreased significantly following the addition of LDHs. Thermogravimetric analysis indicated that LDHs and IFR were characterized by a favorable synergism effect, with the TPU/23IFR/2LDHs possessing good thermal stability. Char residue analysis, including SEM, energy dispersive X-ray, Fourier transform infrared, and Raman spectra, further testified that a synergism effect existed between LDHs and IFR in the TPU composite. Overall, in this study the TPU composites fabricated by SLS technology exhibited excellent flame retardant ability.