Novel polysilazane microencapsulated ammonium polyphosphate as flame retardant and smoke suppressant for thermoplastic polyurethane

To improve the compatibility of ammonium polyphosphate (APP) with thermoplastic polyurethane (TPU), novel phosphorus containing polysilazane was used to microencapsulate APP (APP@SiNP) which was then used for flame retardant TPU. The influence of microencapsulation on the thermal decomposition, mechanical and flame retardant properties of TPU was investigated. The addition of APP@SiNP brought forward the onset thermal decomposition temperature (T5%) of the TPU, but improved the thermal stability of the char layer at high temperatures. The presence of APP@SiNP fillers tended to reduce the tensile strength and elongation at break of TPU, but the tensile strength and elongation at break of TPU/APP@SiNP -10.0 were still higher than those of TPU/APP-10.0, indicating that polysilazane was capable of improving the interfacial interaction between APP and the TPU matrix. Both TPU/APP@SiNP-7.5 and TPU/APP@SiNP-10.0 can achieve UL-94 V-0 level. The PHRR, THR, and TSP values of TPU/APP@SiNP-10.0 were 77%, 58%, and 70% lower than the pristine TPU, which were also better than TPU/APP-10.0. The superior flame retardant efficiency of APP@SiNP was attributed to its catalytic charring capacity and the formation of thermally stable char residues.