Enhanced flame resistance and mechanical property of TPU with triazine silane coupling agent modified APP by wet ball milling

In this study, a flame retardant TPU composite with good flame retardancy and mechanical properties was obtained by adding 5% modified APP. The modified APP (WMTAPP) was obtained by introducing a triazine silane coupling agent which was synthesized by the reaction of KH550 and cyanuric chloride during the wet ball milling process. The results showed that the dispersion of WMTAPP in TPU matrix was improved, and the flame retardant efficiency of WMTAPP was improved. The LOI value of TPU/5WMTAPP was increased from 26.5% of TPU/5APP to 28.9%, and it could pass UL 94 V-0 rating without dropping. In the cone calorimeter test, the pk-HRR, THR and TSR of TPU/5WMTAPP were 206 kW/m2, 56 MJ/m2 and 1344 m2/m2, respectively, which were reduced by 45%, 20% and 32% compared with TPU/5APP. The final char residue of TPU/5WMTAPP was 22 wt%, which was 47% higher than that of TPU/5APP. The tensile properties of TPU/5WMTAPP were also improved. The tensile strength was 26.1 MPa and the elongation at break was 651.6%, which was a little higher than that of TPU/5APP. Micromorphologies of the fracture surfaces showed that the dispersion of WMTAPP in TPU was improved, and the interfacial adhesion between WMTAPP and TPU was enhanced, which is one reason for the improvement of flame retardancy and mechanical properties. Moreover, the triazine groups and silicon-containing groups in WMTAPP are beneficial for the formation of a complete and compact char layer, which is another reason.