The Influence Of Metal Oxides On Intumescent Flame Retardant Thermoplastic Polyurethane Compound

Thermoplastic polyurethane (TPU) is one of the commonly used plastic in the world, which combines the processing of plastics and physical and mechanical properties of rubber, high elasticity, high strength, the high resistance to wear, the radiation resistance, the oil resistance, degree of hardness may in the very wide range adjustable and so on mechanical properties, has the widespread application in national economy's many domains. TPU is extremely easy to burn because of the special structure. When TPU is buring, the flame is fierce with the strong black smoke, the heat release is big, simultaneously has the serious melt drop phenomenon, which cause TPU has very big limitation in the industry. Therefore, the research of flame-resistant thermosplastic polyurethane has been the hot spot in the polyurethane material research.This paper mainly added MgO, MnO2, Fe2O3, Ni2O3, CuO, ZnO, Sb2O3, La2O3 and Y2O3 to the flame retardant system which was composed of the charring-foaming agent (CFA) (a triazine polymer) and ammonium polyphosphate (APP) for the TPU, respectively. From the date of limiting oxygen index (LOI) and UL-94 test, we determined the optimum ratio of APP and CFA was 6:1. However, the IFR system could not solved the dripping problem during TPU burn; it only could pass the UL-94 V-2 rating with 40 wt% IFR content addition. When the 5 wt% of metal oxides respectively added to the TPU-IFR composites with 35 wt% IFR content, we found the TPU-IFR composites with MgO, MnO2, Fe2O3, Ni2O3 and CuO respectively could pass the UL-94 V-0 rating, the tensile strength and elongation of composites were improved. Only the TPU-IFR composites with MgO could still pass the UL-94 V-0 rating with 30 wt% IFR content. Further research showed that TPU-IFR composites with 30 wt% IFR content (7 wt% MgO) had the maximum oxygen index and the best mechanical properties. When continue to reduce the content of IFR or increase the content of MgO in IFR, TPU-IFR composites could not pass the UL-94 V-0 rating.In order to study the synergistic effects of metal oxides to TPU-IFR system, this paper researched the thermal degradation, the combustion behavior and the morphology of carbon residue of TPU-IFR composites with TGA, Cone Calorimeter and SEM. We discovered the curves of HRR, TSP and CO release rate of TPU-IFR composites became gentler; the curves of PHRR, PSPR, PCOP, THR and TSP had decreased greatly, the material ignition time (IT) was also shorter. The thermal degradation and the combustion behavior of TPU-IFR composites had changed when added with metal oxides. In TPU-IFR composites, MgO showed excellent properties in reducing the heat release, further reduced the PHRR, THR and PCOP; CuO showed excellent properties in smoke suppression, greatly reduced the PSRP, TSP and PCOP. From SEM micrographs we can found the surface of char after the combustion of TPU-IFR composites with 35 wt% IFR content became regular and dense, but it have the hole. The surface of TPU-IFR composites with MgO or Ni2O3 was dense, compact, no flaw and the same as the mountain ridge formed by the shrinkage after the char layer expanded. Among nine metal oxides, the char of composites with MgO was the best.