| As an engineering plastic, thermoplastic polyurethane (TPU) has been applied in many fields due to its excellent physical properties. However, the production of much smoke and toxic gases during burning, and its high flammability have greatly limited its broad applications in various fields above mentioned. Therefore, it becomes a real request that new flame retardant systems should be developed to meet the constantly changing demand of applications. In this work, several carbon materials (including carbon black, expandable graphite, carbon nanotubes, and graphite powder) were used as flame retardant and smoke suppression synergism with ammonium polyphosphate (APP) in TPU composites. The related results are shown in the following.(1) Smoke suppression properties of carbon black were studied in flame retardant TPU based on APP. The experimental data from SDT indicated that TPU-CB-2 (1.00 wt.% CB) shows the best smoke suppression performance, with the luminous flux value of 92.1% at the test condition with flame, which is 33% higher than TPU-1. The CCT results show that TSR of TPU-CB-4 (3.00 wt.% CB) is 172.1 m2/m2, which is 70% lower than TPU-0. The HRR is reduced from 154.4 kW/m2 (TPU-1) to 88.5 kW/m2 when 1.00 wt.% CB is added into the composites. TG results showed that CB can improve the thermal stability at high temperature for TPU composites. The TG-IR results show that the aromatic compounds gradually decreased when CB is added into TPU/APP composites at high temperature.(2) The synergistic smoke suppression and flame retardant effects of expandable graphite (EG) and expanded graphite (TEG) have been investigated in the TPU/APP composites. The SDT results showed that the luminous flux value TPU-EG-2 (1.00 wt.% CB) is 92.1% at the test condition without flame, which is 30% higher than TPU-1. However, the value of TPU-TEG-2 is 13% higher than TPU-EG-2. The CCT results indicate that, comparing with the HRR (91.6 kW/m2) value of TPU-EG-3, the HRR value of TPU-TEG-3 is reduced to 77.4 kW/m2. The LOI results indicated that the LOI of TPU-EG-4 is 29.3, which is lower than that of TPU-TEG-4 (30.1). The SEM results show that TEG showed better performance than EG to improve the structure of carbon layer. TG results showed that both EG and TEG can improve the thermal stability at high temperature in flame retardant TPU composites. The TG-IR results showed that the volatilized products (especially aromatic compounds) gradually decreased when EG or TEG is added into TPU/APP composites at high temperature.(3) The synergistic flame retardant and smoke suppression effects of carbon nanotubes (CNT) with APP been studied in TPU composites. The SDT results showed that the addition of 3.00 wt% CNT can effectively decrease the amount of smoke production by 25% in test with, and 20% in test without flame. The CCT results showed that TPU-CNT-4 (with 3.00 wt% CNT) shows HRR value of 105.3 kW/m2, which is 30% lower than TPU-0. The LOI results indicated that the LOI of composites decreased as the increase of CNT; and the LOI of TPU-CNT-4 reaches 31.1. From the SEM, the rigidity and less cracks carbon shell obtained by loading CNT, which can explain why it has low heat release rate and smoke production rate. The TG results showed that the incorporation of CNT improves the quality of char residue in combustion process.(4) The synergistic flame retardant and smoke suppression effects of graphite powder (GP) with APP have been studied in TPU composites. The SDT results showed that the luminous flux of the sample containing 3.00 wt% GP is 80.7% in the test with flame, which is 20% higher than TPU-1. The results of CCT indicated that 0.50 wt% GP can make the HRR value of TPU-GP-1 reduce from 339.37 m2/m2 (TPU-1) to 248.98 m2/m2. The LOI test shows that with the content of GP increasing, the LOI of compositess increased; and the LOI value of TPU-GP-4 is as high as 30.3. The TG results showed that GP can improve the thermal stability at high temperature for flame retardant TPU composites. |
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