| Thermoplastic polyurethane(TPU)is one of the most versatile engineering thermoplastics with properties between plastic and rubber.Because of its excellent properties,including excellent abrasion resistance,high tensile strength,high compressive and tear strength,good flexibility,ageing resistant and good hydrolytic stability,TPU has been widely applied in construction,motor industry,cushion material,pavement materials,etc.However,as many other thermoplastics,due to its flammability,smoke generation and melt-dropping during combustion,the applications are greatly limited.It is urgent and important to improve the flame retardancy of TPU.Due to the high production and processing conditions of TPU,and often with much addition of traditional flame retardants,flame retardant TPU often weakens its original excellent prosperities.Thus,as for these problems,the following researches have been developed.(1)In this paper,a highly efficient synergistic flame retardant Fe-graphene(IG)was prepared by a modified pressurized oxidation-Fe reduction method,a high concentration of TPU/IG masterbatch was prepared by solution blending method.Moreover,the TPU/IG nanocomposites were prepared by high concentration masterbatch-solvent mixing method.(2)Then,the phosphorus based flame retardant ammonium polyphosphate(APP),melamine salt of pentaerythritol phosphate(MPP),aluminum hypophosphite(AHP)were used as flame retardants,respectively,and IG was used as synergistic agent to prepare the flame retardant TPU composites.The flame retardant effects and thermal stability of TPU composites were tested using cone calorimeter test(CCT),scanning electron microscopy(SEM),thermogravimetric analysis(TG),thermogravimetric/fourier infrared spectrum analysis(TG-IR),limiting oxygen index(LOI),UL 94 test and dynamic mechanical analysis(DMA).The test results show that the graphene layers are well exfoliated and reduced with little oxygen-containing groups,and the IG has a good dispersion in TPU matrix.Compared with that of neat TPU,TPU/IG nanocomposites present good flame retardancy and thermal stability.As for TPU/IG with 0.25 wt% IG,PHRR value reduces by 78.0 %,THR value reduces by 23.6 %,PSPR value reduces by 65.7 %,SF value reduces by 65.0 %,and the storage modulus increase by 44.1 % at-60 °C and 39.7 % at 20 °C.Moreover,the addition of IG can reduce the release of toxic and harmful gases containing nitrogenous substances and aromatic compounds in the process of thermal degradation.The test results show that,there present good synergistic flame retardany using Fe-graphene as synergistic agent and using the phosphorus based flame retardants APP,MPP,and AHP as flame retardants for TPU system,respectively.The flame retardant systems show much lower heat release and smoke production,and higher LOI value,and the samples pass UL 94 test.Remarkably,as for sample with 0.25 wt% IG and 9.75 wt% APP,PHRR value decrease by 92.8 %,THR value decrease by 55.6 %,TSR value decrease by 34.7 %,and mass residue increase by 88.6 %;as for sample TPU/MPP/IG-0.25,PHRR value decrease by 91.5 %,THR value decrease by 56.0 %,TSR value decrease by 30.7 %,and mass residue increase by 52.0 %;as for sample TPU/AHP/IG-0.25,PHRR value decreased by 90.2 %,THR value decrease by 67.8 %,TSR value decrease by 56.9 %,and mass residue increase 4.3 times.The char residues after CCT test are all smooth and compact,among the three samples,TPU/AHP/IG-0.25 show the most dense and compact,and the char residue present lamellar structure.TG results show that,the Fe-graphene can catalyze three kinds of phosphorus flame retardants to decompose at lower temperatures,thus improving the crosslinking and charring of TPU composites,so the samples present good thermal stability at high temperature.Meanwhile,during thermal degradation,the flame retardant samples release non-flammable gases,such as H2 O and CO2,and release less toxic and harmful gases. |
