| Thermoplastic foam has been widely accepted because of its light weight, high specific strength, impact load resistance and good insulation properties. However, the foam structure not only reduces the density and cost, but also lowers the mechanical properties, which greatly limits its application. Sporting applications, such as motorcycle racing, soccer, rugby and other sports require body protection against impact but the mechanical properties of regular foam cannot meet such requirements. Therefore, it is necessary to develop a new kind of foam which can meet the mechanical properties required and comfort performance. Thermoplastic polyurethane (TPU) has excellent properties, such as high strength, comprehensive strength, elasticity, wear resistance, vibration damping ability and easy to recycle, these properties make it ideal for sportsmen protection material. Hollow glass bead (HGB) is a new type of lightweight inorganic non-metallic materials, with the advantages of low density, low thermal conductivity, low coefficient of expansion and high compressive strength. Recently. HGB filled composite materials have become a focus for many researchers.In this research work. HGB/TPU composite foam was fabricated by chemical foaming using extrusion and molding preparation methods. HGB/TPU rheological properties were first studied by systematic analysis and discussion on the effects of foaming process conditions as well as process parameters on the microstructure and properties of the foam. The results show that:(1) HGB which was washed by NaOH and then treated by silane coupling agent showed a uniformly modified surface. and showed amine (NH2) absorption peak on FTIR; This was desired as it would improve the interface between HGB and TPU matrix.(2) HGB/TPU melt is a pseudo plastic fluid. The complex viscosity decreases with increasing frequency, showing a typical shear thinning behavior. With the increase content of HGB content, the complex viscosity, storage modulus and loss modulus of HGB/TPU system were gradually increased, and the loss tangent was gradually reduced. With increase of temperature, the apparent viscosity of the HGB/TPU was decreased, and showed a strong frequency dependency in high shear rate region.(3) The effects of AC foaming agent content, HGB content. the die temperature, screw speed, and cooling method on the structure and mechanical properties of extruded for HGB/TPU foam were studied. The best formulation was:97phr TPU.3phr HGB. and1.5phr AC while the best process parameters were:die temperature of180℃. screw speed of35rpm. and cooling by air. Under these conditions. uniform distributed internal cellular morphology of extruded foam sample could be obtained. The cellular size was about approximately56μim, cellular density reached a maximum.apparent density reached a minimum of0.644g/cm5. the foaming ratio was1.86, and the tensile strength was8.21MPa.(4) The effects of AC foaming agent content, HGB content, the temperature, pressure and foaming time on the structure and mechanical properties of molded foam were studied. The best formulation was:97phr TPU,3phr HGB,1phr AC content; the best process parameters were: Temperature of200℃, pressure of5MPa. foaming time of5min. Under these conditions, the foam sample internal cellular distribution was uniform, uniform size was about70μm, cellular density reached a maximum; apparent density reached a minimum0.436g/cmJ. foaming ratio was2.75, tensile strength was4.08MPa, compression strength was16.38MPa, and hardness was48A.(5) The compression strength of molded foam containing3phr of HGB reached a maximum of16.38MPa. about43.9%higher than that of unreinforced TPU foam. |
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