Study On Thermoplastic Polyurethane Foam Beads Via Supercritical CO₂

Thermoplastic polyurethane?TPU?can be used in many fields because of its excellent performance.It has a wide range of applications because of its good elasticity and excellent processability.Due to the porous,thermoplastic polyurethane foam?ETPU?shows much lighter,better elasticity and better cushioning properties.It is widely concerned by the packaging industry and automobile manufacturing industry.However,ETPU is faced with the problems of high shrinkage ratio and high molding cost.Therefore,it is necessary to study the preparation technology of ETPU.ETPU was prepared through autoclave foaming process using supercritical CO₂ as the blowing agent.And the properties of ETPU were investigated.ETPU foam beads were prepared by autoclave foaming using supercritical CO₂ as the blowing agent.The influence of cryogenic liquefaction and two-step depressurization technologies on the ETPU shrinkage ratio were compared.The influence of foaming temperature?T_f?and foaming pressure?P_f?on the thermal and foaming properties of ETPU were investigated by differential scanning calorimetry?DSC?and scanning electron microscopy?SEM?.Cryogenic liquefaction technology was shown to reducing the shrinkage ratio of ETPU to 5.0%on average.The expansion ratio of ETPU increased,the cell density increased and then decreased,and the mean cell diameter decreased and then increased over a range of 120 to 130°C and P_f range of6 to 10 MPa.The foam beads prepared at 120°C and 10 MPa had an expansion ratio of8.23,an average diameter of 40.69?m,and a cell density of 1.2×10⁸/cm³.Thermoplastic polyurethane foams were modified with polyvinyl chloride?CPE?were prepared through autoclave foaming process using supercritical CO₂ as the blowing agent.Thermal behavior,rheological and foaming properties of the samples were evaluated.The results indicate that the addition of CPE can improve the melt strength of TPU and improve its foaming properties.The foaming material that average cell size is smallest?8.851?m?and the cell density is maximum(1.796×10¹²/cm³)was obtained when the content of CPE is 10%.The shrinkage ratio decreased with the increasing CPE content.The addition of CPE had a significant effect on reducing the shrinkage of TPU foam beads.ETPU have attracted attention of researchers in recent years due to their wide use inindustrialapplications.Inthispaper,asmallamountof acrylonitrile-butadiene-styrene copolymer?ABS?was blended with TPU under the assistance of dicumyl peroxide?DCP?and maleic anhydride?MAH?to improve the cell morphology and reduce shrinkage ratio of the resulting blends.These blends were then foamed to prepare TPU/ABS blends foam beads in an autoclave using supercritical CO₂as the blowing agent at different temperatures FTIR spectra,and rheological and foaming properties of the samples were evaluated.The melt viscosity,melt strength and elasticity of TPU/ABS were improved with the increase of the ABS content.These results were attributed to the grafting and heterogeneous nucleation points provided by the ABS.These enhanced properties were used to produce foams with better cell morphology and increased expansion ratio.Furthermore,the TPU/ABS blends foam beads showed lower shrinkage ratios with increasing ABS content.Thus,the addition of ABS is a facile method for improving the cell morphology and anti-shrinkage properties of ETPU.