| Thermoplastic polyurethane(TPU),has been widely used in shoes,aerospace,automobile,sports and many other industries because of its excellent properties such as high elasticity and wear resistance.The TPU foaming material can realize the light weight of the material with keeping the original performance,and the new function of the material can be endowed,so the TPU foam material has become a hot spot in recent years.However,because the molecular chain of TPU is linear,the crystallinity and the stiffness are low,it is difficult to obtain high foam products,and shrink seriously after foam.In this paper,the effect of the hard segment content of TPU on the foam property is studied.The properties of the TPU are further improved by physical blending,chemical chain extension,in-situ fiber-forming,and so on.And the dissolution,diffusion and foam characteristics of the physical foaming agent in the TPU are also studied.A method for the selection and evaluation of a foam physical blowing agent suitable for TPU is established.1.The effects of hard segment content on thermal properties,rheological properties and thermomechanical properties of TPU were studied by differential scanning Calorimeter,dynamic thermomechanical properties and dynamic rheometer,and combined with batch foaming experiment.The effects of hard segment content on the solubility and diffusion of CO2 in TPU,as well as the foam ratio and bubble structure of TPU were studied.the results showed that the higher the content of hard segment in TPU,the higher the viscosity and elasticity.However,it is not conducive to the dissolution and diffusion of foaming agent and the increase of volume expansion ratio.The foam structure of TPU foam material with high hard segment content is better,and the maximum shrinkage is only 27.3%.2.By gravimetric analysis,the solubility and diffusion properties of carbon dioxide,isobutene,isopentane and two new environment friendly fluorine blowing agents in TPU and the relationship between temperature and pressure were studied.The results show that the molecular weight and molecular structure of foam agent directly affect the solubility,and the foam performance is affected by saturated vapor pressure and boiling point.The higher the saturated vapor pressure is,the better the foam performance is,the lower the boiling point foam performance is,and the shrinkage can be less than 40%.3.The influence of microfiber introduction on the viscoelasticity and thermal mechanical properties of TPU melt was studied by one-step extrusion in-situ fiber-forming with twin-screw extrusion.The effect of microfiber introduction on the cell structure and shrinkage rate of TPU was studied in combination with intermittent foaming experiment and SEM.The results show that,after the micro-fiber network is formed in the TPU matrix,the viscoelasticity of the melt is obviously improved,the diameter of the bubble of the foam material is reduced,and the cell density is increased by two orders of magnitude.4.The rheological properties and thermal properties of the modified TPU were characterized by dynamic rheological and DSC analysis,and the effect of the chain extension modification on the foam properties of the TPU was studied by using the multi-functional chain extender.And the degree of branching of the TPU molecules is obviously increased after the melting and chain extension,the viscoelasticity is improved,the foaming property is obviously improved,and the volume expansion rate can reach 11.In order to further decrease the shrinkage of the TPU foam material,the crystallization behavior of the blending system was controlled by blending PA12.The results showed that after the addition of PA12,the change of the foaming rate was not large,the shrinkage rate was not more than 20%,the TPU and the crystalline polymer after the chain extension were blended,and the shrinkage rate was obviously reduced.The cells are more stable. |
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