Study On Modification And Foaming Performance Of Thermoplastic Polyurethane

Thermoplastic polyurethane(TPU)is a high-performance thermoplastic elastomer with both high elasticity of rubber and excellent processability of plastic.The TPU foam materials produced by the foaming process have good shock absorption,wear resistance and other properties,and has been widely used in many fields,becoming a research hotspot.However,due to many problems such as high cost,poor foamability of raw materials,and difficult adjustment of the foaming process,the application of domestic TPU foam materials has been limited.In this paper,the plasticizers are introduced to enhance the crystallization performance of TPU,and the rheological properties of TPU are improved by chain extension modification.On this basis,the foaming process is optimized to study the effect of temperature on the foaming and shrinkage properties of TPU.1.Small molecular polar plasticizers were added into TPU to regulate intermolecular hydrogen bonding and improve the crystallization rate and crystallinity of TPU.The intermolecular hydrogen bonding,crystallization and the influence of rheological properties were studied to reflect the effect of glycerol monostearate(GMS),hyperbranched polyamide HPN202,and stearamide on TPU by fourier infrared spectroscopy,differential scanning calorimeter,and rotary rheometer;the effect of plasticizer on the foaming properties was studied through intermittent foaming experiments.The results show that,the addition of three plasticizers was conducive to the formation of TPU hydrogen bonds,increases the crystallization rate of TPU,increases the crystallization temperature of TPU,increases the enthalpy of crystallization,and the improvement effect was HPN202>stearamide>GMS.Appropriate improvement of crystallization was beneficial to increase the expansion ratio of TPU,increases the cell density and reduces the cell size,but excessive addition will cause adverse effects.The suitable content was GMS-0.5%-1%,HPN202-0.25%,stearamide-1%-1.25%2.Isocyanate was used to modify the chain extension of TPU to improve its melt viscoelasticity.The effects of MDI on the rheological properties,thermal properties and foaming properties of TPU were studied by rotating rheometer,DSC analysis and intermittent foaming experiments.The results show that MDI can react with TPU to increase the molecular chain length and make TPU zero shear viscosity increased significantly,after adding 15%MDI,the zero-cut viscosity reached 104 Pa·s,which was an order of magnitude higher than that of pure material,and the relaxation time increased.The relaxation time of 20%MDI was 4.11s,which was about 9 times that of pure material.The molecular weight distribution becomes wider,which enhances the viscoelastic performance,and the effect is more obvious as the content increases.MDI significantly increased the expansion ratio of the sample,and the improvement effect of the 15%content was the most obvious.The expansion ratio reached 22.2 times at 155℃,which did not improve the shrinkage rate much.3.Heat treatment method was designed to study the crystal structure,foaming performance and shrinkage of TPU.The results show that:in the process of melt foaming,appropriately lowering the melting temperature to enhance the self-nucleation of TPU can improve the crystallinity of TPU,and the initial crystallites as heterogeneous nucleating agents can help cell nucleation and increase the expansion ratio;Increasing the molding temperature helps to increase the crystallization rate and crystallinity of the TPU,which can reduce the cell diameter,reduce cell wall cracking and cell merging,and can effectively improve the shrinkage of the foamed TPU.