Study On The Mechanism And Equipment Of TPU Foaming Particles Prepared By Supercritical Carbon Dioxide

The new TPU particles has the advantages of low density,high resilience,high foaming rate,wear resistance,low temperature performance,which can be widely used in shoes,cushion gasket,solid tire,outdoor track,mattress and protective equipment etc.However,the foaming mechanism of TPU particles is not clear,and the preparation of TPU foam particles is in the exploratory stage.When supercritical carbon dioxide is used as foaming agent,In TPU,the diffusion of supercritical carbon dioxide,the nucleation,growth and the formation of the bubble,which are the study of how to improve the performance of TPU foam particles,improve the foaming process and equipment of the important foundation.Based on the above problems,this paper studies the mechanism and equipment of TPU foam particles produced by intermittent pressure relief heating method,and analyzes the influence of the process conditions on the properties of TPU foam particles.In this paper,four stages of the formation of polymer / gas homogeneous system,bubble nucleation,bubble growth and bubble formation in the TPU foaming process were analyzed.The dissolution and diffusion of supercritical carbon dioxide in TPU were studied.The nucleation mechanism of TPU foaming process was analyzed by means of homogeneous nucleation,heterogeneous nucleation and mixed nucleation,and the key factor affecting the nucleation rate of TPU was obtained.The growth process of bubble in TPU foaming process was analyzed in detail by cell model.In this paper,the importance of the late setting of TPU foam particles is described,and the two methods of rapid cooling and air pressure replacement are proposed.Intermittent pressure relief heating foaming equipment was built.which comprises a supercritical carbon dioxide permeation device,a high temperature water vapor foaming device and a late stage shaping device.What's more,The finite element analysis of the reactor and the sealing ring is designed to ensure the safety and sealing performance.In this paper,the structure and principle of the supercritical carbon dioxide dynamic cycle system,steam heating and foaming equipment and the equipment are introduced in detail.TPU foam particles were successfully prepared by intermittent pressure relief and temperature rising method,and the feasibility of high temperature steam foaming was proved.Based on the experiment and the foaming principle,the paper analyzes the technological conditions,such as osmotic pressure,osmotic temperature,penetration time and pressure relief rate,and effect of foaming temperature on density,foaming rate,shrinkage and apparent characteristics of TPU foam.The law between them can be found.At the same time,the method of setting up the TPU foam particles is studied,and the feasibility of the air pressure compensation method is proved.