Continuous Injection Molding And Properties Of Polyurethane Modulus Gradient Materials

Polymer Gradient Materials(PGMs)refers to a polymer material with continuous component gradients and structural gradients in a specific direction.Its properties vary gradually with gradients and it is widely used in many fields such as instrumentation and aerospace.As polyurethane has excellent properties such as chemical structure adjustment and high elasticity,it becomes a preferred material for preparing gradient materials.At present,the preparation method of polyurethane gradient materials is mainly interpenetrating network and mechanical blending,and the modulus variation range is limited.It is of great significance to study the preparation technology of wide-range modulus controllable polyurethane gradient materials with high degree of automation.In this paper,the automatic injection reaction molding device is used to prepare polyurethane modulus grading material with a wide modulus range along the length by ring trimeric method and variable chain extension method.In addition,this thesis studies the synthesis of polyurethane materials and the mechanism of modulus gradient change in different preparation methods,and it also studies the effects of different chemical compositions and gradient structures on the mechanical and thermal properties of materials.The details are as follows:1.Preparing polyurethane modulus grading material by ring trimeric method.Using Poly propylene glycol(PPG)and aromatic diisocyanate(TDI)as the main raw materials,the injection rate of the two components is gradually changed by continuous injection molding of two components,and the ratio of isocyanate to polyol is gradually increased from equivalence.To a large excess,the excess TDI reacts in situ to form a cyclotrimeric isocyanurate,while the ratio of isocyanate groups to hydroxyl groups is always substantially the same,the proportion of hard segments of polyurethane materials is gradually increased,and the modulus is gradually increased.A material of continuously varying modulus is prepared from the same raw material.The results of FTIR and mechanical properties show that as the TDI content in the component increases,the content of the isocyanurate ring in the large-volume hard segment is increased,in addition,the crosslink density is increased,and the tensile strength and tensile strength of the modulus-graded material are increased.The modulus and hardness increase.The results of DSC and TGA show that the Tg of the material changes slightly when the temperature is around-45?,and the thermal stability of the material increases with the increase of TDI content.The results of DMTA show that as the TDI content increases,the temperature domain gradually broadens,besides,the mechanical properties such as elastic modulus change elastically,which gradually change in a wide temperature range.The elastic modulus gradually changes from 27 MPa to 607 MPa in a wide range,which is 22 times higher than before.This paper further analyzes the side reactions and effects of the isocyanurate ring formation process.2.Preparing polyurethane modulus grading material by variable chain extension method.In order to further expand the range of modulus variation,improve the material properties,and realize automatic molding,this paper studies the preparation of polyurethane modulus grading material by variable chain extension method.It uses a three-component system of isocyanate/polyol/chain extender to gradually change the injection speed of three components with a self-made three-component continuous injection molding device,which can control the relative proportions of the polyol(soft segment)component and the chain extender(hard segment)component,so the continuous gradual transformation of the modulus is achieved in one polymer sample.The results of FTIR and mechanical properties show that as the content of hard segment in the material component increases gradually,the degree of microphase separation increases,besides,the tensile strength and hardness of the material increase gradually.The results of DSC show that the Tg of the material increases from-58? to 47?.With the proportion of chain extender increasing,the content of hard segment increases gradually,and the glass transition temperature increases with the increase of modulus.The results of DMTA show that the Tg of the soft segments of the whole spline is quite different,which keeps the material elastic throughout the wide temperature range.In addition,the elastic modulus gradually changes from 8 MPa to 760 MPa,which is 22 times higher than before.