Preparation And Properties Of High Strength Self-healing Polyurethane

Polyurethane(PU)is widely used in various fields such as national economy and military industry due to its excellent performance.With the broadening of application fields,a series of problems caused by the excessive use of polyurethane have gradually emerging,such as the consumption of fossil resources and the pollution of natural environment.Self-healing is an effective method to solve the problem of micro cracks inside polyurethane.At present,self-healing PU can not only realize the healing of surface and internal damages spontaneously through the flow of molecular chain and the reversible effects of chemical bonds,but also effectively prolongs the service life of polymer.However,the research of self-healing polyurethane is still in its infancy,and it needs to be developed and optimized.Therefore,based on the structural designability of polyurethane and the structural characteristics of oxime-carbamate bond,self-healing polyurethane using different diisocyanates was prepared in this work.Then,shape memory assisted self-healing polyurethane was prepared by the coordination of metal ions with dimethylglyoxime;Finally,the self-healing polyurethane composites with Joule thermal effect were prepared by modifying polyurethane with multi-wall carbon nanotubes(MWCNTs).A series of self-healing properties of the above self-healing polyurethane were studied.The main work is as follows:1.Preparation and properties of self-healing polyurethane based on oxime-carbamate bondFor thermoplastic polyurethane elastomers,the crystallization of hard segments and the degree of microphase separation determine the strength and self-healing ability.In this chapter,the self-healing polyurethane with oxime-carbamate bond was prepared by reaction of different diisocyanate with PTMEG,DMG and TMP.The chemical structure and mechanical properties of polyurethane before and after healing were studied by FT-IR,AFM,TGA,DMA and electronic universal testing machine.The samples without oxime-urethane bond can not self-heal at 65?.In the samples containing oxime-carbamate bond,IPDI-DMG prepared by isophorone diisocyanate(IPDI)possessed medium mechanical properties,and the tensile strength reached 17MPa,and the mechanical properties could be fully recovered within 2 hours at 65?and the comprehensive properties were better than those prepared by other isocyanate.The healing efficiency of self-healing polyurethane could be improved by increasing temperature or prolonging time.DMA proved that the asymmetric structure of IPDI could inhibit the crystallization of the system,reduce the separation of microphase,promote the movement of molecular chain,and realize the fast dynamic exchange of oxime-carbamate bond.2.Preparation and properties of shape-memory assisting self-healing polyurethaneIn view of the problem that the mechanical strength of self-healing polyurethane prepared based on PTMEG was generally poor and the crack could not be closed after damaging,we prepared a shape memory assisted self-healing polyurethane based on coordination bond.Firstly,polyurethane containing oxime-urethane bond was prepared by the reaction of IPDI,PCDL and DMG.;Then Cu²⁺ions were introduced to form coordination bond with dimethylglyoxime,which gave the material shape-memory properties and high mechanical properties.The properties of self-healing polyurethane with different coordination bond content were tested by FT-IR,TGA,XRD and electronic universal testing machine.It was found that the introduction of coordination bond could improve the mechanical properties,healing efficiency and shape recovery rate of the material.When the content of coordination bond was 100%,the tensile strength reached up to 35.98 MPa,which was 2.8 times of that of the sample without coordination bond;Under the synergistic effect of oxime-urethane bond,coordination bond and hydrogen bond,the healing efficiency of93%could be achieved at medium temperature for 60 min;The shape recovery rate was as high as 93%,which could realize active crack closure after material damage.3.Preparation and properties of self-healing polyurethane composites possessing Joule heat effectIn order to further improve the mechanical properties of polyurethane based on oxime-urethane bond and explore the self-healing effect under different initiation conditions,we synthesized polyurethane matrix based on oxime-urethane bond by IPDI,PTMEG,DMG and TMP,and then prepared MWCNTs/polyurethane composite by physical blending.The effects of MWCNTs content on the morphology and self-healing properties of MWCNTs/polyurethane self-healing composites were investigated by scanning microscope(SEM),conductivity test,TGA,DMA,mechanical test and self-healing test.When?(MWCNTs)=7%,the composite showed the best mechanical properties,and its tensile strength can reach 35.01 MPa,illustrating MWCNTs could improve the thermal stability of the composite.When?(MWCNTs)=3%,the self-healing effect of composite material caused by Joule heat effect is the best.When the voltage was 20 V,the healing efficiency of 95%can be achieved in 6 minutes.The research results in this paper will provide useful explorations for the improvement of self-healing polyurethane material synthesis scheme,the improvement of mechanical strength and the expansion of healing conditions,as well as the application in the national defense industry,national economy and other scenarios.