Preparation Of Graphene-modified Thermo-reversible Polyurethane And Its Multi-responsive Self-healing Behavior

Polyurethane material is a kind of polymer compound,and which is composed of flexible soft segment and rigid-hard segments.The flexible soft segment accounts for the majority and is composed of polyol or polyether.It is highly elastic at room temperature and randomly curled at room temperature.Meanwhile,it provides elasticity for the material.The rigid-hard segment is usually composed from the reaction between highly polar diisocyanate and chain extender,etc..Its conformation is not easy to change,and which can make polyurethane materials have higher hardness and wear resistance.It is inevitable that material is damaged during use,and which will affect the service life of materials.Therefore,scientists have introduced thermo-reversible Diels-Alder(DA)bonds into polyurethane materials to make them be self-repaired.In this dissertation,a self-repairing polyurethane material was synthesized by introducing thermo-reversible DA bond into polyurethane.The mechanical properties,thermal reversible properties and self-repairing behavior of self-repairing polyurethane were studied.At the same time,polyurethane materials with multi-response were synthesized by introducing graphene into polyurethane.The infrared and microwave-responsive performance was explored.The main research and conclusions are as follows:(1)Preparation of grapheme-modified polyurethane material: Firstly,polyurethane prepolymer(PPU)was synthesized by polypropylene glycol and diisocyanate.Then graphene/graphene oxide was introduced into the polyurethane prepolymer,and the polyurethane prepolymer was capped with amine in ice-water bath to obtain grapheme-modified polyurethane prepolymer with furan ring as the terminal group.Next,bismaleimide(BMI)was added in proportion according to the molar amount of furan ring to prepare polyurethane with multi-response self-repairing performance.Self-repairing polyurethane with DA bonds was successfully synthesized,and which was proved by di-n-butylamine titration and infrared characterization,and DSC test.(2)Mechanical and repair properties of graphene-modified polyurethane: The surface morphology and interface composition of graphene-modified polyurethane were observed by electron microscope.The tensile behavior of samples was quantitatively analyzed by universal testing machine.The optimal addition amount of graphene and mechanical properties of graphene-modified polyurethane were determined.Results showed that the mechanical properties are reduced to 70% of that of ordinary polyurethane when the content of graphene reaches 0.5 wt%.However,it has little effect on the mechanical properties of polyurethane when the content of graphene is low.Combined with the repair effect and properties of materials,the addition amount of graphene is finally determined to be 0.2 wt%.Next,the repair performance of grapheme-modified polyurethane was investigated by stereomicroscope and tensile test.The results showed that the scratches of the damaged samples were obviously reduced after heat treatment at 130℃for 10 min.Consequently,the macro-cracks disappeared completely after heat treatment at 60℃.The repair efficiency of the material was quantitatively analyzed by universal testing machine.Finally,the optimal heat treatment conditions was selected,and the determined parameters were 10 min at 130℃and.h at 60℃.As a result,the repair efficiency could reach 85.4%.(3)Multi-response behavior of graphene-modified polyurethane: The repair behavior of graphene-modified polyurethane under microwave emission device and infrared ray instrument was observed by digital camera.It was found that graphene-modified polyurethane could effectively absorb and convert the energy in microwave/infrared into the heat needed for DA bond repair.Compared to polyurethane materials without graphene,the repair efficiency was improved effectively and the repair time of polyurethane materials was shortened greatly based ib the infrared repair effect.(4)Research on multi-response self-healing performance of graphene oxide-modified polyurethane: Firstly,the graphene oxide-modified polyurethane was synthesized by introducing graphene oxide into polyurethane.The chemical structure and thermal properties were tested by Fourier infrared spectroscopy and DSC.Analysis showed that the introduction of graphene oxide did not destroy the structure of the DA cross-linked network.By contrasr,the rupture temperature of the DA bond was increased.The sample with cracks could be repaired by an infrared laser with a wavelength of 808 nm.The repair efficiency reached75.3%.However,because the graphene oxide layer was too thick,it caused defects in the material.As a result,the mechanical properties of the material were affected.So to the later explored was needed.