Preparation Of Self-healing Polyurethane And Its Application In Flexible Strain Sensor

Self-healing polyurethanes have been widely studied for their ability to self-heal damage,but it is a great challenge to prepare a self-healing polyurethane with high mechanical properties and high self-healing efficiency.In this paper,two self-healing polyurethanes were designed,which use the non-covalent bond of quadruple hydrogen bonds to provide physical cross-linking point between molecular chains to improve mechanical properties,and then use disulfide bonds to complete self-repair at lower temperature.And it was applied to the flexible strain sensor to give it the ability of selfhealing,the specific contents are as follows:(1)Preparation of self-healing polyurethane based on hydrogen bond.Firstly,5-(2-hydroxyethyl)-6-methyl-2-aminouracil(UPY)was synthesized,and then a series of self-healing polyurethanes with different UPY content were prepared using polytetrahydrofuran(PTMEG-2000)and 4,4'-methylenebis(cyclohexyl isocyanate)(HMDI)as raw materials,UPY and 1,6-hexanediol(HDO)as chain extenders.DSC test showed that the glass transition temperature of self-healing polyurethane increased with the introduction of UPY;TG test showed that self-healing polyurethane had three degradation stages,and the addition of UPY reduced the thermal stability of self-healing polyurethane;tensile tests showed that the introduction of UPY significantly improved the mechanical properties of self-healing polyurethane,and the maximum tensile strength was 25.40 MPa.The self-healing polyurethane can be repaired at 80 ? for 24 hours,and the self-healing efficiency can be up to 100%.(2)Preparation of self-healing polyurethane based on disulfide bond and hydrogen bond.A series of self-healing polyurethanes based on disulfide bond and hydrogen bond were prepared using polytetrahydrofuran(PTMEG-2000)and isophorone diisocyanate(IPDI)as raw materials,UPY and 2-hydroxyethyl disulfide(HEDS)as chain extenders.Disulfide bond was used to realize self-repair at lower temperature,and UPY was used to improve the mechanical properties of self-healing polyurethane.DSC experiments showed that the glass transition temperature of self-healing polyurethane was lower than room temperature,providing favorable conditions for self-healing polyurethanes at 30°C.The tensile test showed that when the molar ratio of UPY to HEDS is 1:1(PUS5),the mechanical properties and self-repair efficiency reach a good balance,the tensile strength is 12.28 MPa and the self-repair efficiency is 63.11% at 80 ? for 24 hours,the self-repair efficiency is 94.79%.(3)Preparation of self-healing flexible strain sensor.The flexible strain sensor was prepared by spraying carbon nanotubes on the surface of PU-S5 as the substrate.SEM proved that the carbon nanotubes were uniformly dispersed on the surface of PU;the flexible strain sensor had good electrical conductivity and could respond to different finger movements with good stability and sensitivity;self-healing experiments proved that the flexible strain sensor could still conduct electricity and respond to the finger movements after self-healing.The selfhealing experiments proved that the flexible strain gauge can still conduct and respond to finger movements after self-healing,and can be repaired several times.