Studies On Preparation And Performance Of Self-healing Polyurethane Initiated By Light Or Heat

Self-healing polymer materials can repair physical damage under certain stimulation,thereby prolonging the life,using safety and reducing production costs of the material.Therefore,self-healing polymer materials have broad application prospects in the fields of protective coatings,flexible electronic skins,and medical materials.Because polyurethane has structural controllability,it is widely used in the preparation of self-healing materials.However,the polymer materials with excellent mechanical properties currently prepared have a higher repair temperature,while the polymer materials with a lower repair temperature have poor mechanical properties.Therefore,the design and preparation of polyurethane materials that have excellent mechanical properties and can be quickly repaired under mild conditions have certain practical application value.In this paper,through the structural design of the polyurethane,dynamic disulfide bonds are introduced into the polyurethane to prepare a thermoplastic polyurethane material with high mechanical properties and rapidly repair under mild conditions.In addition,the polyurethane/polypyrrole(PPy)nanocomposites are prepared by introducing PPy into polyurethane by the solution blending method.Because PPy has excellent photo-thermal effect and biocompatibility,the introduction of PPy can not only improve the mechanical properties and thermal stability of polyurethane,but also endow polyurethane with rapid repair performance under near-infrared light.The main research contents and conclusions are as follows:1.Near body temperature induced self-healing thermoplastic polyurethane.Since it is difficult to improve the mechanical properties and repair performance of polyurethane prepared with a single isocyanate,we use mixed isocyanates to prepare thermoplastic polyurethane.Studies have found that the mechanical properties of polyurethane prepared with mixed isocyanates are better than those prepared with single isocyanate.Among them,the tensile strength,elongation at break and toughness of I-4-P-HM can reach 11.35 MPa,946%and 64.1 MJ/m3,respectively,and repairing at 40? for 2 h can quickly repair its surface scratches and restore to its original tensile strength.Through the analysis of the urea bond that connected with the aromatic disulfide bond,it is found that the lower the content of the hydrogen bond formed by the urea bond,the more favorable the dynamic exchange of the disulfide bond and the promotion of repair.In addition,the segment movement ability of the polymer also directly affects the repair performance of the polymer.Rheological tests show that the stronger the segment movement ability of the polymer,the more conducive to the repair of the polymer.Then compared a series of synthetic thermoplastic polyurethanes and found that I-4-P-HM has faster polymer segment movement ability and more free aromatic disulfide bonds,which makes it have excellent mechanical properties and excellent repair performance.2.Hard,Tough and Fast Self-healing Thermoplastic PolyurethaneThe currently prepared thermoplastic polyurethanes that can be repaired under mild conditions generally have a low Young's modulus.Polycaprolactone(PCL)not only has good crystallization ability,but also has good flexibility and process-ability.Therefore,PCL was used as soft segment and prepared thermoplastic polyurethane which contained mixed isocyanate.The prepared thermoplastic polyurethane(PCL-HM)not only has high Young's modulus,tensile strength and elongation at break,can reach 75.87 MPa,11.83 MPa and 841%,respectively.Moreover,it has excellent repair performance under mild conditions,and can be restored to 92%of its original tensile strength in 1 h at 50?.Then,by analyzing the content of urea bonds that form hydrogen bonds and the mobility of polymer chains,it is found that the more free aromatic disulfide bonds and the stronger the mobility of the polymer chain,the more conducive to the repair of polyurethane.In addition,due to the strong crystalline properties of PCL,the PCL-HM not only has a high Young's modulus and is hard and tough,but also has excellent repair properties under mild conditions.3.NIR induced self-healing polyurethane/polypyrrole nanocompositeCompared with heat-induced self-healing materials,light-induced self-healing materials have spatial and remote controllability.Therefore,we introduced PPy with excellent photo-thermal properties into polyurethane by the solution blending method to prepare polyurethane/polypyrrole nanocomposites.Studies have found that the introduction of PPy can significantly improve the mechanical properties and thermal stability of polyurethane.When the amount of PPy added is 0.25 wt%,the tensile strength and elongation at break of TPU/PPy-0.25 can reach 13.50 MPa and 1650%,respectively.In addition,the introduction of PPy also endows the composite material with excellent photo-thermal properties,allowing it to quickly heat up under near-infrared light.Among them,TPU/PPy-0.25 can recover to 80%of the original tensile strength after 30 s under near-infrared light.The introduction of PPy can not only improve the mechanical properties of polyurethane,but also accelerate the repair performance of composite materials under near-infrared light.This not only solves the contradiction that self-healing materials cannot improve repair efficiency and mechanical properties at the same time,but also broadens the application of PPy in the field of polyurethane.4.Low-intensity NIR induced self-healing polyurethane/polypyrrole nanocompositeBecause disulfide bonds have excellent dynamic exchange properties,and PPy have excellent photo-thermal properties and light stability.Therefore,we introduced PPy into the thermoplastic polyurethane containing dynamic disulfide bonds by the solution blending method to prepare PCL-HM/PPy nanocomposites,whose tensile strength can reach 26.23 MPa.Due to the presence of disulfide bonds,the prepared composite material has excellent repair properties,and its tensile strength can be restored to 20.27 MPa after repairing at 50? for 4 h.In addition,the introduction of PPy also endows the composite material excellent photo-thermal properties.Its tensile strength can reach 17.05 MPa when exposed to near infrared light of 0.64 W/cm2 for 10 min,which is far better than pure polyurethane.This further proves that PPy have broad application prospects in the field of preparing composite materials.