Preparation And Properties Of Self-healing Waterborne Polyurethane

Waterborne polyurethane（WPU）is a kind of stable,safe,non-toxic,and harmless polymer material with excellent properties.It can not only avoid the release of volatile organic solvents in the synthesis process,and is an ideal material in line with the concept of green development.At present,most studies of water-based polyurethane products focus on the basic properties of the material,such as mechanical properties and water resistance,etc.,while WPU materials are prone to external stimulation in the use process,and their internal cracks are easy to form,and such damage will harm its performance and reduce the service life of the material.Therefore,the study of waterborne polyurethane with self-healing properties is of vital significance for increasing the service life and improving the utilization rate of materials.This paper is devoted to studying the preparation,performance changes,and other functional expansion of self-healing WPU,exploring how to make WPU have a good self-healing ability,improve the basic physical and chemical properties of WPU material and expand other functional applications.The key lies in introducing dynamic bonds into WPU and regulating the change of its content,as well as coordinating with other materials.The main research contents are as follows:Firstly,diamines 2,2’-diaminodiphenyl disulfide（AD）were synthesized into the molecular chain of waterborne polyurethane to prepare a self-healing waterborne polyurethane material.The properties of polyurethane were regulated by adjusting the content of AD and polyether diol（PTMG-1000）.The results show that the particle size distribution of the whole modified polyurethane emulsion is narrow and uniform,the polyurethane tensile strength increases from1.1 MPa to 5.6 MPa,the water contact Angle increases from 67.0°to 81.2°with the increase of AD content,and the initial decomposition temperature decreases from 267.33℃to 140℃.In terms of self-healing properties,the tensile strain repair efficiency of WPU-1 in the prepared samples reached 86%and 92%after heating at 70℃and 80℃for 24 h,respectively.Secondly,to solve the problem of poor mechanical performance of the previous system.2,6-diacetylpyridine dioxime was synthesized from 2,6-diacetylpyridine and hydroxylamine hydrochloride.FTIR and ¹H-NMR were used to characterize the synthesis of 2,6-diacetylpyridine dioxime.A series of modified waterborne polyurethane materials DWPU-x were synthesized by the reaction of 2,6-diacetylpyridine dixime and PTMG-1000 with isophorone diisocyanate（IPDI）and 2,2-dihydroxymethylpropionic acid（DMPA）.The particle size of all the DWPU-x emulsions is less than 100 nm.With the increase of the content of 2,6-diacetylpyridine dioxime and the decrease of the content of the soft chain segment,the tensile strength of PU films increases from 3.8 MPa of DWPU-0 to 17.7 MPa of DWPU-3.Meanwhile,based on the dynamic reaction of oxime-urethane bond and hydrogen bond,the healing efficiency of DWPU-2 at tensile strength and tensile strain is 80.2%and 96.7%respectively.Thirdly,to overcome the difficulty of high healing temperature in the previous system,DWPU material was further modified to explore the healing ability of water-based polyurethane in room temperature repair.Based on the formula of DWPU-2,Cu²⁺was added,and the Schiff base structure of 2,6-diacetylpyridine dioxime in DWPU-2 was complex.The self-healing water-based polyurethane material based on coordination bond,oxime-urethane and hydrogen bond was prepared.It is found that DWPU-Cu_0.25exhibits excellent mechanical properties,with a tensile strength of 11.9 MPa and elongation at a break of 1620%.In terms of self-healing properties,the healing efficiency of DWPU-C_0.25at room temperature was 95.8%in elongation at break and 89.1%in tensile strength,respectively.Through the introduction of copper ions,the antibacterial function of the modified material is extended.It was found that DWPU-Cu_xhad obvious antibacterial activity through the experiment of the bacteriostatic circle and shaking flask.Finally,on the basis of the above three systems,in order to obtain self-healing waterborne polyurethane with high healing ability,2-hydroxyethyl disulfide（HEDS）,a diol chain extender,was added to the WPU.On this basis,graphene oxide nanomaterials which can enhance the basic properties of the polymer were added.The test results show that with the increase of GO content,the decomposition temperature of T_5%of WPU-GO-x increases gradually,and the tensile strength of the modified composite film increases from 9.9 MPa of WPU-GO-0 to 19.6MPa of WPU-GO-0.5.The water absorption of WPU-GO-0.25 was less than 10%after soaking in deionized water for 8h at room temperature.In terms of self-healing,WPU-GO-0.25 showed the best healing performance,and the healing efficiency of tensile strain and tensile strength were 90.0%and 93.2%,respectively,after heating at 65℃for 8 h.Due to the special structure of GO,the application of water-based polyurethane materials in the field of corrosion resistance can be expanded.According to the AC impedance experiment,the Z value of WPU-GO-0.25 is an order of magnitude higher than that of WPU-GO-0,reaching 5.9×10⁵Ω.By combining self-healing waterborne polyurethane materials with other materials with special structure,the way to prepare self-healing multifunctional waterborne polyurethane materials is expanded.