Preparation And Properties Of Waterborne Polyurethane Pickering Emulsions

With the enhancement of people’s awareness of environmental protection and the promulgation of environmental laws and regulations,the research and development of environment-friendly and pollution-free water-based materials have been paid more and more attention.Waterborne polyurethane(WPU),as a typical environment-friendly material,has the characteristics of non-toxic and flame retardant,and has been widely used in automotive,wood,adhesives,coatings and other fields.Stable WPU emulsion is the premise of WPU application.In the preparation process of WPU emulsion,stable WPU emulsion can be obtained by external emulsification with a large number of emulsifiers and/or internal emulsification with a large number of hydrophilic groups introduced into the polyurethane molecular chain.The large amount of emulsifier used in the external emulsification method will result in poor water resistance and poor physical and mechanical properties of the final WPU product.The hydrophilic groups in the internal emulsification method can not only improve the storage stability of WPU emulsion,but also make the water resistance of WPU film deteriorate,which limits its application in the field of high-performance materials to a certain extent.In view of the above external emulsification or internal emulsification methods will affect the performance of WPU products to varying degrees,how to further overcome the impact of the use of a large number of emulsifiers or hydrophilic groups on the performance of downstream WPU emulsions is still a focus of attention and a very challenging research content in the field of WPU emulsion preparation.Graphene oxide(GO)has excellent chemical stability.Its extremely low film-forming thickness on the surface of the material can effectively prevent oxygen and water in the air from diffusing and permeating into the material.In addition,the inherent amphiphilicity of GO makes it suitable to be used as nano emulsifier instead of traditional small molecular surfactants,which has a wide range of applications in the preparation of Pickering emulsion.In order to improve the water resistance of WPU products,GO was used as nano-emulsifier to stabilize WPU emulsion in this paper,so as to prepare WPU emulsion with better performance.In order to investigate the effect of GO surface chemical structure on the stabilization of WPU emulsion,two kinds of GO were used to stabilize WPU emulsion respectively in this paper.The specific work is as follows:The first part of work: The classical Hummer method and the improved Hummer method were used to prepare GO and Janus GO,respectively.The GO and JGO were characterized by atomic force microscopy,microscopic Raman imaging and dynamic light scattering.The results show that the oxidation degree distribution of the prepared GO is relatively uniform.High degree of oxidation and surface charge;The degree of oxidation is different in different areas of JGO surface,and its relative degree of oxidation and surface charge are low.Based on the amphiphilic properties of GO nanosheets and JGO nanosheets,Pickering emulsion stabilized by GOs nanosheets and Pickering emulsion stabilized by JGOs nanosheets were prepared,respectively.Polarization results show that GOS nanosheets are parallel to the oil/water interface,and JGOs nanosheets form lash-like liquid crystal arrays with vertical orientation at the oil/water interface.Interestingly,compared with the Pickering emulsion stabilized by GOs nanosheets,the Pickering emulsion stabilized by JGOs nanosheets showed good stability.The second part of work: WPU Pickering emulsion stabilized by GO nanosheets and JGO nanosheets were prepared successfully.By adjusting the p H of emulsifying system and the amount of GOs and JGOs,the influence of emulsifying system on the stability of WPU emulsion was studied.The results showed that the Wpupickering emulsion stabilized by GO nanosheets could not be stored for a long time(less than 30days)under the medium alkaline condition,and eventually subsidence and stratification occurred.However,JGOs stable WPU Pickering emulsion can be stored for a long time(more than 30 days)at p H=8 and concentration of 0.7%,which effectively improves the stability of WPU emulsion.The third part of work: The film formation properties of Wpupickering emulsion stabilized by JGO nanosheets were investigated,and the film properties were characterized.The results show that the uniform dispersion of JGOs nanosheets in the WPU matrix can effectively promote the degree of microphase separation and promote the crystallization of soft segment,and the uniform dispersion of JGOs can effectively improve the water resistance and heat resistance of the film.Interestingly,the introduction of JGOs nanosheets strengthened and toughened the WPU film.When the amount of JGOs is 0.7%,the tensile strength of the composite film is increased to 11.2MPa,and the elongation at break is 710%.In conclusion,the research work in this paper solves the problems of instability and poor water resistance of WPU emulsion prepared by traditional external or internal emulsification methods,and solves the problems of uniform dispersion of JGOs nanosheets in the matrix,which lays a foundation for the preparation of functional WPU composites.