Waterborne Polyurethane (WPU) is a polyurethane system using water as a solvent or dispersion medium. In recent years, with the increasingly strict environmental regulations and the improvement of people's environmental awareness, waterborne polyurethane, as an environmentally friendly material, has received extensive attention and research. First, the characteristics of waterborne polyurethane Environmental protection: Water-based polyurethane uses water as a solvent and does not contain organic solvents, thus reducing the emission of volatile organic compounds (VOC) and meeting environmental protection requirements. Weather resistance: Waterborne polyurethane has good weather resistance and can maintain stable performance under different climatic conditions. Flexibility: Waterborne polyurethane coating has good flexibility, can resist external stress, reduce cracking and peeling phenomenon. Wear resistance: Waterborne polyurethane coatings have high wear resistance and are suitable for applications where frequent friction and contact are required. Chemical resistance: Waterborne polyurethane has good resistance to a variety of chemicals, such as acids, alkalis, oils and so on. Second, the synthesis method of waterborne polyurethane The synthesis of waterborne polyurethane mainly includes the steps of prepolymerization, chain extension, neutralization and emulsification. Firstly, the prepolymer is formed by prepolymerization of polyol, isocyanate and other raw materials. Then, the molecular weight of polyurethane was increased by chain extension reaction with chain extender. Then, the polyurethane was neutralized by neutralizing agent to obtain hydrophilicity. Finally, the polyurethane is dispersed in water by emulsification to form a stable water-based polyurethane emulsion. Third, the application field of water-based polyurethane Paints and coatings: Waterborne polyurethane, as an environmentally friendly coating, is widely used in construction, furniture, automobiles and other fields. Its excellent weather resistance, flexibility and wear resistance make it an ideal coating material. Adhesive: Waterborne polyurethane adhesive has excellent bonding properties and water resistance, and is widely used in bonding wood, leather, fabric and other materials. Textile additives: Waterborne polyurethane can be used as textile additives to improve the softness, wrinkle resistance and wear resistance of textiles. Medical field: Because of its good biocompatibility and hydrolysis resistance, waterborne polyurethane is also widely used in the medical field, such as the preparation of artificial skin and drug carriers. Other fields: Water based polyurethane can also be used in ink, leather finishing agent, fiber treatment agent and other fields.

Water based polyurethane emulsion has soft properties, so that it has good adhesion when attached to the surface of the object; At the same time, it can maintain a certain strength and does not crack. It is especially suitable for articles in high temperature, humid and chemically corrosive environment. This substance also has superior wear resistance and film smoothness, so it can form a uniform and tight film on the surface of metal, plastic, etc., and further enhance the surface adhesion of treated PE, OPP film, TPU, PU leather and other materials to ensure long-term protection and maintenance of objects

The viscosity of waterborne polyurethane emulsion has different distribution range, and the viscosity of waterborne polyurethane emulsion has different requirements when applied in different fields. In addition to adjusting the viscosity by adding thickening agents, it can also affect the viscosity of waterborne polyurethane emulsion from the molecular structure, including the content of hydrophilic groups, the solid content of waterborne polyurethane emulsion, and the degree of neutralization. The content of hydrophilic groups on the structure of waterborne polyurethane affects the size of emulsion particles and its viscosity. In anionic waterborne polyurethane, when the carboxylic acid hydrophilic groups increase, the size of the colloidal particles decreases, the distribution Narrows, and the viscosity of the emulsion increases, because the force between the colloidal particles and water increases. The viscosity of polyurethane emulsion is related to the hydrophilicity of hydrophilic monomer, particle size and size distribution, and particle density in polyurethane emulsion. The influence of solid content on the viscosity and particle size of waterborne polyurethane is also obvious. When the solid content of waterborne polyurethane is low, the content of hydrophilic monomer is fixed, and when the solid content increases, the number of particles in the emulsion also increases, and the force between the latex particles and water increases, so the viscosity of the emulsion increases. When the solid content of waterborne polyurethane emulsion is too large, the prepolymer is difficult to disperse in water, the size of latex particles becomes larger, the distribution becomes wider, and the viscosity of emulsion becomes smaller. The degree of neutralization also affects the viscosity of aqueous polyurethane emulsion. During the preparation of waterborne polyurethane, due to the double action of hydrophilic group and neutralizer, the double electric layer effect affects the viscosity change. As the neutralization increases, the viscosity may increase more, so the neutralization should be strictly controlled when preparing waterborne polyurethanes.

Due to the hydrophobic properties of waterborne polyurethane resin, it is difficult to dissolve in water or disperse uniformly, and the high reactivity of isocyanate groups to water, the direct synthesis of waterborne polyurethane faces many challenges. Therefore, to achieve the preparation of waterborne polyurethane, the primary strategy is to cleverly integrate hydrophilic functional groups (such as carboxyl, sulfonic acid, etc.) into the polymer chain structure of waterborne polyurethane, and then use the force of these hydrophilic groups to promote the successful dispersion of polyurethane in the water phase, so as to prepare water-dispersed polyurethane. In order to further optimize the comprehensive properties of waterborne polyurethane coatings, the researchers explored the technical path of introducing sealers. Specifically, the sealer is able to selectively react with part of the isocyanate group (i.e. -NCO) in the prepolymer to form a stable aminoester bond. In this process, the ammonia ester bond is like a "sleeping" isocyanate reservoir, which can "wake up" and split under appropriate heating conditions, re-release the isocyanate group, and then efficiently combine with the hydroxyl group on the fabric surface to form a strong polyurethane crosslinking network. This significantly enhances the adhesion strength and bonding firmness of the waterborne polyurethane coating and the fabric substrate. Sinograce Chemical is specialized in the production of water based polyurethane resin used on the surface of textile supplies, welcome to consult.