Preparation And Properties Of Waterborne Polyurethane Composites For Waterproofing Coatings

With the ever-growing pursuit of a better life and the relevant criteria constraints,the development of traditional solvent-based polyurethane（S-PU）is restricted,while the environmental friendly waterborne polyurethane（WPU）with water as the dispersion medium has been the research focus and received much attention in recent years.The excellent wear resistance,mechanical properties of WPU give it great potential for application in coatings,adhesives,medicine,textiles and other fields.WPU possess self-emulsifying performance due to the introduction of hydrophilic group in the synthesis process and the crosslinking degree of WPU is lower than typical polyurethane for the lack of organic solvents in the preparation process,resulting in a decrease in material performance.As a result,proper chemical modification of WPU is required.Acrylic resin（PA）is a commonly used polymer that has excellent hardness,photostability,water resistance,aging resistance,and low cost.The waterborne polyurethane acrylic acid（WPUA）composite made from PA and WPU retains PA’s benefits while adding WPU’s high flexibility and stickness.The advantages of nano zirconia（ZrO₂NPs）include a high refractive index,high hardness and low thermal conductivity.The mechanical properties and thermal stability of the material can be significantly improved when it is combined with polymer.In this research,WPU prepolymer was synthesized by means of the combination of prepolymer method and acetone method,and the emulsification process of WPU was carried out using the high gravity technology.WPU emulsion with better performance were explored,and then the preparation of PA,ZrO₂NPs modified WPU composite emulsion was carried out by this processThe main work of this paper are as follows:（1）WPU emulsion was synthesized using a high gravity emulsification method,and the formula of WPU raw materials was explored,with the goal of determining the impacts of R value,DMPA content and hard segment proportion on the mechanical properties and water absorption of WPU.The best emulsion performance was achieved when R=1.7,DMPA=4 wt%and hard segment ratio was 40%,according to the findings.（2）The high gravity emulsification process was optimized by adjusting the emulsification temperature,emulsification time and water phase feeding speed.The results showed that when the emulsification speed was 2000 rpm,the emulsification time was 10min,and waterborne feeding speed was 160m L/min,the emulsion performance was the best,with tensile strength of12.08 MPa,elongation at break of 580.12%,and water absorption of 7.1%.（3）An emulsion copolymerization process was used to make a WPUA composite emulsion,and the effects of the end sealing agent,the amount of PA and the monomer proportion on the characteristics of the composite were explored.When the end sealer content was 30%,the dosage of monomer was50%and hard-soft proportion was70:30,the water absorption of WPUA film was less than 5%.（4）ZrO₂NPs were prepared by hydrothermal method and modified by acetic acid（AA）,methacrylic acid（MA）and citric acid（CA）to obtain three aqueous phase dispersions of ZrO₂.After physical mixing of the dispersions with WPU,it was found that AA and MA modified dispersions quickly demulsified WPU,breaking the stability of the system.Only the CA modified ZrO₂NPs and WPU had good miscibility,and the stability mechanism of WPU was studied.（5）WPU preparation process was obtained by exploring in Chapter 1.CA modified ZrO₂NPs dispersion was used to replace deionized water for WPU emulsification.WPU composite emulsions with different ZrO₂NPs doping amount were prepared by emulsification mixing method.The characterization results showed that the addition of ZrO₂NPs improved the thermal stability and mechanical properties of WPU,enhanced the waterproof performance of WPU,and broaden the application of WPU in the optical field.The experimental results confirmed the feasibility of the high gravity emulsion technology,and also provided a new research idea for the preparation of WPU composite emulsion modified by nanoparticles.