The Controllable Preparation And Application Of MDI-Based Waterborne Polyurethane Nanodispersion By High-Gravity-Assisted Emulsification

Owing to strict environmental and legislative pressures,waterborne polyurethanes(WPU),as an effective substitute for solvent-based polyurethane,has become a research hotspot in the fields of scientific research and industrial applications.The synthesized of WPU using diphenylmethane diisocyanate(MDI)has high reactivity and it's difficult to control the polymerization process due to the specific structural,which severely reduces the widespread application of MDI-based waterborne polyurethane.The introduction of hydrophilic groups gives the polyurethane a good hydrophilicity,but also limits the solid content of WPU.How to achieve the preparation of high solid content WPU by adjust the synthetic formula and strengthening the emulsification process has become a key to improving the quality and efficiency of WPU products.High gravity technology relies on the efficient mass transfer and the enhancement of micro-mixing by rotating packed bed(RPB),has become a new generation of process intensification technology and be widely used in many unit operations like distillation,absorption,gas separation and others.How to use the high gravity technology to realize the intensification of emulsification operation has also become a new research direction.In this dissertation,the emulsification operation of MDI-based waterborne polyurethane is realized by using RPB reactor.The influence of formula is explored.The controllable preparation of WPU is realized by using high-gravity-assisted emulsification technology.The main contents of this paper are as follows:(1)MDI-based waterborne polyurethane emulsion was synthesized by RPB reactor.The effects of synthetic processes such as the introduction method of hydrophilic groups,the degree of neutralization and the acetone volume were discussed.The relationship between the R value(NCO-:OH-)and the content of hydrophilic groups to the particle size,particle size distribution(PSD),water absorption,and difficulty or facility of emulsification was studied.The results show that the emulsion performance is optimal when the R value between 1.25 to 1.4 and the hydrophilic group content is 3-5%.(2)In the research on the controllable preparation of WPU and process amplification with high-gravity-assisted emulsification.The influence of pre-polymer flow rate,circulating flow rate,high-gravity level,and emulsification time to the particle size and distribution of the emulsion been investigated for strengthening of the emulsification process and achieving controllable preparation.The balance between coalescence and breakup of emulsion particles influence the particle size and PSD of the emulsion under the RPB environment.Increasing the rotation speed of rotor or extending the emulsification time can widen the particle size distribution,which enhanced the space utilization and increased the solids content.Besides,in the high-gravity-assisted emulsification process,the high-speed rotating packing provide a larger oil-water interface for the emulsification process,and the interface updated more frequently.It's easy for the hydrophilic groups to move to the surface of the particles because of the larger phase interface.These hydrophilic groups form effective hydrophilicity,thus reducing the dosage of hydrophilic groups.Based on that,a low viscosity WPU emulsion with a solid content of 53%could be prepared by choosing R for 1.25,the hydrophilic group mass fraction for 4.8%,high-gravity level to 135 and the emulsification time to 25 min.(3)The directional freezing method were used for the emulsion synthesized by RPB reactors to obtain a porous polyurethane insulation material with an anisotropy structure.From analyzing the material's thermal insulation performance and the material's micro-pore structure and pore density,the effects about how the emulsification method,solid content,freezing rate to influence the thermal insulation performance and microstructure were discussed.The experimental results prove the superiority of high-gravity-assisted emulsification and provide the new ideas for the green production of anisotropic WPU foam.