The Diffusion Mechanism Research Of Supercritical CO₂ In The Preparation Of Super Light Polymer

Supercritical CO₂ fluid is widely used in the preparation of super light polymer materials（microporous materials） is because of its advantages of high mass transfer coefficient, diffusion ability, can effectively improve the diffusion ability of small molecules in polymer, reaction speed, etc., and obtain more smaller bubble hole. For now, however, most of the preparation of materials and process control were conducted by experience, the key steps in the process of material forming is not clear. Among them, the property of supercritical fluid diffusion in the polymer for scientific research, design, and industrial production are important basis. Based on the above problems, in this paper, the preparation of super light polymer by supercritical CO₂, and the diffusion mechanism of supercritical CO₂ in polymer have been carried on the experimental research.In this paper, the thermoplastic polyurethane elastomer（TPU） particles as the research object, using the single factor method, research the influence factors on the quality of the grain shape in the preparation process of super light TPU granular material, provide the basis for the preparation of the best quality ultra light TPU granular materials. This paper argues that the major factors affect the quality of super light TPU granular material are saturation pressure, foaming temperature and foaming. With the increase of saturation pressure, the density of material size appears the change of increase with the decrease of the first, the density of bubble hole in particals increases gradually, the average diameter of bubble hole decreases; With the increase of foaming temperature, the grain density showed a trend of rise after the first reduce, the average particle size increases gradually,but the particles are broken adhesion in 155℃; high temperature steam foaming effect is best in the four kinds of foam, the best foaming temperature 135 ℃.Used differential pressure method to design the experiment device, measured the diffusion rate and diffusion capacity of supercritical CO₂ fluid in the TPU material, by changing the saturation pressure and saturation temperature conditions. This paper found that supercritical CO₂ diffusion along the direction of the grain diameter in the TPU conforms to Fick diffusion law, and deduced the diffusion coefficient equation. Found that the diffusion coefficient increases with the increase of saturation pressure, but changes smaller at high temperature; with the increase of temperature, diffusion coefficient increases gradually, but the increase amplitude decreases.