Preparation And Structural Evolution Of PVDF Porous Membrane Based On High Critical Co-solvent Temperature Binary Mixed Diluent System

As a physical separation technology,membrane separation technology is favored by people because of its advantages of high efficiency and pollution-free.The choice of materials has an indispensable role in the membrane separation membrane technology.Polyvinylidene fluoride(PVDF)has become one of the main membrane material due to its good mechanical properties,high thermal stability and acid corrosion at room temperature.The preparation of PVDF microporous membrane process has a variety of methods and Thermal induced phase separation method(TIPS)is the most easily achieved membrane structure controllable purposes.In previous studies,most of the microporous membrane were prepared by liquid-liquid phase separation of TIPS,however,the temperature for membrane formation was high and not easy to manipulate.The solid-liquid phase separation of the membrane structure was spherical structure,and it had stored dense cortex and pure size distribution and other shortcomings.In this paper,high performance critical PVDF microporous membrane was prepared by TIPS method with binary mixed diluent With high critical solution temperature.The crystallization kinetics and thermodynamics during the plase separation process were discussed,which provided a theoretical basis for the control of membrane structure.The main research contents and conclusions are as follows:First of all,the effects of influencing factors such as the proportion of diluent mixture,the air gap and the temperature of the coagulation bath on the membrane structure and properties of the PVIDF microporous membrane prepared by TIPS method were studied.The thermodynamics and kinetics were analyzed in the solid-liquid separation system.The experimental results showed that,with the increase of the phase separation effect of the mixed diluent,pores were formed on the spherical particles in the support layer of the microporous membrane,so that the membrane structure permeability was improved.The influence of the delayed fraction caused by the water-soluble diluent PC,on the phase separation was studied.By scanning electron microscopy,the cortical structure of the microporous membrane evolved from a dense cortex to a through-going reticular pore or thin cortical structure was analyzed.The core liquid on the microporous membrane mass transfer heat transfer and the difference between the cooling ratc of the inner and outer cortex in the core solution resulting in a gradient pore phenomenon in the support layer structure of the microporous membrane was researched.The experimental results showed that the prepared of hollow fiber membrane had a small pore diameter and a through membrane structure.Microporous membrane carbon black ink retention rate was 99%,bovine serum albumin retention rate was 95%.Finally,the extraction method of water extraction-alcohol extraction-water extraction was adopted and it reduced the shrinkage rate of the hollow fiber membrane during the drying process.The effects of the extraction process and the stretching-heat setting process on the structure and properties of the microporous membrane were also investigated.