Study On Preparation Of Hydrophilic PP/PPOH Microporous Membrane By Melt Stretching

Microporous membranes made of polypropylene(PP)are considered to be excellent materials for the preparation of microporous membranes due to their excellent mechanical properties and stable chemical properties.Although polypropylene is very popular as a membrane material,its hydrophobicity leads to poor anti-fouling in the application process,which greatly reduces the separation efficiency and service life of the membrane.Therefore,it is necessary to increase the hydrophilicity of the membrane to improve the membrane fouling.In this paper,hydroxylated polypropylene(PPOH)was used for hydrophilic modification of PP.Firstly,PPOH random copolymer was synthesized by high pressure copolymerization,and then melt blended with PP.The prefabricated membrane with a certain degree of orientation was prepared by tape casting of the blend.after thermal annealing,the microporous membrane was prepared by a series of cold stretching,hot stretching and heat setting processes.The research contents are as follows:1.Preparation and properties of PP/PPOH blends.PP/PPOH blends with different PPOH content were prepared by melt blending.The thermal properties,crystallization,hydrophilicity and viscosity of PP/PPOH blends were studied by thermogravimetric analysis,differential scanning calorimetry(DSC),contact angle meter,advanced rotational rheometer and Fourier transform infrared spectrometer(FTIR).The results showed that the hydrophilicity of PP/PPOH blends increased significantly after PP was blended with PPOH,and the water contact angle of PP/PPOH blends was 79.6 °when the blending ratio of PPOH was 20 wt%.The thermal stability of PP/PPOH blends increased with the increase of PPOH content,while the viscosity and crystallinity decreased with the increase of PPOH content.2.Preparation and properties of PP/PPOH prefabricated membrane.Firstly,the prefabricated PP and PP/PPOH films were prepared by tape casting,and then the prefabricated films were annealed to improve the crystal structure.The effects of different outlet mold temperature,drawing ratio and annealing temperature on the crystallinity and orientation of the prefabricated films were measured by DSC and infrared dichroism methods,and the mechanical properties of the prefabricated films at different annealing temperatures were tested.The results showed that the prepared PP/PPOH film prepared by the tape casting process with the outlet mold temperature of210 °C and the drawing ratio of 120 had the best crystallinity and orientation.Annealing treatment significantly improved the crystallinity and orientation of the prepared film.When the annealing temperature was 140 °C,the PP / PPOH film had the best mechanical properties.3.Preparation and properties of PP/PPOH microporous membrane.The post-stretching treatment was performed on the annealed prefabricated membrane.The effects of different coldstretching ratios,hot-stretching temperatures and hot-stretching ratios on the structure and properties of microporous membrane were studied by DSC,gas-liquid membrane pore size analyzer,water flux test and porosity test.The results showed that when the cold drawing ratio was 40 %,the crystallinity of PP / PPOH microporous membrane was the largest,and the pore size and porosity of microporous membrane were the largest.The maximum crystallinity of PP / PPOH microporous membrane was 51.7 % at 130 °C.The porosity and pore size of PP and PP / PPOH microporous membranes increased with the increase of thermal stretching ratio,and the pore size and water flux also increased accordingly.However,the pore size distribution of microporous membranes was not uniform due to the high thermal stretching ratio.