Study On Hydroxylated Polypropylene Hollow Fiber Membrane

Polypropylene（PP）has advantages such as strong corrosion resistance,good processability,wide operating temperature range and low cost.It is an ideal membrane forming material.There is no polar group on the PP molecular chain.When used as a separation membrane,PP is highly hydrophobic,which leads to serious membrane fouling.In order to reduce membrane fouling of PP membranes,prolong servicing life,increase filtration efficiency,especially by modifying hydrophilic functional groups on the membrane surface,improve anti-fouling properties,increase hydrophilicity,and improve the separation performance of PP membranes in the application process,PP membranes need to be modified.In this paper,a copolymerization reaction between propylene and 10-undecen-1-ol was controlled,hydroxylated polypropylene（PPOH）with different hydroxyl insertion rates were synthesized.The polarity of PP,surface energy and hydrophilicity of PP membrane were improved.The crystallization and rheological properties of PPOH with different hydroxyl insertion rates were further studied.PPOH hollow fiber membranes were prepared and the effects of various process parameters on their structure and properties were investigated.The research content is as follows:1.Study on crystallization and rheological properties of PPOH with different insertion rates.PPOH with different hydroxyl insertion rates were synthesized.The non-isothermal crystallization and isothermal crystallization behavior of PPOH with different hydroxyl insertion rates were analyzed by changing the cooling rate and isothermal crystallization temperature.The rheological properties and hydrophilicity of PPOH with different hydroxyl insertion rates were studied.The results show that the increase of hydroxyl insertion rate will reduce the crystallinity and crystallization rate of the system,strengthen the tendency of heterogeneous nucleation,and deteriorate the regularity of the crystals.The thermal stability of PPOH is slightly worse than that of PP.When the hydroxyl insertion rate is 4.5%,the temperature for thermal decomposition of1%is lower than 33.3℃.The viscosity of PPOH increases with the increase of hydroxyl insertion rate and gradually decreases with the increase of shear rate.After inserting hydroxyl groups,the water contact angle of the membrane decreased from 104°to 77°,effectively improving its hydrophilicity.2.Preparation and properties of PPOH initial hollow fiber membranes.PPOH initial hollow fiber membranes were prepared by melt spinning-stretching method（MS-S）,and the effects of different stretching rates and heat treatment temperatures on their properties were studied.Increasing the traction rate from 1.0 m/s to 1.6 m/s resulted in an increase in the crystallinity of PPOH inital hollow fiber membrane from 18.3%to 21.6%,and an increase in the orientation factor from 0.171 to 0.181.Increasing the heat treatment temperature from 90℃to 110℃,the tensile strength of PPOH inital hollow fiber membrane increases from 27.4 MPa to 31.6 MPa,and the elongation at break increases from 221%to 277.When the heat treatment temperature continues to rise to 120℃,the tensile strength decreases to 29.5 MPa and the elongation at break decreases to 259%.The PPOH inital hollow fiber membrane after heat treatment at 110℃has the highest crystallinity and orientation,and the best mechanical properties.3.Study on structure and properties of PPOH hollow fiber membranes.PPOH hollow fiber membranes were prepared by changing cold stretching ratio,heat stretching temperature and heat stretching ratio.Increasing the cold stretching ratio from 15%to 25%,the porosity of PPOH hollow fiber membrane increases from 16.2%to 24.6%,and the water flux increases from1256.3 L·m^-2·h^-1 to 1760.7 L·m^-2·h^-1.Increasing the cold stretching ratio from 15%to 20%,the tensile strength of PPOH hollow fiber membrane increases from 106.3 MPa to 122.5 MPa.Further increasing the cold stretching ratio to 25%reduces the tensile strength to 116.1 MPa.Increases heat stretching temperature from 100℃to 110℃,the porosity of PPOH hollow fiber membrane increases from 19.2%to 22.1%,while the porosity decreases to 21.3%when the heat stretching temperature continued to rise to 120℃.Increase heat stretching temperature from100℃to 120℃,the water flux of PPOH hollow fiber membrane increases from 1366.4 L·m^-2·h^-1 to 2166.2 L·m^-2·h^-1,and the tensile strength increased increases from 117.4 MPa to 122.7MPa.