Study on preparation and technology of ptfe hollow fiber membrane

Hollow fiber membrane is widely used in traditional and new membrane separation components such as ultrafiltration, microfiltration, reverse osmosis and gas separator due to its small area, high filling density, high utilization rate, easy to enlarge and easy to clean.In addition, polytetrafluoroethylene hollow fiber membrane has high mechanical strength, acid and alkali resistance, high and low temperature resistance, low friction coefficient on the surface, so it has great potential in special filtration, gas absorption, ozone dissolution filtration, membrane distillation and other fields.PTFE hollow fiber membrane was prepared by using PTFE dispersion resin as raw material and adding exxonmobil Isopar series lubricants through extrusion and stretching molding.

Average extrusion pressure, pore diameter and bubble point pressure, porosity, water flux, contact Angle, SEM and DSC were used to characterize the structure and performance of PTFE hollow fiber membrane.The experiment mainly discusses the influences of lubricants (types and ratios), extrusion process (compression ratio, length-diameter ratio and cone Angle) and tensile sintering process on PTFE structure and performance, and optimizes the process parameters to provide guidance for PTFE hollow fiber membrane production.

Specific research contents are as follows:

(a)     the experiment changed the lubricant parameters (including the type and ratio of lubricants) and prepared PTFE hollow fiber membrane through the process route of "mixing → pre-molding → extrusion → stretching → sintering → natural cooling".The experiment explored the influence of lubricant type and ratio on the structure and performance of PTFE hollow fiber membrane, and obtained the best combination of lubricant type and ratio and optimized lubricant.

(b)     by changing the parameters of extrusion process molds, the influences of RR, L/D and alpha on extrusion pressure, membrane fracture strength, average pore diameter, bubble point pressure, porosity and water flux were explored to obtain the best extrusion parameters.

(c)     By adjusting the tensile process parameters (tensile multiple and tensile temperature) and sintering process parameters (sintering temperature and sintering time), the influences of tensile sintering process on the average pore diameter, bubble point pressure, porosity and water flux of PTFE hollow fiber membrane were explored to obtain the optimal tensile sintering process parameters and optimize the tensile sintering process.

Experimental results show that:

(1)     PTFE hollow fiber membrane has small average pore diameter, high bubble point pressure and porosity, large water flux fracture strength and contact Angle, and low extrusion pressure in the extrusion process.When the lubricant content is too high or too low, the structure and properties of PTFE hollow fiber membrane will be adversely affected to some extent.

(2)     When RR=185, L/D=20, and alpha =40°, the extrusion pressure is low, the fracture strength is large, the average pore diameter is small, the bubble point pressure is high, the porosity is large, and the water flux is high, which can be used as the extrusion process parameters of excellent PTFE hollow fiber membrane.

The influences of tensile and sintering processes on the microstructure and properties of PTFE hollow fiber membrane are as follows: with the increase of tensile multiple, the average pore size and porosity of PTFE hollow fiber membrane are large, the bubble point pressure is small, and the water flux is large.With the increase of tensile temperature, the average pore diameter and water flux of PTFE hollow fiber membrane increase, the porosity increases, and the bubble point pressure decreases.With the increase of sintering temperature, the pore diameter, bubble point pressure and water flux of PTFE hollow fiber membrane decrease, and the porosity has no obvious change rule.With the increase of sintering time, the average pore diameter, porosity and water flux of PTFE hollow fiber membrane increase, and the bubble point pressure decreases.

The drawing process significantly reduces the crystallinity of PTFE products, while the sintering process further reduces the crystallinity of PTFE products.When the tensile multiple is 100%, the tensile temperature is 300℃, the sintering temperature is 320℃ and the sintering time is 5min, the average pore diameter of hollow fiber membrane is small, and the bubble point pressure, porosity and water flux are large.