Preparation And Properties PVDF/PTFE Composite Membrane

Polymer micro-porous membrane has innumerable micro-pores （aperture:0.1～10μm）and a certain separating function. Polytetrafluoroethylene （PTFE） has become optimalmaterials of micro-porous membrane because of its excellent chemical feasibility andadaptability to extreme temperatures. But the disadvantages of PTFE such as low surfaceenergy and poor cohesiveness have limited its application in cementation, dyeing,biocompatibility, etc. In this paper, we used cold air plasma to treat PTFE micro-porousmembrane to increase its surface energy and cohesive force, so that we can further adopt spin-coating method to prepare PVDF/PTFE composite membrane which has higher mechanicalstrength and excellent water permeable properties.Those main study contents and results are indicated as follows:（1） The preparation of PTFE micro-porous membrane. The effects of biaxial stretchingtemperature, stretching speed, stretching ratio, heating temperature and heating time onaperture and porosity of micro-porous membrane were investigated in this section. The resultsshowed that the aperture and porosity of PTFE micro-porous membrane achieved optimumvalues （aperture, porosity and film thickness achieved85.5%,0.62μm and50μm respectively）under the conditions of stretching temperature was320℃, stretching ratio was6, stretchingspeed was3500%·s^-1, heating temperature was320℃and heating time was3min.（2） The cold air plasma treatment of PTFE micro-porous membrane. The surfacemodification of PTFE micro-porous membrane by cold air plasma and the effects of treatmentconditions on the results through the measurement of contact angle and weight loss werestudied in this section. The changes of surface structure, elements, morphology andmechanical properties were analyzed by ATR-FTIR, XPS, SEM and Stress-Strain analysis.The results showed that the modification effects achieved optimal ones (contact angle:66.5°,weight loss:10.1μg·cm^-2,when tensile strain reached0.57mm·mm^-1, samples still didn’tfractured and tensile strength got to15.98MPa) under the conditions of discharge power was40W, treatment time was20s,distance parameter was40cm and air flow was20cm³·s^-1.Furthermore, the surface structure and morphology analysis indicated that C-O-C, C=O and other active groups were appeared in samples, which led to the growth of oxygen content andwettability.（3） The preparation study of PVDF/PTFE composite membrane by spin-coating method.In this section, different concentration of precursor solution was adhered to the modifiedPTFE micro-porous membrane to prepare composite membrane under a certain spinningspeed and preparing temperature. The tensile strength, water flux and preparing process of thecomposite membrane were also studied. The results indicated that the appropriate preparingtechnology was as follows: concentration of precursor solution should be6g·L^-1, spinningspeed should be2500r·min^-1, preparing temperature and time should be90℃and3hrespectively. In which condition, the tensile strength of composite membrane achieved26.34MPa, while its water flux got to605.2L·m^-2·h^-1. Furthermore, the preparation ofcomposite membrane can be attributed to the results of intermolecular forces between PVDFsol-gel and PTFE micro-porous membrane and hook and nail bonds which were caused by thepermeation of PVDF sol-gel molecular in the pores of PTFE membrane.