Study on the plasma modified PTFE membranes for pervaporation and adhesion properties enhancement

• Main Authors: Chen-Yuan Tu, 杜振源
• Other Authors: Juin-Yih Lai
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/32761893429567993199

博士 === 中原大學 === 化學工程研究所 === 94 === In this work, plasma and ozone treatment processes were applied to modify the PTFE membrane surface. Hydrophilic modification and molecular design on the surface of PTFE membrane was carried out to improve the dehydration performance of the pervaporation and vapor permeation of organic aqueous solution, and the adhesion strength between the PTFE membrane and copper foil. Hydrogen plasma treatment was applied to modify the skiving PTFE (s-PTFE) membrane surface accompany with in-situ diagnose by OES to investigate the mechanism of modification. Regardless of placing s-PTFE membrane on the position of downstream or upstream of the electrode region, the diffusion and convection transport of the active species in the plasma, resulting in the s-PTFE membrane surface can be modified. It was found that optimal position for the surface hydrophilicity enhancement of plasma-treated s-PTFE is at the remote distance of 10 cm from the electrode. Compared with the one time H2 plasma treatment, a more stable and more hydrophilic s-PTFE membrane surface can be created by a repeated hydrogen plasma treatment. However, a small hydrophobic recovery phenomenon appeared due to the thermal motion of the PTFE polymer chain even after repeatedly plasma treated. The hydrophobic recovery phenomenon can be suppressed by introducing longer hydrophilic polymer chains onto the PTFE membrane surface. Thus, the hydrophilic polymer chain is difficult to migrate into the bulk layer; resulting in the hydrophilicity of PTFE membrane surface can be remained. For the porous e-PTFE membranes, both acetylene/nitrogen gas mixture plasma and plasma-induced acrylamide monomer (e-PTFE-g-PAAm) post grafting polymerization method were carried out to improve the surface hydrophilicity of the e-PTFE membrane and to prevent the hydrophobic recovery phenomenon. The contact angle decreases from 109.7oof the e-PTFE membrane to 34.1o of e-PTFE-g-PAAM membrane. For the durability test of the surface contact angle increased from 34.1o to 36.9o for 3 years. For the dense s-PTFE membrane, “Plasma induced Solid-State Polymerization” a new developed method in recently years was carried out. The method is simple but effectively improve the surface hydrophilicity of the s-PTFE membrane and suppress the surface hydrophobic recovery effect. At last, a novel PTFE membrane modification by hydrogen plasma combined with ozone treatment was developed. C-H groups were introduced into the s-PTFE membrane surface through defluorination and hydrogenation reactions under hydrogen plasma treatment. The C-H groups then served as ozone accessible sites to form peroxide groups under ozone treatment. Molecular design on s-PTFE surface was carried out by grafting polymerization by atom transfer radical polymerization which is easy to control the molecular architecture initiating from the peroxide groups, and introduce sodium 4-styrenesulfonate (NaSS) molecular chains onto the s-PTFE membrane (s-PTFE-g-PNaSS) which was further protonized to form s-PTFE-g-PSSA membrane. The modified s-PTFE-g-PSSA membrane was very stable for long-term operation of pervaporation dehydration process attribute to the excellent stability of s-PTFE membrane. The PTFE-g-PSSA membrane was very stable for 58 days operation of pervaporation dehydration process of 90 wt% aqueous IPA solution at 25 oC, and the permeation flux and high water concentration in permeate of 355 g/m2.hr and 99.9 wt% was obtained respectively. Different grafting method utilized to build GMA macromolecular architecture on s-PTFE surface. It was found that both the architecture and chemical composition on the s-PTFE surface influence on the adhesion strength with copper metal. The adhesion between epoxy resin and metals could be further improved by reacting with curing agents. Compared with the unmodified s-PTFE membrane, the 180o peel strength between s-PTFE membrane and Cu foil increases from 0.2 N/cm of the s-PTFE membrane to 5.8 N/cm of the s-PTFE-g-PGMA membrane by reacting with ethylenediamine.