Surface modifications of expanded poly(tetrafluoroethylene) sheets assisted by CO2 antenna coupling microwave plasma

Surfaces of the expanded poly(tetrafluoroethylene) (ePTFE) sheets were chemically modified with the assistance of CO2 cold plasma generated by antenna coupling guided microwave. The plasma pretreated ePTFE surface did not obviously change in terms of morphology of nodes structure but increased Surface tension and promoted subsequent capability to graft polymerization with acrylic acid (AAc). The modified ePTFE were then characterized using FTIR-ATR and X-ray photoelectron spectroscopy (XPS). Morphologies of ePTFE surfaces and the cross-sectioned side of AAc-grafted ePTFE were examined by SEM and FTIR microscopy. Experimental results indicated that AAc penetrated to a depth of ca. 60 mu m and bonded on the surfaces of nodes and fibrils. Generation of COF species on the ePTFE surfaces by CO2 plasma contributed to this initiation effect. Current data also supported that plasma generated by the CO2 antenna-coupling microwave system could efficiently activate the exposed ePTFE surfaces of interior fibrils and nodes. The variations of IR vibrational modes, binding energies of functional groups, and surface tensions were correlated with the chemical modifications applied on the ePTFE sheet. The mechanical strength of the pAAc-grafted ePTFE sheet appeared to be enhanced.