Polyethylene plasma fluorination and permeability relationships to methanol-gasoline mixtures

In the case of cold plasma fluorination we analyzed effects of the main processing conditions (power, exposure time, nature of gas, and number of fluorinated faces) on gasoline permeability of polyethylenes. Optimization of processing conditions gave us a permeability reduction of 30% compared to untreated polyethylene. XPS analysis of fluorinated specimens before permeation experiments shows the PE to be highly fluorinated at the surface with a F/C ratio up to 2. Fluorination appeared to be homogeneous over the disk surface with a concentration depth profile showing a step decline below the extreme surface. However, significant fluorination is achieved only up to a few tens of nanometers (20 to 30). A more interesting effect is the evidence for chain breaking during the process suggests the creation of short chain segments at the surface. These segments would be highly fluorinated but easily leeched out by the diffusing molecules. Leeching seems more important with alcohol containing gasolines. These data show clearly that fluorination by cold plasmas in the conditions under studies has not a permanent effect. © 1996 John Wiley & Sons, Inc.