an on - line film fluorination apparatus cooperative with a continuous polymer film extruding apparatus is set forth . in the preferred and illustrated embodiment , a continuous feed film is introduced into a closed cabinet or housing having alignment and guide rollers for directing the film into the housing . the film passes around a first roller having a portion thereof formed of sintered nickel to enable gaseous impregnation of the surface of the film with a gas flow including fluorine . the gas acts on the exposed face of the film , changing the surface of the polymer film , thereby providing a relatively thick surface upgrading of the film . after exposure to the fluorine , the film passes a closed vacuum container having an open face adjacent to the film surface for drawing off unreacted fluorine for recapture and recycling . this procedure can be optionally repeated on both surfaces of the film ; the film that emerges from the closed cabinet or housing has a modified surface , and the cabinet or housing is evacuated with slight negative pressure .