Surface modification of paper and cellulose by plasma-assisted deposition of fluorocarbon films

Plasma polymerized fluorocarbon films have been deposited on paper and regenerated cellulose surfaces to enhance their barrier properties and to achieve hydrophobic surfaces. The primary monomers used for plasma polymerization were pentafluoroethane (CF3CHF2) and octafluorocyclobutane (C4F8). The equilibrium moisture uptake of films deposited from either precursor was less than 0.14 wt.%. Although water vapor uptake of the fluorocarbon films is low, moisture diffusivity through the films is high; that is, moisture penetrates the films but is not chemically bonded. Quartz crystal microbalance (QCM) studies demonstrate that the absorption of water vapor is a bulk phenomenon in which the moisture penetrates into the film. Transient moisture absorption studies were conducted using the QCM to evaluate the rate of moisture uptake and diffusivity. Although the films allow water vapor diffusion, the films are hydrophobic and are not “wetted” when liquid water contacts these layers. Contact angle studies reveal that a minimum fluorocarbon film thickness of about 70 nm on paper is required to completely cover surface and near-surface fibers, thereby providing the paper with long term hydrophobic character. The films also impart the paper with an improved barrier to lipophilic material.