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Factors influencing the treatment of paper with fluorochemical surfactants for grease-proof applications

Paper and paperboard products are routinely treated with fluorochemicals to limit the rate of penetration by oils, solvents and other hydrophobic materials. Common applications include pet food bags and fast food packaging. In most cases, only paper products based on chemical pulp fibres are treated. Fluorochemicals are not considered to be cost effective In papers based on mechanical pulps. A number of generalizations can be made about fluorochemical applications to chemical pulps and fine papers. Fluorochemical addition levels for a given level of solvent resistance increase with increased pulp refining, with increased filler content and with increased sizing. Refining and filler addition increases the specific surface area of the headbox furnish and thus the fluorochemical demand. Wet end size dispersions also increase the surface area of the furnish. In addition, sizing influences size press pickup for size press fluorochemical treatment. The objectives of this work were to understand why fluorochemicals, added to retard solvent or grease penetration, are more effective in wood-free papers than in mechanical pulp-based papers. Newsprint required about 10 times more fluorochemical than did Whatman # 42 filter paper to achieve solvent resistance. Based on results of kit tests, contact angle measurements and X-ray photoelectron spectroscopy using both paper and regenerated cellulose films, it was concluded that about 40% of the added fluorochemicat demand of newsprint, compared with filter paper, was due to the higher specific surface area of newsprint. The remaining 60% was due to interference by solvent extractable material (i.e. pitch). The negative effects of pitch could be partially circumvented by using hydrophobically modified starch in conjunction with the fluorochemical.