Hydrophobization of cellophane and cellulose nanofibrils films by supercritical state carbon dioxide impregnation with walnut oil

Bio-based films are typically sensitive towards moisture which limits the industrial applicability. In this study the cellulosic films produced from cellulose nanofibrils and cellophane were treated using supercritical state carbon dioxide impregnation with hydrophobic polyunsaturated oil mixture (walnut oil). The effects on surface hydrophobicity with cellophane films were clear and indisputable. Water contact angles of non-treated cellophane, walnut oil impregnated and further 1,6-hexanediol dimethacrylate crosslinked films were 62, 82 and 91°, respectively. Also the moisture absorption and water vapour transmission rate as well as oxygen transmission rate at 80% relative humidity decreased as a result of supercritical state carbon dioxide impregnation. Water vapour transmission rate of walnut oil impregnated cellulose nanofibrils film decreased by 30% as compared to non-treated film. Based on the FT-IR analysis and surface roughness measurements the walnut oil penetrated better into the structure of cellophane as compared to CNF film. The developed hydrophobization method can be exploited in strengthening the position of cellulosic films in high performance film applications.