Capillary penetration in cellulose and polyethylene porous media: effect of contact with vapours and partial saturation with a non-miscible liquid

This work presents the effect of water and oil vapours and of partial liquid water saturation on the rate of capillary penetration in porous media. Two porous media were used: one made of cellulose (wettable both by oil and water) and the other made of polyethylene (wettable only by oil). Sunflower oil was the penetrating liquid. The porous structure of the porous media was characterized using SEM and surface properties were determined by FTIR. In addition, the effective pore radii and contact angles of sunflower oil against each medium were determined. The contact angle of sunflower oil against polyethylene was 0 degrees, and no dynamic contact angle effects were observed. Capillary penetration of sunflower oil in cellulose showed contact angles around 80 degrees in the beginning of penetration which gradually decreased to about 14 degrees. The porous media were also put into contact with water vapours for different times and at different temperatures and results were compared with those obtained in the presence of oil vapours or in the absence of vapours. In addition, experiments were performed by fully saturating the cellulose porous medium with water and then partially drying it. The rate of capillary penetration of the oil in the polyethylene porous medium was not affected by the presence of vapours. On the contrary, the presence of water vapours and partial water saturation in the cellulose matrix significantly increased the penetration rate (up to almost three times) under most of the examined conditions. The reasons for such an effect are being discussed. (C) 2015 Elsevier B.V. All rights reserved.