MFC for paper surface treatment

In this study, microfibrillated cellulose (MFC) was applied in an aqueous suspension as a coating material on paper substrates. Two different coating techniques were used: rod coating and size press.The MFC suspension used has a high water content and water is known to deteriorate the properties of the paper, so water treated paper substrates were prepared as references to give an indication of the effects that the processing has on the final properties of the coated papers.The structure of the MFC coating and associated surface properties were evaluated using scanning electron microscopy (SEM) and by measuring the thickness and the roughness of the coated substrates. A tool to visualise the distribution of the MFC was developed and the tensile properties ofthe MFC coated substrates were characterised. Resistance to air, oxygen and water vapour permeationas well as water and grease absorption were used to describe the barrier properties of the coated papers.The MFC coated paper substrates exhibited a higher roughness than the reference paper substrate. This was due to the sensitivity of the substrate to water and not from the coating material it self since the water treated paper substrates showed an even higher roughness than the MFC coated substrates. The latter showed slightly increased tensile properties compared to the reference paper substrates, and most importantly, reduced air permeance and grease absorption (-100% and -84% respectively); for the rod coated paper substrate with 3 g⁄m2 coat weight. The water vapour transmission rate was also decreased with the applied MFC coatings. Advantages and drawbacks were identified for the coating techniques. The rod coating allowed a good control of the coat weight in a range of 1 to 3 g⁄m2. However, the Mayer rod and the high viscosity of the MFC suspension caused poor MFC distribution and a coating which reproduced the rod pattern. With the size press, coat weights around 1 g⁄m2 were reached. The MFC did not build a coating layer on the paper substrate surface but was impregnated into the paper substrate by the rollers