Oleg Timofeev

Drying of Pigment-Cellulose Nanofibril Substrates

A new substrate containing cellulose nanofibrils and inorganic pigment particles has been developed for printed electronics applications. The studied composite structure contains 80% fillers and is mechanically stable and flexible. Before drying, the solids content can be as low as 20% due to the high water binding capacity of the cellulose nanofibrils. We have studied several drying methods and their effects on the substrate properties. The aim is to achieve a tight, smooth surface keeping the drying efficiency simultaneously at a high level. The methods studied include: (1) drying on a hot metal surface; (2) air impingement drying; and (3) hot pressing. Somewhat surprisingly, drying rates measured for the pigment-cellulose nanofibril substrates were quite similar to those for the reference board sheets. Very high dewatering rates were observed for the hot pressing at high moisture contents. The drying method had significant effects on the final substrate properties, especially on short-range surface smoothness. The best smoothness was obtained with a combination of impingement and contact drying. The mechanical properties of the sheets were also affected by the drying method and associated temperature.

Drying of foam-formed mats from virgin pine fibers

ABSTRACT The purpose of this work was to select an efficient drying technique for drying of highly porous thick fiber foam mats with minimum impact on their structure after forming and drainage. Thick fiber mats were produced from wood fibers using foam-forming technology and dried using several different drying methods. The mixture of pine fibers and surfactant (foaming agent) in water was blended using a high-speed blender. After fiber foam generation, a sample mold was filled with wet fiber foam, and after drainage, drying experiments were performed. For comparison, experiments were carried out in an oven, an impingement dryer assisted with a vacuum, and a combined impingement-infrared dryer. At low moisture contents, through-air drying experiments were also carried out. Drying curves, temperature profiles, and shrinkage were measured from the produced mat structures. The most promising drying technique in this study was the combined impingement-infrared drying, used until the fiber mat became permeable, followed by through-air drying until the desired final moisture content was achieved.