AbstractsBiology & Animal Science

The aim was to understand the role of surface forces in paper machine fouling. Also possibilities to develop antifouling paper machine surface materials were studied. Experiments were focused on adsorption kinetics, adhesion and wetting kinetics of substances causing fouling in paper making. In addition, antifouling properties of photocatalytic titanium dioxide were investigated. Adsorption kinetics were studied with a quartz crystal microbalance with dissipation monitoring (QCM-D). The experiments were made with wood resin, AKD, latex and several other model deposits. Rates of adsorption were found to be diffusion controlled in the beginning of adsorption. Blocking by already adsorbed particles hindered the adsorption at later stages. It was concluded that changes in surface roughness affect the detected dissipation and frequency shifts. Hence, QCM-D can be used to study the spreading kinetics of soft colloids which was demonstrated experimentally with styrene-butadiene latex and wood resin emulsions. Contact angles adhesion and wetting kinetics of lipophilic wood extractives were studied on surfaces present in a paper machine. The adhesion of oleic acid and other lipophilic wood extractives is large to a hydrophobic fluoropolymer and small to hydrophilic surfaces in solution. Therefore, extractives tend to accumulate on hydrophobic paper machine parts and hydrophobic spots on paper web in the wet end. Van der Waals forces determined the adhesion of oleic acid in air on most surfaces studied. A water film is formed between the drop of extractives and the interface prior to spreading in solution. The removal of this water film may take several seconds, which prevents the spreading of aggregated drops of extractives. An increase in surface roughness shortens the pre-wetting period significantly and enhances the contact of extractives. The photocatalytic decomposition kinetics of wood extractives under UV illumination was studied with QCM-D. In the beginning of the degradation measurements, a 0-3 minute long initation period, with hindered or prevented degradation was often detected. After the initiation period, the degradation continued with a relatively constant rate until it decelerated again near the end of experiment. The primary mechanism of removal of the films was photocatalytic degradation, but it was shown that the penetration or formation of water at the TiO2/film interface and the flow of oxygen to the interface are also of importance. Correlation of the flow of oxygen to the rate of photocatalytic degradation was observed. The results can be utilized, when antifouling paper machine surface materials and paper chemicals for deposit control are developed. Tavoitteena oli ymmärtää pintavoimien vaikutusta paperikoneen likaantumiseen. Tutkittiin paperikonetta likaavien aineiden adsorptionopeutta, adheesiota ja leviämisnopeutta. Lisäksi tutkittiin mahdollisuuksia kehittää likaantumattomia paperikonepintoja. Kokeissa käytettin AKD:ta, uuteaineita, lateksia sekä useita muita mallilikoja. Kuten oletettua…