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A study has been made on the mechanism of rosin sizing in papermaking. By using microelectrophoresis and laboratory prepared handsheets, a study of the effect of pH, certain metal salts, and various physical parameters on the overall electrokinetics and sizing efficiency of the system has been made. By the use of a novel sizing method it was possible to effectively size handsheets in the alkaline pH range, which had previously not been possible when using rosin dispersion sizes. This permitted the inclusion of calcium carbonate as a filler, which has particular advantages in the finished paper. Use of the theory proposed by Derjaguin-Landau-Verwey and Overbeek on colloidal interaction, made it possible to explain and predict the likely outcome of sizing experiments, by analysing the electrokinetics of the system components. A comparative study on the effect of rosin fortification and the stabilisation of the dispersions by the use of casein has been made. From the results obtained, fortification leads to an improvement in sizing, particularly if the drying of the paper is not very efficient. Whereas the interactions of casein primarily effect the stabilisation of the dispersion, protein desorption from the solid-liquid interface causes initial flocculation of the dispersion. If the desorption is kept to a minimum, the dispersion is still stable and an effective sizing agent.

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The aims of this thesis were to study the agronomic impact of paper sludge incorporation on agricultural soil. through investigation of crop physiological response to paper sludge incorporation, nutrient cycling, soil parameters, soil moisture retention and then attempting to combine this multidisciplinary approach to the study of paper sludge into one empirical model, or management tool. Paper sludge (from Federal Tait Paper, Inverurie) was characterised to determine its composition and variability. In particular, the concentrations of nitrogen, cellulose and calcite were found to vary greatly. Prior to large scale field scale application and biomass-N studies a preliminary germination trial and biomass-N feasibility study were undertaken. The germination trial assessed the potential for paper sludge incorporation into soil to cause germination failure, due to the production of phytotoxic compounds, (e.g. acetic acid). It concluded that there was no risk of germination failure. However, it also indicated possible crop chlorosis associated with those seedlings grown on soil with paper sludge additions, suggesting N immobilisation. A preliminary biomass-N experiment concluded that large cores were unsuitable for biomass-N determinations and concluded that small sealed flasks with a well homogenised soil and paper sludge matrix would be more suitable for biomass-N determinations. To assess the agronomic effects of paper sludge incorporation into agricultural soil, a series of field experiments were carried out. Soil samples were regularly removed to assess soil parameters (e.g. soil pH). The incorporation of high N-concentrations of paper sludge was associated with no reduction in crop growth, harvest index, grain weight or grain numbers per ear. However, grain N-concentration and straw N-concentration were significantly increased as compared to those plots receiving no paper sludge additions. The increase in grain N-concentration approached that permissible by the malting industry of Scotland. The incorporation of low N-concentration paper sludge into soil was associated with significant decreases in crop growth, harvest index, grain numbers per ear and grain and straw N-concentrations, as compared to grain from those plots receiving no paper sludge additions. The decrease in crop growth and grain and straw N-concentrations suggest that N was limiting crop growth. Supplementary inorganic-N additions reinforced this hypothesise that N was limiting, as inorganic-N additions partly negated the reduction in crop growth associated with those plots receiving low N-concentration paper sludge additions. However, significant crop growth reductions were also associated with those plots receiving lime additions ( 8 t ha-1), suggesting that over liming of the soil could also cause crop growth reductions. As the paper sludge has a calcite component it was not possible to distinguish between the influence of the paper sludge affecting soil-N cycling and soil pH alterations in reducing crop growth. Paper sludge significantly increased soil pH. The moisture release characteristics of soil on plots receiving paper sludge applications were also significantly affected so that soil in plots receiving paper sludge additions held more moisture (at particular moisture tensions) than control soils. The biomass-N / N-immobilisation study demonstrated the rapid rise in biomass-N associated with paper sludge incorporation. Significant increases in biomass-N after 3 days of incubation, were associated with the soil receiving paper sludge. The potential for paper sludge to increase soil biomass-N was clearly demonstrated. To analyse the effect of individual paper sludge components on crop growth, a core experiment investigated the relationship between total biological yield (TBY) and those properties of the paper sludge considered to affect the crop growth (i.e. N-concentration, calcite concentration and cellulose concentration) using multiple linear regression techniques. Statistical modelling of the effect paper sludge incorporation into soil had upon crop TBY, explained 74.3% of the observed variation. The NCON (N-concentration of the paper sludge) variable was the largest influencing factor in determining the TBY (r=0.803).

Tri-helical, gravure roll coating, operated in reverse mode, is investigated via a combined experimental, theoretical and computational approach. New experiments were conducted on a pilot coating rig, designed to simulate the industrial process. Flow visualisations reveal the underlying flow structure within the roll-to-web transfer region and highlight when loss of coating stability (streaking) occurs. The latter is found to be influenced by the depth of the tri-helical grooves and the capillary number. Experiments show that as the web-to-roll speed ratio is increased, so too is fluid pickout from the grooves, although the coated film thickness may decrease. A key feature of the present investigation is the formulation of a novel complementary mathematical model. By starting with a simplified form of the coating process and progressively adding complexity a set of models are developed, first for simple zero pitch angled rectangular grooves then for grooves of arbitrary shape and groove pitch. A further extension to the model is the inclusion of a non-Newtonian model for the fluid (specifically a shear thinning power law formulation). Analysis of the application of shear thinning fluids to the moving substrate is also conducted. The base model developed is that for rectangular grooves of zero pitch, which takes the form of an analytical solution of the flow equation (a Poisson equation) along a groove. An extension to this model is made by solving the Poisson equation for non-rectangular grooves using the finite element method. Simple meniscus models were applied to make the problem tractable. Agreement between experimental data and predictions from the model is seen to be good for the range of operating conditions considered up to the onset of streaking. A final extension to the model considers grooves at non-zero pitch angles, representative of the industrial coating process. The limitations of this model, when compared to experimental data are examined and a physical explanation is postulated for the breakdown of the model at steep pitch angles. Under conditions of breakdown, the high pressures within the groove are consistent with the idea that elastohydrodynamics is an important mechanism in the transfer of fluid within the coating bead for discrete cell gravure coating.