Pulp Suspension

Paper may be colored by dyeing the fibers in a water suspension by batch or continuous methods. The classic process is by batch dyeing in the beater, pulper, or stock chest. Continuous dyeing of the fibers in a water suspension is adaptive to modem paper machine processes with high production speeds in modem mills. Solutions of dyestuffs can be metered into the high density or low density pulp suspensions in continuous operation. 

Aliphatic acids or esters Mostly high-molecular-weight compounds diethyl phthalate laiiric acid Papermaking wood-pulp suspensions water-based paints food processing... 

Refining is the most important of all the processes to which fibres are subjected, in terms of developing pulp suspension characteristics and final sheet properties, and a great deal of research has been carried out into understanding the process more fundamentally. Whilst there is still much controversy about certain aspects of the refining process and its effects upon the fibres, a number of things are widely accepted. Firstly the primary cell wall, which does not... 

It is also possible to measure surface area from the water adsorption isotherm, and this is arguably more relevant to aqueous pulp suspensions as it measures the surface area which is accessible to water. Values of up to 140 m2g-1 have been obtained from the... 

NMR imaging techniques were applied to the measurements of velocity field in opaque systems such as tomato juice and paper pulp suspensions [58-60]. In both cases, the particle concentrations are sufficiently high that widely applied techniques such as hot film and laser Doppler anemometry could not be used. The velocity profile for a 6 % tomato juice slurry clearly showed a power-law behavior [58, 59]. Row NMR images for a 0.5 % wood pulp suspension provided direct visual of three basic types of shear flow plug flow, mixed flow and turbulent flow as mean flow rate was increased. Detailed analysis of flow NMR image is able to reveal the complex interaction between the microstructure of suspensions and the flow [60]. 

Sodium Borohydride Treatment. The pulp (1% consistency) together with EDTA (0.15% consistency) was suspended in water and stirred for one hour at room temperature, after which it was washed and filtered. The pulp was then suspended in water (1% consistency) and sodium borohydride was added (50% on pulp basis). The pulp suspension was stirred at room temperature for two days, followed by filtration, washing with water and air-drying at room temperature. 

The work described in this paper uses gamma rays to generate free radicals in situ in a pulp suspension. It is hoped that this proximity of radicals and chromophoric moieties in lignin will lead to enhanced bleaching and a better understanding of the bleaching and yellowing processes of TMP. 

Co-irradiation experiments with chemicals were carried out according to the following procedure. To the unbleached TMP pulp suspension (DTPA pre-treated, saturated with Nitrogen by bubbling) a small amount of hydrogen peroxide (H202 1%) or... 

The results imply a competition for the reaction sites between the lignin and the cellulose, and therefore a low specificity of the reaction between the reactive species and the surrounding pulp suspension has been observed. The intensity of the variation in the measured properties (die increase in ISO brightness or the decrease in physical properties) is proportional to the dose rate used, and therefore to the concentration of... 

The next experiments consisted of irradiating the unbleached TMP pulp suspension in the presence of 1% hydrogen peroxide or 0,3% sodium borohydride. This was done to measure the influence of an oxidizing and a reducing chemical co-irradiated with the pulp suspension. Also, H202 is known to react with e solv to produce OH (equation 8). The effect of saturated nitrous oxide in pulp suspension was also studied. In presence of yrays, N20 is known to react with e-solv to generate OH. The experimental results are shown in Figure 5. 

Figure 5. ISO brightness versus dose for concurrent chemical treatment of an unbleached TMP with 1% H202, 3% NaBH4 or saturated N20 in pulp suspension for a 2.5 Mrad dose...

In order to carry this concept of fluidfoil impellers at a uniform velocity of discharge further, the A312 Impeller (Fig. 4) was developed and is used primarily in paper pulp suspensions. Carrying it further is the A320 Impeller (Fig. 5). The A320 has been studied particularly in the transitional area of traditional Reynolds numbers. This is shown in Fig. 6. This figure shows its performance and Reynolds numbers between 10 and 1,000. 

A reduction in the volume of water needed at the paper machine is almost impossible because paper formation will be disturbed if the consistency of the pulp suspension becomes too high. Currently, the stock suspension (i.e., pulp and additives) in the head box of a paper machine contains 97%-99.9% water. The constraint of maintaining pulp suspension consistency means a reduction in water intake has to be realized by reusing the process water. Due to the different purposes and applications in which water is used, the water quality demands vary considerably. Membrane processes can be chosen to produce a specific water quality and are attractive alternatives to facilitate the reuse of water, either alone or combined with biological processes or other chemical and physical processes. In addition, membrane processes are an efficient way to recover raw materials, e.g., coating pigments, from effluents. 

Multiphase Thermodynamics of Pulp Suspensions Table 2 Data input for the ESA and TMP models... 

The present thermochemical model describes the acid-base, ion exchange and solubility cbaracteristics of a homogeneous pulp suspension. The important feature of the thermodynamic multiphase approach is that it provides the possibility to incorporate specific interactions of practically unlimited number of constituents into the system. Due to its general thermodynamic basis, the multiphase method can be applied both in the fibre line processes in pulp production and in the wet end chemistry of paper-making. 

E. Rasanen, Modelling Ion Exchange and Flow in Pulp Suspensions, Doctoral Thesis, Helsinki University of Technology, VTT Publications 495, Espoo, Finland, 2003. 

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