Additives in the Paper Formation Process

Chemicals which are used to modify bulk sheet properties usually have to be added to the wet fibre suspension so that they become well distributed throughout the -direction of the sheet. Chemicals which are added as a surface treatment to the dry sheet are usually only able to influence surface properties. 

For the period from around 1840 to the early 1970s paper was usually made in an acidic environment at pHs of around 4-5. This was because many grades required the use of rosin and aluminium sulfate for the control of water penetration (sizing), and solutions of aluminium sulfate exhibit a pH of around 4.5. Aluminium sulfate has also been popular with paper makers because it assists the flocculation of colloidal particles and therefore behaves as a mildly 

This chapter attempts to describe some of the more important groups of chemical additives used in paper making and their mechanism of action. 

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In the pulp and paper industry, anionic and cationic acrylamide polymers are used as chemical additives or processing aids. The positive effect is achieved due to a fuller retention of the filler (basically kaoline) in the paper pulp, so that the structure of the paper sheet surface layer improves. Copolymers of acrylamide with vi-nylamine not only attach better qualities to the surface layer of.paper, they also add to the tensile properties of paper in the wet state. Paper reinforcement with anionic polymers is due to the formation of complexes between the polymer additive and ions of Cr and Cu incorporated in the paper pulp. The direct effect of acrylamide polymers on strength increases and improved surface properties of paper sheets is accompanied by a fuller extraction of metallic ions (iron and cobalt, in addition to those mentioned above), which improves effluent water quality. 

In this paper, we present a preliminary analysis of the steady-state and time-resolved fluorescence of pyrene in supercritical C02. In addition, we employ steady-state absorbance spectroscopy to determine pyrene solubility and determine the ground-state interactions. Similarly, the steady-state excitation and emission spectra gives us qualitative insights into the excimer formation process. Finally, time-resolved fluorescence experiments yield the entire ensemble of rate coefficients associated with the observed pyrene emission (Figure 1). From these rates we can then determine if the excimer formation process is diffusion controlled in supercritical C02. 

Corrections of consequence to a paper that has already been published should be sent to the editor. Most journals publish corrections soon after they have been received. Some journals have a specific format for additions or corrections check the author guidelines. In books, errata sheets will be printed and included in every book, and the book itself will be corrected before reprinting. However, additions and corrections generally reflect poorly on the authors, and careful manuscript preparation and attention to detail in the entire publication process can prevent the necessity for subsequent corrections. 

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. 

Legrand and co-workers [8] and the important NMR work by Brinker and co-workers on the formation of silica in the sol-gel process [9]. We assume that much of this is covered elsewhere in this volume. In addition, the huge subject of template-synthesized mesoporous silicas, for which there is a very large recent NMR literature, is omitted from this paper, which focuses on what is commonly referred to as amorphous silica, e.g., silica gels, precipitated silicas and fumed silicas. 

Additional data may be found in the paper by Soundy and Williams, who obtained indirect values for the rate of the charge transfer reaction during their study of the atomic ion-electron recombination process. Their analysis does not allow for compound formation, of particular... 

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