Wet-end paper chemistry

Au, C.O. and Thorn, 1. (eds) (1995) Applications of Wet-End Paper Chemistry, Blackie Academic Professional, Chapman Hall. 

Encycl.Polym.Sci.Engng. (2.) 10,761 Che on Au, Ian Thom Application of Wet-end Paper Chemistry Blackie Acad. Professional (1995) Ullmann (5.) A10,611... 

Solarek D, Tessler MM, Jobe P, Peek L. Cationic Starch Aldehydes - Wet End Additives for Temporary Wet Strength and Improved Dry Strength. Paper Chemistry Symposium Stockholm, Sweden STFI and SPCI organizers 1988 Sept. 27-290... 

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. 

Retention systems have become increasingly more sophisticated as our understanding of wet-end chemistry has improved and paper machines have become more demanding. Often two, three or even four chemicals are necessary to attain the retention, drainage and formation balance on modem machines. This sometimes involves a coagulant to neutralise anionic trash, then silica sol or bentonite, anionic or cationic polyacrylamides (or even both) and cationic starch to flocculate the stock. 

Fibre types - changes in fibre type which cause a variation in wet-end chemistry also need to be monitored. Use of BCTMP in fine papers for increased bulk, for instance, can lead to increased demand for retention aid as well as for other effect chemicals, e.g. size, optical whitener. Variation in carry over of chemicals from de-inking plants can cause variable wet-end chemisfiy at the paper machine and where swings are significant this needs to be confiolled. Addition of fixative may be necessary to reduce negative impacts. 

The two major types of synthetic size employed at the wet-end of a paper or board machine, AKD and ASA, will be dealt with jointly as in many respects the wet-end chemistry is the same. Individual problems related to tlie sizes thanselves will be dealt with later in this section. 

On a fine paper machine, size press starch addition is typically 1.2 gsm per side. For a 70 gsm copier grade this equates to 34 kg/t. Hence if a mill is running 10% broke the returned size press starch amounts to 3.4 kg/t in the furnish. This can have considerable impact on wet-end chemistry. Size press starch is of necessity viscosity-reduced, and so contributes little to the paper strength on recycling. However, it is believed that while the starch chains are too short to bridge between fibres in the forming sheet, it may contribute to an increase in relative bonded area after pressing. 

Now more than ever, in an era of economic uncertainty, constrained resources and environmental sensitivity, paper producers are facing increasing challenges. Over the last decade, we have wimessed a growing interest in the field of wet-end chemistry. 

Sometimes the path from lab experiments to successful implementation of new chemistry concepts on paper machines is a difficult one, and interactions between the many constituents of the wet-end system have to be taken into consideration. A striking example is the accumulation of salts and colloids caused by the ever-increasing closure of water loops. 

Figure 3B.22 Internal paper sizing using rosin and fortified rosin. (Hubbe, M. Rosin Soap Size, Mini-Encyclopedia of Papermaking Wet-End Chemistry, BioResources, NC State University, Dept of Forest Biomaterials, Raleigh/USA, http //www4.ncsu.ed u/ hubbe/SOAP.htm iv/f/) kind permission.)...

This paper describes the development of a novel dynamic predictive and optimal control method for the wet end of a papermaking systems. This part of the system plays an important function in the process in terms of its controllability and potential for optimisation. The wet end process is complicated and the control systems are always multivariable and dynamic in nature. Due to the severe interactions between each variable, general physical and chemistry based modelling techniques cannot be established. As such, feed-forward neural networks are selected as a modelling tool so as to build up a number of non-linear models that link all the variables to the concerned quality outputs and process efficiency. 

Recently Granat (1978) has analyzed data on sulfur concentration in precipitation and sulfur wet deposition obtained in European Atmospheric Chemistry Network. According to his paper the deposition has been constant during the last ten years over North-West Europe. It is postulated that sulfur emitted in this area is transported and deposited over other areas, probably in an eastward direction (see Subsection 3.6.6). However, using the nitrate data of the same network, Soderlund (1977) reports an overall increase of 50-100 % in the nitrate wet deposition at many stations during the 20 years ending in 1973. 

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