1985 Volume 2
Latest proceedings
The mechanism of sizing with soluble rosin soap size differs from the sizing mechanism of dispersed rosin acid size. Cationic fixing agent has to be used with the latter size to assure proper attachment of the size to furnish components. The problem of size attachment is not unlike that for the alkaline AKD size emulsion. The relative extent of attachment is assessed by a high shear stirring test.
Sizing involves a complex array of interactions in which surface reactions play an important role. The large surface area fines and fillers in the furnish reduce sizing efficacy. Size accumulates on fillers/fines to a higher extent than expected from surface area alone. On the basis of experimentally determined adsorptivities, size
distribution in a furnish can be estimated. Size on fiber appears to be more efficient than on fillers/fines, compared at equal surface coverage. This requires that we minimize the amount of fine particulates in the furnish. Fillers/fines capture a significant amount of applied size; thus, first pass fillers/fines retention has to be maximized to retain size in the sheet. Size distribution also can be affected by the proper choice of process conditions.The principle of reactive sizing is discussed, and the variety of sizes which have been considered is reviewed.
The reactivity of tetradecyl ketene dieter towards water and model compounds for cellulose has been shown to be very low and the results suggest that very little ß -keto ester formation would be expected under normal papermaking conditions.
A study has also been made of the retention of C-14 labelled tetradecyl ketene dimer in laboratory handsheets, and of the degree of sizing which is induced. The results show that the dieter is present in the sheet predominantly in its unreacted form, but that a small percentage is present in a form which is not amenable to extraction by chloroform. This residual size exerts a considerable sizing effect, and the amount present in the sheet is related to the curing conditions used. The nature of the unextractable material has been studied by mild hydrolysis and the results are compatible with a low level of ß -keto ester formation. Comparisons have been made with C-14 labelled hexadecyl hexadecanoate, a compound of similar structure and physical characteristics but which is unable to undergo reaction with cellulose.
A study has also been made of the influence of aluminium sulphate on alkyl ketene dieter sizing. The retention of size in sheets made in the presence of aluminium sulphate is reduced, but not to a sufficiently low level to account for the loss in sizing which is observed. An explanation in terms of the inhibition of reaction of the dieter with cellulose as a result of adsorbed aluminium species is proposed.
According to Smoluchowski’s and Komagata’s theory, the electroosmotic and electrophoretic velocities vary with the depth of cell such that the distribution of velocities must be represented by a symmetrical parabola. However, in practical measurements of the electrophoretic velocities of sedimentary particles such as pulp fines and fillers, the distribution curve of velocities was found to be asymmetrical about the cell center. Thus use of the conventional method often gives rise to a serious error. The reasons for this are discussed and an improved method is proposed.
The time-dependent changes in zeta potentials (ZP) of clay and monodispersed polystyrene latex with added polyethyleneimine (PEI) or cationic polyacrylamide were investigated by the improved method. For instance, the ZP of clay, which was -42 mV originally, became +9 mV just after addition of PEI at a level of 0.1 % on clay, decreased rapidly at an initial stage, became -13 mV after
1 hr and finally reached -17mV. The rate of change in ZP varied widely with the degree of agitation, the addition level of polymer, the molecular weight and so on. The highest difference between initial and final ZP we have obtained hitherto is over 50mV. These phenomena must be closely related to the conformational change of polymers sorbed on solid surface and will offer important and fundamental information on how to use polymer additives in papermaking.It has long been known that certain simple chemicals can either accelerate or retard the rate of refining of pulps. Based on surface adsorption and osmotic pressure considerations, a hypothesis is proposed to provide a rationale for the behavior of these chemicals. The validity of this theory is demonstrated by the prediction of the effectiveness of a colorless, photostable chemical as a new beating aid and the verification of its performance as an accelerator for the refining of both chemical and mechanical pulp as well as secondary fibers.
The adsorption of a cationic polyelectrolyte onto cellulose fibers in the presence of aluminum species was investigated. Solutions of either aluminum chloride or aluminum sulfate (alum) were used in the pH range 4.1-5.5. An apparatus was designed to simulate the mixing and turbulent conditions and to permit the short polyelectrolyte adsorption times found on typical paper machines. The effect of the aluminum species on the polymer adsorption depended on their concentration, counter-ion, pH, and time. From a knowledge of the equilibria of the aqueous aluminum species, it was possible to identify two distinct pH regions for aluminum and polyelectrolyte adsorption. At low pH, only soluble aluminum species were present and both aluminum salts reduced the rate and amount of polymer adsorption. At high pH the two aluminum salts formed distinctly different precipitates having very different effects upon polymer adsorption. The adsorption characteristics of each region are discussed and related to papermaking.
The carboxyl group content of a series of carboxymethylated pulps has been determined by a colloid titration method, by conductometric titration and by means of 14C-labelling and the values obtained by the different methods have been compared.
It is shown that, under certain experimental conditions, the colloid titration method can be used to determine the carboxyl group content of cellulose fibers.
- 1985
Oxfordpp 543-576The Relationship Between Strength and Light Scattering Coefficient for Filled PapersAbstractPDFThe apparent light scattering coefficient of a filler can be shown to be dependent on pulp type, freeness and sheet forming conditions . This is because a large part of this apparent light scattering is in fact due to the effect filter has on pulp. In this paper an attempt is made to provide a mechanistic model for the interaction and provide a quantitative expression relating light scattering to the effect of filler on the fibre as represented by the change in sheet strength. Examples are given of the use of this model to explain the effects of changes in wet pressing pressure and filler aggregation on the apparent light scattering of the filler.
Lack of surface strength in coated paper can cause significant problems both in offset printing and in different converting operations. Several factors can influence this surface strength. The first part of this paper summarizes previous work concerning the relation between the mechanical properties of the coating film itself and the dry surface strength of coated paper. From studies including both clay and CaC03 pigments, it was concluded that both the in-plane mechanical properties of the coating films and the dry surface strength were to a large degree determined by the choice of pigments and the type of styrene-butadiene (SB) copolymer used as binder. The difference between clay-based and CaCO3-based coatings was of special interest in this study. The second part of this paper describes a laboratory method for measuring the wet strength of coated paper. The method has been applied to paper coated with either clay or CaC03, the coatings being bonded with different amounts of SB. The fracture in the coating in the wet state is shallow and, contrary to the fracture in a dry coating, does not penetrate down to the base paper. The particles removed are also rather small, typically 10-30 4m in diameter. Paper coated with CaC03 had a higher wet surface strength than paper coated with clay. This may be due to a higher degree of adhesion between CaC03 and SB than between clay and SB, which would yield a higher water resistance.
A reliable and reproducible testing procedure for the development, product improvement and production control of pressure sensitive copy papers (PSP) is described.
The crucial aspect of the testing procedure (FM-test) is the alignment of many small individual areas so close to each other that a full tone area results from the contact between and partial overlapping of the individual areas. The full tone area surface copies of practically any size, characterized by a very uniform appearance of intensity, can be measured very simply by means of commercially available remission photometers or densitometers. Another important aspect of the FM test is very good reproducibility and adjustment of the writing force, which is the key to reliable conclusions concerning changes of quality and their causes.
Mathematical and statistical evaluations point out that the quality of PSP can be described by a “characteristic curve” (CC), showing the change of image intensity as a function of writing force. A three-parameter equation for the CC allows an easy calculation of several quality criteria characterising the PSP, without the need of performing a multitude of different tests. In an example, discussed in more detail, it is shown, which paper qualities affect the performance of a PSP and how quickly and reliably the correlations can be evaluated by the FM-test.
The distribution of filler particles in printing papers increases in importance with increasing filler content. In this paper it is shown that conclusions about the chalk distribution can be made from formation measurements on sheets before and after removing the chalk respectively. Chalk can be chemically removed using an HC1-Propanol solution.
Measurements of filler distribution have been made on fine paper containing 35-70% chalk. The sheets were formed in a twin wire, roll former laboratory machine at 500 m/min. A three component dry strength,/retention aid system was used, including starch, one anionic polymer component, and one cationic polymer component. Both when using a strategy for maximum retention and for optimum formation it was found that the local filler grammage was proportional to the local fiber grammage.
Measurements of formation on base paper and roll coated paper respectively revealed that there is a strong negative correlation between local filler grammage and local fiber grammage, which results in very even formation of the coated sheet.