Retention of fillers

The retention of fillers in the sheet during the forming process is important. Both hydrodynamic mechanisms and colloidal or coflocculation phenomena are significant in determining filler retention (7). Polymeric retention aids are used to bridge between filler particles and fibers. Talc is sometimes used with mechanical pulp furnishes in order to reduce the deposition of pitch-like materials onto paper machinery. 

This means that the retention of fillers is likely to be very sensitive to pH and this is indeed found to be the case in commercial machine operation. There are also other important implications of the effect of pH on charge in the paper-making system, in particular on the interaction of fibre and filler components with cationic additives and these are discussed more fully both later in this chapter and in Chapter 7. 

Jaycock, M.J. et al.. Effect of cellulose fibre fines on the retention of fillers, J. Appl. Chem. Biotechnol., 26, 370, 1976. 

Blancol . [Rhone-Poulenc Surf.] Sodium naphthalene-formaldehyde condensates thinning, dispersant, peptizing agent, dye-leveling agent used in paper industry for slime ctmtrol, improved retention of fillers or fines, improved sizing. 

Retention - increased first-pass retention of fillers and fines, increased ash content of the sheet, reduced losses to effluent... 

Poor retention of fillers and fines caused by the poor retention and/or wet-end imbalance can also result in deposits of filler/fines/size at the presses and press felts and pre-dryer doctor blades. 

Uses Paper sizing aids retention of filler and fiber aids pH control boiler water treatment food additive migrating to foods from paper/paperboard... 

Higher magnification of the washed composite fillers shows that filler is precipitated in the pits and surface of the pulp fibres (Fig. 5.10). Significant proportion of filler is agglomerated and patches of filler are observed on the surface of the fibres and fibrils with Supermass colloider refined samples. Valley beater shows reduced agglomeration and retention of filler in the washed samples. Also, a minor fraction of calcium carbonate is precipitated inside the pits of fibres. 

New insights into the retention of fillers with VEO. Journal of Pulp and Paper Science, 22 (7), 1257-1263. 

Another difference between hot and cold elastomeric SBR latices is that hot types are carried to < 90% conversion and not normally shortstopped. The cold latices are usually shortstopped at ca 60—80% conversion. Again the desired physical properties of the contained copolymer are responsible for these differences. Cold latices are used in applications where the modulus, eg, in foam, or retention of physical properties at high filler loadings, eg, in fabric backing, are required. The cold latices are generally suppHed at a higher soHds concentration than the hot series because of these uses. 

Resin cements have excellent aesthetic quahties and are essentially insoluble in mouth fluids. Compressive strength is low, but can be increased by the addition of fillers. They have no inherent adhesion to the tooth. Retention is dependent on mechanical locking when the cement flows into irregularities on the surfaces of the substances being cemented. 

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. 

Retention and drainage aids are chemicals which are added to the fibre and filler suspension to assist the efficiency of the filtration process. Growth in recent years in the use of retention aids has been greater than that of almost any other paper chemical additive. It has been caused by a combination of factors increased machine speeds, the increased use of filler in alkaline systems, the increased use of recycled paper and the growing tendency to use fillers in newsprint. Retention aids are water-soluble polymers which may be cationic,... 

The property retention when the temperature rises is generally excellent but depends on the matrix, the nature and level of fillers and reinforcements, and the base properties. 

Alkyd molding compounds, when molded into finished parts, may have excellent arc resistance (180 sec. minimum) and excellent arc track resistance. Other good electricals such as dielectric strength and insulation resistance can be obtained. The filler combinations may also result in excellent dimensional stability and outstanding retention of electrical and physical properties after exposure to elevated temperatures (450°F.) for long periods of time. Water absorption values are extremely low, which helps to maintain electrical values. 

The UL temperature indexes for a variety of engineering plastics are in Table 4. Glass-filled PPS compounds exhibit a high UL temperature index, which indicates excellent retention of properties for long-term exposure to high temperature. Other fillers, eg, mineral (talc), may also be used. ... 

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