Microparticle retention, paper

In the pulp and paper industry, mineral raw materials are traditionally called pigments , whether or not they are used to affect color. The use of mineral pigments in the pulp and paper industry fall into five major catagories filling, coating, pitch control, deinking of recycled papers, and microparticle retention. The minerals comonly used for each job are ... 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Combinations of cationic starch and anionic microparticles are useful commercial systems. Shear-sensitive flocculation occurs, allowing microscale reflocculation in the formed paper sheet, which improves dewatering and retention.63,75,76 The microparticles can be colloidal silica, aluminum silicate, poly(silicic acid) or bentonite of specific size and surface area.77 79 Cationic, anionic or polymeric aluminum-containing compounds can be additional components. A three-part coacervate system uses a high molecular weight anionic polyacrylamide, cationic starch and silica.80 Cooking cationic starch in the presence of an anionic silica hydrosol was reported to improve drainage and retention.81... 

A novel sizing strategy utilizes a microparticle system that enhances retention.166 A representative example is a combination of cationic potato starch (DS = 0.04), a metallosilicate hydrosol and AKD. In an approach to combine elevated filler retention, effective sizing and high paper strength, calcium carbonate is reacted with a starch-soap complex and combined with AKD.167168... 

In contrast to microparticle-containing systems, which were widely used in the paper industry, the classical dual retention aid systems (polymer-polymer) are said to give high retention combined with a poor dewatering [19]. But, some researchers were able to show that an optimized polymer-polymer system has many advantages, such as good dewatering, superior retention, and shear-resistant floes. 

For multi-component-retention systems the cationic species is added before the screens and the resultant floe are allowed to be broken down before the anionic microparticle(s) is (are) added just before the headbox. The paper making process is illustrated schematically in Figures 6.22 and 6.23. 

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