Precipitated calcium carbonate filler

Fig.2. Transmission electron micrograph of a typical precipitated calcium carbonate filler (courtesy of Zeneca Resins)...

Surface treatment also improves adhesion to the polymer matrix and resulting physical properties. The combination of particle size and surface treatment is critical in the selection of precipitated calcium carbonate fillers to obtain desired properties. Often graded combinations of ultrafine precipitated CaC03 and larger CaC03 particles are used for optimum properties and value. 

Clays - Most commercial clays are classified as hydrous. They are undesirable for use in liquid polysulfide base compounds because of their low pH. However, calcined clays have been found to be satisfactory for use in polysulfide compounds because they are less acidic. The best use of calcined clay fillers is in conjunction with precipitated calcium carbonate fillers to produce a compound with a relatively neutral pH value. For example, calcined clay of the type similar to Icecap K has given good results. 

Calcium hydroxide is used to make precipitated calcium carbonate filler. 

Calcium oxide (calx, quicklime) is hydrated to calcium hydroxide, which is reacted with carbon dioxide to produce precipitated calcium carbonate (filler). 

Vanerek, A., Alince, B. and van de Ven, T.G.M. (2000) Colloidal behavior of ground and precipitated calcium carbonate fillers Effects of cationic polyelectrolytes and water quality. Journal of Pulp and Paper Science, 26 (4), 135-139. 

Plastics. The fastest-growing use of whiting (microcarbonate fillers) is in the plastics industry where dry, pulverized limestone is used intensively for most types of plastics. Other carbonate fillers, precipitated calcium carbonate, oyster sheU, marble, and wet-ground limestone, are also used. 

Calcium carbonate is one of the most versatile mineral fillers (qv) and is consumed in a wide range of products including paper (qv), paint (qv), plastics, mbber, textiles (qv), caulks, sealants (qv), and printing inks (qv). High purity grades of both natural and precipitated calcium carbonate meet the requirements of the Food Chemicals Codex and the United States Pharmacopeia and are used in dentifrices (qv), cosmetics (qv), foods, and pharmaceuticals (qv). 

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOi) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

In an industrial application dissolution/reprecipitation technology is used to separate and recover nylon from carpet waste [636]. Carpets are generally composed of three primary polymer components, namely polypropylene (backing), SBR latex (binding) and nylon (face fibres), and calcium carbonate filler. The process involves selective dissolution of nylon (typically constituting more than 50wt% of carpet polymer mass) with an 88 wt % liquid formic acid solution and recovery of nylon powder with scCC>2 antisolvent precipitation at high pressure. Papaspyrides and Kartalis [637] used dimethylsulfoxide as a solvent for PA6 and formic acid for PA6.6, and methylethylketone as the nonsolvent for both polymers. 

Sulfite paper has a relatively short life span, since residual acid will continue to hydrolyze the cellulose and cause embrittlement. Further sources of acid include aluminum sulfate (which is added together with resin to suppress bleeding or feathering of ink into the paper) and S02 and NO from the atmosphere. Much of the world s library collections and archives will soon be lost as the paper crumbles. Various deacidification treatments (e.g., with ammonia, morpholine, cyclohexylamine carbamate, or diethyl-zinc) have been proposed and tried, but at best they can only halt the process of embrittlement and cannot reverse it.14 With the move to kraft pulping, alkaline peroxide bleaching, and increasing use of precipitated calcium carbonate as a filler, the high quality papers produced today are intrinsically acid free and should also resist subsequent acidification by S02-polluted air fairly well. 

Precipitated calcium carbonates are generally surface-treated to render them hydrophobic and to improve their dispensability in hydrophobic systems. Conventional surface treatment of CaC03 is with fatty acids. However, the use of different types of acids yields subtle differences in filler wettability and polymer compatibility. 

Particle size is important and, for some applications requiring good weathering and impact performance (window profile), the ultrafine milled, high whiteness, natural version is normally used. To ease dispersion, the filler is usually coated with stearic acid. Coated ultrafine and precipitated calcium carbonates are claimed also to have a positive effect on impact properties in impact modified formulations (52, 294, 462). The abrasive wear of calcium carbonate, on melt processing equipment, is not significant but increases with increasing levels (177). 

Uprating PVC compounds often involves the careful specification and addition of mineral fillers. This article discusses calcium carbonate, talc and glass fibre, taking into account their size and their shape factor. Rigidity is sensitive to the shape factor of the filler as is the dimensional stability. This study shows that glass fibre is the most efficient filler. Talc is more efficient than calcium carbonates. The impact performance is very sensitive to the particle size. Precipitated calcium carbonate is the only filler to act as an impact modifier. 12 refs. 

Absorption of C02 in aqueous slurry of lime for the manufacture of precipitated calcium carbonate (which is reused in large quantities as a rubber filler, a pigment, etc.). Here lime is sparingly soluble in water and the reaction occurs between the dissolved carbon dioxide and OH" ions. 

Calcium carbonate fillers are synthesized by precipitation processes. This accounts for the usual term cep being an abbreviation of calcium carbonicum praecipitatum. The following three precipitation processes are used ... 

Calcium carbonate fillers are either of ground limestone type or precipitated chalk type. They are inexpensive and have low oil-absorption, which allows considerable freedom in filler levels while keeping the viscosity under control. Relatively coarse particle size fillers ranging from 30 to 100 mesh are used to incorporate high loadings. 

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