Kaolin grades, properties

Table 13.2 Typical physical properties of water-washed hydrous and calcined/silane-treated kaolin grades [8].

Table 13.3 Miscellaneous properties of specific kaolin grades.

Kaolinite, 2 345t 6 659-664, 686-687, 718 composition in bauxite used for alumina production, 2 346t structure and composition, 6 668 in unit layer mixtures, 6 671 Kaolins, 6 686. See also Kaolin dry process, 6 673-675 estimated total production, 6 683 grades for polymer applications, 6 694t properties relating to applictions, 6 686t uses, 6 686-696 wet process, 6 675-679 Kapok, 11 297... 

It has good dielectric properties, electrical resistivity and chemical resistance, and is particularly favoured in polymers for electrical cable insulation. Grades for wire and cable are normally first calcined, i.e., strongly heated to remove most of the surface hydroxyl groups. Between 450 and 700 °C kaolin is converted to metakaolin, and at temperatures around 1000 °C it imdergoes further changes to form defect spinel. 

Kaolin deposits are cored and analyzed before mining to determine quality. Mined clays are then either wet or dry processed by air floatation or water fractionation. Surface-modified clays can be made by treating standard, delaminated, and calcinated grades with surface modifiers. The treatment can be performed by either the supplier or the end user. These surface modifiers include silane, titanate, polyester, and metal hydroxide. The objective of these surface treatments is to increase filler loadings and/or improve physical properties such as melt viscosity, thermal stability, and modulus without loss of physical characteristics. Electrical applications represent the largest use of surface-modified kaolin in plastics. 

Mineral fillers are used to improve the physical and optical properties of paper. Usually, they comprise 5-15% of the weight and even more than 30% in some paper grades. The most common fillers are clay (kaolin), calcium carbonate, talc and titanium dioxide. Different dyes and pigments are added to the stock to colour the paper. Basic dyes are in most abundant use today, but acidic and direct dyes are also used. 

The properties of two raw polymers (PBT and ABS) are shown in Table 1. These would be averaged by the blending of two pol3rmers. Reinforcements of PBT/ABS blends were done with glass fibers, glass flakes, mineral fillers (mica, talc, kaoline, and/or wollastonite). Due to the increase of PBT crystalhnity the reinforced grades show great increase of the heat deflection temperature (this phenomena is absent in the amorphous polymers). 

The grade of kaolin employed is selected so that the volume median diameter is greater than about 2 microns and less than about 10 microns. Depending on the physical and biological properties of the particular active ingredient, the Irnal concentration of pesticide in granules can be as low as 10% w/w or as high as 80% w/w. 

Kaolin (clay) is a widely used filler for thermoplastic polymers because of its reinforcing effects on mechanical properties, such as stiffness and strength, with however certain negative effects on impact resistance. Clays are typically used at 20-50% wt in polymer composites, and commercially available grades have aspect ratio between 4 and 12, and average particles in the 0.5-2.3 pm range. Because kaolin has a platelike structure with a high... 

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