Kaolin physical properties

Special surface modifications are available to further improve reinforcement. The objective of the surface treatment is to increase filler loading and/or improve physical properties without loss of rheological characteristics. A variety of surface-modified kaolins have been introduced including clays treated with silane, titanate, polyester, and metal hydroxide. Silane-treated kaolin is used in applications requiring maximum aging characteristics in the service environment. 

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

Kaolin s physical properties (Table 4.4) depend on the calcining temperature as well as on contamination by minerals. Calcination increases the oil absorption and improves the optical brightness, opacity and dielectric properties, together with the water absorption and hardness, but decreases the reinforcing capacity. 

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. 

Standard water-washed kaolins come in a variety of particle size distributions, ranging from 0.2 to 9.5 pm in median particle size. These wet-processed clays tend to have more uniform physical properties and are preferred for uniformity and specific properties such as increased loadings and improved molding characteristics. Water-washed clays can be used as rheological modifiers in conjunction with other extenders to optimize flow characteristics and reduce cost... 

Calcined kaolin elay acts as ingredients, used in formation of washing powder and liquid blue. It is eomposed of Fe203, AI2O3, Ti02 and moisture content. Whiteness and fine partieles are main two characteristic features of it. Percentage of physical property and chemieal eomposition are listed in Table 12.6. 

Consists of up to 95% mullite crystals. Made from pure kaolins. Chemical and physical properties are those of mullite. (See MULLITE, KYANITE, CLAY.)... 

Special fine-particle kaolin clays are commonly used in rubber compounding as economic diluents, mainly to reduce the cost and improve processability. Clays that are used by the rubber industry require further processing to remove larger particles and impurities, which prevents the decrease of the rubber product s cured physical properties. 

Vimonses, V., Chong, M., and Jin, B. (2010) Evaluation of the physical properties and photodegradation ability of titania nanocrystalline impregnated onto modified kaolin. Microporous Mesoporous Mater., 132, 201-209. 

When maximum loading of the carrier is not required a combination of carrier and solid diluent may be employed. Often in these situations a first concentrate of liquid active on a sorptive carrier such as attapulgite will be prepared. The concentrate is then diluted with a solid diluent such as kaolin or diatomite. A solid diluent other than the carrier will be used to impart a particular physical property such as free flow, or will be used to reduce the possibility of chemical decomposition of active ingredient during storage. 

Inert matrix—normally, the inert matrix is a clay, such as kaolin, used to confer physical properties ... 

Additives. There are many types of additives used by the papermaker to modify the physical and optical properties of the sheet. The most commonly used include kaolin and titanium dioxide for optical properties, starch for strength and rosin sizes for water repellency. All these materials can affect the electrical properties of the paper since they can eventually modify the nature of the interfiber contact as well as the fiber itself. These changes can influence the flow of charge through the sheet. 

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. 

---