Kaolin in plastics

Fajardo W L, Kaolin in Plastics and Rubber Compounds. Engelhard Corporation, 1993. 

Fajardo, W. (1993) Kaolin in plastic and rubber compormds. Technical Report, Engelhard Corp., Iselin, NJ. 

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. 

The major use of kaolin in plastics is for calcined grades in PVC wire insulation to improve electrical resistivity. Air floated and water washed grades are used in thermosets to ensure a smooth surface finish, and... 

Layered clay silicates, generally from the intermediate-grained montmorillonite kaolin clay, are often used as filler in plastics and in the production of pottery and other ceramic items. These silicates consist of the silicate sheets held together mostly by the sodium cation with lesser amounts of other metal ions, such as iron, copper, nickel, etc. There are several approaches to open these silicate layers. 

Kaolin in the mixes has been partially or completely replaced by white-firing clays with good plasticity (cf. Table 4). The mix composition varies over fairly wide ranges some types also contain CaCOj. The so-called hard feldspar earthenware has the following composition 50 —55% clay components, 35 —45 % quartz, 6 —12% feldspar. 

Kaolins.— The first class of materials, usually of geologically primary origin, consists, in the purified state, of white clayey matter, containing both the crystalline and amorphous varieties of clay base. In some of these clays the crystalline constituents predominate, as in the North Carolina kaolins. The plasticity of these clays is but feebly developed, though where the granular matter has been broken down by the action of water or other agencies to the amorphous condition, a fair working quality may result. These clays, on account of their whiteness, are used in the pottery industries. 

Forming techniques used for clay-based ceramics require control of water content in the batch. Water content, in turn, affects the response of the clay during forming [27], As the water content of the batch increases, the yield point of the clay-water mixture, and thus the force required to form the desired shape, generally decreases [26], However, the relationship is complex and depends on the composition of the clay, its structure, additives to the batch, and other factors [14], One method for quantifying the behavior of clay-water pastes is to measure the plastic yield point as a function of water content [14], The water contents and maximum yield points in torsion are compared for several clays in Table 9. Kaolins and plastic fire clays require the least amount of water to develop their maximum plasticity, ball clays require an intermediate amount, and bentonite requires the most. 

Mineral fillers such as mica, kaolin, calcium carbonate, and talc are frequently incorporated in thermoplastics to reduce the costs and improve the properties of the polymers such as rigidity, durability, and hardness [30]. Talc is common filler in plastics as it serves as the most cost effective filler. Previous researchers have... 

Chem. Descrip. Kaolin CAS 1332-58-7 EINECS/ELINCS 296473-8 Uses Extender, pigment in paints and primer systems, bulk molding, compds. in plastics, water-based adhesives, caulks, sealants, and letterpress inks... 

Kaopaque 10 [IMERYS] them. Descrip. Kaolin CAS 1332-58-7 EINECS/ELINCS 296-473-8 Uses Pigment for aq. paints, interior emulsion paints pigment and antiblocking agent in plastics (sheet and film)... 

Surface treatment is another value-added step that can improve the performance of kaolin. Since the filler is naturally very hydrophilic due to its hydroxyl groups, a treatment can be applied to render its surface hydrophobic or organophilic. These surface-modified kaolins are useful especially in plastics and rubber industries, where they improve adhesion and dispersion and hence act more effectively as functional fillers. Silanes, titanates, and fatty adds as discussed in Chapters 4-6, respectively, may be used to modify the surface charaderistics of either hydrous or calcined kaolins, promoting dea lomeration, often lower viscosities, and improved mechanical and eledrical properties. 

In North America, about 11000 tons of hydrous kaolin was sold for 2.1 million to the plastics industry in 1999 forecast for 2004 was a 2.5% growth in tons per annum to 12 000 tons [11]. Of the calcined kaolin consumed, the use in plastics accounted for... 

Metakaolin is an effective functional filler in plasticized PVC wire insulation at loadings of about 10 phr. It better protects the insulation from cracking or treeing, a term that describes the physical breakdown of the cable polymer matrix due to moisture or other external influences. Volume resistivity greatly improves when metakaolin is incorporated compared to other minerals (see Table 13.9) [15], although the color is not as white as with higher temperature fully calcined kaolin. In addition,... 

Kaolin is a low cost, naturally occurring, white or pale coloured mineral, very widely used in the paper industry but also to a lesser extent in plastics for cable insulation, wire coating, footwear, flooring, pipes, window frames, garden furniture, agricultural film, medical devices and automotive parts. It is mined in North America, Brazil, the CIS, Europe and Australia. 

Kaolin or china clay, like many minerals, is used much more widely outside the plastics industry than within it, especially in the paper industry but also to a lesser extent in paint, rubber and pharmaceuticals. It is currently used to improve the electrical properties of PVC wire and cable insulation. Other applications are in automotive parts and as an antiblocking agent in plastic films. It can benefit thixotropy, and calcined kaolin can improve dimensional stability. (Calcined kaolin is also competing with silica in the antiblocking agent market.) Polarite 102A from Imerys is an example of a premium kaolin product, targeted at polyamide automotive applications. 

Kaolin producers have been under pressure from over-capacity and have also faced intense competition from groimd calcimn carbonate in the very large paper market. Because of this, some suppliers have diversified. Kaolin accounts for 6% of all fillers used in plastics worldwide, mostly in PVC and polyamides. 

US consumption of fine particle-sized calcium carbonates (which improve brightness and reduce absorption in a variety of polymer matrices) is expected to reach about 176 SOO tonnes by 2003. valued at US 38.6 million. Use of fine-particle kaolin and other clay-based fillers in plastics will total 57 600 tonnes, valued at US 21,7 million, and compounders and resin producers are expected to increase use of fine-particle and surface-treated alumina trihydrate by 6.2% per year, from about 30 800 tonnes in 1998 to 41 700 tonnes by 2003. 

The role of mineral fillers in plastic compounds is changing. In the past they were used to reduce costs by replacing polymer content by a less expensive material. Now they have a more important role to play since their use can modify processing characteristics or the properties of the finished part. Other uses include their ability to reduce the content of more expensive additives, notably pigments, flame retardants and impact modifiers. Nanomaterials are coming to the fore as potential fillers along with the more traditional options of alumina trihydrate, barium sulfate, calcium carbonate, kaolin and talc. 

The largest alternate use for kaolin clay is in paper manufacture. Kaolin clay is also used as an extender and filler in plastic compounds as well as in adhesives and coatings formulations. Last but not least, it is used in the production of ceramics. 

The primary mineral fillers and reinforcements in plastics are calcium carbonate, kaolin, talc, mica, wollastonite and silica. Calcimn carbonate is by far the mineral most commonly used to fill plastics. This is mainly because it is low in cost, widely available and provides a good balance of properties. Calcium carbonate may be pure or in combination with magnesium carbonate as a dolomitic limestone. Dolomitic limestone is harder than pure calcium carbonate and is preferred when abrasion resistance is needed, as in floor tiles. 

The market for talc in the United States based on the 1995 U.S. Geological Survey Annual Review (3) is summarized in Table 2. Ceramics was the biggest market, having almost 35% of the total, followed by paint, paper, and plastics. Outside of the United States, especially in Asia, paper is the principal apphcation. In that region talc is available locally at lower cost than competitive minerals such as kaolin. 

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