Clays silane-treated calcined clay

Clay minerals are widely used in the filler industry and the production of the various types has been described by Hancock and Rothon [85]. The products available range from unaltered kaolin to products produced by calcination. Kaolin deposits are widespread throughout the world. While simple clay minerals are extensively used as fillers in elastomers, their use in thermoplastics is more restricted and the principal products used are those obtained by calcination of ka-olinite. Thus metakaolinite finds application in PVC and silane treated calcined clay in polyamides. The production of these forms only is discussed below. 

When silane-treated, calcined clay can be used in polyamide and polybutylterephthalate (PBT) moulding compounds and in very high-voltage rubber cable insulation. Each application needs a silane with a different functionality. 

Silane treated, calcined clay 70.0 Mineral filler Level 1 filler evaluation... 

Non-black fillers may also be employed, but it is important to use neutral or medium high pH grades such as silane-treated calcined clay, synthetic sodium aluminum silicate, platy talc, neutral pH silicas, diatomaceous earth, hydrated aluminum silicate, calcium meta silicate, precipitated calcium carbonate, and so on. An indication of non-black filler requirements for one point of hardness increase is shown in Table 5.10. 

Organofunctional silanes are used to promote polymer-to-filler bonding with clay or siHca fillers. Vinyl silanes are used in peroxide-cured wire insulation to promote stronger bonding with calcined clay fillers. Mercapto silanes are used to treat kaolin clay in sulfur-cured compounds. 

Both kaolin and calcined clays are available with surface treatments. Many treatments may be applied but few have any commercial importance. Kaolins are available treated with surfactants and pH adjusters, which produce kaolins that may be dispersed directly into water, (e.g., rubber latices), or with amines to enhance cure performance. Stearic acid treated products may provide ease of dispersion. The most important treatments, technically, are the organo-silanes. 

The calcined clays such as Whitetex are neutral and have lower water absorption and better electrical properties, but slightly lower physical properties. Vinyl silane surface treated calcined clays such as Translink 37, amino-silane treated calcined Translink 445 have even better water resistance and electrical properties. 

With filled compounds, it is necessary to avoid consumption of the adhesion promoter through coupling instead to the filler surface. Thus, calcimn carbonate is the preferred filler with silane adhesion promoters. Calcined clay or ATH may be used if previously silane-treated. Compounds containing reactive silanes should be processed promptly. The use of titanates or zirconates as adhesion promoters should be carried out in close cooperation with the additive supplier. 

Clays are probably second in popularity after carbon blacks in their use in the rubber industry. There are various qualities grouped under the terms soft, hard, calcined, and treated. Sometimes they are sold treated (e.g. with fatty acids, oils, silanes and silicones) to improve properties. Calcined clays are particularly important in EPMs and EPDMs and they are currently used in the production of insulating compounds for low, medium and high tension cables. 

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. 

There are many versions of clays (hydrated aluminum silicate) available including soft clay, hard clay, air floated, water washed, calcined, and surface-treated versions. Surface treatments include stearates, mercapto-silane, vinyl silane, and amino silane. Select the silane treatment that is compatible with the cure system to be used. Clay may be used in large quantities, is inexpensive, easy to incorporate, calender or extrude and provides some reinforcement to NBR compounds. 

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