Clays silane-treated kaolins

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. 

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. 

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. 

If silica or kaolin clay is treated with a silane coupling agent that is reactive in a sulfur-cured rubber formulation, these minerals can replace carbon black... 

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. 

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. 

Kaolin clay (Superex, J.M. Huber Co.) was treated in aqueous slurries with silanes and dried. All of the rubber clay compositions were prepared by mill-mixing the clays into the rubber before adding the remaining ingredients. Recipes shown in Table 3 were selected from data from suppliers to the rubber industry however, since a control was included with each rubber, the treated samples can best be evaluated in comparison with each other. 

Vinylsilane oligomers, such as a partially hydrolyzed vinyltrimethoxysilane and vinyltrimethoxysi-lane (sometimes including dimethylsiloxy species in the structure), have been developed as premium treating liquids for kaolin clay reinforcements [19]. Silane additives, such as vinyltriethoxysilane or vinyl (tris-methoxyethoxy) silane are often added during compounding to enhance properties. 

Surface-treated clay - This is processed kaolin diat has been surface modified (e.g., with stearates or silanes) to improve compatibility with and performance in organic matrices. 

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