Silane-modified kaolin

Zhang et alP prepared highly filled NR composites based on silane-modified kaolin (SMK), precipitated silica (PSi) and their mixed-compound additions (SMK + PSi) by melt blending. It was found that these highly filled NR/SMK composites exhibited outstanding mechanical properties, exeellent gas barrier properties and much higher thermal stability, compared to the pure NR. The gas barrier properties of NR composites with SMK and PSi were much higher than those of NR/PSi composites, and better than those of NR/SMK. 

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. 

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. 

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. 

Additives used in final products Fillers antimony trioxide, aramid, barium sulfate, boron nitride, calcinated kaolin, carbon black, carbon fiber, glass fiber, glass spheres, mica, montmorillonite, talc, titanium dioxide, zinc borate Antistatics antimony-doped tin oxide, carbon nanotubes, polyaniline, polyisonaphthalene Antiblocking calcium carbonate, diatomaceous earth, silicone fluid, spherical silicone resin, synthetic silica Release calcium stearate, fluorine compounds, glycerol bistearate, pentaerythritol ester, silane modified silica, zinc stearate Slip spherical silica, silicone oil ... 

Wollastonite and kaolin are most frequently modified by silanes. " Several water-borne products are now available for this purpose, including those with functional amines, diamines, and vinyl-amines. ... 

One of the reactions which occurs on the surface of filler particles is that involving silanes. Vinyl silanes and mercapto silanes being typical examples. Kaolin modified with an isocyanate can react with polyols. Magnetic resonance spectroscopy was used to identify various crosslinks involving the filler and this shows that crosslinked rubber chains were attached to the surface of the carbon black. 

The immobilisation of optically active alkenes on the silica surface by combined hydrosilation and sol-gel technology has been studied. The silanol and silyl groups in silicas which have been silylated with Cg chains have been estimated by Si NMR spectroscopy. Dehydroxylation and silanisation of the surfaces of sihca have been investigated. A A1 and Si NMR study of silane surface modified calcined kaolin has been reported. C NMR spectroscopy has been used to establish the bonding trihydrosilane to Ti02 particles. ... 

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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