Surface-modified 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. 

PolarlinkR. [ECChit l.] Surface-modified kaolins for rubber industiy. 

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. 

Surface modifier Chalk Precipitated CaCO, Kaolin Precipitated S102... 

Applications. The following uses of contact angle were reported in the literature surface energy of different sizes for fibers, correlation between contact angle of fiber and interlaminar shear strength of composite, effect of surface treatment of fillers for paints, the matrix-filler adhesion parameter for PS filled with CaCO, dispersion stability of PEO-modified kaolin particles, determination of contact angle of carbon fibers and its dependence on treatment, wettability of fiber sur-... 

In another study, a highly impact-modified copolymer PP resin was extruded and then injection molded. The surface-treated kaolin doubled the flexural modulus... 

Description Surface-modified, high brightness low residue calcined kaolin, giving direct reaction with compatible polymer compounds in presence of a peroxide ... 

Boron oxide particles were incorporated to silicone rubber-based mixes containing fumed silica (reinforcing filler) and reference mineral fillers - aluminum hydroxide, wollastonite, calcined kaolin, mica (phlogipite) and surface modified montmorillonite with dimethyl-dihydrogenatedtal-low quaternary ammonium salt. Acidic character of boron oxide, which can disturb the peroxide curing process, was compensated by addition of magnesium oxide. The influence of boron oxide particles on properties of composites was determined and mechanism of their ceramization process studied. 

Scanning electron microscopy (SEM) pictures of composite samples ceramized slowly under heating from room temperature to 1000 °C during 2 h demonstrate good adhesion between ceramic phase components in the composites filled with mica (MIC - Cl, C2), wollastonite (WOL - El, E2) and aluminum hydroxide (ALOH - Al, A2). Far worse adhesion is observed for the samples containing calcined kaolin (C-KAO - Bl, B2) and surface modified montmorillonite (M-MMT - Dl, D2) (Fig. 8.8). 

FIGURE 8.8 Micromorphology of composites after heating form room temperature to 1000 °C during 2 h SEM photographs of composites containing (a) aluminum hydroxide, (b) calcined kaolin, (c) mica, (d) surface modified montmoiillonite and (e) wollastonite. 

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. 

The BET specific surface area values are listed in Table 2. Acid treatment at room temperature did not significantly modify the surface area of the metakaolin, thus confirming the low effectiveness of this treatment. Activation at 90°C during 6 h produces solids with relatively high surface area, 200 m g, when the kaolin is calcined from 600 to 800°C. These high values are due to the formation of an amorphous silica phase during this acid treatment. However, the solid obtained from MK-900 has a surface area of only 59 m g", due to the above mentioned sinterization of the kaolin at this temperature. 

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. 

Surfactant adsorption on the reservoir surface is another important factor to be considered when using foams in EOR processes is discussed in [258]. Adsorption experiments with surfactants of different structures were performed on cores of a number of materials (quartz, sandstones, kaolin, calcite and others), both clean and modified (impregnated) with hydrocarbons of various structure ( light oil, high-viscosity oil, asphaltenes). Minimum adsorption, as well as maximum oil recovery based was observed when using amphoteric surfactants as well as surfactant mixtures, e.g. diphenyl ether disulfonate - a-olefin sulfonate (DPES-AOS). 

A new area of development is to incorporate the filler permanently into the polymer matrix, by use of coupling reactions. This can increase impact strength and thermal properties of polyamides and modify the anisotropy of partially crystalline plastics, such as polyamides and polyesters. In polypropylene, bonding with kaolin can also improve scratch resistance, which is a useful benefit for automobile interior applications. Surface modification of fillers such as silica, mica, and wollastonite allows these to penetrate markets that were formerly the province of reinforcements such as carbon black and glass fibre. 

The interaction between modified starch and sticky-containing wastewater was mentioned in Sect. 3.2. of this article [67, 68]. Mihai [141] investigated chitosan-based nonstoichiometric PECs (NPECs) as specialized flocculants. Such NPEC were more effective than chitosan in kaolin separation. Their main advantage is the increase in critical concentration for kaolin restabilization. The NPEC particles were adsorbed on the kaolin surface, protecting them more efficiently against re-dispersion. 

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