Chalking sealants

HR is also used to a limited extent in making chalking sealants. 

Calcium carbonate occurs in nature as hmestone in various forms, such as marble, chalk, and coral. It is probably the most widely-used raw material in the chemical industry. It has numerous apphcations, primarily to produce cement, mortars, plasters, refractories, and glass as budding materials. It also is used to produce quicklime, hydrated lime and a number of calcium compounds. It is produced either as powdered or precipitated calcium carbonate. The latter consists of finer particles of greater purity and more uniform size. They also have many important commercial apphcations. Various grades of precipitated calcium carbonate are used in several products, such as textiles, papers, paints, plastics, adhesives, sealants, and cosmetics. 

C-792 TM for effects of heat ageing on weight loss, cracking and chalking of elastomeric sealants. 

Drying sealants are represented by solutions of rubber blends in organic solvents. As soon as the solution is impregnated into the clearance and the solvent evaporates, the sealant becomes rubbery and gains elasticity. The original compositions contain adhesive additives (coumarone, terpenic and phenolic resins, rosin or its esters), PI and solvents (toluene, xylol, benzine, etc.), fillers (chalk, titanium dioxide, talc, etc.) and stabilizers. These compositions can be easily impregnated with Cl [15]. 

Acetoxy sealants are widely being used in a large number of applications in the construction industry. Where they are incompatible with specific substrates, they can be replaced by neutral cure systems. The alkoxy and oxime cure systems are available in either transparent (silica-filled composition only), or non-transparent/solid colour (silica-and/or chalk-filled composition containing appropriate pigment) versions. Their chemical neutrality enables these systems to offer a wide range of adhesive-bonding capabilities to... 

The classes of fillers used in formulating polysulfide oligomers are calcium carbonate (wet or dry ground limestone, chalks, or precipitated carbonates), carbon blacks (furnace and thermal), clays (calcined), silica and silicate fillers, and titanium dioxide (rutile is chalk resistant and preferred over anatase). In general, sealants are prepared using a combination of fillers to attain desired properties. 

Fillers reinforce and increase the volume of the sealant. Fillers also reduce formulation costs and affect the technical properties of the sealant itself Common fillers for sealants are calcium carbonate (chalk), aluminum silicate (clay), barium sulfate and sihdc acids. Finely divided fillers, such as talc and Microdol 1, reduce the surface tack while simultaneously stiffening the film. Thixotropic fillers, for example fumed silica or Si02, improve the gunnabihty and reduce the sag of the compositions. Pigments are used to color sealants the white pigment used is usually titanium dioxide. 

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