Calcium carbonates , fillers aragonite

Calcium carbonate (1873) (aragonite, calcite, chalk, limestone, lithographic stone, marble marl, travertine, and whiting) n. CaCOs. Grades of calcium carbonate suitable as fillers for plastics are obtained from naturally occurring deposits as well as by chemical precipitation. The natural types are prepared by dry grinding, yielding... 

Calcium carbonate exists in three crystalline modifications (calcite, aragonite, vaterite), but only calcite has practical importance. It can be found in large quantities all over the world, but fillers mined at different locations differ considerably in purity, size of the crystals and origin, which all influence their use as fillers. In nature, it can be found in three different forms limestone, chalk and marble. Limestone is a consolidated sedimentary rock formed by the deposition of shells and skeletons of marine organisms, chalk is soft-textured limestone laid down in the cretaceous period and consists of nanofossils marble is metamorphic limestone formed under high pressures and temperatures. CaCOj occupies second place in usage behind talc in PP. 

Unfavorable combinations and/or choice of chalk (natural calcite, precipitated cal-cite/aragonite) may cause discoloration in the form of yellow spots in chalk-filled PVC [685]. The formation of yellow spots is attributed to oxalic acid (salts) detected by FTIR-spectroscopy. The creation of oxalic acid (salts) depends on the presence of calcium carbonate. The type of filler and stabilization determine the rate of calcium oxalate creation [685]. 

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