Calcium carbonates , fillers chalk

Calcium carbonate fillers are either of ground limestone type or precipitated chalk type. They are inexpensive and have low oil-absorption, which allows considerable freedom in filler levels while keeping the viscosity under control. Relatively coarse particle size fillers ranging from 30 to 100 mesh are used to incorporate high loadings. 

Calcium Carbonates - Calcium carbonate fillers are available in a wide range of particle sizes and can be obtained as wet or dry ground limestone, chalks, or precipitated carbonates. The carbonates with a coarse particle size reinforce slightly and increase viscosity slightly. However, they are used to adjust rheology and lower the cost of a compound. The coarse and fine carbonates are generally used together. 

In other parts of the world, plywood adhesive fillers are obtained from local sources and may be quite different than those used in North America. In Southeast Asia, banana flour is quite important. In Europe, calcium carbonate (chalk) is often used. Nearly any fibrous material or fine particulate material capable of forming a functionally stable suspension can be made to work if the formulator is sufficiently skillful. However, the mix formulator will be very specific about the type and grade of filler to be used in a particular mix. Substitutions may lead to serious gluing problems. 

Calcium carbonate (CaCO ) can be in the form of an odorless crystal or powder and is one of calcium s most stable compounds, better known in its natural state as limestone, marble, chalk, calcite, oyster shells, and the minerals marl and travertine. Calcium carbonate is the source of lime and is used as a filler for many products, including paints, plastics, and foods (bread), and as an antacid. 

Calcium carbonate is the most commonly used extender. It is widely available and low in cost, and it provides for improvements in certain performance properties. The material is a mineral that is mined throughout the world. Common forms of calcium carbonate include limestone, marble, calcite, chalk, and dolomite. It is manufactured by precipitation processes and is commercially available from a number of sources. Calcium carbonate is available in many different particle sizes and in various grades. To improve dispersion in certain resins, the filler is often coated with calcium stearate or stearic acid. 

Calcium carbonate (also known as chalk) is the most commonly used filler for PVC. This material is mined as calcite mineral and ground to a particular particle size range. It may also be precipitated from solution to give a fine particle size suitable for use in high performance areas. 

Fillers are mainly used for reasons of economy, but in many cases they also improve some properties of the polymer. The most important fillers for polymers are minerals such as talc, chalk and china clay. Filler content generally used with plastics is up to 60 wt%. The most common practice is to feed the filler downstream into the melt by means of a twin-screw side feeder (Figure 6.3). It is well-known that thermoplastic melts with high loadings of small particles such as calcium carbonate, carbon black and titanium dioxide give both yield values in shear flow [58, 59], and uniaxial extension [60, 61]. 

Examples of inert or extender fillers include china clay (kaolin), talc, and calcium carbonate. Calcinm carbonate is an important filler, with a particle size of about 1 pm. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases, the calcium carbonate may be treated to improve interaction with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is a filler with a lamellar particle shape. It is a namral, hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar structures. Other fillers include woUastonite, silica, barium sulfate, and metal powders. Carbon black is used as a filler primarily in the rnbber industry, but it also finds application in thermoplastics for conductivity, for UV protection, and as a pigment. Fillers in fiber form are often used in thermoplastics. Types of fibers inclnde cotton, wood flour, fiberglass, and carbon. Table 1.3 shows the fillers and their forms. An overview of some typical fillers and their effect on properties is shown in Table 1.4. Considerable research interest exists for the incorporation of nanoscale fillers into polymers. This aspect will be discussed in later chapters. 

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 is readily available in all continents and its use in the plastics industry is much greater than that of any other filler. (Quantities used are discussed in Chapter 6.) Important sources of calcium carbonate include limestone, chalk and marble. Ground chalk is sometimes called whiting. 

Calcium carbonate is an important filler with a particle size of about 1 p,m. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases the calcium carbonate may be treated to improve the bonding with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is an important filler with a lamellar particle shape. It is a natural hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar stracture. Carbon black is used as a filler primarily in the rubber industry. 

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. 

In terms of weight, calcium carbonate is the most important filler for plastics and it is also widely used in rubber and paints. Calcium carbonate is, in fact, much more than chalk (as it is universally described in the plastics industry). The term covers natural chalk, limestone, and marble - and also precipitated calcium carbonate, which has a very fine particle size, is relatively expensive, and offers some interesting properties in polymer compounds. 

The addition of chalk increases thermal stabihty of the filled PVC sample, indicated by a longer induction period of dehydrochlorination. Also, the rate of HCl-elimination is lower in the presence of calcium carbonate. Other investigations with unstabihzed PVC samples have shown that the filler acts as a trap for the split-off hydrogen chloride, but it has no influence on the decomposition of PVC. This is confirmed by the UV-spectra of PVC which was heat-treated in the absence and in the presence of chalk. Under both conditions, the same unsaturated sequences in PVC are formed, as shown in Figure 8 (curve a and b). On the contrary, in the presence of stabilizers (curve c) practically no polyene sequences are formed during the induction period. 

Some more investigations, such as variation of the concentration of filler and change of the particle size, were made to get further details about the influence of chalk in PVC. It could be shown that the stabilizing effect increases with the content of calcium carbonate in the mixture. But there is a maximum at about 30 phr filler because of the increase in shear viscosity in the used processing machines which leads to an increasing thermomechanical treatment of the material. Another limiting factor is the change of the mechanical behavior from... 

The study of the adsorption of stearic acid onto calcium carbonate from alcohol solution by Ivanishchenko and Gladkikh [6] has already been mentioned. They also determined adsorption isotherms and the variation of ohmic resistance and water adsorption with coating level for shorter chain acids. Acids with ten and twelve carbon atoms appeared to form mono-layers on chalk with 1.5 x 10 moles g of filler while longer chain acids only required 0.9 x 10 moles g (unfortunately the surface area of the filler was not specified). With the shortest chain acid (Cjo), about three molecular layers were required to maximise hydrophobicity, but when more than 14 carbon atoms were present then only one mono-layer was needed. Their results also indicated that, for the shorter acids at least, the first molecular layer was packed differently from subsequent layers. 

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