Fillers calcium carbonates CaCO

Non-reinforcing fillers (passive) Ground calcium carbonate (CaCO ) Reduce formulation cost adjust rheology, and mechanical properties. 

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. 

Particulate filler comes in a variety of geometries as shown in Fig. 6.2. For effective reinforcement, they should be approximately the identical dimensions in all directions. Examples of particulate filler include talc, calcium carbonate (CaCOs), mica, and natural silica [30]. Their strength depends on the stress transfer between the particles and the matrix. The applied stress can be effectively transferred to the well-bonded particles from the matrix (Table 6.2). 

Calcium carbonates (CaCOs), with a density of 2.7 g/cm, are commonly used filler materials for packing applications [57, 58]. CaCO filler improves flex modulus, impact strength, stiffness, tear strength, gas and water barrier properties, and printability. PE/carbonates are commonly used in the food packaging industry. 

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOs) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

P-Tiicalcium phosphate (P-TCP) fillers were also used in PCL electrospun fibers [65,67] to obtain bioactive nanocomposite fibers for applications in the bone tissue engineering field, as weU as calcium carbonate (CaCOs), which was incorporated in PCL membranes for guided bone regeneration [68]. 

Of the various mineral fillers used, calcium carbonate (CaCO ) is one of the most common, due mainly to its availability in readily usable form and low cost [76]. However, the incompatibility of its high energetic hydrophilic surface with the low-energy surface of hydrophobic polymers, e.g., polyethylene (PE) and polypropylene (PP), is a particular problem. For this and other reasons, the surface of calcite is often rendered organophilic by a variety of surface modifiers such as silanes, titanates, phosphates, and stearic acid. 

In all cases, it can be seen that the addition of fillers whether they are particulates like calcium carbonate (CaCOs) or glass fibers (GF), systematically moves the entire curves to a higher level. The viscosity increase is greater at lower shear rates whereas lower at higher shear rates. The extent of the effect would, of course, depend on the nature of the pol)mier and the filler type, size, size distribution, etc. 

The development of hybrid materials such as CNT/inorganic hybrids has drawn great interest for its combination of multiphase characteristics of nanocomposites with the synergistic function of each hybrid constituent. Utilization of the hybrid filler is one of the ways to improve the properties of composites. Some work has demonstrated hybrid systems made of CNTs with inorganic fillers such as mica, silica (Si02), magnesia (MgO), and calcium carbonate (CaCOs). All of these inorganic materials have been extensively employed as fillers in composites, because of several remarkable benefits such as abundant raw-material resources and stable properties. 

Figure 10.1 shows the effect of the addition of fillers to polypropylene on its crystallinity. This study was conducted under the same conditions for all specimens tested. There is a difference in the effect of CaCO-, and talc. Calcium carbonate lacks surface functional groups so it tends to have a very small influence on crystallinity and the crystallization behavior. Talc has interacting functional groups on its surface which cause the increase in crystallinity along with the concentration increase. 

Figure 16.13. Viscosity of polyester resin filled with calcium carbonate and microspheres (total content of filler (CaCOs+microspheres) is 60 wt%). [Data courtesy of Abrasivos Y Maquinaria, SA, Barcelona, Spain] ...

The predominant filler used in PVC formulations today is calcium carbonate. A typical CaCO employed would have an average particle size of 0.07 to 0.50 pm, contain no particles larger than about 44 pm (in some cases... 

Prominent markets today for fine CaCOs are as fillers in paper, paint, PVC, rubber, putty, cosmetics, and toothpaste and as an antacid and a calcium supplement in foods. Surface-coated grades are also produced and are more easily dispersed in organic materials. CaCOs is also used to coat paper, and its use as a filler has increased rapidly with the increase in alkaline papermaking. Many small precipitation plants now operate at papermill sites. Controlled precipitation of calcium carbonate allows control of crystal geometry and particle size distribution. This allows custom production with attractive properties for various markets. With the recent expansion in precipitated calcium carbonate capacity, there are fewer possibilities for disposal of the relatively low-quality material from a brine plant. 

Selected unsaturated carboxylic acids are particularly useful as coupling agents for calcium carbonate-type fillers. They interact strongly with the basic surface of the carbonate, unlike silanes that only show a weak interaction. In addition, unlike simple saturated carboxylic acids, which just have a beneficial effect on impact strength, unsaturated carboxylic acids may increase tensile strength. Table 6.5 illustrates this effect in a 60% filled CaCOs/PP homopolymer system. This system is heavily stabilized with both hindered phenol and phosphite-type antioxidants, and a small amount of peroxide was therefore added. 

Examples of a few are alpha cellulose, ash, calcium carbide, calcium carbonate, carborundum, channel black, china clay, coral, coke dust, diatomaceous earth, dolomite [double carbonate of lime and magnesia filler having the formula (CaCOs) and (MgCOa)], ferrite, flint, fuller s earth, glass spheres, hemp, keratin, lampblack, leather-dust, macerate... 

The thermal stability of calcium carbonate (CaC03) nanoparticles on polybutadiene rubber (PBR) were studied by Shimpi and Mishra [105]. They observed that the incorporation of nano CaCOs in PBR shows better thermal stability. At 12 wt% of nano CaCOs (21, 15, and 9 nm) filled in PBR shows decomposition temperature at 491, 483, and 472 °C, respectively. At 4 wt% loading of filler, decomposition temperature is observed to be 488,480,450 °C for nano CaCOs (21, 15, and 9 nm), respectively. This enhancement in thermal stability is due to uniform dispersion of nano CaCOs throughout the matrix that keeps the rubber chains intact on cross-linking, which prevent out diffusion of the volatile decomposition product [106]. The presence of nanoinorganic particles in between the mbber chains is responsible for preventing the diffusion of the volatile decomposition products firom the mbber nanocomposites at same time. It is clear that nanoinorganic filler provides better thermal stability as compared with commercial micron size filler. 

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... 

Zhou and co-workers [27] used calcium carbonate as a reinforcing agent for sulfonated PEEK. The calcium carbonate particles were surface treated and the effect of this on the mechanical and thermal properties were determined. The modulus and yield stress of the composites increased with CaCOs particles loadings. This increase was attributed to the bonding between the particles and the PEEK matrix. DSC experiments showed that the particle content and surface properties influenced the Tg and the T of the composites. The Tg increased with the content of fillers while Tn, decreased. The treated fillers were found to give a better combination of properties, which indicated that the sulfonated PEEK played a constructive role in the calcium carbonate/PEEK composites. 

---