Precipitated Calcium Carbonate (PPC)
Chemical formula : CaCO3
PCC is made by direct carbonation of Hydrated Lime, known as the milk of lime process.
The Making of PCC
PCC is produced from a high purity Calcium Carbonate rock called Limestone.
Firstly, we crush the rocks to the particle size needed for processing and isolate some of the impurities from the crushed rock. These include feldspar and other siliceous minerals, as well as heavy metals.
Limestone is then fed into a Limekiln. Under the temperature of approximately 1050°C, Calcium Carbonate is taken apart, forming Calcium Oxide (CaO) and Carbon Dioxide gas (CO2). The Carbon Dioxide can be captured for reuse.
CaCO3+ Heat →CaO + CO
2
↑
Calcium Oxide is then mixed with water to form Calcium Hydroxide (Hydrated Lime or Slaked Lime).
CaO + H
2
O→Ca (OH)2
Impurities are separated from the Hydrated Lime. Hydrated Lime is then mixed with the captured Carbon Dioxide to form Calcium Carbonate. Since Calcium Carbonate is insoluble in water it precipitates out.
Ca(OH)2+ CO2→CaCO3↓+ H2O
The fineness of the grain and crystal form (aragonite or calcite) of PCC are controlled by process of reaction time, temperature, agitation, pressure, rate of carbon dioxide addition, and post-crystallisation processing. These shapes - Needles, Cubic or Rosaline - each have different physical properties such as powder density, surface area and oil absorption, which give them outstanding performance in many applications.
Developments in processing technology mean that a wide range of PCC grades is available. This opened up new applications for PCC in paper coating, titanium dioxide replacement and acid paper-making process. The control of crystal morphology has also allowed higher filler loadings.
Compared to grinding limestone rock, the precipitation process also allows the growth of very fine particles, down to nanometers or hundredths of a micron. These Ultra-fine PCCs have special applications where high performance is required.
The Uniqueness of Precipitated Calcium Carbonate
The physical properties of PCC including particle size, particle shape, surface area, surface chemistry and particle size distribution can be altered to meet and bring best performance in the end use.
In the PCC process, products can be made with very small sizes with high surface areas, high oil absorptions, and the narrow size distribution of PCC means that the material dose not pack easily and hence can be used to add bulk.
Coated PCC
The traditional choice of coating agent for PCC has been fatty acid such as stearic acid with a percentage of 1 to 3 percent.
Coated PCC can improve its dispersion in polymer matrices, allow faster wetting, lower water absorption and ensure lower level of filler-polymer interaction.
Why Industries choose Precipitated Calcium Carbonate (PCC) over Ground Calcium Carbonate (GCC)?
Both Precipitated Calcium Carbonate (PCC) and Ground Calcium Carbonate (GCC) are having the same chemical formula therefore many people has thought that they are the same. But they are not. PCC has higher purity than natural GCC, since impurities are removed in the production process.
The main differences in properties of various types of PCC and GCC are such as brightness, surface area, abrasion, particle size and oil absorption. PCC has much narrower particle size distribution than GCC. Hence this allows the generation of high oil absorptions which is useful in certain applications.