Calcium carbonate is used in paper mill as a filler material in the alkaline papermaking process. Now a days Calcium carbonate dominant over other papermaking filler materials; though at the first stage of papermaking kaolin was 1st choice. The main reason behind the preference of calcium carbonate is the demand for brighter and bulkier paper.
There are significant benefits to the use of calcium carbonate in the al¬kaline papermaking process. But Calcium Carbonate filler is unsuitable in acid papermaking and wood-containing paper.
Usually Calcium carbonate occurs in three natural forms such as limestone, chalk and marble. Naturally it is forms between the reactions of calcium salt and carbon dioxide. This process is still going on in the Oceans.
There are two types of calcium carbonate used in paper mill – ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC).
Ground calcium carbonate (GCC)
Ground calcium carbonate is manufactured by grinding limestone or marble because of their high brightness and purity. Generally the particle shape of ground calcium carbonate is rhombohedral. This filler material is used in alkaline wood free papermaking process. The brightness of GCC is 86-95%.
Advantages of Ground calcium carbonate (GCC)
GCC is cheaper and it has high brightness.
GCC creates a porous surface on the paper sheet due to its rhombohedral particle shape.
GCC is hydrophobic as a result it is liberate water more rapidly.
Lower binder demand
Disadvantages of Ground calcium carbonate (GCC)
The rough particle shape of GCC creates a problem; it is more abrasive and shortens the life of paper machine clothes.
Precipitated calcium carbonate (PCC)
Precipitated calcium carbonate is the form of CaCO3 which is manufactured by chemical reactions and the process is known as carbonation process. PCC improve the drawback of GCC, it is provide better gloss and opacity properties for the paper. Because of the structure of PCC is different from the structure of GCC. The crystal structure of PCC are needle-shaped, rhombohedral(cubic), scalenohedral (triangular) and prismatic. The brightness of PCC is 90-97%.
Advantages Precipitated calcium carbonate (PCC)
Increase machine speed and productivity.
Improve water drainage
Improve machine runnability
Improve print quality
Cost-effective papermaking process
Increased opacity and brightness
PCC is less abrasive than GCC
Reduce fiber consumption compared with GCC or talc
More retention compare than other paper fillers
Disadvantages Precipitated calcium carbonate (PCC)
PCC containing paper sheets are poorer formation than GCC containing paper sheets.