Analysis of Calcium Sulphate Filler and its Application in Papermaking Process as Functional Filler

Calcium sulphate is rich in natural resources and by-product of many industrial processes. However, most calcium sulphate product was only used with low added value or treated as waste, harmful to environment. If the calcium sulphate can be used as papermaking filler, very high added value can be gained and also the environment problem can be solved. In this paper calcium sulphate from by product of industry was characterized by X-ray diffractometer (XRD) and scanning electron micrograph (SEM), and then used as papermaking filler. The influence of calcium sulphate filler on pulp suspension and paper properties was studies. The results showed that the calcium sulphate fillers were composed of three crystal forms, dihydrate, hemihydrate, anhydrite, and it was needle or fiber shape, hollow in the middle; calcium sulphate showed high brightness and high conductivity in water, compared with talc or ground calcium carbonate(GCC) filler. When calcium sulphate filler was used in papermaking process the filler retention was very small because of its high solubility in water. Calcination at high temperature can lower the solubility of calcium sulphate and slightly increase the retention, but the retention was still quite small. The future work should focus on controlling the solubility of calcium sulphate.