Fibril-calcium carbonate composites

Keywords Biopolymers Calcium carbonate Cellulosic fibrils Composites Coprecipitation Micro- and Nanofibrillated cellulose Morphology Pigments Properties... 

This chapter aims to introduce the concept of nanocellulosic-fibril and precipitated calcium carbonate (PCC) composites. The effect of cogrinding of lime and pulp fibres and different precipitation conditions on the production of PCC and modification of its morphologies are analysed in this chapter. 

The composite of nanofibriUar material formed with precipitated calcium carbonate (c-PCC), as described above in Sect. 5.2.2.1, seems to consist of precipitated nanocrystals aggregated into ellipsoidal shapes, as shown in Fig. 5.5. The precipitation occurs at random sites mostly on the end of fibrils and, hence, the fibrils are partially covered with calcium carbonate fillers. The particle size of the primary colloidal c-PCC particle is less than 100 nm. 

Higher magnification of the washed composite fillers shows that filler is precipitated in the pits and surface of the pulp fibres (Fig. 5.10). Significant proportion of filler is agglomerated and patches of filler are observed on the surface of the fibres and fibrils with Supermass colloider refined samples. Valley beater shows reduced agglomeration and retention of filler in the washed samples. Also, a minor fraction of calcium carbonate is precipitated inside the pits of fibres. 

Nanocellulosic fibrils can be used as a substrate for the production of precipitated calcium carbonate-nanocellulose composites. These, PCC-nanocellulose composites can contribute toward increasing the strength and optical properties of paper. We investigated formation and properties of a new composite paper composed of fibrillar fines and calcium carbonate as the base furnish in combination with cellulosic fibres as reinforcing elements. 

Equivalent amounts of calcium hydroxide suspensimi were added to preformed fibrillated cellulosic gels, in order to obtain 2 1 and 1 1 PCC-pulp fibril mixtures, which were then carbonated to cocrystallise PCC with colloidal-, fine and coarse rhombohedral-, and scalenohedral-t3q)e structures. Reference PCC precipitates, composed of four different morphologies, were crystallised in the absence of cellulosic fibrils. The experimental precipitation conditions were similar for composite and reference PCC filler samples. 

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