Binding fillers for paper applications using nanoscale calcium silicate hydrate coating and nanofibrillated cellulose

Raw materials form a major portion of costs in papermaking. Thus it is particularly desirable to replace more valuable raw materials such as pulp with less expensive ones such as fillers. However, the strength properties of paper are impaired when the amount of filler increases. Here we present a novel way to increase the strength of paper by using filler particles coated with nanoscale calcium silicate hydrate (CSH) structures. The structures were grown on the surface of filler particles by a nucleation process. The length and shape of nucleated hairs can be adjusted by the reaction time and external conditions. These hairs enhance the bonding ability to other particles and fibres. We consider their effect on paper strength with and without nanofibrillated cellulose. The chemical and cement adding CHS treatment processes were studied in SC paper application. When using CHS cement treated fillers, the modulus of elasticity increased nearly 20% and tensile strength ~10% compared to situation when untreated reference filler particles were used. Together with nanocellulose the strength properties of paper were enhanced even more. Opacity of papers increased as the function of pigment treatment intensity whereas the brightness decreased. Similarly, the air permeance decreased with both chemical and cement adding CSH treatment. The achieved benefits for CHS treated fillers were comparable to those obtained using untreated filler particles with nanocellulose. In conclusion, the binding potential of filler particles can be enhanced by nanostructuring their surface using a relatively simple process. The potential of calcium silicate hydrated fillers was shown in case of SC paper but we believe that the results apply also for other paper grades.