The effect of micro and nanofibrillated cellulose water uptake on high filler content composite paper properties and furnish dewatering

The use of micro and nanofibrillated celluloses (MFC, NFC or collectively MNFC) as a reinforcement fibre in composite papers and films has been an area of intensive research recently. The large relative surface area of MNFC makes it a promising material to improve strength and other properties of paper and board products. However, the high swelling of MNFC can lead to challenges in web dewatering. In this work, we have studied the dewatering and paper properties of a composite consisting of 70 % precipitated calcium carbonate (PCC), 20 % MNFC and 10 % kraft pulp fibers. The water uptake of the MNFC was controlled by changing the number of passes of the pulp feed stock through a microfluidizer. Additionally, the water binding was changed by precipitating PCC onto the MNFC surface, thus changing the surface conditions. Swelling, gravimetric, and press dewatering of the material were measured from composite handsheets. The results show that while increasing MNFC fibrillation decreases dewatering performance, this effect can be overcome by the in situ precipitation of PCC without decreasing important sheet properties. It was also evident that the in situ precipitation method can be used to fine tune the dewatering and material properties of the composite paper to achieve desired combination of process/material performance. The results show that the optimum combination of strength and dewatering is obtained by one pass through a microfluidizer. Further passes decrease dewatering and do not improve strength.