Improvement of deinked old newspaper/old magazine pulp suspensions by means of nanofibrillated cellulose addition

During their recycling, cellulosic fibres suffer irreversible damage caused by repeated wetting and drying cycles, beating stages and bleaching reactions. This damage decreases the mechanical properties of the paper prepared from recycled pulp. Soft beating of the pulp is a simple way to partially recover the original mechanical properties, but it is limited by the high degradation of fibres, fines generation and decrease in drainage rate that recycled fibres already present. The present research studies the use of nanofibrillated cellulose (CNF) as an alternative to mechanical beating to improve the strength properties of paper produced from a deinked recycled pulp obtained by disintegration and flotation of a mixture of old newspapers and magazines. Different percentages of CNF were added to this mixture with a retention aid. A fraction of the same pulp without CNF was also beaten at different intensities in a PFI mill. Morphological properties of both beaten and CNF-reinforced pulp suspensions, as well as structural and mechanical properties of handsheets made thereof, were analysed and their results compared. Paper containing 1.5 % of CNF presented a higher tensile strength and stiffness than paper from beaten pulp with similar freeness and water retention values. A higher amount of CNF further improved the mechanical properties, up to double the tensile index, which opens new possibilities of use for recycled paper.