Nanofibrillated cellulose as an additive in papermaking process: A review

•Review of the latest advances on cellulose nanofibers (CNF) in paper.•Study of effect of CNF in physical and strength properties of different pulps.•Pretreatment, amount of CNF and additives influence the reinforcing effect.•Different pulps develop strength at different rates at equal CNF content.•Review of the strengthening mechanism of cellulose nanofibres in paper. During the last two decades, cellulose nanofibres (CNF) have emerged as a promising, sustainable reinforcement with outstanding potential in material sciences. Though application of CNF in papermaking is recent, it is expected to find implementation in the near future to give a broader commercial market to this type of cellulose. The present review highlights recent progress in the field of the application of cellulose nanofibres as additives in papermaking. The effect of CNF addition on the wet end process is analysed according to the type of pulp used for papermaking. According to the literature consulted, improvement in paper’s overall properties after CNF addition depended not only on the type and amount of CNF applied, but also in the pulp’s origin and treatment. Bulk and surface application of CNF also presented significant differences regarding paper’s final properties. This review also revises the mechanisms behind CNF reinforcing effect on paper and the effect of chemically modified CNF as additives.