Effect of nanofiber addition on the physical–mechanical properties of chemimechanical pulp handsheets for packaging

The effect of nanofiber addition on the physical–mechanical properties of industrial chemimechanical pulp handsheets was evaluated. The nanofibers (3 wt%) were added to industrial pulps taken from two positions of the approach flow, trying to reproduce the real paper machine process. Significant correlations between the characteristics of the cellulose nanofibers, the drainability of pulp suspensions, and the physical–mechanical properties of handsheets were found. The increase in the degree of fibrillation decreased significantly the drainability of the pulp suspensions. Nanofibrillation yield, transmittance, viscosity at 0.5% consistency, and carboxylic content positively correlated with °SR, whereas turbidity, and ξ-potential correlated negatively. Nanofiber incorporation increased Tensile Index (up to 21%), Burst Index (23–37%), E modulus (up to 17%), concora medium test (up to 27%), ring crush test (up to 28%), and short-span compression test values up to 23% in the handsheets where nanofibers from bleached kraft pulp were added. A positive correlation was found between the Tensile Index and nanofibrillation yield, and between E modulus and viscosity at 0.5% consistency for all pulps and a high linear relationship between both variables was found for nanofibers from pine pulps. Finally, the values of air permeability decreased up to 80% respect to the control.