Stability and efficiency improvement of ASA in internal sizing of cellulosic paper by using cationically modified cellulose nanocrystals

Alkenyl succinic anhydride (ASA) is a reactive sizing agent that can impart good water repellence to paper by decreasing the wettability of the cellulose fibers. However, ASA can undergo hydrolysis, which is detrimental to the ASA sizing efficiency. In order to improve the ASA emulsion stability and ASA sizing efficiency, we used cationically modified cellulose nanocrystals (CNCs) to stabilize the cationic starch-emulsified ASA. Transmission electron microscope observation revealed that ASA droplets were well shielded by both the cationic CNCs and cationic starch, which may be responsible for the improved stabilization of ASA. The Hercules size test sizing degree, contact angle and particle size measurements demonstrated that cationic CNCs–ASA sized paper exhibited improved results in comparison with the control (without cationic CNCs under otherwise the same conditions). Furthermore, the resulting cationic CNCs–ASA system can improve the tensile index and burst index of the sized paper.