Wet-end addition of nanofibrillated cellulose pretreated with cationic starch to achieve paper strength with less refining and higher bulk, TAPPI JOURNAL July 2018

ABSTRACT: Nanofibrillated cellulose (NFC) treated with cationic starch was evaluated as a bonding system to permit lower degrees of refining and lower apparent density of high-mass handsheets made from bleached kraft pulp. Mixed pulp (70% hardwood, 30% softwood) was formed into sheets with the optional addition of 5% by dry mass of NFC. The default addition of NFC was compared with a system in which the NFC had been pretreated either with cationic starch (at various levels) or optionally followed by colloidal silica. Comparative tests also were carried out with separate addition of cationic starch to the main furnish. Unrefined fibers (514 mL CSF) were compared with low-refined (473 mL CSF) and high-refined (283 mL CSF) pulp mixtures. The NFC that had been pretreated with cat-ionic starch at a high level was especially effective at boosting the tensile strength and stiffness of sheets prepared from pulp that had been refined at a low level, thus achieving improved strength at relatively low apparent density (high bulk) of the handsheets. The results support a strategy, for applicable grades of paper, of using cationic starch-pretreated NFC in place of refining energy applied to the main fiber furnish. It was further established that colloidal silica can be employed as a further pretreatment of the cationic starch–treated NFC as a means of promoting dewa-tering in the combined system.

Application: Higher caliper at a defined basis weight, while maintaining tensile strength and stiffness, can be achieved by use of cationic starch–pretreated nanofibrillated cellulose, while decreasing the main refining of kraft fibers. Mills can consider this technology for paper and board grades for which low apparent density and maintain-ing stiffness are primary goals.

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