Strengthening of Recycled Paper by Lignocellulosic Nanofibers (LCNF) Assisted by Polyelectrolyte Complexes (PECs)

CARLA N. SCHNELL; MARÍA V. GALVÁN; JOAQUÍN TARRES; MARC DELGADO-AGUILAR; MIGUEL A. ZANUTTINI

Espoo

Congreso; Congreso Iberamericano de Investigación en Celulosa y Papel (CIADICYP).; 2016

CIADICYP

The effect of cellulose nanofibers (CNF) as reinforcement of papermaking process has been of great interest in the last years. An appropriate retention agent is necessary to ensure the adsorption of the CNF onto fibres surface and avoid a high decrease in drainability in the paper manufacturing process. This work proposes a novel procedure of using polyelectrolyte complexes (PECs) with the ability to act simultaneously as retention agent of lignocellulosic nanofibers (LCNF) and as strength agent on a lignified recycling pulp. It have been shown that cationic complexes of (poly(allylamine hydrochloride - PAH)/(polyacrylic acid - PAA) are strongly adsorbed on cellulosic surfaces and an increase considerably the papermaking properties. Cationic complex, with 50% of free charge, was formed by adding solution of the anionic polyelectrolyte (PAA) on a solution of the cationic polyelectrolyte (PAH). The formation of PECs was made at a dosage rate of 30 mL/h under continuous stirring (300 rpm), ionic strength of 0.01N NaCl and pH 7.5. Mechanical LCNF was obtained from pulp of partially lignified pine sawdust (Kappa N° 25) using a pressure homogenizer. An advantage to use sawdust is that it does not require further mechanical treatment for size reduction. The effect of different dosages of PECs (0.3; 0.5; 0.75; 1.0% PECs on dried pulp) and 3% of LCNF (on dried pulp) onto recycled unbleached softwood kraft fibres was evaluated. Britt Dynamic Drainage Jar was used to evaluate the amount of LCNF and fines retained into fibre slurry and the colloidal titration ratio method (CTR) was employed to determinate the total colloidal charge of materials. The results show a maximum retention when 0.75% of PEC was added on LCNF-fibre suspension and the results of log CTR showed a value near to zero, indicating that an optimum balances between negatively and positively charged materials was achieved. The best drainability result (18°SR) was obtained for a dosage of 0.75% of PEC. Finally, evaluation of handsheets showed that in comparison to the reference pulp, all the treatments led to an increase in mechanical properties. The higher increase in tensile strength was obtained (+48%) for a PEC dosage of 0.75% and also, with this dosage, an excellent increment in compressive strength CMT was achieved (+72%). PECs are a possible alternative to assist the application of LCNF in papermaking.