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7 Abstract Water-soluble cationic cellulose deriva-8 tives were synthesized by three different procedures, 9 cationizing bleached hardwood kraft pulp with (3-10 chloro-2-hydroxypropyl) trimethylammonium chlo-11 ride. The first procedure involved a previous depoly-12 merization step with orthophosphoric acid. The 13 second one consisted on dissolving cellulose in 14 NaOH/urea before cationization. For the third proce-15 dure, the reaction medium was heterogeneous since it 16 was carried out with a part of cellulose with high 17 degree of polymerization. Oppositely to the common 18 methods, cationization occurred under mild condi-19 tions. Differences among the three derivatives are 20 illustrated by X-ray diffraction patterns of pretreated 21 samples, infrared spectra, and determinations of the 22 degree of substitution, the zeta potential, the charge 23 density and the molecular weight. The performance of 24 these polyelectrolytes for the flocculation of mineral 25 fillers used in papermaking was tested by laser 26 diffraction spectrometry. The flocculant with the 27 highest degree of polymerization and charge origi-28 nated the best results, particularly when the filler used 29 was kaolin, proving that water-soluble cationic cellu-30 lose derivatives can aid in the flocculation of fillers 31 used in papermaking. On the contrary, the shortest-32 chained derivative was not effective. The results were 33 interpreted in terms of the characteristics of the 34 cellulose derivatives flocculants and of the fillers, 35 and neutralization and patching were proposed as the 36 dominant mechanisms. 37Keywords Cationization Á Cellulose Á Fillers for 38 papermaking Á Flocculation Á Laser diffraction 39 spectrometry 40 Introduction 41 Non-renewable and scarcely biodegradable polymeric 42 aids, such as cationic polyacrylamides (CPAM) or 43 polyethyleneimine (PEI), are often applied in paper 44 mills to achieve good retention of mineral fillers. The 45 particle size of these fillers is generally much smaller 46 than the wire mesh at the forming and drainage section 47 of the paper machine, and thus mechanical retention A1 Electronic supplementary material The online version of A2 this article

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Cationized fibers and other kinds of chemically modified fibers impart many advantages in papermaking, but unfeasibly long reaction times are necessary to attain acceptable degrees of substitution, due to the low reactivity of bleached kraft pulps. In this work, different aqueous pretreatments were tested in order to activate cellulose towards a 60 min-long etherification with a quaternary ammonium reagent. Severe decrystallization treatments, namely alkalization with NaOH 20%, NaOH/urea or FeTNa, conducted to the best reactivity results (substitution from 2 to 10%), but the fiber properties were harshly affected. Pretreatments involving H 3 PO 4 at different concentrations were also performed, with distinct results, from unnoticeable effects at 20% to amorphization and excessive depolymerization at 80%. Finally, aqueous ammonium thiocyanate was tested as activator and had little effect on fibers, although the addition of ammonia resulted in high degrees of substitution, while maintaining the pulps' capability to retain inter-fiber water and cellulose I as the prevalent allomorph.