Tuning rheology and aggregation behaviour of TEMPO-oxidised cellulose nanofibrils aqueous suspensions by addition of different acids

L Alves; E Ferraz; A F Lourenço; P J Ferreira; M G Rasteiro; J A F Gamelas

doi:10.1016/j.carbpol.2020.116109

Tuning rheology and aggregation behaviour of TEMPO-oxidised cellulose nanofibrils aqueous suspensions by addition of different acids

Carbohydr Polym. 2020 Jun 1:237:116109. doi: 10.1016/j.carbpol.2020.116109. Epub 2020 Mar 4.

Authors

L Alves¹, E Ferraz², A F Lourenço³, P J Ferreira³, M G Rasteiro³, J A F Gamelas⁴

Affiliations

¹ CIEPQPF, Department of Chemical Engineering, University of Coimbra, Pólo II - R. Silvio Lima, 3030-790 Coimbra, Portugal. Electronic address: luisalves@ci.uc.pt.
² Techn&Art, Polytechnic Institute of Tomar, Quinta do Contador, Estrada da Serra, PT - 2300-313 Tomar, Portugal; Geobiotec, Geosciences Department, University of Aveiro, Campus Universitário de Santiago, PT - 3810-193 Aveiro, Portugal.
³ CIEPQPF, Department of Chemical Engineering, University of Coimbra, Pólo II - R. Silvio Lima, 3030-790 Coimbra, Portugal.
⁴ CIEPQPF, Department of Chemical Engineering, University of Coimbra, Pólo II - R. Silvio Lima, 3030-790 Coimbra, Portugal. Electronic address: jafgas@eq.uc.pt.

PMID: 32241451
DOI: 10.1016/j.carbpol.2020.116109

Abstract

The present work intends to study the variations in the rheological properties and aggregation behaviour of TEMPO-oxidised cellulose nanofibrils (CNF) aqueous suspensions, as a function of changes in concentration and systematic changes in the pH, by addition of acids with different anions. It was found that CNF suspensions form strong gels at mass fractions higher than 0.35 % and the gel point is ca. 0.18 %. On the other hand, aggregation is enhanced at acidic pH conditions due to lower charge repulsion among fibrils, leading to an increase of the suspension viscosity. However, distinct rheological behaviours were presented by CNF suspensions as different acids were applied. It was found that phosphate ions resulted in significant aggregation leading to formation of particles of large size and very strong gels, at pH 2.3; distinctly, the presence of acetate ions resulted in lower aggregation, lower particle size and weaker gels, at the same pH value.

Keywords: Acids; Aggregation; Cellulose nanofibrils; Charged nanofibrils; Hofmeister series; Hydrogels; Protonation; Rheological properties.