Monovalent salt and pH-induced gelation of oxidized cellulose nanofibrils and starch networks: Combining rheology and small-angle X-Ray scattering

Zakir Hossain, Vincenzo Calabrese, Marcelo da Silva, Saffron Bryant, Julien Schmitt, Jennifer H. Ahn-Jarvis, Frederick J. Warren, Yaroslav Z. Khimyak, Janet L Scott, Karen Edler

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Abstract

Water quality parameters such as salt content and various pH environments can alter the stability of gels as well as their rheological properties. Here, we investigated the effect of various concentrations of NaCl and different pH environments on the rheological properties of TEMPOoxidised cellulose nanofibril (OCNF) and starch-based hydrogels. Addition of NaCl caused an increased stiffness of the OCNF:starch (1:1 wt%) blend gels, where salt played an important role in reducing the repulsive OCNF fibrillar interactions. The rheological properties of these hydrogels were unchanged at pH 5.0 to 9.0. However, at lower pH (4.0), the stiffness and viscosity of the OCNF and OCNF:starch gels appeared to increase due to proton-induced fibrillar interactions. In contrast, at higher pH (11.5), syneresis was observed due to the formation of denser and aggregated gel networks. Interactions as well as aggregation behaviour of these hydrogels were explored via ζ-potential measurements. Furthermore, the nanostructure of the OCNF gels was probed using small-angle x-ray scattering (SAXS), where the SAXS patterns showed an increase of slope in the low-q region with increasing salt concentration arising from aggregation due to the screening of the surface charge of the fibrils.

Original languageEnglish
Article number951
Number of pages17
JournalPolymers
Volume13
Issue number6
DOIs
Publication statusPublished - 19 Mar 2021

Funding

Acknowledgments: The authors would like to thank the EPSRC for funding this project (Grant numbers EP/N033310/1 (Bath) and EP/N033337/1 (UEA)). V.C. thanks the University of Bath for supporting his PhD studies. The authors thank Diana Lednitzky of the Material and Chemical Characterisation Facility (MC2) at the University of Bath for helping with the TEM imaging. Professor Nick Terrill, Andy Smith, and Tim Snow are thanked for their assistance with the SAXS experiment (Experiment no. SM20409-1) at the I22 beamline, Diamond Light Source, Didcot. This work benefited from the use of the SasView software (developed under NSF Award DMR-0520547) containing code developed under the EU Horizon 2020 programme (the SINE2020 project Grant 654000).

FundersFunder number
National Science FoundationDMR-0520547
Horizon 2020 Framework Programme654000
Engineering and Physical Sciences Research CouncilEP/N033337/1, EP/N033310/1
University of East Anglia

Keywords

  • Cellulose nanofibrils
  • Rheology
  • SAXS
  • Salt
  • Starch
  • pH

ASJC Scopus subject areas

  • General Chemistry
  • Polymers and Plastics

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