Monovalent Salt and pH-Induced Gelation of Oxidised Cellulose Nanofibrils and Starch Networks: Combining Rheology and Small-Angle X-ray Scattering

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 TEMPO-oxidised 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.

Stable Cellulose Nanofibril Microcapsules from Pickering Emulsion Templates

“…A further solidification of the outer shell of these MCs was achieved by lowering the pH further, here attributed the proton-induced interfibrillar interactions of OCNF networks. 30 On the contrary, at higher pH (8.5), dye release increased to ∼6.4% (after 1 day) and ∼7.5% (after 7 days). This is tentatively attributed to the presence of Na + ions (used to increase the pH), which screened the external 5.…”

“…With decreasing pH, after 1 day of storage at room temperature, the dye release percentage of the third MCs decreased marginally, from ∼2.4% (at pH 6.5) to ∼2.2% (at pH 4.0); however, after 7 days, the dye release percentage reduced from ∼4.6% (at pH 6.5) to ∼3.6% (at pH 4.0), as can be seen in Figure c. A further solidification of the outer shell of these MCs was achieved by lowering the pH further, here attributed the proton-induced interfibrillar interactions of OCNF networks . On the contrary, at higher pH (8.5), dye release increased to ∼6.4% (after 1 day) and ∼7.5% (after 7 days).…”

“…The OCNF was further purified via dialysis under ultrapure DI water to remove any salt and preservatives, as described elsewhere . Briefly, approximately 20 g of OCNF slurry was dispersed in 100 mL of deionized water and stirred at room temperature for 30 min.…”

“…25,28 The OCNF was further purified via dialysis under ultrapure DI water to remove any salt and preservatives, as described elsewhere. 30 Briefly, approximately 20 g of OCNF slurry was dispersed in 100 mL of deionized water and stirred at room temperature for 30 min. After being acidified to pH 3 using 1 M aqueous HCl solution, the OCNF dispersion was dialyzed against DI water (cellulose dialysis tubing molecular weight cut-off (MWCO) 12,400) for 5 days (medium replaced twice daily).…”

Starch-Based Hydrogels as a Drug Delivery System in Biomedical Applications

“…Ion-induced gelation is a technique where ions are used to trigger the formation of 3D networks in starch-based hydrogels [51,52]. This method is based on ionic interactions between starch molecules and multivalent ions.…”