Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

Abstract

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration.

Quantification of energy input required for chitin nanocrystal aggregate size reduction through ultrasound

“…The dominant break up mechanism is expected to be fragmentation as deduced from the various size distributions ( Figure 5 & Figure 6), which also corresponds well with observations of others 18,40,41 . Like Graves et al (2016) we nd that the E input was the dominant factor for nanoparticle aggregate break up.…”

“…Ultrasound treatment clearly reduced the chitin nanocrystal aggregate size (Figure 2 & Figure 4), as was found for different nanoparticles including carbon nanotubes 20 and cellulose nanocrystals 18 . Our results suggest that weakly bound micro meter agglomerates can be broken down at low E input < 16 kJ / g chitin nanocrystals (Figure 4), which corresponds to the general observation that break up occurs at the weakest spot inside the aggregate.…”

“…Application of ultrasound has shown to be an effective way to break down nanoparticle aggregates 4,18,20 , and was for that reason used to quantify the aggregation energy (E aggregate ) within chitin nanocrystal aggregates. The energy input (E input ) produced by ultrasound was determined calorimetrically for different sonication power settings, enabling an E input up to 9650 kJ / g chitin nanocrystals (Supplementary information 1).…”

“…However, the reported dependency on E input is not always observed 18 . This may be related to the calculation of the energy input through the implosion of a bubble in case of Beuguel et al (2018), and determined calorimetrically by Graves et al (2016) and the current study. The reasons for this strong dependency on E input are not yet elucidated.…”

Influence of Nanoparticle Pretreatment on the Thermal, Rheological and Mechanical Properties of PLA-PBSA Nanocomposites Incorporating Cellulose Nanocrystals or Montmorillonite

“…The dispersibility of dried CNC powder in water is a critical requirement for producing colloidal suspensions. This can be achieved by ion exchange (from acidic form to neutral sodium-form), the use of additives [16] and large energy input (e.g. shear mixing, sonication), etc.…”