Length distributions of nanofibrillated celluloses (NFCs) were evaluated by dynamic birefringence measurement of their dispersions. Two types of NFCs with weighted-average lengths <i>L</i><sub>w</sub> of 340 and 410 nm (hereafter referred to as NFC-340 and 410, respectively) were prepared from softwood bleached kraft pulp by TEMPO-mediated oxidation and subsequent sonication in water. Lengths of ~150 individual fibrils were measured by microscopy to evaluate length distributions of the NFC samples. The solvent of the aqueous NFC dispersions were replaced by glycerol according to a previously reported method, and then NFC/glycerol dispersions were obtained. The NFC/glycerol dispersions were subjected to dynamic birefringence measurement at 5-40 °C using a He-Ne lazar (λ=488 nm). The complex shear strain-optical coefficient K* (=K’+iK”) of the NFC/glycerol dispersions were experimentally evaluated. Their theoretical K* values were also determined from length distributions of the NFCs obtained by microscopy using a theory for viscoelasticity of dilute rod-like polymer solutions. The experimental K’ values were in good agreement with their theoretical K’ values at the solid concentration of 0.02 and 0.005 wt% for NFC-340 and NFC-410, respectively. These results show that length distributions of the NFCs can be determined by dynamic birefringence measurement by applying theories of viscoelasticities for rod-like polymers. In contrast, the experimental K” values departed from the theoretical K” values in the high frequency region. This is probably because the NFCs did not behave like completely rigid rods but semi-flexible polymers.

Length distributions of nanocelluloses can be evaluated by rheological measurements of their dispersions

255th National Meeting (2018)

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