A. Isogai. Determination of length and width of nanocelluloses from their dilute dispersions. In Advances in Pulp and Paper Research, Oxford 2017, Trans. of the XVIth Fund. Res. Symp. Oxford, 2017, (W.Batchelor and D.Söderberg, eds), pp 801–811, FRC, Manchester, 2018.
Length/width and their distribution of nanocelluloses, prepared from wood pulps with or without chemical pretreatment, are key factors in application to high-strength and light-weight composites, transparent optical films, gas-barrier films, electronic devices, etc. Although microscopy images provide some length/width information, the number of measurable nanocellulose elements is limited. In this paper, three methods to determine nanocellulose lengths and widths are presented. The field-flow-fractionation (FFF) method combined with static light scattering was applied to dilute aqueous TEMPO-oxidised cellulose nanofibril (TOCN) dispersions to obtain avarage lengths, length distributions, and widths of different TOCNs. Although TOCN elements with lengths > 300 nm coiuld not be separated properly according to their lengths by the FFF system, TOCNs with lengths < 300 nm were adequately separated, depending on the lengths by the FFF system, and provided length/length distributions and widths, well corresponding to those obtained from microscopy images. Intrinsic viscosities of TOCNs with different lengths and widths were obtained viscosities of TOCNs with different lengths and widths were obtained uusing shear viscosity measurement of dilute aqueous TOCN dispersions . When the obtained intrinsic viscosities of TOCN dispersions were compared with aspect ratios p of TOCNs measured from their microscopy images, these two factors had good relationship, when the constant value of TOCN density (), =0.15*p1.9 was used. Compared to length measurement from microscopy images, the viscosity methods provide average lengths og numerous amounts of TOCN elements present in the dispersions. Seven types of nanocelluloses with different average widths and width distributions as well as those with different network strictures were prepared via different mechanical and chemical/mechanical processes, and the turbidities of their dilute dispersions were measured. The widths of nanocelluloses were calculated from the respective turbidity plots based on the theory of light scattering for thin and long particles. The turbidity-derived widths of the seven nanocelluloses ranges from 2 to 10 nm, and showed good correlations with the thickness of nanocelluloses measured from their microscopy images.