Abstract
A regenerated cellulose with a weight-average molecular weight Mw of 8.0×104 was dissolved in 8 wt% aq sodium hydroxide (NaOH) solution under adequately chosen conditions. The solution viscosity and light scattering measurements were carried out over a wide range of temperature T ranging 0.6 to 46°C and 3.5 to 45°C, respectively. The apparent Mw of the sample, determined by the light scattering in aq NaOH, remained practically constant (7.9×104) at 10≤T≤45°C, being in good agreement with the true Mw (8.0×104), evaluated by the light scattering method in cadoxen. This means that cellulose dissolves molecularly in 8 wt% aq NaOH. This solution was found to be a Flory theta solvent at about 40°C, at which the second virial coefficient A2 vanishes. The Flory viscosity parameter Φ was ca. 1/5 the theoretical value (2.87×1023) of the unperturbed undraining chain, indicating that cellulose is a partially free draining chain when dissolved in aq NaOH. The unperturbed chain dimension A decreased with T. The flexibility of the cellulose chain in aq NaOH lies between those in cadoxen and iron sodium tartarate and all of them are classified as semi-flexible. The negative temperature dependence of the limiting viscosity number [η] was explained as mainly due to a large negative ∂A/∂T.
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