Rheological Properties and Gelation of Aqueous Cellulose−NaOH Solutions

Abstract

The shear rheology of a microcrystalline cellulose dissolved in a 9% NaOH aqueous solution was studied in the steady and oscillatory modes. The cellulose-(9% NaOH-H(2)O) mixtures show not to be true solutions. In the dilute regime, with cellulose concentration below 1%, the rheological behavior is typical of the one of suspensions. The formation of cellulose aggregates is favored when temperature is increased. In the semidilute regime, an irreversible aggregate-based gelation occurs, being faster with increasing temperature.

On the dissolution state of cellulose in cold alkali solutions

“…1b we present the measured shear viscosity, g _ c ð Þ, plotted as a function of the shear rate, _ c. As can be seen, g is independent of _ c, and we measure a zero-shear viscosity g 0 ¼ 3:7 mPas, corresponding to g rel ¼ g 0 =g s ¼ 2:54, where g s ¼ 1:455 mPas is the solvent (2.0 M NaOH(aq)) viscosity. This value is fairly close to the value of roughly 2.7, reported by Roy et al (2003) for 1 wt% MCC in a 9 wt% NaOH solution.…”

“…However, the fit gave a value of g ½ of 21 cm 3 / g, which, if it is a true estimate, would yield a critical overlap concentration, C Ã , of 0.048 g/cm 3 based on C Ã $ 1= g ½ . This value fits well with other estimates of C Ã of the same MCC (Behrens et al 2016) and Roy et al (2003) obtains a similar concentration dependence for MCC in a 9 wt% NaOH solution. The increase in relative viscosity seen is an indication of attractive interactions between the cellulose chains as more and more chains have the chance to interact with each other with increasing concentration.…”

“…Roy et al (2003) performed gelation experiments on cellulose in 9 wt% NaOH solution, but only showed kinetics for a 5 wt% cellulose concentration which gelled after roughly 50 h in room temperature. The difference in cellulose concentration makes their timescale difficult to relate to the one for a solution of 0.010 g/cm 3 ( $ 1 wt%); there should be no doubt that our samples would gel eventually in room temperature, but they are stable far longer than 50 h. Figure 2 demonstrates the change in scattering intensity with time for a fresh sample, the same sample after 3 weeks, as well as after 2 months, and, as can be seen, no significant changes are recorded.…”

“…The cellulose solution stability is strongly temperature dependent. Roy et al (2003), in an extensive rheological study, performed time resolved measurements of the linear viscoelastic properties of cellulose solutions in 2.2 M NaOH(aq) at different temperatures, C. The studied solutions (5 wt% cellulose) were initially viscous with the storage modulus, G 0 , being smaller than the loss modulus, G 00 . At all temperatures, the solutions, after some time, turned into gels with G 0 [ G 00 , however, with different rates.…”

Agregação de cadeias de acetatos de celulose em LiCl/DMAc: avaliação via viscosimetria

“…Embora estes recursos sejam usados com certa frequência, nem sempre é levado em conta que a dissolução de derivados de celulose também pode não levar a uma dispersão molecular, mas a um estado coloidal, consistindo de cadeias agregadas [4] . A formação de agregados (processo irreversível) ou associados (processo reversível) de celulose e seus derivados em solução pode ser investigada através de medidas viscosimétricas [5] . No entanto, pode-se considerar que muitos aspectos referentes aos processos de agregação e/ou associação ainda precisam ser investigados.…”