The influence of fibre wall thickness on the undissolved residuals in CMC solutions

Abstract

An industrial calcium sulfite pulp was fractionated in a hydrocyclone to four fractions that differed in dimensions and composition due to differences in density. The intention was to investigate whether the fibre dimensions had any influence on the properties of carboxymethyl cellulose (CMC) produced from the fractions and especially how the properties of the unreacted material differed. It was surprisingly found that the fraction containing thin-walled fibres gave CMC and dissolved residuals in the CMC-solution that had the lowest degree of substitution (DS). It was therefore believed that the thin-walled fibres were collapsed and more closely bound in the fibre network after drying of the pulp and that this impeded the chemical diffusion in the subsequent CMC-process, i.e. the diffusion of the CMC-chemicals into the cell wall was slower. There was thus a correlation between thinner fibres and a lower degree of substitution for CMC made from such fibres. It was also found that tick-walled fibres had a higher degree of substitution than the thin-walled fibres but that the highest degree of substitution was obtained if a mixture of thin-and thickwalled fibres were used.

Characterization of Sodium Carboxymethyl Cellulose Aqueous Solutions to Support Complex Product Formulation: A Rheology and Light Scattering Study

“…Consistent with Jardeby and co-workers’s observations, ,, microscopy reveals the existence of particulates as fibers (Figure S1A), swollen and ballooned fibers (Figure S1B), or swollen ring-like fragments (Figure S1C) at more advanced dissolution stages. It is worth noting, that studying these particulates using optical microscopy can be difficult.…”

“…The presence of similar residuals in Na CMC solutions was reported as early as 1942 by Höppler. 70 Further investigations on Na CMC samples with a low DS (around 0.7) were performed more recently by Jardeby and co-workers, 29,71,72 who concluded that these residuals were made of non-or poorly-substituted cellulose originating from less reactive cellulose fragments in the raw material used for Na CMC synthesis. Because of their lower DS, these residuals could not undergo full dissolution and would exist in solution as fibers (DSresiduals ≈ 0.1), 'ballooned' fibers (DSresiduals ≈ 0.3-05) or gel particles (DSresiduals ≈ 0.5-0.6).…”

“…Jardeby and co-workers have previously isolated particulates from Na CMC solutions (see Figure S1 and Jardeby and co-workers' papers 29,71,72 ) using filters, and the same filter types (i.e. ROBU ® VitraPOR ® Borosilicate 3.3 filter tunnels) were thus tried in the present study, using the smallest available pore size (1.0-1.6 m).…”

Cellulose dissolution in aqueous NaOH–ZnO: effect of pulp pretreatment at macro and molecular levels

“…Le Moigne and Navard (2010) have suggested that the high swelling along the fibers without unswollen sections and helices is induced by the secondary cell wall and that it indicates that the primary cell wall is not present anymore. The flat rings similar to what was observed for the pulps MC220, HC350 and HC336 in NaOH-ZnO have been suggested to originate from ballooned fibers or swelled pores (Jardeby et al 2005) or, alternatively, cutting of the highly swollen fibers (Le Moigne and Navard 2010).…”

Dissolution mechanisms of wood cellulose fibres in NaOH–water

“…Similar sections and flat rings were first described by Stawitz and Kage (1959) after the swelling of carboxymethyl cellulose (CMC). More recently, undissolved residuals were observed by optical microscopy in CMC solutions and it was suggested that highly swollen sections and flat rings may come from the ballooned fibres or from swelled pores (Jardeby et al 2005). Considering the dimension and the shape of the sections and the rings, the hypothesis that they come from the cutting of the highly swollen fibres is the most probable.…”