Influence of hydroxyethyl and carboxymethyl celluloses on the rheology, water retention and surface tension of water-suspended microfibrillated cellulose

Autor: Vanja Kokol
Rok vydání: 2022
Předmět:
Zdroj: Cellulose. 29:7063-7081
ISSN: 1572-882X
0969-0239
DOI: 10.1007/s10570-022-04737-w
Popis: Water-soluble polymers have been shown to improve the flow rigidity and water retention ability of highly-branched (flocculated) and polydisperse water-suspended MFC, thereby also modifying and controlling their rheological behaviour. The addition of hydroxyethyl (HEC) and carboxymethyl (CMC) celluloses of different content (5–10–20 w/w%), molecular weights (MW, 90.000–1.300.000 g/mol) and degrees of substitutions (DS, 0.7–1.2) to 1.5 wt% MFC suspension, have thus been studied by evaluating their microstructure (SEM imaging), strength and rheological properties, i.e. the yield stress and flow under rotational (viscosity vs. shear rate) and oscillatory (viscoelastic) regime, using cone-plate measuring geometry at a rather low truncation gap. The pure MFC suspension showed high-viscosity at lower shear stress and shear-thinning behaviour at higher rates, with two yielding zones, indicating a secondary deflocculation of smaller and more stiffly packed fibril structures and their orientation/aligning in the direction of flow. This behaviour was reduced substantially by the addition of high-MW HEC, or almost eliminated completely by medium-MW CMCs with higher DS, yielding suspensions with higher and stability-prolonged zero-shear viscosity, as well as a more linearly decreased and irreversible viscosity profile after the shear load removal at higher shear stresses. The carboxylic groups at CMC additionally decreased the interactions between the fibrils, and subsequently reduced the fibrils’ flocks, or formed larger aggregates with their integrations, while increasing the MFC suspension gel-strength, improving its flow and viscoelastic behaviour through higher water retention ability and surface tension properties, and also its recovery after deformation.
Databáze: OpenAIRE
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