Effect of molecular weight on the ability of guar gum to enhance "weak gel" rheology of microdispersed oxidised cellulose (MDOC)

Carbohydrate Polymers
Xuehai XieEdwin R Morris

Abstract

MDOC comprises small, essentially insoluble, particles which associate to form "weak gel" networks at concentrations above ∼4wt%. Association is promoted by guar gum, causing an increase in G' at low levels of addition and a decrease at higher concentrations, due to excessive aggregation of the MDOC particles. For guar gum samples with molecular weights ranging from ∼60 to ∼1800kDa, we found that the concentration required to give maximum G' for 5wt% dispersions of MDOC increased systematically from ∼0.005wt% for the lowest molecular weight to ∼0.3wt% for the highest. We propose that guar gum drives self-association of MDOC to reduce enthalpically-unfavourable (segregative) interactions between the two materials, and that large coils are less effective than smaller ones because a higher proportion of chain sequences are buried in the interior of the coil, where they cannot make segmental contacts with the MDOC particles.

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