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

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.