  Concentrated fabric softeners are water-based formulations containing around
10 - 15 wt. % of double tailed esterquat surfactants primarily synthesized from
palm oil. In recent patents, it was shown that a significant part of the
surfactant contained in today formulations can be reduced by circa 50 % and
replaced by natural guar polymers without detrimental effects on the deposition
and softening performances. We presently study the structure and rheology of
these softener formulations and identify the mechanisms at the origin of these
effects.
  The polymer additives used are guar gum polysaccharides, one cationic and one
modified through addition of hydroxypropyl groups. Formulations with and
without guar polymers are investigated using optical and cryo-transmission
electron microscopy, small-angle light and Xray scattering and finally
rheology. Similar techniques are applied to study the phase behavior of
softener and cellulose nanocrystals considered here as a model for cotton.
  The esterquat surfactants are shown to assemble into micron-sized vesicles in
the dilute and concentrated regimes. In the former, guar addition in small
amounts does not impair the vesicular structure and stability. In the
concentrated regime, cationic guars induce a local crowding associated to
depletion interactions and leads to the formation of a local lamellar order. In
rheology, adjusting the polymer concentration at one tenth that of the
surfactant is sufficient to offset the decrease of the elastic property
associated with the surfactant reduction. In conclusion, we have shown that
through an appropriate choice of natural additives it is possible to lower the
concentration of surfactants in fabric conditioners by about half, a result
that could represent a significant breakthrough in current home care
formulations.
