Design of eco-friendly fabric softeners: structure, rheology and interaction with cellulose nanocrystals

TL;DR

This study investigates eco-friendly fabric softeners with reduced surfactant content, demonstrating that natural guar polymers can replace up to 50% of surfactants without compromising performance, through detailed structural and rheological analysis.

Contribution

It introduces a formulation strategy using guar polymers to lower surfactant levels in fabric softeners while maintaining their structural and functional properties.

Findings

Guar polymers do not impair vesicle stability at low concentrations.

Cationic guars induce local lamellar order in concentrated formulations.

Adjusting polymer concentration can offset reduced surfactant elasticity.

Abstract

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.