Hand dishwashing and emulsion stability

  • Joana I Pinheiro Da Silva Pinto

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

When washing dishes, consumers expect a complete removal of grease. To avoid a slippery feeling due to grease redeposition, it is important to guarantee emulsion stability. Emulsion stability was assessed across typical dosages (0.1 to 10 wt%), water hardnesses (2 and 15dH) and temperatures (25 to 45oC), with commonly used soils and a model with triolein and oleic acid. Stability was evaluated through the turbidity profile over time.
The dishwashing liquid used was Joy (P&G) containing 29.9wt% of surfactant in a 2.85:1 anionic/amphoteric ratio. In tallow and corn oil emulsions, we observed that lower dosages had a higher emulsion stability (between 0.5 and 1wt%), decreasing for higher product dosages. DLS data showed an increase of droplet size for concentrations above 5wt%. Under very dilute conditions (0.1wt%), instability was observed. Temperature-wise, a non-linear dependence of tallow emulsion stability was observed, with maximum instability at 35oC, although tallow was melting over the ranged temperatures. In corn oil emulsions, higher temperatures led to a decrease of stability. When using only triolein, emulsions were unstable and temperature independent. Adding oleic acid improved stability.
The effect of a poloxamer, L64, on the formula was studied. Although it leads to an increase in emulsion stability, UK consumer tests revealed a negative impact on its performance. The UK’s typical wash process is characterized by elevated temperatures, hard water and dilute conditions. The negative feedback was due to adsorption of the polymer to the surface at high temperatures, where contact angle measurements showed an hydrophobization of the ceramic surface. Similarly, QCM-d measurements identified the adsorption on silica surfaces.
Numerous factors have been identified to improve emulsion stability. Free fatty acids were beneficial to stability, along with lower temperatures and specific dosages. This could have notable impacts on marketing and ecological awareness by saving energy and dishwashing product.
Date of Award25 Jan 2022
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorWuge H Briscoe (Supervisor), Karl Braeckman (Supervisor) & Julian Eastoe (Supervisor)

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