Introduction

Sustainability can be approached through different perspectives and challenge our formulation habits and manufacturing practices. When big production volumes are involved, such as for hair conditioners, the manufacturing process has a particular significance in improving the carbon footprint. Indeed, traditional hair conditioners, containing waxy components such as fatty alcohols and cationic agents, require hot manufacturing. In addition, this type of formulation has largely demonstrated its effectiveness but also brings some constraints related to a frequent change in consistency over time, and a sensitivity to temperature variations during storage. These inconveniences can finally disturb the distribution outside the packaging during use, especially from spray pumps and affect the formulation spreadability on hair. The purpose of this work was to reformulate a hot-processed hair conditioner in a cold-processed formulation while maintaining its stability and improving its usability. Rheology experiments were carried out to analyze the effects of ingredient substitution, to screen formulation behavior during use at this early stage of the formulation development and select the composition to the most favorable profile. Texture and sensory analysis on hair completed the evaluation on usability on the most suitable formula option.

Methods

• Reformulation of a classical hot-processed hair conditioner was done by removing one by one the waxy components and replacing their association by a liquid thickening-conditioning polymer looking for the optimized dosage and cold process. The reference formula was composed of water, C16-C18 fatty alcohols, C18 ethoxylated fatty alcohol, a cationic surfactant, glycerin and preservative. Formula stability and characteristics were monitored.
• Rheology experiments were conducted on the different formulations using a rotational Controlled stress/ strain (DHR2 from TA Instruments; Aluminum cone 40mm/2°). Flowing experiments were performed at 20°C to evaluate the global flowing profile. Rate index (with the best fit analysis) and yield stress (steady state flow protocol; Onset mode) were determined. Viscoelasticity was analyzed using oscillatory experiments in different conditions: frequency sweep at 20°C (0.1 to 100 rad/s) and temperature sweep from -5°C to 80°C (1Hz/ anti-evaporation cap). Evolution of storage modulus (G’) and mean G’/G” ratio were followed.
• Texture analysis was realized (TA XT- PLUS from Stable Micro System) using an hemispheric probe going down into the product packaged in a petri dish filled to the brim, then up (diameter: 50mm; Standard protocol at 20°C). Force profile was followed as a function of time. Maximum force and compression energy were determined as indicators of the product consistency during use (mean of 5 replicates at different positions of the sample).
• A triangular sensory random test was conducted with an expert panel on medium discolored caucasian hair tresses (Level II; 10 panelists; Tastel® software). After a standard pre-washing, hair conditioner was spread on wet hair (0.4g of product/tress), let pause 5 minutes, then rinsed. The tresses were dried at room temperature for 24 hours with 45% Relative Humidity. 5 attributes were examined: ease of combing, shine, volume, slipping, oily feeling, natural feeling.

Results

Flowing experiments highlighted the significant yield stress of the hot-processed reference despite lotion-like texture, in line with reported distribution issues from packaging over time and non-smooth flowing observed during storage. Oscillatory experiments also demonstrated the elastic structure contributing to stability and helped to visualize the sensitivity to temperature variations. The gradual reduction of waxy components to the increase of the liquid thickening-conditioning polymer led to a decreasing yield stress, in line with a smoother flowing. Playing with the polymer dosage helped to reach the same level of elasticity as the reference while preventing sensitivity of the structure to temperature variations. A cold-processable formulation was optimized with a stable elastic network from 2°C to 80°C. Texture analysis confirmed similar consistency to the hot-processed reference. The two formulations were considered to provide a similar effect on hair tresses according to the 5 selected descriptors (95% confidence interval).

Discussion and conclusion

Rheology helped to better understand the effects of the substitution of the waxy components and support the optimization of a cold-processed formula using a liquid thickening-conditioning polymer. The resulting hair conditioner showed similar effects on hair tresses than the reference while enabling to reduce carbon emissions and improved usability (smoother flowing; stable structure up to 80°C).