New Additives for Improving the Conditioning of 2-in-1 Shampoos
Improving the efficacy of 2-in-1 shampoos with conditioning is an ongoing challenge for formulators. Two new additives (Polyquaternium-77 and Hydroxypropyl Bis-Hydroxyethyldimonium Chloride) are evaluated for their ability to produce dilution-dependent complexes and as a result provide a significant improvement of conditioning in use.
Mitigating the effects of lipid removal from hair is an important aspect of daily shampoos. Most shampoos contain at least one ingredient to refat and/or condition hair. A shampoo surfactant package is most typically comprised of three major components:
- Anionic surfactant(s) for high foam and cleansing
- Amphoteric surfactant(s) for reduced irritation and foam stabilization
- Nonionic surfactant(s) for additional foam modification and enhanced salt response
Conditioning aids are added to provide refatting, cuticle smoothing, frizz/flyaway control and shine enhancement. In a shampoo, effective conditioning aids are those that are maintained on the hair after rinsing. Quaternary molecules with or without repeating quaternary structures (polyquats or quats) are the best selections, as they have an attraction to the anionic surface of hair. For optimal formulation clarity and foam, polyquaternium structures built on cellulosic (Polyquaternium-10) or other polysaccharide (Guar Hydroxypropyltrimonium Chloride) backbones are highly preferred.
Ideal polyquats have a charge density that is low enough as to not form insoluble complexes at the concentrations that yield the desired end properties. Unfortunately, as the compatibility improves, the conditioning potential is diminished. Formulators seeking to improve conditioning performance may attempt to add more of the polyquat, resulting in negative impacts.
Dilution deposition, or “The Lochhead Effect”, utilizing coacervates, is a more effective means of utilizing polyquaternium conditioning aids. Coacervates are polymer-rich domains that exist within a separate continuous phase, similar in some ways to the familiar emulsion. Importantly, when the continuous phase becomes more dilute, the coacervates fail, releasing the coacervate “payload”. The effect can be visually observed by a reduction in clarity upon serial dilutions. The polymer complex, incompatible with the continuous phase and unable to form a stable solution, will be more readily adsorbed by the hair, a ready compatible substrate.
A model 2 in 1 shampoo and the additives on interest were formulated per the following scheme:
|Sodium Laureth-2 Sulfate1||11.5% solid content|
|Disodium Cocoamphodiacete2||2.6% solid content|
|Polyquaternium-103||0.5% solid content|
|Citric Acid4||qs to pH 6.0|
|Water||qs to 100.0%|
The following additives were assessed:
- Linoleamidopropyl PG-Dimonium Chloride Phosphate (LCP)5, a long-chain amphoteric surfactant previously demonstrated to be effective in producing dilution-depended complexes
- Polyquaternium-77 (PQ-77)6, a polyquat surfactant based on a coco-glucoside backbone, with trimethyl quaternary groups along the backbone
- Polyquaternium-81 (PQ-81)7, a polyquat surfactant based on a lauryl glucoside backbone, with stearyl quaternary groups along the backbone
- Hydroxypropyl Bis-Hydroxyethyldimonium Chloride (HHC)9, a compact humectant diquat with interspersed hydroxyethyl or hydroxypropyl functional groups
Additives were initially assessed at range of actives from 0.3% to 2.0%, narrowing additives through various phases of assessment based on efficacy.
Three endpoints were assessed to assess efficacy of the various additives in forming coacervates and generating dilution-dependent complexes.
The shampoo concentrate and serial dilutions were measured directly for their degree of clarity using a HACH Turbidimeter. Turbidity is reported in NTUs, an arbitrary unit. Increased values indicate increased turbidity, or reduced clarity of solution.
Rubine Dye Test
The rubine dye test predicts cationic polymer deposition on hair by measuring the amount of an anionic red dye that gets deposited on a wool swatch in a wash event compared to the same wool material washed without the cationic polymer. Depending on test conditions, the test may not work with quaternary molecules smaller than ~1000 Da.
For each of the products tested, a 2”x2” wool swatch is washed under a standard wash procedure and then measured L*a*b a* (green-red axis) color value using a Hunter Labs MiniScan 4000S.
Increased a* values denote increased red intensity, thereby indicating greater amount of red dye deposition and in turn increased cationic polymer deposition.
Comb Force Reduction of Human Hair
Lightly bleached brown hair swatches were washed with various test articles and then the force required to comb the hair was instrumentally measured using a DiaStron FibreOne combing apparatus.
Measurements were taken under the same conditions as in the rubine dye testing.
In the initial assessment phase, turbidity testing, all four additives were assessed at a variety of active levels over a range of dilutions in the test shampoo. (Figure 1)
For this phase of testing only the highest active level of PQ-77 and HHC were tested, as they demonstrated the largest difference between additives in the turbidity testing. The dye results demonstrate that while the shampoo with the PQ-10 successfully deposited some polymer to the wool the substrate, the deposition was significantly increased with the additives. (Figure 2)
When the identical test articles were tested for comb force reduction under typical shampoo conditions, similar results were obtained, though the increase in conditioning was more pronounced than anticipated by the dye results. (Figure 3)
A wide variety of additives were tested to identify those that would provide the best dilution-activated conditioning effect. Two additives, a long-chain amphoteric surfactant (LCP) and a polyquaterium surfactant with a long chain quaternary substitution (PQ-81), despite having themselves shown some efficacy as conditioning aids, failed to generate a significant amount of dilution-activated complex. Such additives would likely only provide a modest increase in conditioning, with most of the mixture remaining in solution and failing to deposit to the surface. Rubine dye test results demonstrate the predictive ability of the turbidity testing while the comb tests definitively demonstrate how the PQ-77 and HHC, with little to no inherent conditioning benefit in the shampoo formulation substantially improve the combability of hair relative to the shampoo alone or the shampoo with the PQ-10 alone. While the HHC provably demonstrated the best efficacy in the testing conducted, formulators would still see substantial benefits from the PQ-77 and may preferentially select it for a variety of reasons, including the greater degree of biobased feedstocks. Importantly, ingredient selection and use rates will change, dependent on individual formulation characteristics.
1 Colonial SLES-2 2 Cola®Teric 2C 3 UCARE™ Polymer JR-400 4 Citric Acid Anhydrous 5 Cola®Lipid SAFL 6 Poly Suga®Quat TM-8610P 7 Poly Suga®Quat S1210P 8 Cola®Moist 200
This poster was completed thanks to the contributions of the following:
Molly McEnery, for initial formulation optimization and testing
Taryn Davis, for additional testing and data collection
Jordan Taylor, for method development, testing, and statistical analysis