Clara Goh, Dow Chemical T.V. Drovetskaya, Amerchol Corporation
A new generation of cationic conditioning polymers (Polyquaternium-67) has been engineered. Polyquaternium-67 (PQ-67) is a family of high viscosity quaternised hydroxyethyl cellulose (HEC) polymers with cationic substitution of trimethyl ammonium and dimethyldodecyl ammonium. These novel polymers were found to provide enhanced aesthetic feel and good compatibility with surfactant systems without the complication of associative thickening.
These polymers have been evaluated in both a clear shampoo and a two-in-one silicone containing shampoo and their performance compared with commercially available polymers, namely Polyquaternium-10 high molecular weight low-charge density (PQ-10 HL) and guar hydroxypropyltrimethylammonium chloride. Performance parameters evaluated were wet comb, wet feel, silicone deposition and build-up effect.
PQ-67 demonstrated superior combability for wet and dry comb, excellent feel for different hair types and improved silicone deposition in all shampoos evaluated. Moreover, they retained other good qualities for their PQ-10 structural analogs such as enabling crystal clear formulations and showing no build-up or volume-down effects on hair. These new polymers were also found to be efficient conditioning agents in different surfactant systems with or without silicones.
Polymer composition
PQ-67 are high viscosity quaternised HEC polymers with cationic substitution of trimethyl ammonium and dimethyldodecyl ammonium (Figure 1). Their degree of cationic substitution has been fixed at ~0.2, which corresponds to a weight-percent nitrogen of ~1%. Low levels of hydrophobic dimethyldodecyl ammonium substitution (HS = 0.01) were used to impart hydrophobic character to the PQ-10 type polymers. Four polymer grades available are PQ-67 (5), PQ-67 (30), PQ-67 (60), and PQ-67 (100) (Table 1). Numbers listed in the PQ-67 nomenclature are relative to the degree of hydrophobic substitution. PQ-67 (5) has the lowest amount of hydrophobe whereas PQ-67 (100) has the highest amount of hydrophobe for all samples.
Performance in clear shampoos
Two surfactant platforms were used in the formulation of clear shampoos. They are Sodium Laureth Sulfate (SLES)/Disodium Cocamphodiacetate (DSCADA), 15.5/2.6 weight-percent (wt %) active base and Sodium Laureth Sulfate (SLES)/Cocamidopropyl Betaine (CAPB)/Cocamide Monoethanol Amine (MEA), 10/3/2 wt % active base.
Conditioning polymers were incorporated at 0.2-0.5 wt % level. Formulations containing PQ-67 and PQ-10 were visually water-clear measuring less than 4% haze (Nippon Denshoku 300A hazemeter, 50 mm pathlength, 0.3% polymer). Clarity is an important aesthetic requirement for these types of systems. It is noted that identical formulations containing cationic guar were cloudy at ~40% haze.
In the two shampoo systems, cationic polymers were designed to perform as conditioning agents. PQ-67 has been shown to fully address this need. These new polymers with low levels of hydrophobic substitution demonstrated superior performance compared with both commercial controls used in this study.
Objective wet combability
Wet combing was evaluated with the use of a load cell of a Dia-Stron miniature tensile tester. When a comb was pulled through a wet hair tress, the total work done (TWD) and end-peak combing force (EPF) associated with the removal of entanglement of hair fibres were measured. Percent reduction in TWD and EPF of a shampoo-treated hair tress compared to the same tress treated with a blank formulation (no polymer) was calculated.
In every study TWD and EPF showed identical trends in polymer performance comparison, therefore only the TWD will be discussed in this article. Commercial Single-Bleached European hair was used in wet combability experiments. At 0.3% usage level, PQ-67 samples performed significantly better in TWD reduction compared to both controls, PQ-10 and guar hydroxypropyltrimonium chloride, showing up to 64-126% improvement in SLES/DSCADA system (Figure 2) and 27-48% in SLES/CAPB/cocamide MEA system versus the benchmarks (LSD/2 intervals at 90% confidence level were ~5-7 percent units [based on pooled within-group standard deviation]. PQ-67 (5) and PQ-67 (30) were the best performing polymers in both formulations.
Coacervate studies
Haze measurements were performed using the Nippon Denshoku 300A hazemeter in a 50 mm path length cell. Clear formulations of PQ-67 and PQ-10 at 0.3 wt % in SLES/DSCADA surfactant base were used in the coacervate study (formulation containing guar hydroxypropyltrimonium chloride was hazy). As discussed earlier, cationic polymers are known to form coacervates with surfactants. Clear in a concentrated form, surfactant solutions with PQ-10 and PQ-67 cationic polymers become hazy upon dilution. This haziness, which is an indicator of coacervate formation, was measured over a dilution range of 0-20 to obtain the haze (coacervate) curves. As shown in Figure 3, the coacervate curves of PQ-67 (5) and PQ-67 (30) were ‘higher’ and extended over a broader range of dilution compared to the PQ-10 control. This is a known indicator of more coacervate being formed that raises expectation of superior conditioning performance.
At the same time, the PQ-67 (60) graph, even though covering a larger area compared with PQ-10, yields to both PQ-67 (5) and PQ-67 (30). These observations are in agreement with earlier findings from the wet combability test (Figure 2 – see previous discussion), and provide some insights to the conditioning aspects of PQ-67’s performance.
Subjective panel testing on hair tresses
Individual pairs of European virgin brown hair tresses were distributed to expert panelists skilled in evaluating conditioning properties of hair. Each pair had one tress treated with a PQ-67 (60) shampoo and one tress treated with a PQ-10 shampoo control. SLES/DSCADA formulations containing 0.3 wt % polymer were used in this study. Panelists were asked to choose one hair swatch that was easier to comb and one that felt smoother/softer. Each panelist performed comb and feel evaluations twice on different pairs of hair tresses.
PQ-67 (60) was preferred over the PQ-10 control for both wet comb (8/10) – exact significance level 89% (binominal distribution) and wet feel (7/8) – exact significance level 93% (binominal distribution). After the hair dried, panelists’ choices indicated no statistical difference in dry comb and feel between swatches.
Polymer deposition patterns
The polymer substantivity and build up on hair were measured indirectly by detecting the amount of anionic Red 80 dye bound by the cationic polymer deposited on the hair. The method used in this study is indirect. It measures the amount of Red 80 dye rather than the amount of polymer deposited on hair. Many factors such as hydrophobicity, charge and its distribution/accessibility, and other compositional variables may change the affinity of the Red 80 dye to a particular polymer, making it look as if the polymer was more/less substantive to the hair. This method does not allow quantifying and comparing the amounts of polymers deposited. Nevertheless, the anionic dye method is a valuable tool for assessing deposition and build-up patterns of a particular polymer as a result of multiple treatments.
The cationic polymers deposited on the shampoo treated hair tresses of European virgin brown hair were complexed with Red 80 dye. The dye/polymer complex was then extracted from the hair by 50/50 (v/v) of isopropanol/de-ionised water. A UV spectrophotometer was used to detect the dye concentration of the extracted solution at 533 nm and the micrograms of dye per gram of hair was calculated (experimental error: ±10%). Figure 4 shows the amount of Red 80 dye absorbed on the hair tresses treated with shampoos containing 0.5 wt % polymers, PQ-67, PQ-10, and guar hydroxypropyltrimethylammonium chloride in a SLES/DSCADA surfactant base. The dye uptake was measured for up to fifteen consecutive washings.
Similar slopes for the PQ-10 and PQ-67 substantivity curves indicated that the introduction of a small amount of hydrophobic substituents had no negative impact on the polymer deposition patterns. It did not create any build-up excessively on hair in course of multiple shampoo applications. The guar hydroxypropyltrimethylammonium chloride curve, however, was steeper. One could observe a step change between one and five washings, and after that, cationic guar was accumulating on hair faster than the other two polymers.
Hair volume
The hair volumising effect of shampoos was evaluated by using the Diastron volume measurement method in a controlled environment (~25°C, 50% humidity). The pulling work (or compression energy) of a hair through a confined ring was related to the initial volume of the hair assembly. The change of the pulling work for the shampoo treated and untreated hair samples was finally converted into the Volume Index based on the top volume control with a defined Volume Index of 100 (commercial extra body shampoo) and the bottom volume control with a defined Volume Index of 0 (commercial conditioner-experimental error: ±10%).
Figure 5 shows the volume index of shampoos made from 0.5 wt % polymers: several grades of PQ-10*, guar hydroxypropyltrimethylammonium chloride, and the PQ-67 in the SLES/DSCADA surfactant base. (*PQ-10 HL, MH and HH were all supplied by Amerchol Corporation. The first letter indicates the molecular weight, H for high and L for low, and the second indicates charge density: thus ‘HL’ denotes a polymer with high molecular weight and low charge density.)
According to the data presented in Figure 5, the PQ-67 shampoo had dramatically better volumising ability than that containing guar hydroxypropyltrimethylammonium chloride. In comparison with the top control, a commercial extra body shampoo for fine hair and the commercial volume care shampoo, the results indicated that PQ-67 is an excellent volume enhancer similar to different grades of PQ-10 included in this study. In contrast, the shampoo prepared using guar hydroxypropyltrimethylammonium chloride showed a negative volume index of -25, lower than the bottom control of a commercial nourishing conditioner.
Performance in two-in-one shampoos with silicone
The same surfactant systems of SLES/DSCA and SLES/CAPB/Cocamide MEA in combination with 1 wt % dimethicone blend (Dow Corning 1664 is a non-ionic emulsion of high molecular weight polydimethylsiloxane with 50% silicone content. DC 1664 is a mixture of dimethicone with Laureth-4 and Laureth-23 non-ionic surfactants) and 2wt % ethylene glycol distearate were used to formulate two-in-one silicone-containing conditioning shampoos. Conditioning polymers were incorporated at 0.25 wt. % level. In the tested two-in-one shampoo systems, cationic polymers were designed to perform as conditioning agents and assist deposition of silicone benefit agents. PQ-67 has shown to improve conditioning performance and silicone deposition compared to PQ-10 and cationic guar benchmarks.
Objective wet combability
Wet combing was evaluated on commercial single-bleached hair using the Dia-Stron miniature tensile tester as described above. In both surfactant systems tested, PQ-67 (5), PQ-67 (30) and PQ-67 (60) showed enhancement in TWD reduction over the controls. Directional improvement of ~10% was observed in the SLES/DSCADA system where all shampoos performed at the excellent level of ~70% of TWD reduction. In the SLES/CAPB/Cocamide MEA surfactant system, an improvement in TWD reduction ~60-100% was registered for PQ-67 (5), PQ-67 (30), and PQ-67 (0) (Figure 6).
Subjective panel testing on tresses
Panel testing was conducted on commercial European single-bleached hair tresses following the protocol described above. This is the same type of hair that was used in the objective wet combability method. This hair type falls into the category of bleached/damaged hair. It typically needs more care and conditioning. Without proper care this hair feels rough, straw-like and is hard to manage.
A PQ-67 (5) two-in-one shampoo in the SLES/DSCADA base was evaluated against a guar hydroxypropyltrimethylammonium chloride control. After one shampoo treatment, panelists clearly preferred the PQ-67 (5) sample over the control for the wet comb and feel (both 8/10). After tresses were dried, no statistically significant difference could be detected in comb and feel properties. At the same time, panelists perceived the PQ-67 treated samples as having more body/volume before (10/10) and after (9/10 – exact significance level 98% [binomial distribution]) combing them.
Next the tresses were treated two more times with the same formulations with drying and combing between washes. After a total of three applications, another panel study was conducted. This time panelists could not distinguish beween the tresses for wet comb and feel. This may be attributable to the accumulation of conditioning agents on hair. When hair is well conditioned, the differences might be less apparent. In contrast, the differences in dry properties were apparent for both dry comb (9/10) and feel (10/10). Most of the panelists noted a ‘big difference’, clearly preferring the PQ-67 over cationic guar.
Panelists used the following wording in their commentary section to describe how the hair treated three times with the cationic guar shampoo was different from the other swatch: ‘crunchier, stiffer, harder/rougher, more crinkly and coarse’. Hair treated with PQ-67 (5) shampoo felt ‘soft, clean, and conditioned’.
Silicone deposition
The total amount of silicone deposited on hair treated with two-in-one formulations of 0.3 wt % polymers in SLES/DSCADA base was measured. PQ-67 (5) and PQ-67 (30) were evaluated in this study versus the PQ-10 HL and guar hydroxypropyltrimethylammonium chloride controls.
Commercial European single-bleached hair was washed once with each formulation. The silicone was extracted from the hair by a 50/50 (v/v) methyl isobutyl ketone/toluene solution. Atomic absorption spectrophotometry was used to measure the silicone content, and then the micro-gram silicone per gram hair was calculated (LSD/2 intervals at 95% confidence level were ~20 µg/g hair [based on pooled within-group standard deviation]).
The results of this study (Figure 7) agree with previous findings and provide explain the superior performance of PQ-67 (5) and PQ0-67 (30) polymers in two-in-one conditioning systems. Conditioning performance of these shampoos is largely due to the presence of silicones and their ability to reach hair and stay behind (in small amounts) after the rinse-off cycle is complete. Ability to deposit silicone is therefore crucial and greatly contributes to the overall conditioning effect. Polymers SL were found to provide better assistance in silicone deposition on the single-bleached hair. The best performing polymer, PQ-67 (30), showed up to 88% enhancement over the PQ-10 and up to 43% enhancement over the guar hydroxypropyltrimethylammonium chloride control (Figure 7). The enhanced ability of PQ-67 to deliver benefit agents to the hair from shampoos is not limited to silicones. For example, according to our preliminary data, the hydrophobic substitution proved beneficial for the deposition of zinc pyrithione, the most widely used anti-dandruff additive.
Conclusion
PQ-67 is a new class of cationic conditioning polymers which has been prepared and evaluated in shampoo formulations. These polymers are quaternised HEC, structurally similar to the PQ-10 polymers except for the addition of a small amount of hydrophobic substitution. The polymers were evaluated against commercial conditioning polymers: PQ-10 of a high molecular weight and low charge density grade, and guar hydroxypropyltrimethylammonium chloride. They demonstrated superior performance in all major categories of conditioning and showed enhancement in silicone deposition from two-in-one systems. Moreover, they retained the well-known, desired qualities of their PQ-10 structural analogs, such as enabling crystal clear formulations and showing no build-up or volume-down effects on hair. All grades of PQ-67 were found to be efficient conditioning agents in different surfactant systems with and without silicones.