A new class of cationic conditioning polymers (Polymer SL) has been prepared and evaluated in shampoo formulations. Polymer SL is a family of high viscosity quaternized hydroxyethyl cellulose (HEC) polymers with cationic substitution of trimethyl ammonium and dimethyldodecyl ammonium (Figure 1). SL compositions benefit from hydrophobic character to deliver superior conditioning performance in hair care applications. At the same time, low levels of hydrophobes have been chosen to assure good compatibility with surfactant systems without the complications of associative thickeninga.
The polymers have been evaluated in clear shampoo formulations and two-in-one silicone containing shampoos using objective lab methods and subjective panel evaluation on hair tresses. Commercial conditioning polymers: Polyquaternium-10 (PQ-10)b (UCARE Polymer LR-30MTMc) and Guar Hydroxypropyltrimethylammonium Chloride (Jaguar C-13S®d) were used as performance benchmarks. The new hydrophobically-modified cationic polymers demonstrated superior performance in all major categories of conditioning and showed improved silicone deposition from two-in-one systems. Moreover, they retained other good qualities of 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.
Background
The principal intent of shampooing is to clean the hair. However, products that are designed solely for cleansing can leave hair tangled and unmanageable while wet, and raspy dry and “lifeless” due to the lack of luster upon drying1.
This problem is especially severe for certain hair types, such as bleached and/or damaged hair. The number of consumers who daily work with their hair, color and bleach it, and frequently change styles is growing globally at a fast pace. Combined with the damaging effects of sun and industrial environment, this trend promotes consumers’ concern and awareness of their hair condition and triggers market needs in new efficient conditioning products and ingredients.
Many conditioning polymers and various benefit agents, e.g. insoluble silicones, can improve the hair condition by reducing combing friction of hair and providing a soft, smooth feel and healthy shiny appearance. Cationic polymers, such as PQ-10, are known to work alone or in combination with insoluble actives. They are assumed to form a polymer-surfactant complex (coacervate phase) that separates and precipitates onto the hair during the rinse-off cycle1, 2, 3. Coacervates can optionally incorporate insoluble actives such as silicones, thus assisting in their deposition on hair4, 5. Experimental polymers described in this paper are believed to perform along this line. They represent a new generation of cationic conditioning polymers. New compositional features empower their conditioning performance, which was found superior compared to both the PQ-10 structural analog and cationic guar.
Results and discussion
Polymer composition
A new class of cationic conditioning polymers (Polymers SL) has been prepared. These new compositions are high viscosity quaternized 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 ~1.0%. Low levels of hydrophobic dimethyldodecyl ammonium substitution (HS = 0.01) were used to impart hydrophobic character to the PQ-10-type polymers. Polymers SL-5, 30, 60, and 100 have been prepared (Figure 2). Numbers after the SL in the nomenclature are relative to the degree of hydrophobic substitution. Polymer SL-100 had the highest amount of hydrophobe of all the samples.
The Polymers SL were evaluated in clear shampoo formulations and 2-in-1 silicone containing shampoos using objective quantitative lab methods and subjective panel evaluation on hair tresses. Commercial conditioning polymers: structural analog UCARE Polymer LR-30MTM (PQ-10) and Jaguar C-13S® (cationic guar) were used as performance benchmarks.
Performance in clear shampoos
Two surfactant systems were used to formulate clear shampoos: Sodium Laureth Sulfate (SLES)/Disodium Cocamphodiacetate (DSCADA), 15.5/2.6 weight-percent (wt. %) active base and 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 Polymers SL and PQ-10 were visually water-clear measuring less than 4% hazee. Clarity is an important aesthetic requirement for these types of systems. Note that identical formulations containing cationic guar were cloudy at ~40% haze.
In the tested clear shampoo systems, cationic polymers were designed to perform as conditioning agents. Experimental Polymers SL have been shown to fully address this need. These new polymers with low level hydrophobic substitution demonstrated superior performance compared to both commercial controls used in this study.
Objective wet combability/detangling
The wet combing was evaluated by using the 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 entanglements of the hair fiber were measured. Per cent 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 here and later in this paper only one of them, the TWD, will be discussed. Commercial single-bleached European hair was used in wet combability experiments. At the 0.3% usage level, Polymer SL samples performed significantly better in TWD reduction compared to both controls, PQ-10 and cationic guar, showing up to 64-126% improvement in SLES/DSCADA system (Figure 2) and 27- 48% in SLES/CAPB/Cocamide MEA system versus the benchmarksf. SL-5 and SL-30 were the best performing polymers in both formulations.
Polymer SL-60 with a medium-high amount of hydrophobe was then incorporated in the SLES/DSCADA system at different usage levels (Figure 3). At 0.2 wt. % usage level, performance of SL-60 was statistically no different from either control at 0.3 wt. %. Remarkably, at 0.5% usage level, Polymer SL-60 demonstrated performance of > 90% TWD reduction, which is a performance level more commonly expected from rinse-off conditioner products rather than shampoos.
Coacervate studies
Haze measurements were performed using the Nippon Denshoku 300A hazemeter in a 50 mm path length cell. Clear formulations of Polymers SL and PQ-10 at 0.3 wt. % in SLES/DSCADA surfactant base were used in the coacervate studyg. As discussed earlier, cationic polymers are known to form coacervates with surfactants. Clear in a concentrated form, surfactant solutions with PQ-10 and SL cationic polymers become hazy upon dilution. This haziness, which is an indicator of coacervate formation, was measured over a dilution range of 0-20 and haze (coacervate) curves were obtained. As shown in Figure 4, the coacervate curves of Polymers SL-5 and SL-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 expectations of superior conditioning performance. At the same time, the SL-60 graph, even though covering a larger area compared to PQ-10, yields to both SL-5 and SL-30. These observations are in agreement with earlier findings from the wet combability test, Figure 2 (see discussion above) and provide some insights on the mechanistic aspects of Polymer SL’s outstanding performance.
Subjective panel testing on 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 an SL-60 shampoo and one tress treated with a PQ-10 LR-30MTM 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.
SL-60 was preferred over the PQ-10 control for both wet comb (8/10h) and wet feel (7/8i). 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 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-ionized water. A UV spectrometer was used to detect the dye concentration of the extracted solution at 533 nm and the microgram dye per gram hair was calculatedk. Figure 5 shows the amount of Red 80 dye absorbed on the hair tresses treated with shampoos containing 0.5 wt. % polymers, SL-60, PQ-10 LR-30MTM, and cationic guar, in a SLES/DSCADA surfactant base. The dye uptake was measured for up to 15 consecutive washings. Similar slopes for the PQ-10 and SL-60 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 issues: slopes were nearly parallel to each other and were not steep signaling that both polymers would not build up excessively on hair in the course of multiple shampoo applications. However, the cationic guar curve was steeper. One could observe a step change between one and five washings, and after that cationic guar accumulated on the hair faster than the other two polymers.
Hair volume
The hair volumizing effect of shampoos was evaluated by using the Dia-Stron Volume Measurement Method in a controlled environment (~25°C, 50% humidity). The pulling work (or compression energy) of a hair tress of European virgin brown 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 non-treated 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)l. Figure 6 shows the volume index of shampoos made from 0.5 wt. % polymers: several grades of PQ-10 (LR-30MTM, JR-400TM, and JR-30MTMm), cationic guar Jaguar C-13S® and the SL-60 experimental polymer in the SLES/DSCADA surfactant base. According to the data presented in Figure 6, the SL-60 shampoo had dramatically better volumizing ability than the shampoo containing cationic guar. In comparison with the top control, a commercial extra body shampoo for fine hair and the commercial volume care shampoo, the results indicated that the experimental polymer SL-60 was an excellent volume enhancer similar to different grades of PQ-10 included in this study. In contrast, the shampoo prepared using cationic guar 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 blendn and 2 wt. % 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. Experimental Polymers SL have shown to improve conditioning performance and silicone deposition compared to PQ-10 and cationic guar benchmarks.
Objective wet combability/detangling
The wet combing was evaluated on commercial single-bleached hair using the Dia-Stron Miniature Tensile Tester as described above. In both surfactant systems tested, Polymers SL-5, 30, and 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 Polymers SL-5, 30, and 60 (Figure 7).
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. An SL-5 two-in-one shampoo in the SLES/DSCADA base was evaluated against a cationic guar (Jaguar-C13S®) control. After one shampoo treatment, panelists clearly preferred the SL-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 SL-treated samples as having more body/volume before (10/10) and after (9/10o) 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 the tress for wet comb and feel. It may be attributed to the accumulation of conditioning agents on hair. When hair is well conditioned, the differences might be less perceivable. In contrast, the differences in dry properties were perceivable for both dry comb (9/10) and feel (10/10). Most of the panelists noted a ‘big difference’. 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 SL-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. Polymers SL-5 and SL-30 were evaluated in this study versus the PQ-10 LR-30MTM and cationic guar 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. An atomic absorption spectrophotometer was used to measure the silicone content, and then the microgram silicone per gram hair was calculatedp. The results of this study (Figure 8) agree with previous findings and provide an explanation for the superior performance of SL-5 and SL-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 (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, SL-30, showed up to 88% enhancement over the PQ-10 and up to 43% enhancement over the cationic guar control (Figure 8)q. 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.
Conclusions
A new class of cationic conditioning polymers has been prepared and evaluated in shampoo formulations. Polymers are quaternized HEC, structurally similar to the PQ-10 products except for addition of a small amount of hydrophobic substitution. The polymers were evaluated against commercial conditioning polymers: PQ-10 (UCARE LR-30MTM) and cationic guar (Jaguar C-13S®). 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 good qualities of their PQ-10 structural analogs, such as enabling crystal clear formulations and showing no build-up or volume-down effects on hair.
The SL Polymers were found to be efficient conditioning agents in different surfactant systems with and without silicones.
References
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