The consumer's interest in multifunctional benefits is what currently drives the global personal care market. Within the hair care market, rinse-off products such as shampoos remain the most popular means for hair care because consumers spend more time washing their hair and less time applying additional treatments. This being the case, consumers are more likely to rely on shampoo that conditions, protects and repairs the hair, as well as provides enhanced sensorial attibutes.
From a formulation standpoint the challenge is to control deposition of benefit agents such as cationic polymers, silicones and/or vegetal oils under rinse off in order to provide optimum performance. One response is cationic polymer derivatives such as cationic guar for surface management and delivery of multifunctional benefits.
Hair Surface Management
Cationic guars are polysaccharide derivatives, produced from the quaternization of guar gum. Guar gum is a natural and renewable resource extracted from the seeds of guar bean (Cyamopsis tetragonoloba taub). Guar gum is made of beta 1,4-glycosidic mannose units that statistically alternate between having and not having one alpha 1,6-bound galactose unit forming a side branch (see Figure 1).
The study of the physico-chemical behavior of polymers in surfactant environment has enabled more perfect control of cationic guar properties for optimum uptake on the hair.
The deposit of cationic guars does not rely solely on the fact that they are cationic and the hair’s surface is anionic. Due to the unique structure of cationic guars they interact well with surfactants to reach the hair’s surface.
The challenge is to formulate a stable shampoo system that contains oppositely charged species (cationic guar, mixture of anionic and amphoteric surfactants) that will eventually need to become destabilized to allow for polymer deposition. Within a few seconds of shampoo application onto wet hair, dilution occurs as a result of increased water content in the system. Driven by entropy, a surfactant/polymer complex forms due to the release of the counterions into the bulk.1
The three-phase diagram in Figure 2 illustrates the typical destabilization mechanism that leads to polymer uptake onto the hair.
Besides its intrinsic effectiveness, the polymer/surfactant complex acts as a net to capture and deliver dispersed particles on the hair fiber during precipitation. Thus, cationic guar can be used to perfectly control and enhance the delivery of particulate agents, such as silicone emulsion, to modify the hair’s surface.2 Hair surface modification could ultimately be translated into consumer benefits.
Hair Conditioning and Repairing Performance
Uptake: The uptake efficacy of cationic guar from a given shampoo formulation was tested on a hair-like surface. We monitored the amount of a fluorescence-tagged cationic guar deposited onto a negatively charged surface that mimics the hair. When applied onto wet hair, a shampoo is diluted by six to ten times according to the quantity of water retained in the hair. Thus, for optimum polymer deposition, precipitation should take place when diluted between six and ten times.
As depicted in Figure 3, maximum uptake of guar hydroxypropyltrimonium chloride occurs at the dilution factor six before the rinsing stage regardless of the type of shampoo formulation system. This performance is achieved by optimizing the physico-chemical characteristics of the polymer.
Conditioning: Beyond optimum uptake properties, when used in conjunction with silicone emulsions, cationic guar allows the best conditioning system to be created. Furthermore, when compared to other types of cationic polymers classically used in shampoo formulations, such as polyquaternium-10 (PQ-10) or polyquaternium-7 (PQ- 7), cationic guar helps to optimize conditioning performance.
Figure 4 represents the silicone deposition yield obtained from a sodium laureth sulfate and sodium cocoamphoacetate (SLES/CAMA) shampoo base containing different types of cationic polymers. Silicone emulsion deposition yield has increased by almost two fold when using guar hydroxypropyltrimonium chloridea compared to polyquaternium-10. The use of cationic guar contributes to reducing the total amount of silicone needed in a shampoo, while maintaining conditioning performance.
From a formulation standpoint the challenge is to control deposition of benefit agents such as cationic polymers, silicones and/or vegetal oils under rinse off in order to provide optimum performance.
Cationic guar delivers conditioning attributes at low usage concentration levels. Ease of wet combing and half-head salon tests illustrate such conditioning performance effectiveness. Ease of wet hair combing was carried out using Diastron equipment. Shampoos containing from 0.1% to 0.3% of hydroxypropyl guar hydroxypropyltrimonium chloride and polyquaternium-10 were compared for their conditioning effect using Caucasian hair tresses treated with one shampoo application. As little as 0.1% cationic guar in the shampoo was sufficient to minimize wet-combing force, whereas 0.3% polyquaternium-10 was originally required.
Half-head salon tests were performed at the Schrader Institute (Germany) with 20 female volunteers to compare conditioning attributes of shampoos based on either guar hydroxypropyltrimonium chloride or polyquaternium-10. Cationic guar alone at 0.1% outperforms polyquaternium-10 at 0.3% for all the shampoo characteristics and most of the conditioning attributes. Shampoo’s foam texture and wetcombing were significantly improved.
Repair: Beyond hair conditioning, there is an increasing consumer need for hair repair in order to achieve healthier looking hair. The condition of the hair can deteriorate as a result of frequent shampooing, applying chemical treatments (such as dyes or perms) or exposure to environmental aggressions (such as UV and pollution).3 From a microscopic view, damaged hair results in cuticle uplift and cracking. As the cuticle separates from the cortex the hair fiber becomes weaker and porous, thus leading to increased water absorption, which impacts its mechanical properties.
As demonstrated by Scanning Electron Microscropy, multiple treatments of a hair fiber with a shampoo containing cationic guar reversed hair damage by cementing the uplifted cuticle back onto the cortex. This contributes to the restoration of the hair fiber strength.
In another demonstration of cationic guar’s impact on hair repairing, the porosity and hydrophilic nature of damaged hair were shown by use of a Kruss balance apparatus to measure the wetability of a hair fiber as it is immersed in distilled water.4 Damaged hair fiber absorbs water as it is submerged, which generates abnormally high wetting forces. Virgin hair is more hydrophobic and repels the water as cuticle uplift is reduced. Thus, hydrophobic hair is being pushed up from the water and the load on the balance is reduced.
As illustrated in Figure 5, the hydrophobic character of Caucasian virgin healthy hair could well be differentiated from the hydrophilic characteristics of damaged hair. Sodium laureth sulfate shampoo formulations containing either guar hydroxypropyltrimonium chloride or polyquaternium-10 were compared for their ability to restore hydrophobic character of damaged hair. Shampoo formulations were applied six times on damaged hair fibers and the results clearly indicated that cationic guar repairs damaged hair by greatly reducing its hydrophilic nature in comparison to polyquaternium-10.
Enhancement of Sensorial Benefits
Beyond the primary properties of shampoo—cleaning, conditioning or repairing—shampoo sensorial aspects provided through the foam are essential. Lather characteristics of shampoo are critical as consumers tend to associate first sensory experience with product performance. For psychological and sensitive reasons, consumers want to feel foam when they use a shampoo. Therefore foam must remain stable in the presence of soil and sebum that cover the hair, so it should not begin to dissipate immediately when used.
Foam bubble size distribution: Foam can be described as a non-equilibrium dispersion of gas bubbles in a liquid.5 Foam stability is greatly influenced by properties of air/water interface. To study the effect of cationic guar on foam stability, we first compared foam bubble size distribution of two shampoos, one of which was formulated with hydroxypropyl guar hydroxypropyltrimonium chlorideb (see Figure 6). Foam bubbles generated out of the cationic guar-containing shampoo were found to have a mono disperse distribution with particle size centered around a small diameter. As a result, bubbles become more compact and uniform, leading to nicer, whiter and shinier foam.
Most of cationic guars tested show higher foam firmness than the levels achieved by the other tested cationic polymers.
Foam bubble size over time: Next, we measured foam stability by monitoring average bubble diameter over time (see Figure 7). The rate of bubble coalescence from a shampoo base containing hydroxypropyl guar hydroxypropyltrimonium chloride was slower than that of the same shampoo without the polymer. As a consequence of increased film elasticity, the bubbles expand or rupture more slowly. Cationic guar contributes to extending foam life by modifying bubble film characteristics.
Foam firmness: Evaluation tests were specifically developed to further compare foam sensorial attributes to measurable physical parameters. The objective was to set up easy-to-use equipment enabling a fast screening ofcationic polymers and their impact on foam properties such as foaming power and rheology.
One of the most commonly used methods to characterize foaming power is the Ross-Miles characterization methods (ASTM standardized) measuring both foaming ability and stability. A known amount of shampoo solution is poured into a column; measurements are taken of the foam height initially and again after 5-10 min. Furthermore, foaming power measurement was also achieved in the presence of sebum well-known to have detrimental effects on foam stability. A known amount of synthetic sebum emulsion is introduced to the solution tested in order to represent moderately dirty hair.
The characterization of foam rheology is an important aspect of foam sensorial attributes. Although a creamy and dense lather can be directly felt by the consumer’s fingers and could be linked to foam consistency, we wanted a specific test to measure the consistency of freshly produced foam or its resistance to an applied force. Therefore, we developed a device to reproduce the foam that would match the characteristics of the foam generated from a shampoo worked through wet hair. A deformation force is applied onto the calibrated foam. The absolute maximum resistance force (mN) is then recorded over time. This force value relates to the foam’s firmness. A variation of 2 mN in force would translate to a significant change in sensorial signals for an untrained consumer panel.
Different sources of cationic polymers were assessed for their influence onto physical foam properties. Polymer derivatives were from guar origin (guar hydroxypropyltrimonium chloride), cellulose (polyquaternium-10) or synthetic origin (polyquaternium-2, polyquaternium-7). All the cationic polymers were formulated at 0.2% active content in ALS/ALES/ CAPB (ammonium lauryl sulfate/ammonium laureth sulfate/cocamidopropyl betaine: 7/7/2 respective ratio) added with 0.15% NH4Cl shampoo base.
The effect of each the cationic polymers on foam firmness of the ALES shampoo base is shown in Figure 8. Most of cationic guars tested, including the one shown in Figure 8, show higher foam firmness than the levels achieved by the other tested cationic polymers. Similarly, all cationic guars, including the one shown in Figure 9, outperformed polyquaternium-2 and polyquaternium-10 as foam height was significantly improved in the presence of sebum.
Furthermore, changing the co-surfactant nature, from cocamidopropyl betaine to sodium cocoamphoacetatec or sodium lauroamphoacetated impacted the foam properties. Combining amphoacetate surfactant derivatives with cationic guar enhances both foam volume in the presence of sebum (see Figure 10) and foam firmness compared to polyquaternium-10.
With appropriate choice of cationic guar, formulators can adjust hair surface management and delivery of benefits agents from shampoos. Cationic guars can significantly improve the mechanical and sensorial attributes of foaming shampoos. Foam abundance and elastic property can be fine tuned in order to give a different sensorial trigger to consumers. With a better understanding of the in-use interactions between cationic guar and the different ingredients of a rinse-off formulation, formulators can achieve outstanding performance that translates into multifunctional consumer benefits.
Acknowledgements: The author wishes to acknowledge Olivier Anthony, Patrick de Lanty, Anne-France Leron and Mélissa Manuszak for their contribution to the work discussed in this article.