Can Cationic Surfactants Really Protect Hair Against Damage?
Introduction and Background
Hair care is a strongly growing market within the personal care industry. The most representative sectors of this market are hair conditioners, shampoos, and hair dyes.
Currently, there is a growing trend to formulate products that are safe, both to humans and to the environment, due to consumer perception and to regulations. In addition, regulations in Europe are getting more and more restrictive [1], so there is a great deal
of market interest in readily biodegradable and nonenvironmentally-toxic products [2].
Alkyl amidoamines properly neutralised with an acid, are a good alternative to monoalkyl quats, such as Cetrimonium or Behentrimonium Chlorides, in hair rinse formulations [3].
In general, alkyl amidoamines, when compared to monoalkyl quats, are more compatible with anionic surfactants and easier to work with.
Furthermore, these molecules in the cationic form show a higher affinity for the hair surface than do the commonly used quats and impart a much better antistatic effect to hair (see Figure 1).
Most hair rinses nowadays include claims that go further than just softening and making hair smoother and easy to comb. A widely extended claim is “protection against damage”.
Among the types of damage that hair can suffer daily are UV exposure, brushing and blow-drying [4-5]. Moreover, our hair is further damaged on a regular basis by bleaching, perms or hair colouration treatments, which include hydrogen peroxide.
Hair damage can be studied by several methods, each of them revealing the state of a part of the hair structure. Contact angle measurements are extremely useful in determining the hydrophobicity, and thus how damaged the hair surface is.
Scanning Electron Microsco (SEM) helps to corroborate visually the extent of damage
to the hair cuticle. On the other hand, techniques such as tensile strength determination, are thought to assess damage to the inner part of the hair fibre (cortex).
Using all the above techniques, it is possible to study the potential hair protection benefits of alkyl amidoamines compared to those of linear monoalkyl quats, which is the main aim of this work.
Materials and Methods
Materials Hair was supplied by Kerling GmbH. Natural dense and bleached dense hair tresses were used. Cocamidopropyl Dimethylamine (CAPDMA) was synthesized at Kao
Chemicals Europe and was employed without further purification.
Stearamidopropyl Dimethylamine (SAPDMA) corresponds to product AMIDET® APA-18 and Behenamidopropyl Dimethylamine (BAPDMA) to AMIDET® APA-22.
Cetrimonium Chloride (CTAC) is the active ingredient of QUARTAMIN® 60W25 (25% active, solvent: water) while Behentrimonium Chloride (BTAC) is the active ingredient of QUARTAMIN® AB (85% active, solvent: isopropyl alcohol).
Cetearyl alcohol corresponds to KALCOL® 6850P. All the surfactants are marketed by
Kao Chemicals Europe.
Bleaching (or Oxidation)
Process Hair tresses were immersed for 30 minutes in a 6% H2 O2 solution at 30ºC. Afterwards, they were rinsed for 1 minute.
Tensile Strength and Combing Force Measurements
The two experiments were performed with an Instron dynamometer (model 5543, cell 1 kg). For the tensile strength determination approximately 30 hair samples with a diameter of 80 ± 10 µm were selected.
Fibres were extended at a rate of 100 mm/min. Results were expressed as force during fluence (average) and force to break the fibre [6-8]. For the combing force measurement, a hair tress of approximately 20 g was combed at a rate of 500 mm/min.
Force was recorded after 1 minute treatment with test sample and subsequent rinsing for 1 minute. 10 measurements were averaged to obtain the final combing force value [9].
Scanning Electron Microscopy
Hair fibres of a diameter of 80 ± 10 µm were selected and mounted using conductive carbon tape and coated with gold/palladium. The fibres were studied with a JEOL JSM 6100 scanning electron microscope [10-11].
Contact Angle
A tensiometer (Krüss K12) was used to evaluate the contact angle between single hair fibres (φ = 70 µm) and water at 25ºC. The dynamic advancing angle was recorded from six pieces of each hair fibre. At least 5 fibres were used for each sample of hair. Results were averaged [12].
Cationic Adsorption
A solution containing 6.67·10-4 meq/g active cationic surfactant was prepared from test samples. Hair tresses were immersed in 150 mL of this solution for one minute. Cationic active matter in the solution was analysed by potentiometric titration with SLS at acid pH
before and after immersion of the hair tress. The difference between these values was assumed as being the cationic surfactant retained on the hair [13].
Results and Discussion
The study of the hair protection effects of alkyl amidoamines was divided into three possible stages:
the prevention of hair damage through pre-bleaching treatment with these products, the minimization of hair damage through the introduction of alkyl amidoamines as gelling agents into hair colouration bases and, finally, the conditioning effect on bleached hair by using alkyl amidoamines as cationic surfactants in hair conditioners for damaged hair.
Hair Damage Prevention
Virgin Caucasian hair tresses were treated with Cetrimonium Chloride (CTAC) or different alkyl chain length amidoamine solutions (0.04 meq/g) and with water (blank) before applying an oxidation treatment (bleaching). This process was repeated 15 times.
After this process extent of damage to the hair fibre was analysed by tensile strength determination and contact angle (Tables I-II).
It is observed that slightly higher forces are needed to break the fibres when they are treated with the long chain alkyl amidoamine BAPDMA, indicating a lower damage with the use of this product as pre-bleaching treatment.
This result is confirmed by the higher contact angle obtained for this product compared to
that of shorter chain alkyl amidoamines and Cetrimonium Chloride. High contact angles indicate that the hair surface is less hydrophilic after the bleaching process, and thus less damaged.
Despite this better behaviour of BAPDMA, the effect is small since differences are not statistically significant.
Damage Minimization During Hair Dyeing
Alkyl amidoamines can be used as gelling and levelling agents in permanent hair colouration treatments. The performance of alkyl amidoamines as gelling or levelling agents is equal or superior to that of market standards.
Besides these properties, the alkyl chain length might play a role in hair damage minimisation during dyeing. To study this effect, different chain length amidoamines, have been used in a typical hair colouration base (5% w/w concentration).
A patent has been filed with the results of this work [14]. This base is used together with a developer, which is an emulsion containing H2 O2 . For this reason, some damage is expected to occur due to the hair coloration treatment.
The amides used were Cocamidopropyl Dimethylamine (CAPDMA), Stearamidopropyl Dimethylamine (SAPDMA) and Behenamidopropyl Dimethylamine (BAPDMA). The contact
angle between single hair fibres and water depends on the nature of the hair fibres.
The more hydrophobic the hair surface is, the higher the contact angle. As damage level increases, contact angle decreases. Natural hair shows typically contact angles of approximately 90º, while values for bleached hair are shifted to lower values (from 50 to 75º) depending on the damage extent.
From the table above it can be concluded that the longer the alkyl chain is, the more hydrophobic the hair surface becomes. This can be confirmed visually by SEM analysis,
as Figure 2 shows.
In the right-hand picture (BAPDMA) no damage can be observed while in the one on the left (SAPDMA), scales are more separated. As a conclusion, when using long chain
amidoamines such as BAPDMA in hair colouration treatments, not only is surface hydrophobicity improved, but also hair becomes less damaged than when using shorter
chain amidoamines.
Repair After Hair Damage
In order to study the performance of alkyl amidoamines after damage is produced, hair conditioners were prepared containing different cationic surfactants.
To compare the adsorption on natural and damaged hair and the post-bleaching conditioning ability of the cationic surfactants shown in Figure 1, four hair conditioners with equal cationic surfactant content were prepared.
In the case of the two amidoamines, they were pre-neutralised with lactic acid. All formulations were adjusted at pH=4 with the same acid. The affinity of damaged hair for short and long chain alkyl amidoamines, was determined by analysis of cationic matter adsorbed on hair tresses.
For natural hair the best value is obtained for BAPDMA, almost doubling the amount of cationic retained in the case of SAPDMA. For damaged hair, the C22 amidoamine
(BAPDMA) shows still higher retention values than the C18 amidoamine (SAPDMA).
Thanks to the high affinity for damaged hair of the C22 amidoamine, this surfactant is able
to condition effectively this kind of hair, as demonstrated by combing force measurements
(Figure 3). Particularly good properties are observed in dry conditions for BAPDMA on bleached hair tresses.
Conclusions
Hair damage produced by oxidation can not be completely prevented by the use of common cationic surfactants such as Cetrimonium Chloride or by using alkyl amidoamines, since the hydrogen peroxide molecule is able to pass through the layer of surfactant adsorbed on the hair surface, but long chain amidoamines, in particular BAPDMA, do have a slight effect in damage prevention compared to short chain amidoamines and CTAC.
On the other hand, long chain alkyl amidoamines (C22) do play a role in minimising hair damage during the application of hair colouration treatments. It has also been proved that long chain amidoamines are able to attach efficiently to damaged hair fibres and there fore condition damaged hair very effectively.
Besides its good performance on damaged hair, the C22 amidoamine is readily biodegradable and non-toxic for the aquatic environment, which is in line with current market trends.
Other aspects of hair protection are now open for alkyl amidoamines, since large size molecules such as hair dyes might not be able to cross the surfactant layer deposited onto the hair surface, and for this reason it might be possible to use long chain alkyl amidoamines in colour protection shampoos and conditioners.
[caption id="attachment_140892" align="aligncenter" width="313"]
Tablo 4. Test edilen formüller. Table IV. Test formulations.[/caption]
In hair conditioners, AMIDET® APA-22 works as a cationic surfactant. Moreover, AMIDET® APA-22 can be incorporated as a non-ionic surfactant, working as a conditioning and color protection agent in 2-in-1 shampoos and as a gelling and hair protection agent in hair
coloring creams.
This multifunctional and high performance profile, together with good biodegradation and low aquatic toxicity compared to currently used cationic surfactants, make AMIDET® APA-22 a very interesting eco-friendly alternative for the hair care market.
References
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[12] Rogasik S, Martin N, Ricca JM, Wielinga W, Anthony O, SÖFT-Journal, 1999: 32.
[13] Watanabe H, Okumura T, Hayashi S, Kao Corporation Japan internal report.
[14] EP1714677 (A1)
Authors:
Maria Minguet, Neus Subirats, Pilar Castán
KAO Chemicals Europe
Translation and Compilation:
Serpil Tatlıdil Salman
Technical Solutions Leader
Organik Kimya
