Socially, diversity is increasingly valued and hair styling is an essential part of expressing oneself. To maintain a desired look, sufficient stiffness is required to hold hair in place throughout the day, even after vigorous activity. Without some level of flexibility to relieve stress forces, though, the style is easily broken and difficult to repair. Thus, for desirable hair styles, both stiffness and flexibility are necessary – but the two properties are generally considered incompatible.
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Socially, diversity is increasingly valued and hair styling is an essential part of expressing oneself. To maintain a desired look, sufficient stiffness is required to hold hair in place throughout the day, even after vigorous activity. Without some level of flexibility to relieve stress forces, though, the style is easily broken and difficult to repair. Thus, for desirable hair styles, both stiffness and flexibility are necessary – but the two properties are generally considered incompatible.
Setting polymers used in hair styling products generate a film by coating the hair and providing sufficient stiffness to hair styles,1 although it is well-known that setting polymers alone cannot provide enough flexibility. As a solution, additives such as polyols are often used in combination to increase flexibility, but this, in turn decreases stiffness by affecting polymer film formation.
The film created by polymers often causes flaking as well, due to its hard and brittle properties. While moisturizers are added to suppress this, they tend to leave a sticky and undesirable texture.
Furthermore, since many setting polymers used are synthetic and petroleum-derived materials, they have raised environmental concerns; for example, how they impact aquatic ecosystems after rinse-off. Yet, existing natural setting polymers and additives cannot completely replace synthetic ones in terms of functionality. As such, new hair-styling ingredients that are sustainable and that impart both stiffness and flexibility to hair styles are much desired.
In response to these functional and environmental demands, an isomalto-oligosaccharide (IMO) hair styling additivea was developed. IMOs – i.e., carbohydrate liquids mainly composed of isomalto-oligosaccharide – naturally exist in Japanese traditional fermented products such as sake and soy sauce. They have α-1,6-glycosidic bonds (see Figure 1 below) and they are readily biodegradable. Notably, α-1, 6-glycosidic bonds have a different molecular orbital from α-1, 4 glycosidic bonds (general glycosidic bonds), and it is believed that the balance of these two kinds of glycosidic bonds contribute to the formation of firm and flexible film.
To create the described hair-styling ingredient, IMOs are manufactured from starch via an enzymatic technology using microorganisms. The present study compares the effects of IMOs on hair style stiffness and flexibility with those of other commonly used materials. Additional properties of texture/stickiness and flaking are compared as well.
Materials and Methods
Test formulas: To assess stiffness and flexibility, hair tress samples were treated with test styling mists containing either a common 5% maltitol/5% polyethylene glycol (PEG) mixture (total 10% additives) or 10% IMO (% solids ≥ 74%) with 5% setting polymer (VP/VA 60:40 copolymer – a generally used styling polymer) (see Formula 1 below).
Stiffness and flexibility (bending test): Samples were first prepared by fixing 1 g of hair tresses flat with 0.5 g styling mists and drying them by hanging at 22ºC and 50% RH for 24 hr. The stiffness and flexibility properties of tresses were then measured using the three-point bend configuration testb.2 For this test, the tresses are placed below a rheometer probe on two parallel supports and the probe migrates down to the center at a rate of 1 mm/s, bending the tresses (see Figure 2 below).
The bending force is measured and the data is plotted as force versus migration length. The maximum value (Fmax) of bending force is taken as a parameter of stiffness, while the migration length until the bending force drops to 1/2 Fmax (half of its maximum value) is regarded as a parameter of flexibility (see Figure 3 below). Three tresses were treated with one gel each and each tress was measured only one time.
Texture (friction test): In addition, the texture/stickiness of hair tresses treated with a styling gel containing 3% IMO was compared with that of a gel containing a 2% glycerin/1% sorbitol mixture – a common combination of moisturizers used in commercial hairstyling products (see Formula 2 below). For this test, hair tresses were attached at 1-mm intervals on a glass slide and placed on the base of a friction testerc. The test gels were applied (5 µL) to the middle of the probe, which ran on the hairs while measuring the friction force. The coefficient of static friction was calculated as a parameter of stickiness. Three glass slides with hair were prepared, each for one gel sample, and each slide was measured only one time.
Flaking (visual assessment): Flaking also was assessed visually by applying 0.8 g of the same gels uniformly to 4 g of hair tresses, which were dried completely at 50°C for one hour. After one hour of storage in a climate-controlled condition (22°C, 58~60%RH), photographs of portions of the tresses were taken after 5 min of combing.
Reduction of synthetic polymers: Finally, the ability of IMO to decrease the amount of synthetic setting polymers required was assessed by replacing part or all of the setting polymer (VP/VA copolymer) contained in the hair styling mists with IMO (see Formula 3 below) and again, measuring effects on stiffness and flexibility.
Results
Stiffness and flexibility: In terms of stiffness and flexibility, conventional additives increased flexibility but decreased stiffness, compared with the setting polymer alone (see Figure 4a below). This result clearly demonstrated the known drawback of typical additives. On the other hand, 10% IMO increased both flexibility and stiffness, suggesting it successfully combines both properties (see Figures 4a-b below).
Texture and flaking: As noted, to prevent film-forming polymers from flaking, moisturizers often are incorporated but these tend to impart a sticky texture. Indeed, in the described tests, the gel containing typical moisturizers was highly sticky after treatment, whereas the IMO gel was less sticky (see Figure 5 below). Additionally, IMO showed less flaking than the common moisturizers (see Figure 6 below).
Reduction of synthetic polymers: Finally, in terms of decreasing synthetic polymers, while the styling mist with IMO alone showed significantly less stiffness than the mist with polymer alone, replacing up to 50% of the polymer with IMO maintained hair style stiffness (see Figure 7 below). This result shows that IMO can be expected to decrease the dependency on synthetic polymers.
Conclusion
Expressing one’s individuality fits with today’s focus on diversity and inclusivity – and can be achieved in part through hair styling. As a hair-styling additive, IMO can successfully marry stiffness with flexibility for lasting hold, as shown here. Furthermore, this naturally derived ingredient offers increased stiffness while reducing environmental impact by decreasing the need for synthetic setting polymers. Functionality and environmental benefits taken together, IMO offers a solution to break through the challenges hair styling has faced for years.
a Lissenare (INCI: Hydrolyzed Corn Starch (and) Water (Aqua)) is a product of Nagase Viita
b Rheometer CR-500DX-SII, Sun Scientific Co., Ltd.
c Friction tester TL201Ts, Trinity-Lab, Inc.
References
1. Saruwatari, S. (2016) From the point of view of adhesive for hair. J. Adhesion Soc. Jpn. 52(5) 122-126.
2. Rafferty, D.W., Zellia J., … Mullay J., et al. (2008). Polymer composite principles applied to hair styling gels. J. Cosmet. Sci. 59 497-508.
