Celebrities and designers are setting global hair styling trends and thereby challenging manufacturers to formulate products that deliver ultra flexible styles. This article evaluates a variety of curl perfecting styling polymers in the quest to add the spring factor to curled hair
Curls are back, and they’re better than ever. With celebrities like Beyoncé, Sarah Jessica Parker and Katie Melua wearing hair in a mass of curls, luscious locks seem set to continue as a major fashion trend. Professional salon and designer brands as well as mainstream consumer brands have all moved quickly on this. Launches include John Frieda Dream Curls curl perfecter, Tresemmé Curl Care Bouncy Curls defining gel and L’Oréal’s CurlVIVE range of curl moisturising shampoos, conditioners and styling products claiming to enhance curls with define and shine technology. Out of the 1616 new hair styling products launched in Europe in 2005, an impressive 8.4% (136) were curl related (Mintel GNPD). Curls are definitely back.
Perfect curls
The resulting challenge for the hair care industry has been to develop more advanced curl supporting technology that helps curls keep their shape for longer. The functionality of traditional styling polymers is based largely on their hair fixative properties, ie ability to impart different levels of hold. Whilst effective style retention is essential, a good curl perfecting agent needs to do much more. The latest curled styles demand natural hair movement and flexibility, so the curl memory and dynamic curl retention benefits of styling agents is critical. In creating manageable, well-defined curls it is equally important that styling ingredients should not impair the sensory properties of the hair. Other important issues therefore include frizz control, hair feel/softness and shine.
The cationic styling agent, polyquaternium-72 [trade name: MiruStyle CP] is a new generation plant-derived polymer. It imparts hold by coating hair fibres with a flexible film that provides curl memory benefits, and has been proven to hold high-energy, frizz-free curls for longer, whatever the humidity. The greater hair flexibility imparted by polyquaternium-72 means styles are moveable and more natural. Curls are therefore soft and non-crispy with touchable hold. Using a range of laboratory test methodologies, the curl performance and sensorial properties of this polymer were compared against a number of leading curl-boosting ingredients and the results are reported here.
Curl memory
It is well known that if human hair is held in a desired formation while drying it will tend to retain that shape; for example, if hair is dried in rollers it will result in the hair being curly. This is temporary and the hair will revert back to its natural state over time. Styling aids retard the rate at which the hairs revert back to their natural shape. To measure curl memory, an extension method was used to evaluate not only curl retention but also springiness of the test polymers, ie the ability of curls to bounce back.
Test protocol - Virgin European hair tresses were soaked in a 10% SLES solution for 30 seconds, rinsed and allowed to dry under ambient conditions. A standard aqueous alcoholic spritz was used to apply the test polymers:
• polyquaternium-72
• polyimide-1
• polyurethane-14 (&) AMP acrylates copolymer
• PVP
• PVP/VA copolymer
The spritz formulation containing no styling agent was used as the control. Ten pump sprays of the test spritz were applied to the hair tresses. The tresses were then combed to ensure even coverage before being wound into a roller and allowed to dry under ambient conditions overnight. The rollers were then removed and the curl length of each tress was measured. Each hair tress was extended to a straight conformation and held in position for 5 seconds before release. This was repeated 50 times and the curl length was measured after every 10 extensions. Comparative statistical analysis of the results between polymer types demonstrated that polyquaternium-72 outperformed the other styling polymers, providing excellent curl memory benefits (Figure 1).
Curl flexibility
Curl compression studies were used to compare the flexibility and dynamic nature of curls held by the different polymers. A Diastron MTT 675 was used to assess reaction to mechanical deformation when curls are held by the various styling agents. The Diastron MTT consists of two arms, one static (attached to a force load cell) with sample holder, and one moveable arm. The arm moves, compressing the hair loop by 25%, and the load cell measures the forces and records them as plot of force against distance. The changing force/distance profile with repeated compressions helps to build up a picture of how styling agents respond to deformation.
Test protocol - Five pump sprays of the standard test spritz formulations were applied to washed and dried hair tresses. The hair tresses were then wound around a 30mm diameter roller and left to dry under ambient conditions. All the hair tresses were then acclimatised at 60% RH for 1 hour before being compressed on the Diastron MTT.
Curl compression studies can be used to calculate the Modulus Ratio, which is directly related to the flexibility of the styling agent under test. The Modulus Ratio compares the initial resistance to deformation of the first compression with that of successive compressions.
Modulus Ratio = En / E1
where E1 = the initial resistance to deformation of the first compression and En = the initial resistance to deformation of the nth compression
The closer to value 1 the Modulus Ratio, the more flexible the hold. The Modulus Ratio of polyquaternium-72 after 20 compressions was higher than that of other commonly used styling agents, indicating superior hold flexibility (Figure 2).
Moveable hold
Polymers possessing good curl memory and flexible hold benefits will retain curls even where the hair is being moved about excessively. Dynamic curl retention is an important parameter for curl perfecting polymers and can be measured using the Head Banger test. This method utilises a mannequin head and tests the curl retention properties of styling polymers after the head has been shaken. This is a half head test where each side of the head has been styled in exactly the same way but with different styling polymers. This provides a direct comparison between the curl retention properties of the two polymers under evaluation.
Test protocol - Test polymers were applied to the left of the mannequin head from the basic spritz formulation at 2.5% active and a second styling agent was applied to the right side. The hair was then curled on rollers and allowed to dry overnight under ambient conditions. Once dry the curlers were removed. The head was then subjected to a controlled nodding movement. Each head was shaken 60 times in a 90° arc.
Figure 3 compares the style retention properties of polyquaternium-72 (left) versus polyurethane-14 AMP acrylates copolymer after vigorous shaking. Polyquaternium-72 was found to either outperform all of the test polymers or, in the case of polyimide 1, provide equivalent hold.
Frizz control
Frizzing is due to a reconfiguration of the hydrogen bonds within the hair and occurs more readily at high humidity. Naturally wavy or curly hair is particularly prone to frizzing.
Test protocol - The spritz formuations were applied to both wet and dry hair tresses. All the tresses were left to dry overnight under ambient conditions before being placed at 90% relative humidity for 3 hours. A visual frizz assessment was carried out before and after the tresses were placed under high humidity conditions. Photographs were taken of the tresses. Polyquaternium-72 proved to be a highly effective frizz control agent, ensuring that curls are manageable and well-defined, whatever the humidity (Figure 4).
Touchable curls
A panel of trained evaluators was used to assess the sensorial properties of the styling agents. Polyquaternium-72 was found to impart a non-crispy, touchable hold without dulling or flaking, and to produce well-defined, frizz-free curls (Figure 5).
There are many styling ingredients available claiming curl memory performance and offering varying degrees of sensory benefits. Of the polymers evaluated in this study, polyquaternium-72 was shown to optimise curl hold, bounce-back and flexibility whilst leaving hair feeling soft and natural. The curl care sector has firmly established itself as a key market category and it is imperative that manufacturers ensure brands deliver on promises now so that they retain loyalty, and market share, in the future.