Using Texture Analysis to substantiate claims in Haircare. Quantifying product effectiveness

Transcription

1 Using Texture Analysis to substantiate claims in Haircare Quantifying product effectiveness Stable Micro Systems

2 Using Texture Analysis to substantiate claims In Haircare Janusz Jachowicz, Science Fellow, ISP, and Jo Smewing, applications manager, Stable Micro Systems The Stable Micro Systems TA.XTplus Texture Analyser Combability tests... have provided interesting results. Recent market analysis paints a picture of contrast in today s haircare and hair styling market. While global retail sales of haircare products increased by 5% in 2011 to reach $73.7bn ( 47.2bn, 55.2bn) boosted by spending in the emerging markets of China, India, Brazil, Russia and Mexico North America, Western Europe and Japan failed to grow at all between 2007 and 2011, and showed an increase of only 0.3% in 2012 i. So stagnation is the watchword for the UK, France and Germany Europe s major markets particularly in basic products like shampoos, where market penetration has reached almost 100%. As a result, it is more important than ever for manufacturers to be able to differentiate their products and substantiate claims about them. Extensive work recently completed by International Specialty Products (ISP) has focused on quantifying the effectiveness of hair products by testing the products themselves, but also on treated hair samples. Conditioning shampoos and conditioners There are three main reasons for the degeneration of hair condition: mechanical Photo 1: Hair Combing Device (from brushing, or friction), chemical (through colouring, perms etc) and environmental (UV damage, heat from blowdrying etc). Conditioning shampoos and conditioners aim to nourish and protect the hair, and sometimes even to reverse previous damage. Agents such as cationic surfactants, polymers, emolients, vitamins, amino acids and UV filters are commonly used for this purpose. When successful, consumers may observe: increased softness, smoothness and shine; reduced static properties, breakage and split ends; and / or improved manageability and combability. Wet combability testing Combability tests on hair treated with conditioning agents have provided interesting results. Wet combability is measured under controlled conditions using an objective method, in which the force required to push a comb through a wet hair swatch (or tress) is measured. The Hair Combing Device (see Photo 1) allows repeated combing of the hair within one test. The comb is fixed to the instrument arm which moves down through the hair tress at a user defined speed. At the target distance a mechanical stop tips the comb away from the hair tress and the instrument can return to the start position (without backcombing the hair) ready for the next combing cycle. Prior to testing, hair should be detangled and then tangled again in a controlled and reproducible way to ensure consistency. Hair swatches containing only water are tested to establish an initial benchmark. For this, the hair is brought to a wet state by spraying the swatches with water until a water regain of 60% weight is achieved. The initial force necessary to comb the hair swatch is measured by a texture analyser under climatised conditions (20ºC, 65% RH). Dry combability testing This type of test is equally effective for assessing combability of dry hair. When 1 Using Texture Analysis to substantiate claims in Haircare

3 modified, all hair types show an increase in dry combing forces (compared to virgin hair) as quantified by combing measurements. The combing work (g cm) and force as a function of tress distance would be substantially higher for all modified hair types than for virgin hair. This method can therefore be used to assess, for example, the effect of applying smoothing serums to dry hair. Tensile testing Assessing the tensile strength of a single strand of hair, or a tress, is another way to evaluate the effectiveness of strengthening properties of conditioners and conditioning shampoos. The strand, or fibre bundle, is held in tensile grips (see Photo 2). As the arm of the TA.XTplus rises, the sample is stretched to breaking point to assess its tensile properties. Maximum load, extension at maximum load, energy (or work) required to extend fibres by a specific % and total energy to break are all valuable properties closely related to the consumer perception of hair strength. Fixatives Coupled with shinier, healthier hair, consumers today demand a more natural, but longlasting, style. Hair fixatives, particularly hairsprays, have traditionally fixed a style by increasing the stiffness of a fibre assembly. But this sticky, stiff or unnatural style has fallen out of favour: touchable is now the buzzword. However, the consumer s perception of touchable actually comprises a number of physical and aesthetic characteristics, including flexibility and memory properties of the style set, hair softness, and the lack of stickiness. The next generation of hair fixative polymers will reflect these new sensory performance measures. Synthetic polymers are the ones most commonly found in the mass and salon markets. However, naturally-derived polymers, such as modified starches, can provide similar hair-holding properties with the added benefits of touchable hold, low Photo 2: Tensile Grips tack, and a natural feel. But switching to natural polymers necessitates objective analysis to measure the extent of these changes and quantify (and substantiate) the desirable claims. Various tests can be employed to assess the hair s physical qualities of the hair which are potentially affected by formulation modifications. Hair bending strength A simple and objective stiffness or bending strength test can be performed, in which hair swatches are treated with polymeric solution, dried, and allowed to equilibrate at constant temperature and humidity conditions. The hair swatch is then placed in tensile grips and bent to a certain degree. The force that has to be exerted is measured by the texture analyser. The test can yield information about the strength or stability of the examined hairs (the more resistance, the greater the stiffness) and the resulting hair volume, because flexural strength is one of the factors that have a considerable influence on hair volume. Dynamic hairspray analysis ISP has recently developed a new method, termed dynamic hairspray analysis, to study the mechanical behaviour of pre-set hair tresses, untreated and modified by hairspray resins, under a wide range of bending... touchable is now the buzzword. Using Texture Analysis to substantiate claims in Haircare 2

4 Texture Analysis in Haircare Figure 1: Experimental set-up for dynamic hairspray analysis This approach allows the simultaneous determination of parameters such as stiffness of untreated and resin-modified hair, duration of tack, maximum value of tack force, and time of drying. The hair is wetted, dried and shaped... deformations ii. This technique also employs the TA.XTplus texture analyser, which acts as vertical tensile testing machine and measures force in both compression and extension modes. The instrument, which includes a sample holder and spraying devices, performs the test in three stages: a) applying low intermittent deformations to a preformed hair tress in order to determine the properties of untreated hair b) treating the fibres with a hairspray c) measuring the changes both in adhesive properties of a hairspray solution on the surface and in mechanical stiffness of the fibre assembly as a function of drying time. Experimental setup The complete dynamic hairspray analysis system, including the texture analyser, sample holder, and spraying devices, is housed in a plexiglass box equipped with a humidity controller. A drawing of the experimental setup is shown in Figure 1. Two aerosol cans, each containing 100 g of the same hairspray formulation, are positioned nine inches away from the hair tress at an angle of 60 from the horizontal plane, using three-prong clamps. The hair is wetted, dried and shaped into an omega loop, and dried at 50% relative humidity (RH) for at least 12 hours to form a set maintaining geometrical dimensions at low humidity for a period of time necessary to apply the fixative. Test method The hair tress is weighed and positioned under the texture analyser s probe. It is fastened to the base plate with two plastic tabs set 1.2 cm apart as shown in Figure 2. Each test is performed by oscillating a clear plastic probe Figure 2: Scheme showing geometry of samples shaped into omega loops 3 Using Texture Analysis to substantiate claims in Haircare

5 (25 mm in diameter) between the fibre surface and the calibration height of 10 cm. After touching the surface of hair and sensing a 2 g force, the probe produces an additional 1 mm deformation of the loop before returning to the calibration height. Initially, the stiffness of untreated hair is measured. After a baseline value has been established, each side of the tress is sprayed with an aerosol hairspray formulation for two seconds. The measurements are continued for 80 minutes, after which the tress is weighed again to determine the amount of deposited resin. For a hairspray drying experiment as described above, the plot of force as a function of time is a series of peaks, with each peak corresponding to one deformation cycle of a hair loop. The maximum positive and negative values of force, together with the corresponding displacement values, are recorded. The peak forces have been found to be proportional to the stiffness modulae of the fibre assembly. Curve interpretation Figure 3 shows a typical hairspray drying curve in which the force (g) (peak force) is plotted as a function of time. The variation of the geometrical dimensions of a loop is described by the plot of the differential tress height as a function of time (upper curve and the right hand y axis). The initial portion of each drying curve corresponds to untreated hair. After the assessment of unmodified hair as a reference point, the fibres were sprayed for two seconds, followed by intermittent measurements of stiffness and tackiness forces for seconds. The negative peak forces indicate the adhesion of the probe to the resin-modified hair surface and can be used as a measure of the magnitude of hairspray tackiness (maximum tackiness). The duration of tackiness and the total amount of time elapsed between hairspray application and the disappearance of stickiness (dry time) can also be calculated. Other parameters Figure 3: Force and differential tress height Shown as a function of drying time for a typical hairspray composition (55% VOC) shown in this figure include the stiffness ratio (the ratio of the maximum stiffness of resinmodified hair to the stiffness of untreated hair) and the total time to reach maximum stiffness (total dry time). Analysis of hair tackiness Most hairspray solutions become tacky after partial evaporation of the solvent. Parameters such as tack duration or the magnitude of the adhesive force are crucial attributes of hairsprays which are perceptible to consumers. The analysis of hair tackiness during drying of hairspray resins on the hair surface was carried out at ISP by applying 0.07 g of a hairspray solution (polymer concentration 5.71% w/w) to a dry loop of hair and following the time dependence of adhesive forces by intermittent flexing by a texture analyser. A typical example of this experiment is presented in Figure 4. This diagram illustrates an increase in duration of adhesive forces for compositions (based on ethyl ester of PVM/MA copolymer) containing progressively higher levels of water. The observed average tackiness periods (three measurements) were 194 ± 6s, 292 ± 28s and 540 ± 100s for 100% VOC, 80% VOC, The negative peak forces indicate the adhesion of the probe to the hair surface... Using Texture Analysis to substantiate claims in Haircare 4

6 Texture Analysis in Haircare Figure 4: Time dependence of adhesion forces Comparison of the time dependence of adhesion forces for a) 100%, b) 80%, and c) 55% VOC hairspray compositions based on the ethyl ester of PVM/MA copolymer over the tress surface, thoroughly saturating the fibres between the plastic tabs. In order to preserve the circular shape of the loops for stiffness measurements, teflon-coated, cylindrical rods were inserted into the loops immediately after treatment and left in place while they were dried and conditioned overnight in a 50% RH and 70*F atmosphere prior to measurement at 90% RH. The measurements consist of intermittent loop deformation with a given force or deformation strain, and monitoring the negative force in each deformation cycle as a function of time for 80 minutes. Example results are shown in Figure 5, which displays the variation in tackiness forces for PVP/VA copolymer E-735 and for a blend PVP/VA copolymer (E Vinyl Caprolactam/PVP/Dimethylaminoethyl Methacrylate copolymer). The data demonstrate a large reduction in both the magnitude and duration of tackiness for a polymer blend (System D) compared to the one-component PVP/VA copolymer (System A). The results can be presented in the form of plots such as those in Figure 5 or, after integration, as the values of the work of adhesion. and 55% VOC compositions, respectively. It is also noteworthy that the magnitude of the tack forces does not increase for watercontaining hairspray solutions. On the contrary, the results of the experiments point to a progressive reduction in adhesion for compositions of lower VOC content. Measuring dry film adhesive force ISP has also evaluated the tackiness of dry films exposed to high humidity levels. The hair was shaped into omega loops and treated with hairspray solution using an Eppendorf pipette. The deposited hairspray (0.15g per 0.2g hair sample) was uniformly distributed Analysing the stiffness and flexibility of polymer-treated hair The mechanical behaviour of pre-set hair tresses modified with styling polymers can be examined using a texture analyser. Wet hair tresses are prepared and secured in the shape of omega loops (16mm diameter) using special holders. Hair samples are then dried on a roller under controlled humidity to form a permanent set. The mechanical measurements are carried out by oscillating a plastic probe between the fibre surface and the calibration height of 4 cm (see Figure 2). After touching the surface of hair and sensing a 2.0 g force, the probe deforms the loop by a further 1-4 mm (6.25% - 25%) before returning to the calibration 5 Using Texture Analysis to substantiate claims in Haircare

7 height. 1 mm deformation is typically within the elastic limit of both untreated and resin modified hair iii, iv. 4mm deformation (25%) usually results in irreversible damage to polymer-treated hair and is employed to study the flexibility of styling products v. The raw data from the experiment include the values of force and distance as a function of time. The presentation of data as force as a function of time gives a series of peaks, with each peak corresponding to one deformation cycle of a hair loop. Plotting force as a function of distance provides an immediate test of the linearity and allows a judgement about the elasticity of the treatment. For most of the systems investigated in 0-6 % deformation, the mechanical response was a linear plot of force = f (distance). It is usually reversible, showing only a small hysteresis. A typical force corresponding to 1 mm deformation for untreated hair varies from 10 to 15 g, depending on the batch of hair and its type. After treatment with styling solutions, this value increases times. A parameter to characterise the stiffness of hair after treatment was defined as a ratio of the measured maximum force at 1mm deformation for treated and untreated hair. Stiffness Ratio = F treated (1mm) F untreated (1mm) Experimental data at high deformation of 25 % (4 mm) can be presented in a plot of force as a function of distance, as shown in Figure 6, for the first deformation (a) and the first ten consecutive deformation cycles (b). The data in these figures correspond to a brittle polymer characterised by an elastic response in the deformation range of 0 to 1mm. It is in this deformation range that we calculate the ratio of modulae, E 10 /E1, {modulus is calculated as the slope for the dependence of force = F (distance) in the linear portion of the curve}, which can be used as a measure of sample (hair treated with a polymer) flexibility. In order to further characterise the Figure 5: Tackiness as a function of time Tackiness as a function of time for PVP/VA Copolymer E-735 (System A), and a blend PVP/VA Copolymer E Vinyl Caprolactam/PVP/ Dimethylaminoethyl Methacrylate Copolymer (1:2) (System D) [10]. Figure 6: typical experimental trace of force as a function of distance A typical experimental trace of force as a function of distance obtained in a Dynamic Hairspray Analysis experiment. E 1, E 10 = Elastic modulae (slope) in the first and tenth deformations Using Texture Analysis to substantiate claims in Haircare 6

8 Texture Analysis in Haircare flexibility of the polymer used as a hair treatment a parameter F 10 /F 1 can be calculated as a ratio of the maximum force in the tenth deformation (F 10 ) to the maximum force in the first deformation (F 1 ). As illustrated by the curves in Figure 6, at a deformation of about 2 mm in the first cycle, the polymer bonds between fibres break, resulting in a reduction of maximum force (F) and modulus (E) in subsequent deformations. A plasticity parameter denoted as H 10 /H 1 can be calculated as: 2H1 H10 H1...the polymer bonds between fibres break... where H1 and H 10 are deformation distances in the first and tenth deformations. H1 is equal to 4 mm while H 10 represents 4 mm plus the distance resulting from the omega loop geometry change. The plasticity parameter scales from 1 corresponding to the case of no change in sample dimensions (no plasticity, H10=H 1 ), to 0, which corresponds to doubling of the deformation (2H 1 =H 10 ). Analysing product texture This article has focused on texture analysis as a method for assessing the effectiveness of hair care products. You may also like to read the complementary article which looks at using texture analysis to help with formulation issues in a range of haircare products. i Source: Euromonitor ii JACHOWICZ, J. & YAO, K. (1996). Dynamic hairspray analysis. I. instrumentation and preliminary results, Journal of the Society of Cosmetic Chemists, 47, iii JACHOWICZ, J. & YAO, K. (1996). Dynamic hairspray analysis. II. Effect of polymer, hair type, and solvent composition, Journal of Cosmetic Science, 52, 281 (2001) iv JACHOWICZ, J. Dynamic hairspray analysis. III. Theoretical considerations. Journal of Cosmetic Science, 53 (5), 249 (2002) v JACHOWICZ, J. & McMULLEN, R. The mechanical analysis of elasticity and flexibility of virgin and polymer-modified hair. Journal of Cosmetic Science, 53 (6), 344 (2002) Text originally published in Cosmetics & Toiletries (US) International Specialty Products Inc. (ISP) is a leading multinational manufacturer of specialty chemicals (including advanced specialty chemicals for personal care industry), synthetic elastomers and mineral products. ISP sells over 400 specialty and industrial chemicals and synthetic elastomer and minerals products to approximately 6,000 customers from variety of industries in over 90 countries. ISP s headquarters is located in Wayne, New Jersey, USA. 7 Using Texture Analysis to substantiate claims in Haircare