2010 TRI/PRINCETON CONFERENCE 267 ASSESSING HAIR DAMAGE BY PHYSICAL TOOLS Differential scanning calorimetry (DSC). DSC was used to measure hair damage by assess- ing hair keratin degradation and the effect of cosmetic pretreatments. DSC measure- ments were performed on tresses after the 12-minute controlled hot ironing treatment schedule. Two thermal parameters derived from the DSC peak were used to assess hair damage: the denaturation temperature, Td, of the helical protein and the denaturation enthalpy, ΔH. All hair samples were run on a Q2000 DSC (TA Instruments) at a heat- ing rate of 2°C per minute. Between 8 to 13 milligrams of cut hair fi bres were used per run in high volume stainless steel pans. Fifty microliters of water were added to each pan prior to sealing. The sealed hair fi bers were hydrated in their pans overnight before running. FTIR spectroscopic image analysis of hair fi bers. Fourier transform infrared imaging spectros- copy (FT-IRIS)was utilized to examine the molecular modifi cation of hair keratin from thermal insult with and without protective treatment. This novel technique provides signifi cant advantages of direct spatially resolved concentration and molecular structure information for sample constituents. In this study, hair cross sections were imaged by a Perkin Elmer Spotlight system which couples a FT-IR spectrometer to an optical micro- scope. The system consists of a linear array mercury-cadmium-telluride (MCT) detector and an automated high precision XY sample stage. In the FTIR images, each pixel size is 6.25μm and 16 scans were collected for each spectrum with 8μm−1 spectral resolution. Five-micrometer-thick hair cross sections were prepared by slicing a short hair bundle which is embedded into ice mounted on the top of a sample holder under -30°C using a Leica CM 1850 Microtome. Hair cross sections were collected on CaF2 windows for conducting FT-IR imaging analysis. Spectral Dimensions Isys 3.1 software was used for data analysis and image construction. Spectral data were baseline-corrected before peak heights and integrated area were measured. Scanning electron microscopy (SEM). SEM was used to examine the morphological changes of cuticle layers on the hair surface after thermal treatment with and without the protective treatment. The Amray Model 1820 SEM was used to collect digital photomicrographs. Four to fi ve fi bers were examined for each hair sample treatment. Dynamic vapor sorption analysis (DVS). The sorption and desorption of water vapor on hair were determined with a DVS Advantage-1 gravimetric vapor sorption analyzer (Surface Measurement Systems Ltd., London, UK). The experimental temperature was 25.0 ± 0.1°C and the total N2 gas fl ow was 200 ml/min. Approximately, 40mg of hair samples formed into a 20-30 strands of loop were loaded onto a tared quartz sample pan. The di- ameter of the hair fi ber, which was chosen as the average of 30 fi bers (59 um), was deter- mined using a Mitutoyo micrometer. The sorption sequence consisted of the following steps: 1. The hair sample was initially wet at 95% RH for 1 hour. 2. The hair was dried at 25 °C and 0 %RH for 12 hours. 3. The hair samples were exposed to an isothermal humidity ramp from 0–90 % RH followed by a 90–0% RH desorption in 10% RH steps. Each sorption-desorption step was 4 hours in duration to approximate gravimetric equilibration. 4. At the end of each partial pressure, step points were averaged to produce an isotherm plot, which showed the change in mass of hair samples as a function of relative humidity.
JOURNAL OF COSMETIC SCIENCE 268 Atomic force microscopy (AFM). Specimen preparation. European dark brown hair fi bers were mounted onto a steel sample disk using a nail polish liquid. A thin layer of the liquid was brushed on the surface of the metal disk. When the liquid hardened into a tacky state, hair fi bers were carefully placed on the metal disk. The liquid dries quickly to keep the hair fi bers fi rmly in place. Instrumentation. AFM was performed using a Mutimode Nanoscope V supplied by Veeco Instruments, Inc (Santa Babara, CA) at ambient conditions (22°C, 50% humidity). A sharp Nitride lever (SNL) probe combining a sharp silicon tip with a silicon nitride cantilever was used for the topographic imaging acquisition. The nominal radius of the tip was about 2 nm and the spring constant of the cantilever is 0.06 N/M. The scan was fi rst carried out perpendicular to the longitudinal axis of the hair fi ber. After the tip was centered over the cross section and located at the very top of the fi ber, the scan direction was changed to parallel with the longitudinal axis of the hair fi ber. A scan rate of 1Hz was used for all measurements. The data collection was set to defl ection channel and the error signal images, which are very sensitive to the changes in height, were recorded at 15×15 and 5×5 μm2. The image data presented in this paper are raw and unfi ltered. Hair temperature measurement during hot fl at ironing with thermal image analysis. In order to evalu- ate the heat control effect of polymer pretreatment, hair temperature during hot fl at ironing was measured. An infrared camera (Flir P series) was used to measure hair temperature after hot fl at ironing with an IR beam aiming on hair. Hair tresses were hot fl at ironed from the top of the tress to the bottom, with three 5-second strokes as one heating cycle, and the maximum temperature was taken during the third stroke. Three hair tresses were tested for each treat- ment and the average temperature of hair was taken from the three tresses. ASSESSING HAIR THERMAL DAMAGE BY QUANTIFYING HAIR BREAKAGE FROM COMBING Hair breakage is quantifi ed by combing the dried tresses that was exposed to the 12 minutes thermal treatment and washed with 12% SLES. To do so, a translucent plastic is fi rst placed under the tress. The tress is then combed vigorously 100 times with a fi ne-toothed comb. The fragments of hair that are collected as a result of combing are secured by tape and numbered. Five hair tresses were tested for each treatment and the average number of hair breakage was taken from the tests of fi ve tresses. The % hair breakage reduction by a cosmetic pretreatment is calculated as the number of hair pieces of control (untreated) minus the number of hair pieces from the polymer pretreatment test divided by the number of hair pieces of the control: C T % Hair breakage reduction 100 C = × where C = the number of hair pieces collected for the control and T = the number of hair pieces collected for the test. RESULTS AND DISCUSSION THERMAL DEGRADATION OF HAIR KERATIN FROM THERMAL TREATMENT Hair is composed primarily of proteins. The cortex region contains the bulk of the hair keratin fi bers. There are different types of protein components in human hair, with the
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