2010 TRI/PRINCETON CONFERENCE 271 pretreatments provide about 50% thermal protection to the hair protein in Asian hair subjected to 205°C thermal treatment. In addition, these polymer pretreatments reduce hair breakage from subsequent combing, i.e. by 52% with VP/acrylates/lauryl methacry- late and 31% for PQ-55. However, the homopolymer, PVP which contains no fi lm mod- ifying groups or hydrophobic units shows no protection against protein thermal degradation and no anti-breakage effect. The thermal protective effect of selected polymer pretreatments was also tested with dark brown European hair. Table II summarizes the results of Td and ΔH for European hair after thermal exposure at 232°C with and without the protective polymer pretreatment. The DSC results show the thermal degradation of hair keratin, indicated by a 25°C re- duction in denaturation temperature Td and a 17.2 J/g loss of enthalpy ΔH. The protein denaturation enthalpy is associated with the energy required for the helical protein dena- turation and, therefore, depends on the amount and structural integrity of the α-helical material in the intermediate fi laments of human hair cortex (9). Therefore, the enthalpy reduction after the current thermal treatment corresponds to approximately 90% loss of helical protein compared with the enthalpy reduction of the untreated hair sample. The helix content occupies about 40% of hair cross section, suggesting that the helix protein degradation from the thermal treatment is responsible for at least 36% degradation of overall hair protein. The DSC data in Table II also shows that the polymer pretreatments signifi cantly reduce the protein degradation. The ΔH reduction is especially low for 1% VP/acrylates/lauryl methacrylate copolymer and 2% PEC where it is observed that ΔH losses are than 10% for these polymer pretreated hair. These polymers are made in 0.5% hydroxyethylcellulose (HEC), a thickener to enhance distribution on hair. However, the pretreatment with HEC alone shows only small protein protection (Table II). Figure 3 shows the hair breakage results of thermally treated European hair with and without polymer pretreatment before heating. Thermally stressing hair led to increased hair breakage from 52 to 214 fragments when subjected to combing. The pretreatment of hair samples with the polymers tested provides anti-breakage effect on the subsequent combing after heating. Among them, 2% PEC and 1% VP/acrylates lauryl methacrylate copolymer treatments show the highest anti-breakage effect, 76% and 55%, respectively. Although three polymers were formulated with 0.5% HEC, the data clearly show that Table II DSC Results of Thermally Treated Hair at 232°C with and without Polymer Pretreatment (dark brown European hair) Dark brown European hair, 232°C heating Td °C ΔH(J/g) Td Loss ΔH Loss % ΔH Loss % Td Loss No thermal treatment 141.6 19.1 Thermal-treated 116.7 1.9 25 17.2 90.1 17.7 HEC and heat damage 123.6 4.9 18 14.2 74.3 12.7 Polyquaternium-55+ HEC 131.6 12.4 10 6.7 35.1 7.1 VP/DMAPA acrylates copolymer+HEC 133.6 13.2 8 5.9 30.9 5.6 VP/acrylates/lauryl methacrylate copolymer+HEC 141.2 18.6 0.4 0.5 2.6 0.3 2% PEC 140.2 17.2 1.36 1.85 9.7 1.0
JOURNAL OF COSMETIC SCIENCE 272 the HEC pretreated hair does not have an anti-breakage benefi t. The error bars of VP/ DMAPA acrylates copolymer and polyquaternium-55 pretreated hair indicates that their results are not statistically different, however, the trend of hair breakage numbers shows that these two polymers provide anti-breakage effect, which is supported by the results of DSC and FTIR imaging analysis. The hair breakage results of 2% PEC and 1% VP/acrylates lauryl methacrylate copolymer pretreatment are statistically different. Robbins has studied the pathways of hair breakage and suggests that extending and impacting or compressing hairs with fl aws or cracks and/or chemically weakened hair during combing may be one of the possible pathways for hair breakage (10). Alleviation of weakening of the thermally insulted hair through polymer pretreatments allows the hair to withstand these combing stresses and indicates thermal protection through a reduction in fi ber fragmentation. PROTEIN STRUCTURE MODIFICATION FROM THERMAL TREATMENT—FTIR IMAGE ANALYSIS OF HAIR CROSS SECTION One type of protein denaturation is a change in protein conformation. The undamaged hair has a α- helical coiled coil protein confi rmation, a well organized structure in the cortex. Once the protein is damaged, it can unfold and convert into the extended protein chain or beta sheet structure. The protein conformation changes will change the hydro- gen bonding structure that stabilizes the helical structure and, therefore, may change the water accessibility to hair. Further, IR image analysis was conducted on thermally treated hair fi bers to examine the hair keratin damage at the molecular level such as protein structural changes due to heat treatment. FTIR image analysis provided the spatially resolved spectroscopic imaging of chemical components over the cross section of hair. It consists of an array of detectors that Figure 3. Hair breakage reduction of thermally treated hair at 232°C with polymer pretreatment, 1% poly- mer solution + 0.5% HEC. European dark brown hair.
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