2010 TRI/PRINCETON CONFERENCE 269 organized α-helical protein accounting for about 40% of the fi ber's cross section (8) in the fi brous cortex surrounded by the multicellular fl at cuticle sheath. One way of showing the degradation of hair by thermal treatments is through DSC. Figure 1 shows the DSC results of thermally treated hair at two temperatures, 205°C and 232°C. DSC yields two thermal parameters from protein thermal transition: protein de- naturation temperature or the DSC peak temperature, Td and the denaturation enthalpy or the area of the peak, ΔH. The results in Figure 1 show the reduction of Td and ΔH after thermal treatment of European hair, indicating protein degradation. With the heat- ing temperature increasing from 205°C to 232°C, Td is reduced by an additional 20 de- gree. Also, ΔH is reduced by an additional 14.9J/g. Therefore, at higher heating temperature, the protein degradation becomes more severe. THERMAL PROTECTION OF HAIR KERATIN BY VARIOUS POLYMER TREATMENTS AND THEIR ANTI-BREAKAGE EFFECT A thermal protection route was developed aiming to putting polymer barrier on the hair surface to reduce overheating spots, and to improve hair vapor retention/restoration which can serve as a heat sink to reduce thermal damage from repeated heat treatment. Polymers with different chemistries are evaluated for their effect on hair thermal protec- tion. Figure 2 shows the structures of these polymers. From a structure-property point of view, high molecular weight polymers having fi lm-modifying groups for a smooth and fl exible fi lm formation and polymers having hydrophobic units were evaluated. The poly- electrolyte complex (PEC) of a high molecular weight anionic polymer and cationic poly- mer was included in the study as it forms a smooth fi lm on drying. All polymers studied contain PVP (polyvinylpyrrolidone) in the repeated unit. A copolymer of VP and DMAPA acrylates contains a fi lm modifying group, DMAPA (dimethylaminopropyl methacryl- amide) for smooth and fl exible fi lm formation. Its analogue, polyquaternium-55 (PQ-55) contains a quaternary group with a lauryl chain. Another VP copolymer, VP/acrylates/ lauryl methacrylate copolymer, is anionic with a lauryl chain. Figure 1. DSC results of thermally treated hair at two temperatures, 205°C and 232°C. Dark brown Euro- pean hair.

JOURNAL OF COSMETIC SCIENCE 270 Table I summarizes the results of peak temperature and denaturation enthalpy from the DSC analysis of thermally treated Asian hair at 205°C with and without cosmetic pretreatment. The hair breakage results during the subsequent combing are listed in Table I as well. The thermally treated hair shows reduction in both parameters, Td and ΔH, indicating that thermal treatment causes hair protein damage. The shaded areas in Table I is the hair fi bers pretreated with the polymer containing a fi lm modifying group or a hydrophobic unit and made in 1% polymer solutions. The results demonstrate that the polymer pretreatment provide signifi cant reduction in Td and ΔH loss. The percent- age of protein thermal protection was calculated based on the difference in ΔH reduction between the untreated hair sample and the polymer pretreated hair sample. The polymer Table I DSC Results of Peak Temperature and Denaturation Enthalpy from DSC Analysis of Thermally Treated Asian Hair at 205°C with and without Polymer Pretreatment and Hair Breakage Results During Subsequent Combing Asian hair, 205°C thermal treatment Td°C ΔH(J/g) Td loss ΔH loss % Protein protection No. of breakage/ anti-breakage (%) No thermal treatment 140.4 20.5 Thermal treated, no protection 136.5 16.0 3.9 4.5 193 Polyquaternium-55 139.6 18.6 0.8 1.9 57.7 132/31% VP/acrylates/lauryl methacrylate *copolymer 138.7 17.9 1.7 2.6 42.3 91/52.5% VP/DMAPA acrylates Copolymer 138.9 18.5 1.5 2.0 55.5 130/32.6% PVP K-90 135.0 14.6 5.5 5.9 0.0 192/0% Figure 2. The chemical structures of polymers tested for their thermal protective effects.