2004 ANNUAL SCIENTIFIC SEMINAR 495 Permanent dye products, as described above, are by far the most popular type of hair colorant in the US, but there is still a significant market for less permanent dyes based on direct (intrinsically colored) dyes. These products, usually termed semipermanents, do not need chemistry to develop color, but rely on transfer of color from the application medium to hair by diffusion. Since no chemical changes are involved, the process is reversible, and color is relatively easily removed by shampoo. An understanding of the relationship between dye structure and color, and its effects on dye properties has been critical in developing dyes with improved coloring and stability towards shampoo removal for these products.

496 JOURNAL OF COSMETIC SCIENCE THERMAL CONDUCTIVITY OF HUMAN HAIR MODELING AND MEASUREMENT OF HEAT TRANSFER Yash K. Kamath, Ph.D. and Elena Petrovichova, Ph.D. TRl/Princeton, Princeton, NJ 08542 Introduction Hair grooming practices often involve thermal treatments of hair, such as blow-drying and heat curling. Thermal treatments also include straightening of hair using heated flat irons. In the past this practice was confined to African American hair after relaxation to eliminate the fine residual crimp in the hair. But now this practice has been extended to Caucasian hair to straighten the hair from long-wave curl or eliminate frizziness. The damage suffered by the fiber during these treatments depends on the air temperature in the case of blow-drying and the surface temperature of the devices used in heat curling and straightening. The damage to the cortex of the fiber depends on the temperature that the cortex experiences over the period of treatment. For a given surface temperature of the device, the temperature in the cortex depends on the thermal conductivity and the time of treatment. In this paper we have made an attempt to study heat transfer into hair and hair assemblies. We have also made an attempt to model, theoretically, the temperature profiles in a single hair fiber and in fiber assemblies of defined geometry. Furthermore, we have tried to measure the thermal conductivity of hair and hair assemblies containing moisture. Experimental Hair Drying: The rate of heat transfer through a hair assembly controls the dxying of the assembly. At TRI this is measured with an apparatus known as the Gyrotherm, which is shown schematically in Figure 1. It consists of a hollow cylinder mounted at the end of a rotating arm. A 1 cm 2 copper plate is mounted on the cylinder surrounded by 8 more copper plates of the same area and mass acting as ballasts. A thermocouple is connected to the center plate and its output is monitored to obtain temperature as a function of time. The flattened hair tress is mounted on the copper plate and the arm is rotated at an appropriate speed to give the required air velocity over the specimen. The room is maintained at 24øC and 50%RH. The cooling rate is obtained from the thermocouple output as a function of time. Copper Insert Insulated Cylinder Themnocouple Lead Counterweight / Motor Fig. 1 Schematics ofTRI Gyrotherm©. Thermal Conductivity: Thermal conductivity apparatus is shown in Figure 2. The apparatus consists of 4 plates from bottom to top. Bottom plate is heated at a constant rate. The topmost plate is the cold plate, which acts as a receiver of heat. The PVC plate with a known resistance (1•) is the second from the bottom The plate with the hair sample (R•, Resistance unknown) at the center is placed in contact with the PVC plate. There are three thermocouples placed across the PVC and the sample plates to measure the temperature differences across the PVC and the hair sample plates. A weight is placed on top to ensure