282 JOURNAL OF COSMETIC SCIENCE Another factor affecting the mechanical performance of a fixative is an adhesion between a polymer and the hair. It can be influenced by the presence of solvents, which can strongly interact with fibers by swelling them or by altering the ionic equilibrium of carboxyl or amine groups in the keratin protein. This paper explores the effect of the above-mentioned factors on the performance char- acteristics of several hairspray systems employing commercially available or experimen- tal polymers. The procedures of dynamic hairspray analysis, which utilize a texture analyzer to measure several mechanical properties, were employed to derive parameters sensitive to the physical or chemical characteristics of the investigated systems. EXPERIMENTAL INSTRUMENT The instrumentation and experimental procedures were similar to those employed in previous work (1). Hair treatment was by application by an Eppendorf pipette of a hairspray solution to hair shaped into omega loops. A typical deposited amount (0.15 g or 0.07 g of a hairspray solution per 0.2 g of hair sample for stiffness and tackiness studies, respectively) was uniformly distributed over the tress surface, thoroughly satu- rating the fibers between the plastic tabs. In order to preserve the circular shape of omega loops for stiffness measurements, the drying of wet loops was carried out by using teflon-coated, cylindrical rods inserted into the loops immediately after treatment. The hair samples prepared in such a way were dried and conditioned overnight in a 50% RH and 70øF atmosphere prior to measurements by the texture analyzer (Model TA-XT2, Texture Technologies Corporation). For tackiness measurements, low intermittent de- formations were applied to an omega-shaped hair tress, and both negative and positive forces characterizing the adhesive and stiffness forces were recorded during drying, following the application of a hairspray solution on the hair. The humidity resistance measurements were carried out at 90% RH by following the variation of a maximum force in each deformation cycle as a function of time for 80 minutes. Most of the experiments described in this paper were carried out in the elastic region of the polymer-modified omega loops, i.e., in the deformation range from 0% to 6.25% (which corresponds to 1 mm strain). We also performed measurements in the non-elastic range by subjecting omega loops to 4-mm deformations equal to 25% strain. From these measurements we could determine the maximum force in the first deformation, F•, and flexibility parameters F•o/F•, E•o/E•, H•o/H • as described in previous papers (2,3). HAIR SAMPLES Commercially blended, caucasian, virgin brown hair, fine hair, blended oriental hair, and triple-bleached hair, were all purchased from DeMeo Brothers, New York. The fibers were washed with 3% ALS solution prior to measurements. The diameters of the hair fibers, estimated from SEM micrographs, were 100 pm, 70 pm, and 50 Inm for oriental, caucasian, and fine caucasian hair, respectively.

DYNAMIC HAIRSPRAY ANALYSIS 283 POLYMERS AND FORMULATIONS Ethyl ester of PVM/MA copolymer (10% neutralization, 0.046 g AMP/1 g polymer), butyl ester of PVM/MA copolymer (10% neutralization, 0.041 g AMP/1 g polymer), vinyl caprolactam/PVP/dimethylaminoethyl methacrylate copolymer, octylacrylamide/ acrylates/butylaminoethyl methacrylate copolymer (95% neutralization, 0.168 g AMP/1 g polymer), and acrylates copolymer (100% neutralization, 0.25 g AMP/1 g polymer) were commercial products sold under the tradenames of Gantrez 225 (ISP) or Omnirez (ISP), Gantrez 425 (ISP), Gaffix 713 (ISP), Amphomer (National Starch), and Luvimer (BASF), respectively. Poly(vinylpyrrolidone) (PYP K60) was a commercial product char- acterized by the average molecular weight of 400,000, VA/butyl maleate/isobornyl acrylate copolymer (15% neutralization, 0.047 g AMP/1 g polymer) was an experimen- tal polymer similar in structure and properties to a commercial product, Advantage CP (ISP). Co(vinyl pyrrolidone-methacrylic acid-lauryl methacrylate) (20% neutralized, 0.05 g AMP/1 g polymer) was an experimental material prepared by a solution copo- lymerization of vinyl pyrrolidone, methacrylic acid, and lauryl methacrylate. Hairspray formulations had the following composition: polymer (5.71% w/w), ethanol/ water to satisfy a given VOC requirement, and AMP (amount varying according to the polymer manufacturer's specification to produce a given degree of polymer neutraliza- tion). For ethyl ester of PVM/MA copolymer at 20% neutralization: 100% VOC formulation Ethyl ester of PVM/MA copolymer: 1.85 g AMP: 0.09 g Ethanol: 15.56 g 80% VOC formulation Ethyl ester of PVM/MA copolymer: 1.85 g AMP: 0.09 g Ethanol: 11.65 g Water: 3.91 g 55% VOC formulation Ethyl ester of PVM/MA copolymer: 1.85 g AMP: 0.09 g Ethanol: 5.40 g Water: 10.16 g The VOC level of the above systems is based on 25 g total formulations, including 7.5 g (30%) propellent. RESULTS AND DISCUSSION EFFECT OF POLYMER CONCENTRATION AND MOLECULAR WEIGHT The effect of the polymer concentration on the stiffness of a hairset is illustrated by the data presented in Figure 1, obtained for ethyl ester of PVM/MA copolymer. The ex- periments were carried out by depositing a constant amount of polymer solution (per unit weight of hair), with the concentration of the polymer in the treatment varying