DYNAMIC HAIRSPRAY ANALYSIS 291 Table I Average Parameters Stiffness Sample F• ratio F• o/F• E•o/E • Hn/H • 100% VOC 501 _+ 9 25.4 0.72 0.30 0.92 80% VOC 670 _+ 20 30.3 0.72 0.30 0.92 55% VOC 794 -+ 2 30.4 0.82 0.33 0.88 purpose of using a multi-component system is to adjust the final properties of a product in terms of feel, resistance to humidity, stiffness, or tackiness. Mixed resins are fre- quently employed to lower the cost of a product. The behavior of the main polymeric component can be also modified by the addition of low-molecular-weight compounds such as oils or surfactants. For example, nonionic surfactants can be employed as plas- ticizing agents, which impart a softer feel to a stiff hairspray polymer. On the other hand, rosin gum, which is a complex polymeric material, is employed as an additive to increase stiffness or to produce a perception of "harsher feel." In this work, we have investigated the blend of ethyl ester of PVM/MA copolymer with poly(methylvinylether) (PMVE). The components of this mixture have widely disparate physical properties. Ethyl ester of PVM/MA copolymer forms stiff, hydrophobic, and water-insoluble films under use conditions, i.e., at low neutralization degrees of 10- 20%. In contrast to this, PMVE is a water-soluble, hydrophilic polymer, which forms 40 500 35 3O o 25 n,, 20 • 15 10 f i I I 400 300 •_ 200 100 0 20 40 60 80 100 % PMVE ß Stiffness ----Glass Transition Figure 8. Stiffness of a hairset and theoretically calculated temperatures of glass transition as a function of the blend of PMVE and ethyl ester of PVM/MA copolymer. Stiffness measurements carried out on hair treated with 80% VOC compositions.

292 JOURNAL OF COSMETIC SCIENCE soft films at room temperature as a result of a low glass transition of -20øC. Both materials are compatible and form a single-phase polymer blend as evidenced by the transparency of their films. Figure 8 presents the results of stiffness measurements and theoretically calculated [by the Fox equation (13)] glass transition temperatures as a function of the blend compo- sition. It shows that at low contents of PMVE, in the range of 0-10%, there may be a small increase in the stiffness ratio (within experimental error) followed by a fast decrease at higher proportions of PMVE above 40%. The variation in stiffness ratios follows essentially the same trend as changes in theoretically calculated glass transitions of the polymer blend except for the low-PMVE content region. It is noteworthy that a reduc- tion in the hairset stiffness ratio occurs for compositions characterized by a glass tran- sition slightly above or below room temperature, at PMVE contents in excess of 40%. This may suggest that the hairset stiffness may not be sensitive to glass transition as long as it is far above room temperature. Only for polymer mixtures with Tg approaching room temperature are the mechanical properties of a hairset affected, as evidenced by the observed softening effect. Figure 9 shows the dependence of residual stiffness, as measured after 80-minute expo- sure to high humidity, as a function of blend composition. This parameter is very sensitive to an increase in the content of a hydrophilic component, PMVE, and shows a significant decrease for blends containing only 5% PMVE. Further increases in the proportion of PMVE result in greater hydrophilicity of the mixtures, as reflected by the reduced residual stiffness values. 8O o• 60 • 40 0 o • 20 0 20 40 60 80 100 % PMYE Figure 9. Residual stiffness, after gO-minute exposure to 90% RH, for hair treated with the blend of PMVE and ethyl ester of PVM/MA copolymer applied from 80% VOC fbrmulations.