275 Enviromechanical Assessment required to break bleached fiber films than virgin fiber composites, demonstrating that maximizing interfacial adhesion is an essential fixative design element. However, whereas the work to rupture lower MW PVP K-30 and PVP K-30/PEG 400 composites followed the trend: neat bleached virgin, the work to break PVP K-15 and imidized p(IB/ MA) virgin and bleached fiber composites was greater than the work to break their neat films, where bleached =virgin neat. Hence, the addition of oxidized or hydrophobic fibers to PVP K-15 and imidized p(IB/MA) solutions formed synergistic film composites, in which the breaking mechanisms for PVP K-15 and imidized p(IB/MA) neat films were rendered less brittle by the addition of elastic hair fiber snippets. Interestingly, the work-to-break trends are reversed for the higher MW composite films, wherein the work required to fracture films with virgin fiber snippets was marginally higher than the compulsory work to break bleached fiber composites however, like trends with lower MW composites, more audible emissions were discharged when breaking bleached instead of virgin composites. One plausible reason for the apparent discrepancy is that viscous fixative solutions prepared with cationic and higher MW globular chains engaged the chemically oxidized fiber surface (DCA =71°), but less intimately intermingled with the pores, cracks, and asperities of the fiber prior to drying to rigid and glassy films however, where efficient contact was made, the entangled chains at the interface bound strongly to a myriad of anionically charged cysteic acid moieties (14,20,21). Consequently, instead of cohesive properties driving lower-humidity crack propagation in higher MW bleached fiber composites, fracture probabilities and #AED were presumably associated with adhesion failures in which disorganized interfacial bonding limited the composite film strength. In distinction, interactions of higher MW (pseudo)cationic polymers with virgin hair cuticles— which are quite hydrophobic (DCA =100°)—were likely less charge-specific hence, it is conceivable that the organization of the fiber-weld interface was improved by balancing electrostatic attractions with increased dispersive adhesion and optimized chain entangling. In a supplementary experiment, a section of a triple-bleached hair tress was delipidated in an organic solvent to determine whether removal of additional lipids and surfactant Figure 9. Effect of bleached snippets on the maximum force of compression and associated #AED for composite films ruptured at 50% RH. In general, the chemistry of the fiber surface had minimal influence on the maximum force to burst composite films (compare to the work-to-break trends in Table II) however, for all composite films except imidized p(IB/MA), the #AED liberated by composites containing bleached snippets was greater than films prepared with virgin snippets.

276 JOURNAL OF COSMETIC SCIENCE promotes increased film toughness and #AED. Figure 10 summarizes the film-rupture results performed at 50% RH and demonstrates that extracting lipophiles from bleached snippets with a 4:1 (w/w) chloroform–methanol solvent increased the #AED for all films—except composites prepared with imidized p(IB/MA). In addition, we noted that the work-to-break results for the delipidated-bleached snippets were statistically similar to the work-to-break results for composites prepared with triple-bleached snippets. EFFECT OF AMBIENT MOISTURE ON COMPOSITE FILM FAILURE Hairstyling products physically bind together groups of aligned hair fibers into user- defined spot and seam welds. The chemical composition of welds may be complex, where interfiber films may include fixatives, thickeners, neutralizers, conditioners, plasticizers, emollients, surfactants, natural extracts, waxes, oils, fragrances, and preservatives. Each formulated component likely influences perceptible tactile properties including 24-hour durability, stiffness, style plasticity, tack, dry time, film flaking, and water vapor absorption properties. However, in the current work, we employed simple formulations in which the dried films included only fixative, fibers, and absorbed water vapor. Hence, before initiating work on the mechanical testing of films, we used DVS and DSC-RH experiments to characterize the moisture management and thermal response of neat and fixative-fiber composite films. Figure 11 shows DVS moisture regains (Figure 11 inset) and trends in the T g of each polymer as a function of ambient temperature and changes in applied environmental humidity. The results indicate that all tested polymers were influenced by absorbed water vapor, but only imidized p(IB/MA), poly(VP/DMAPMA), and poly(VP/MAPTAC) showed steady-state water-plasticized glass transitions at isohumes ≥75% RH. Together with the DSC-RH and DVS results, Table III directly associates water vapor plasticization and moisture regain with increased fixative ductility, wherein the DMA-RH critical humidity is the environmental isohume required to facilitate a mechanical T g in the composite film at ambient temperature. Columns 1 and 3 in Table III show results for polymer-fiber composites, whereas the second column contains data for polymer- impregnated PET felt strips. Interestingly, the critical humidity results for PET-fixative composites are statistically identical to film-fiber composite and omega loop results, indicating that polymer–hair fiber interactions and the shape of the treated fiber assembly Figure 10. Total #AED released at ambient humidity (50 ± 5% RH) by ruptured polymer-fiber composite films comprised of virgin, bleached, and delipidated snippets. Using single-fiber Wilhelmy methodology, DCA values for virgin, bleached, and bleached-and-delipidated fibers were determined to be 100 ± 6°, 71 ± 4°, and 67 ± 4°, respectively, in which higher DCA values indicate greater hydrophobicity of the fiber surface. EDB=virgin European dark brown hair snippets.