277 Enviromechanical Assessment do not significantly contribute to humidity-induced decreases in style stiffness. For the composites, we observed that all films—except composites prepared with imidized p(IB/ MA)—showed the propensity to creep at isohumes less than 75% RH, where the augmented film ductility associates with the 75% RH critical humidity results in Table III, E’ at 75% RH in Table IV, and the 90% RH tensile extension work expressed in Figure 12. Table III Critical Humidity Levels for Composite Films (DMA-RH 26°C 0.5% RH/min) Polymer Polymer-fiber snippet film (±1.0% RH) PET felt composite (±1.2% RH) Treated omega loop (±0.8% RH) Imidized p(IB/MA) 84 84 83 PVP K-120 72 68 70 PVP K-90 72 69 71 PVP K-60 71 69 70 PVP K-30 68 68 66 poly(VP/DMAPMA) 66 66 69 poly(VP/MAPTAC) 63 63 64 PVP K-15 55a 57 59 PVP K-30/PEG-400 51 51 50 a Red values =The red values indicate that the critical humidity values are below the average outdoor humidity levels in Wayne, NJ, which were assessed at 59 ± 8% RH between 2010 and 2012. Figure 11. DSC-RH results at 0%, 25%, 50%, and 75% RH. The 0% RH results were taken from standard dry DSC experiments (pinhole, second heat). The inset shows the DVS regain results for the 0%, 25%, 50%, and 75% RH isohumes (26°C). The legend key below the graphs, going from left to right and then down, corresponds to bars in the chart on moving left to right.

278 JOURNAL OF COSMETIC SCIENCE Fixative durability may be investigated by employing complementary linear and nonlinear deformation schemes. While DMA introduces infinitesimal stresses to materials to probe changes in linear viscoelasticity, methods including texture analysis, tensile strength, and impact testing introduce large molecular displacements to probe factors that contribute to irreversible film deformation (18,22). As a case in point, the importance of ambient humidity, E′, and tensile strength on style longevity is underscored by Equation 1, which relates the adhesive debonding energy to dissipative adhesion. Equation 1 (18) implicitly specifies that at low-to-moderate humidity—where lower MW and glassy fixatives demonstrate brittle failure—less tensile work is required to fracture and delaminate rigid welds: P lσ2 E′ =(1) where P is the peel strength l is the film thickness σ is the tensile strength, and E′ is the elastic modulus. For a given l, the dissipation ratio (σ 2 E′ )shows that debonding strengths increased for softer films with higher σ. Interestingly, Figure 12 (*)and Table IV show that only imidized p(IB/MA) had a measurable tensile strength and appreciable E′ at ≥75% RH, which are attributes related to intrinsic humidity resistance, intrafilm ionic crosslinking, and tough interfiber strings that bridge and constrain seam-weld fissures. It is well known that the probability of fracturing a film is highly affected by changes in film ductility. By way of illustration, the light microscopy images in Figure 13A and 13B show seam-weld dislocations and complete interface failure in welds composed of PVP K-60 and virgin hair snippets (30% RH), suggesting that debonding occurred primarily at the interface at lower humidity. For comparison, the SEM images in Figure 13C and D illustrate the humidity-induced dichotomy of adhesion failure. At 30% RH, the composite film cracked and splintered, but friction between the fibers and fragments held the shattered components in place (Figure 13C) however, at 90% RH moisture absorption plasticized the PVP K-60 welds and fibers, whereby adhesion between the film and fiber remained strong and failure occurred near interfacially, in which debonding ensued near the interface (i.e., the fibers remained coated with a thin layer of polymer) and led to fibers being pulled from the sticky restrictions of the flexible film as the texture analyzer probe pushed through the composite (Figure 13D). In addition to combining texture analysis with AED to evaluate the mechanical characteristics of films at 50% RH, AED was similarly used to evaluate the release of AE Table IV E′ (±25 MPa) and Tan ∂ (±0.01) Versus %RH Results for Virgin Fiber Film Composites Polymer E′ (MPa) /Tan ∂ 20% RH E′ (MPa) /Tan ∂ 35% RH E′ (MPa) /Tan ∂ 50% RH E′ (MPa) /Tan ∂ 75% RH poly(VP/DMAPMA) 490 /0.05 483 /0.05 504 /0.07 8.30a /1.02 PVP K-90 445 /0.05 448 /0.05 407 /0.07 8.40 /0.20 PVP K-120 441 /0.04 439 /0.05 409 /0.07 5.98 /0.23 poly(VP/MAPTAC) 390 /0.05 389 /0.06 328 /0.09 1.08 /0.41 PVP K-60 288 /0.06 292 /0.05 261 /0.07 6.65 /0.41 Imidized p(IB/MA) 239 /0.05 241 /0.05 235 /0.05 82.0 /0.28 PVP K-30 176 /0.04 177 /0.04 179 /0.05 3.47 /0.28 PVP K-15 68.4 /0.13 75.3 /0.10 94.4 /0.17 4.07 /0.33 PVP K-30:PEG 400 35.1 /0.02 34.8 /0.05 26.4 /0.15 3.33 /1.02 a Red values =soft and ductile films blue values =elastic response.