273 Enviromechanical Assessment Figure 6. SEM fractographs reveal rupture patterns in brittle and elastoplastic neat fixative films. Brittle failure with smooth fractured surfaces was observed in PVP K-30 (A,B), whereas plastic deformation with jagged fractured crevices was noted in the poly(VP/DMAPMA) film (C,D) (50% RH). Figure 7. Overlay of force and AED responses for (A) PVP K-15 neat film (B) PVP K-15 virgin fiber composite film (C) PVP K-120 neat film and (D) PVP K-120 virgin fiber composite film. The force trace is in blue and individual #AED events are represented by discrete red vertical lines. Note that numerous AED events in (C) and (D) were produced by friction between the composite and probe after the film had ruptured. The integrated area beneath the force-versus-time trace is proportional to the mechanical work required to rupture the film.

274 JOURNAL OF COSMETIC SCIENCE differently, the neat films released a handful of sharp and discrete “crunch or crack” noises, with long continuous fractures immediately forming in the film, whereas fiber composites released numerous “crispy” sounds as many small cracks merged within welds and augmented the observable film haziness. One obvious interpretation is that the neat films failed 100% cohesively, whereas added fibers diffused crack growth while obstructing crack initiation and catastrophic propagation pathways. To further illustrate crack propagation patterns in the neat fixatives, a falling dart test was used to produce fractures by introducing an abrupt and blunt force to the film surface. Figure 8 summarizes trends in impact resistance for studies performed at 48% RH. None of the films failed completely—however, as was observed in texture analysis with AED testing, neat films composed of lower MW polymers suffered the most damage while producing the greatest number of cracks emanating from the impact zone. In contrast, higher MW systems possessed the intrinsic toughness to dissipate excessive crack-growth energy. Additionally, we noted that plasticizing PVP K-30 with PEG 400 at 10% (w/w) did not significantly decrease the number of cracks typically produced in a PVP K-30 film instead, the addition of PEG 400 appeared to blunt the average crack length by improving stress dissipation (i.e., increased ductility and higher tan ∂). EFFECT OF FIBER SURFACE CHEMISTRY ON COMPOSITE FILM FAILURE Although fracturing events in films containing fiber snippets released abundant #AED, the composites showed mixed trends regarding their work-to-break results. Table II and the maximum compression force versus #AED scatterplot in Figure 9 summarize details from the AED with mechanical testing experiments completed at 50% RH using 1) neat films 2) composites with virgin fiber snippets and 3) composite films comprised of bleached fiber snippets. Without question, the composites containing fiber snippets released stress quite differently than their respective neat films, wherein #AED bleached #AED virgin #AED neat. In addition, apart from PVP K-15 and imidized p(IB/MA), which surprisingly formed stronger composites than neat films, composites with 0.1-g snippets generally required significantly less work-to-break but did not suffer long-range catastrophic structural failure. Furthermore, using lower MW polymers, more work was generally Figure 8. Impact testing results revealed that lower MW materials produced more cracks having longer crack lengths (48 ± 2% RH).