42 JOURNAL OF COSMETIC SCIENCE CUTICLE REINFORCEMENT BY CATIONIC HAIR CONDITIONERS S. B. Ruetsch, Y.K. Kamath and H.D. Weigmann TRl/Princeton, P.O. Box 625, Princeton, NJ 08542 Introduction In l•evious investigations we have studied lifdng of the surface cuticle cells dttring extension of hair fibers which had experienced stanclaxd grooming practices, cosmetic chemical treatments, mechanical fatiguing, UV irradiation as wen as combinations of these treatments. Scale lilting observed by microfiuorometry during extension of the untreated hair fiber is facilitated by failure in the endocuticular domains of the surface cuticle cell. In this investigation we report on the effects of catJoint conditioners of high and low molecular weight on the scale lilting behavior and on hair fiber creep. Discussion To study the effects of single and multiple applications of cationic conditioners on the scale lifting, we detenuined the chaages in autofluorescence in the UV excitation beam during extension of untreated and conditioner treated hair fibers. The extension levels at which urndom, common and extreme scale lifting, and finally hair fiber failure occurred,. were measured and plotted. Figure I displays the typical distribution of extensions at which the various levels of scale lifting occur in untreated hair fibers. Figure 2 shows the significantly changed distribution of extensions at which the various levels of scale lifting occur, or do not occur, in conditioner Ixeated hair. Fig. 1 A = unextended A -- unextended B = random scale lifting Fig. 2 • = random scale lifting C = common scale • C = common scale • D = extreme scale rifting D = extreme scale liflgxg E = fiber failure E = fiber failure - 30 - 10 StreSS phenomena

PREPRINTS OF THE 1997 ANNUAL SCIENTIFIC MEETING 43 Fig. Subsequent scanning electron microscopy of the extended hair fibers provided greater detail about the nature of scale lifting and the failure location. Surface cuticle cells of untreated hair fibers tend to respond with a scale litting mechanism to release the stress of extension. During extension, shear forces ate generated between the different layers of the cuticle cell, and at high levels of extension and shearing, stress concentrations at the scale edge of the surface cuticle cell lead to failure in the easily extensible, weakly cross-linked endocuticular domain.• This failure within the endocuticle results in delamination and lilting of the unexteusible, highly cross- linked upper layers of the surface cuticle cell, thus producing the scale lilting phenomenon, (Figure 3). During extension of conditioner treated hair, the high level of scale litting, so characteristic of unaltered hair, is almost completely eliminated. Even intermediate and low levels of scale litting occur at higher extension levels or not at all. This suggests that the conditioning compounds modify the upper cuticular layer by reinforcing the scale edges and/or the intercuticular zone. However, when scale lifting occurs in the conditioner treated hair fiber, it involves intercellular failure in the CMC beneath the surface cuticle cell, rather than intracellular failure in the endocuticle as observed in the case of untreated hair, (Figure 4). This suggests that the conditioners modify the deformation behavior of the endocuticle which becomes reinforced and resists intracellular failure/fxaeture. This behavior is true also of low moleeulat weight quaternary. compounds and may involve hydsophobic bonding of lipid chains. When scale lifting can not take place, stress is released by scale cracking. This ol•en leads to fiber fracture and occurs only at high levels of extension. The ease of scale lifting is directly associated with the ablation of cuticle cells during grooming. Conditioner treatments which make scale lifting mor• difficult, thus provide ablatlon resisting properties to the cuticle and therefore are beneficial in preventing longterm grooming damage to hair fibers. Besides affecting scale lifting as a mechani•m of stress release during extension, the conditioners also affect hair fiber creep. Multiple applications of the high molecular weight quatemized cellulose derivative significantly change the creep behavior of hair fibers in comparison to the untreated controls. This change in creep behavior suggests conditioner-induced Improved cohesion within the intercellular cement and the weakly cross-linked endocuticle of at least the outer layer of the cuticular sheath, which in fine hair fibers, stops movement of the cuticle cells relative to each other, when limiting levels of shear deformation have been reached. Our studies lead to the conclusion that at least at slow strain rates the propexties of the cuticula in fine fibers can have a direct bearing in the creep deformation behavior of the cortex, contrary to generally accepted concepts. I Fig,4 I