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Tensile properties of twisted hair fibers
Abstract
Hair is routinely twisted during grooming processes, which can cause tangles and lead to breakage of hair fibers. To evaluate the damage caused by twisting hair, the tensile stress-strain properties of single twisted hair fibers were measured by two different experimental procedures: (A) twist at constant length, followed by extension to break (without untwisting); and (B) twist and untwist at constant length, followed by extension to break. In procedure (A), the strength, extension, and initial modulus decreased with increase in twist factor, whereas in procedure (B), the strength and extension did not significantly change from control values, although the initial modulus decreased with increase in twist factor. Furthermore, the degree of recovery from torsional deformation was studied by a variant of procedure (B), where the fiber after untwisting was relaxed for 5 and 10 minutes, respectively, prior to extension to break. The major conclusion from this study was that at low and moderate twist levels, the tensile mechanical properties of human hair are recoverable.
... The use of the polar rather than the torsional moment of inertia (6) assumes the limiting case that no warping of the test specimen occurs (7), which is plausible for small deformations and low resonance frequencies (8), as realized in this study. The situation is certainly different for combinations of high tensile and torsional strains (9). The approach was furthermore chosen to provide better comparability of data with previous investigations (4,10,1 1) including those, which are based on the assumption of circular hair cross-sections (1,12,1 3). ...
... This relates to about six layers of cuticle in the cross-section, which are assumed to be constant along fi ber length and independent of fi ber diameter. Equation (9) was fi tted to the G″ data using the established nonlinear regression method (3). This approach accounts for a certain fraction of the variance of the data and also yields estimates for the torsional loss moduli of cortex and cuticle together with their 95% confi dence limits. ...
... The decrease as such is in line with the core/shell model [equation (9)] and implies that the cuticle has a higher G″ value than the cortex, as related to the limiting values for G″ at low and high values of I, respectively. The observation that G′ and G″ values both decrease with increasing moment of inertia (3) implies that both storage and loss modulus are higher for the cuticle than for the cortex. ...
Torsional analysis of single human hairs is especially suited to determine the properties of the cuticle and its changes through cosmetic processing. The two primary parameters, which are obtained by free torsional oscillation using the torsional pendulum method, are storage ( G ′) and loss modulus ( G ″). Based on previous work on G ′, the current investigation focuses on G ″. The results show an increase of G ″ with a drop of G ′ and vice versa , as is expected for a viscoelastic material well below its glass transition. The overall power of G ″ to discriminate between samples is quite low. This is attributed to the systematic decrease of the parameter values with increasing fiber diameter, with a pronounced correlation between G ″ and G ′. Analyzing this effect on the basis of a core\/shell model for the cortex\/cuticle structure of hair by nonlinear regression leads to estimates for the loss moduli of cortex ( G ″ co ) and cuticle ( G ″ cu ). Although the values for G ″ co turn out to be physically not plausible, due to limitations of the applied model, those for G ″ cu are considered as generally realistic against relevant literature values. Significant differences between the loss moduli of the cuticle for the different samples provide insight into changes of the torsional energy loss due to the cosmetic processes and products, contributing toward a consistent view of torsional energy storage and loss, namely, in the cuticle of hair.
... INTRODUCTION Wool 1-3 and human hair [4][5][6] are important fibrous keratinous materials that have been widely studied due to their superior mechanical strength and importance in the textile (wool) and hair care industries 7,8 and keratin-based biomaterials fields. In the early 1900s, a patent 9 described a process for extracting keratins from animal horns using lime. ...
The hair of mammals varies in diameter across species from ∼60 μm in humans to over ∼400 μm in giraffes and elephants. Here, we establish that the tensile strength of hair generally decreases with increasing diameter. Although there is a commonality in the morphology of the hair in such differing species as they all possess a cortex surrounded by cuticles, there are also significant differences in the hierarchical structure that contribute to the observed differences in strength. In this work, the internal structure of the hair from different species is examined, with some unique peculiarities in javelina and capybara hair uncovered. The dimensional dependence of hair strength is compared using Weibull predictions. The good correlation of the strength of hair using such Weibull analysis suggests that the failure strength is dictated by the probability distribution of flaws within the cortex.
... However, twisting alone reduced the properties of hair such as moduli, strength, and strain values. [2] Nikiforidis et al. [3,4] studied hair tensile properties of two age groups considering one scalp position and also studied the properties of one age group (15-20 years) considering two scalp positions (P1-frontal and P4-occipital [ Figure 2a]). His group reported the need that the tensile breaking force of hair has not shown any significant dependency on gender, age, and presence of dyes. ...
Background
Hair tensile properties play a crucial role in cosmetology regarding functionality and quality. Commonly, scalp positions are subjected to varying magnitudes of environmental and physical stimuli and correspondingly different hair balding patterns are observed.
Aim
This study is aimed at comparing the tensile properties of hair from four different scalp positions and quantifying the differences using statistical methods. Further, the second aim is to investigate the structure–property relationship with respect to the tensile properties obtained from hair in order to obtain a better understanding of the heterogeneous and composite structure of hair.
Materials and Methods
Hair samples were subjected to tensile testing and position wise data was compared using relative rating and grey relational analysis. Scanning electron microscopy was used to study the fractography of tensile specimens.
Results
The modulus, yield stress, maximum stress, and work of elongation were in the range of 2–6 GPa, 60–190 MPa, 130–340 MPa, and 30–100 MJ/m³, respectively. The postyield incremental modulus change at around 33% strain correlated well with fracture features wherein significant macrofibril pullout was observed indicating the fourth region in the stress–strain plot.
Conclusion
From the statistical analysis, it was found that there was no significant difference in terms of rating of hair samples from different scalp positions. This may be attributed to the presence of microscopic and nanoscopic structural heterogeneities.
... Fibrous keratin fibers, such as wool [1][2][3], human hair [4][5][6], and whale baleen [7] have been widely studied due to their superior mechanical strength [8,9]. These fibers usually have a protective and defensive function for animal bodies and yet yield some unnoticed properties. ...
Statement of significance:
Hair has outstanding mechanical strength which is equivalent to metals on a density-normalized basis. It possesses, in addition to the strength, a large ductility that is enabled by either the unfolding of the alpha helices and/or the transformation of these helices to beta sheets. We identify the deformation and failure mechanisms and connect them to the hierarchical structure, with emphasis on the significant viscoelasticity of these unique biological materials.
... Relaxation tests by Barnes and Roberts [10] and Robinson and Rigby [11] showed that the moduli are dependent on the time as well as strain and that the thiol content affects the mechanical properties. It was also demonstrated that the tensile properties are highly dependent on the influences of various factors: a high relative humidity decreases the Young's modulus and increases the extensibility [12]; an increase in temperature leads to a decrease in Young's modulus and an increase in extensibility [13]; twisting creates damage to the hair fibers [14] and this effect leads to the decrease in the breaking stress, breaking strain and Young's modulus. Ethnicities and age also affect the properties of human hair. ...
... One would assume that this would be helpful, but if the patient is African American and selects a natural twisted style such as that used in versions of dreadlocks or twists, damage may continue at the twist site. In a study of the tensile properties of twisted hair fibers, Dankovich et al. (2004) showed that only at low and moderate twist levels, is tensile mechanical property of human hair recoverable. While this study was not conducted using African hair, the recovery of tensile strength may be less probable in this population. ...
Dandruff and seborrheic dermatitis (D/SD) share an etiology dependent upon three factors: sebum, microbial metabolism (specifically, Malassezia yeasts), and individual susceptibility. Advances in microbiological and analytical techniques permit a more detailed understanding of these etiologic factors, especially the role of Malassezia. Malassezia are lipid-dependent and demonstrate adaptation allowing them to exploit a narrow niche on sebum-rich skin. Work in our and our collaborators' laboratories has focused on understanding these adaptations by detailed analysis of biochemistry and gene expression. We have shown that Malassezia globosa and M. restricta predominate on dandruff scalp, that oleic acid alone can initiate dandruff-like desquamation, that M. globosa is the most likely initiating organism by virtue of its high lipase activity, and that an M. globosa lipase is expressed on human scalp. Considering the importance of M. globosa in D/SD (and the overall importance of commensal fungi), we have sequenced the M. globosa and M. restricta genomes. Genomic analysis indicates key adaptations to the skin environment, several of which yield important clues to the role Malassezia play in human disease. This work offers the promise of defining new treatments to D/SD that are targeted at changing the level or activities of Malassezia genes.
... One would assume that this would be helpful, but if the patient is African American and selects a natural twisted style such as that used in versions of dreadlocks or twists, damage may continue at the twist site. In a study of the tensile properties of twisted hair fibers, Dankovich et al. (2004) showed that only at low and moderate twist levels, is tensile mechanical property of human hair recoverable. While this study was not conducted using African hair, the recovery of tensile strength may be less probable in this population. ...
Hair breakage and fragility are a large problem for many patients as well as a treatment challenge to the dermatologist. Understanding the factors that lead to acquired hair shaft fragility and breakage is paramount to recommending appropriate treatment to affected patients. African or Black hair is known to be more affected by breakage with easily observed fragility in vivo. To date there are no known structural or chemical differences in Black hair as compared to Caucasian or Asian hair that explains this observed fragility. This review explores the impact of hair care practices on the development of hair breakage with a focus on patients of color. The examination and recommended ancillary testing for the process are discussed, and advances in the measurement of mechanical fracture of human hair are reviewed.
Even though hair exhibits no biochemical activity and is considered metabolically “dead”, it is produced by an impressively dynamic organ: the hair follicle. In fact, hair can be described as the holocrine secretion of the follicular bulb. Each strand of hair on the body is truly unique in terms of length, size, caliber, color, etc., but also in terms of exact chemical composition and concentration in organic and inorganic ingredients.
Aim:
Utilize a matrix of single fiber hair testing methodologies to mechanistically understand the impact of common oiling treatments - Coconut Oil and Mineral Oil - on hair strands. Further, the effect of hair twisting - experienced in everyday grooming practices - on hair strength was investigated under different scenarios.
Methods:
Study involved multiple surfactant wash cycles of hair swatches with and without overnight hair oil treatments. Instrumental testing was done on strands from hair swatches - Tensile Extension, Torsional Stretching and Tensile Extension of twisted hair fibers.
Results:
Differentiation was observed in tensile and torsional testing parameters with 20 wash cycles - while no statistical significance was observed in single wash. However, when we combine the two stresses together by extending the twisted hair strands a clear differentiation was seen even in single cycle for coconut oil in comparison with mineral oil and surfactant wash. The differentiation in tensile parameters for twisted fibers becomes much more prominent with multiple cycles. Penetration of coconut oil in hair strands makes the fiber core more flexible and thus, help negotiate the torsional stress at the time of extension.
Conclusions:
Product benefit discrimination in single strand testing can be amplified by combining multiple stresses in one testing methodology. Observing the consumer habits and incorporating the torsion component in standard tensile testing of hair helps differentiate the two commonly used hair oiling treatments. Coconut Oil was found to significantly increase the tensile strength of twisted fibers owing to its penetration inside hair core.
This chapter describes tensile, bending and torsional testing including different parameters of each of these deformations and how these are affected by different types of hair including different types of hair damage. Expanded data sets are included for elastic moduli and other parameters of these deformations. A new section describing the historical development for assessing and measuring hair fiber curvature along with a new method for curvature has been developed and applied to more than 2,400 persons from more than 20 different countries. This method and data are featured in this section. Methods to determine the different dimensions of hair fibers including axial (length and curvature) and transverse dimensions (diameter, cross-sectional area and ellipticity) are described with much expanded data sets. Information on hair fiber friction (both high load and low load friction) and how friction varies with fiber diameter, comb composition and hair damage are included. Mechanical fatiguing, extension cycling and their effects on hair damage including scale lifting are described in the final section on the physical properties of hair fibers.
Single fibers were twisted to various amounts prior to tensile testing. The variations with twist in tenacity, breaking extension, modulus, and contraction or contractive stress on twisting have thus been measured. Experiments were carried out for both constant- tension and constant-length twisting; subsidiary experiments show the effect of other factors. The results are compared with those of other workers; explanations of them are offered.
The tensile stress-strain properties of twisted para-aramid fibers have been measured by three experimental procedures: (A) twist at constant length, followed by extension; (B) initial extension, followed by twisting; (C) and twist at constant small tension with contraction, followed by extension. Additionally a fourth procedure of twisting and untwisting was used to examine the act of twisting, not the presence of twist. The strength and breaking extension of aramid fibres decreased at much lower twist factors than nylon and polyester. The contraction on twisting lies between the predictions of two theoretical models.
The results of torsional measurements on fibers of different diameters suggest that the hair cuticle, while tough and resilient in the dry state, undergoes water plasticization to a much greater extent than the hair cortex. The change in the torsional moduli of fibers exposed to chemical modification can be related to the configurational stability in water and be of sonhe utility in predicting the setting behavior of hair.