Effect of Scalp Position on Tensile Properties of Single Hair Fibers

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/m(3), 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.