Nanoindentaion and tensile testing of human hair fibres

Hair fiber comprises of cuticle, cortical cells made up of crystalline keratin molecules (α-helix keratin) embedded in amorphous sulfur rich crosslinked keratin matrix and innermost medulla. Since single fiber tensile test takes into account all the components of hair, nanoscale mechanical characterization is imperative in investigating the characteristics related exclusively to cortical cells. This paper lays out the method of specimens preparation for nanoindentation to obtain hardness and modulus of hair obtained from members of four families. Single fibre tensile tests were also performed and compared with nanoindentation data. DSC and TGA tests were performed on the hair samples to further corroborate mechanical analysis with thermal transitions and thermal stability. Nanoindentation modulus and hardness values in the range of 5–8 GPa and 222–400 MPa were obtained respectively. Single fibre tensile data revealed tensile modulus and yield strength in the range of 2–5 GPa and 50–180 MPa, respectively and this data correlated with the nanoindentation data satisfactorily well. From DSC studies it was found that the onset of endothermic melting peak of α-keratin in the range of 222–234 °C correlated well with the nanoindentation results.