Curl Reversion and Damage: The Effect of Different Temperature Treatments on Hair

Abstract

Background and objective: Consumers following the Natural hair movement want to style their hair without thermal damage concerns. When women used a hotter styler, their hair could not revert back to its natural pattern after wetting and they expressed anxiety about heat damage. This study supports these observations using objective measurements of reversion and damage after heat treatment. Methods: Curly tresses were straightened fifty times at 185°C or 220°C. Reversion was compared between treatments and to natural variation after immersion in water. The damage was explored using differential scanning calorimetry and tensile testing. Results: The treatment at 220°C causes a significant shift to less curly types indicating that the fibres were unable to revert back to their original curl pattern. The DSC and tensile results suggest that the cortex structure has been damaged and the fibres have become less stiff and break more easily after the treatment at 220°C but not at 185°C. Conclusions: The structural damage at 220°C suggests that the shape memory effect cannot be triggered adequately by the presence of water and the fibres cannot return to their natural curl state.