Friction of hair fibres: effects of load, speed and sliding direction

Hair shampoos and conditioners commonly include lubricating ingredients that facilitate detangling, reduce combing damage and enhance the perception of smoothness. The quality of the lubrication imparted is routinely assessed using sensory tests as part of product development. The performance can also be investigated using instrumental measurements at an array level, for example, to mimic combing scenarios. In contrast, fundamental studies of friction at the fibre level are much less well-developed. This paper describes stick-slip friction measurements made on single pairs of crossed fibres using a Hanging Fibre Tribometer based around a microbalance. The effects of load and speed are described and interpreted using existing tribological models. Also quantified are differential friction effects associated with the directional surface topography of mammalian hair fibres, and discussed in the context of recent results obtained on hair using friction force microscopy. Finally, results are described concerning the lubrication imparted by some representative hair care ingredients