Dynamic humidity curl retention - Assessing polymer hold performance

To further explore the potential of today’s styling products, the development of an in-depth analysis method is described. Dynamic humidity curl retention is employed to quantify the humidity dependent curl retention of polymer treated human hair. A comprehensive investigation of the influence of water on a polymer-hair system is conducted with sudden relative humidity decrease and increase, respectively. The dynamic relative humidity approach allows a more realistic simulation of consumer reality through the change of the environmental conditions. The curl retention performance of the commonly used model polymers Poly (N-vinyl pyrrolidone) and Poly (N-vinyl pyrrolidone/vinyl acetate) is analysed. Lowering the humidity compared to the starting period demonstrates that water desorption has comparable effects on the polymer treated hair as water absorption after a relative humidity increase. An elongation of curls is observed. The loss in hold performance at decreasing relative humidity may be attributed to the effects of physical ageing and de-aging in the hair fibre. Physical ageing has an explicit effect on curl retention, which needs to be added to the assessment of polymers on hair. Its contribution varies according to the size of a relative humidity change and whether plastici - zation of the polymer becomes relevant.