A study of friction mechanisms between a surrogate skin (Lorica soft) and nonwoven fabrics*

Hygiene products such as incontinence pads bring nonwoven fabrics into contact with users' skin, which can cause damage in various ways, including the nonwoven abrading the skin by friction. The aim of the work described here was to develop and use methods for understanding the origin of friction between nonwoven fabrics and skin by relating measured normal and friction forces to the nature and area of the contact (fibre footprint) between them. The method development work reported here used a skin surrogate (Lorica Soft) in place of skin for reproducibility. The work was primarily experimental in nature, and involved two separate approaches. In the first, a microscope with a shallow depth of field was used to determine the length of nonwoven fibre in contact with a facing surface as a function of pressure, from which the contact area could be inferred; and, in the second, friction between chosen nonwoven fabrics and Lorica Soft was measured at a variety of anatomically relevant pressures (0.25-32.1 kPa) and speeds (0.05-5 mm s(-1)). Both techniques were extensively validated, and showed reproducibility of about 5% in length and force, respectively. Straightforward inspection of the data for Lorica Soft against the nonwovens showed that Amontons' law (with respect to load) was obeyed to high precision (R-2 > 0.999 in all cases), though there was the suggestion of sub-linearity at low loads. More detailed consideration of the friction traces suggested that two different friction mechanisms are important, and comparison with the contact data suggests tentatively that they may correspond to adhesion between two different populations of contacts, one "rough" and one "smooth". This additional insight is a good illustration of how these techniques may prove valuable in studying other, similar interfaces. In particular, they could be used to investigate interfaces between nonwovens and skin, which was the primary motivation for developing them. (c) 2013 Elsevier Ltd. All rights reserved.