**2.2 Fiber-Fiber friction force measurements using an electronic microbalance**

An experimental device was set up using an electronic microbalance to measure fiber-fiber friction. An electronic microbalance having a sensitivity of 10-8 N was used since friction forces measured for two monofilaments of diameter 11 µm sliding against each other are of the order of a few micronewtons. The microbalance was equipped with an inner chamber to protect test samples from contaminants and to perform experiments in specific environmental conditions (humidity of 45%, and 25°C). The data acquisition and control station allowed force measurements at the sample weighing position, as a function of the vertical displacement of the platform.

During friction force measurements the vertical fiber was connected to the microbalance at the sample weighing position (see Fig. 3 A) and a load of 1 mg was applied at the other end of this fiber so as to maintain it in a vertical position. The horizontal fiber was fixed to a metallic holder, and brought into contact with the vertical fiber until the deflection angle of the vertical fiber was equal to 2.3°, which is also equal to the wrap angle of the horizontal fiber by the vertical one. The platform was then raised at a fixed speed of 2 µm/sec which induced sliding of one glass fiber against the other one. The force was recorded by the balance as a function of the vertical displacement of the platform. The total sliding distance along the vertical fiber was fixed to 2 mm.
