2. Observation of fiber orientation

2.1 Observation techniques

The most common technique is to observe polished sections using optical reflection microscopy or scanning electron microscopy. Fibers appear as rods when they belong to the cutting plane, or as ellipses when they form an angle with this plane (figure 2 a and b ). Note that in the case of long-fibre granules, the fibres can be curved (figure 2 c ). In such cases, the notion of orientation is difficult to define. Scanning electron microscopy can also be used to observe fracture surfaces, giving a rough idea of the fiber arrangement (figure