An essential part of foods consist of fibre products (e.g. cereals, spreads, sauces, dressings, etc). In the processing of such products the food industry deals with problems based on the behaviour and the orientation of fibres in complex flows (e.g. extrusion, filtration, dispersion, etc). In other processes, such as freezing, the behaviour of rodlike and ellipsoid particles is also of great importance. Another field of interest is the production of biomaterials (packing industry) where a controlled structuring of the fibres determines the properties of the final product.

The examination of single-fibre systems (fibre in viscous fluid) lays the foundation for the understanding of complex multi-fibre systems. In a first step the examined fibre is placed in the linear shear field of a Newtonian fluid. The measurement of the angle of the fibre (with respect to the direction of the streamlines) is done by the means of digital image processing. The parameters of interest are the viscosity of the fluid, the difference in density of particle and fluid, and most importantly the dimensions of the rodlike particles. The complexity of the system is increased with the use of non-Newtonian fluids. In a second step of the study, the laser light sheet technique allows the observation of the behaviour of fibres in a transparent tube (Poiseuille flow). The application of stereoscopic picture recording will finally allow a reconstruction of the three dimensional movement of the fibre in the flow.

In food processing, when shear induced structuring of the product is involved, the interactions of the fibres in the flow appear to be relevant to the properties of the final product. Our investigations must therefore focus on the different possibilities to influence the flow (and hence the orientation of the fibres) in order to get the desired characterization of the resulting product. The parameters to be influenced are: the type of deformation (e.g. shear flow, extensional flow), the magnitude of the deformation (i.e. the applied forces) and the structure of the medium itself (e.g. length of the fibres).