Research

Rheology of plant-derived materials

Principal investigator:

The development of renewable energy sources relying on the biochemical conversion of biomass materials has spurred substantial interest in the rheology and fluid mechanics of hyper-concentrated suspensions of lignocellulosic fibers; these suspensions behave effectively as viscoplastic fluids, and show a dramatic dependence of the yield stress on solid concentration. They are extremely difficult to mix. While they have characteristics similar to granular suspensions, they have peculiar features deriving from their microstructure (see figure 1), such as high porosity and partial softness. These systems constitute a new challenge for fluid mechanicians, soft matter physicists and engineers, and rheologists.

Fig. 1: A cross section of Miscanthus, a high-yield energy crop. The cross section has been stained to highlight the chemical heterogeneity of the material. Notice the high porosity of the plant. Because of this feature, a 12% w/w concentration of Miscanthus fills space almost completely, which makes the suspension extremely

Fig. 2: A suspension of Miscanthus particles at 10% w/w concentration. Removing the spindle of the rheometer leaves a permanent cavern, which is visible for several tens of minutes! In spite of the absence of interparticle attraction (e.g. due to van der Waals), the suspension exhibits marked yield stress behavior, like a gel.