Capillary rheometry as a model methodology for obtaining insight in feed mash behaviour at conditions approximating pellet manufacturing

Pellet manufacturing is a useful tool for improving the handling of livestock feed. Pellet manufacturing consists, among others, of a compaction step, which is strongly affected by feed formulation. The role of feed formulation is thought to result from the fact that feed mash physicochemical properties change depending on ingredient composition. This variation in physicochemical properties subsequently affects mash behaviour during compaction, leading to variation in both physical pellet quality and energy costs during pellet manufacturing. Methodologies that allow for the study of material behaviour at pellet manufacturing conditions are needed to investigate the effect of feed formulation on mash flow behaviour. Such methodologies, however, are currently not generally available in the field of feed manufacturing. In this short communication we aim to discuss the application of capillary rheometry as a potential method for studying feed behaviour in the die, at conditions comparable to those during pellet manufacturing. The similarity between the design of the capillary rheometer and the geometry of a ring-die compactor allows for the simulation of some of the conditions experienced by feed mash during compaction, using smaller quantities of sample materials. The observed relation between flux and pressure gradient, for feed mashes evaluated in this short communication, resembles a Herschel-Bulkley relation, indicating that the increase in pressure gradient depends non-linearly on flow rate. While individual pressure gradients provide insight in the relative energy costs of compaction, a modelling approach is recommended to simulate the behaviour of feed mash at conditions more closely approximating those during pellet manufacturing. In summary, capillary rheometry provides an option for studying feed mash behaviour at conditions approximating those in the pellet press during pellet manufacturing.