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Department of Chemical Engineering and Biotechnology

Pastes and Soft Solids 

The aims of the work in this area are, in broad terms, to investigate the deformation and flow behaviour (rheology) of particulate-based soft solid materials. This includes improving the understanding of paste processing operations, the development of pragmatic design models for forming operations, and developing fundamental understanding of the rheology of such materials. The activity dates back to work on axisymmetric extrusion models by John Benbow in the late 1960s. The group at Cambridge was formed when John Bridgwater joined the Department from the University of Birmingham in 1993 and has expanded in size and activity to cover a range of soft-solids, from catalysts to chocolate. The links with Birmingham continue.

Early work in Cambridge centred on the application of Benbow's axisymmetric model to more complicated flow geometries, such as those encountered in screw extruders and injection moulding processes. More recent work has looked at some particular difficulties associated with extrusion (extrudate surface fracture and liquid phase migration), the analysis and interpretation of extrusion data, imaging of flowing pastes and numerical modelling of the complex flows in extrusion dies, drying and debinding. While the group still conducts research on ceramic pastes, the materials studied have become more diverse; work has been carried out, for example, on foodstuffs (chocolate, biscuit doughs, cakes and starch based snack foods), pharmaceuticals and hard metals.  Many of these materials belong to the family of granular pastes, where the microstructure is very sensitive to the processing history. In all cases, we have been interested in quantifying and modelling links between microstructure and processing.


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