The performance of peristaltic pumps is mainly governed by their tubing or hose materials. Research and development in this area is therefore very important for peristaltic pump manufacturers to keep in front of the competition and to open up new applications to enable further market penetration. Another aspect of this is of course price; performance and cost have to be in balance.
As an approach to fabricate a new tube material, the field of negative Poisson's ratio (or: auxetic) materials is explored. The combined deformations of tensile, compression and shear in a peristaltic pump tube may well benefit from the specific characteristics of auxetic materials. Materials can be designed to keep their dimensions constant in directions perpendicular to an applied load. This is referred to as “auxetic balancing”. Finite element modelling shows that lowering the Poisson's ratio will rapidly decrease the maximum stresses in the cross-section of an occluded tube. Optimum values for the Poisson's ratio are found to be between −0.1 and +0.1, preferentially being 0.
The re-entrant honeycomb structure is selected for initial trials, but manufacturing of this structure at the desired dimension proved to be too difficult at this time. Instead, electrospun nanofibre membranes are selected as the reinforcement structure. A liquid silicone elastomer is used as the matrix material. Key characteristics for the new material are derived from baseline test results on existing tubing.
Laminates are manufactured from electrospun nylon6 nanofibre membranes coated with a liquid silicone rubber. Compression moulding is used to cure the nylon6-silicone rubber laminate, to give two effects: it ensures impregnation of the membrane and the compression deforms the nanofibre structure in such a way that it will become auxetic through-the-thickness. Flat sheet laminates of 2 mm thickness are manufactured with 14 layers of reinforcement. A reinforcing effect and substantial lowering of the through-the-thickness Poisson's ratio is observed for the laminates at low strains. At higher strains (>50%) the effect of the reinforcement diminishes and the Poisson's ratio of the laminate and pure silicone rubber equalises. Finally, tubular laminates are manufactured and the resulting tubes are tested in a peristaltic pump with some promising results (>1 million occlusions before failure). Tube performance is not yet at the required level, but with further optimisation of the laminating process, mould design and (post-)curing large steps forward can be made.
|Date of Award
|6 Jun 2012
|Michele Meo (Supervisor)
- negative poisson's ratio
- tubular laminates