Process structuring of polymers – science, technology and applications

Presented by Professor Phil Coates, University of Bradford.

It is increasingly recognised that properties of polymers and polymer composites depend on the structure imparted during processing, which we term ‘process structuring’.

Solid phase orientation processing at temperatures between Tg and the melting point provides a most striking example of process structuring, in terms of the magnitude of property changes which can be achieved—eg, several hundred percent enhancements in physical properties. Molecular orientations and large scale effective morphological reorganisations achieved by drawing or other forming processes can be locked into the final product, which remain stable in final products. The products can be used for significant load bearing applications, or orientation may be intentionally recoverable in a controlled manner, for ‘shape memory’ products. Remarkable cost-effective improvements in properties can consequently be achieved in many polymers and polymer composites by solid phase orientation processing, with applications including medical technology (eg tissue fixations, stents, drug eluting implants), construction (the spin-out at ), high performance pipes, and personal products.

Die drawing is a unique technology where solid polymers are drawn through a die or over mandrels, to achieve controlled enhancement of physical properties for many polymers, including selected axial or biaxial orientation distributions, at commercially viable production rates and at a range of length scales, eg 100 micron wall thickness tubes for bioresorbable stents, to tens of millimetres thick sections for structural applications, in either batch or continuous mode processing. Our fundamental studies of polymer deformation, include necking and structural evolution analyses, and FEA of processing, including current collaborations with leading Chinese research groups, in Sichuan and Changchun, for structure developments, and the potential for using oriented polymers in medical technology applications.

Secondly, our precision micro moulding area involves controlled process-structuring of polymers, including control of morphologies eg for shape memory products, blends, electrically conducting materials, and geometries, eg surface feature control. We employ and develop extensive in-process measurements. Some commercialised or developing products, particularly in the medical devices area, are discussed. Initial results of novel ultrasound mircromoulding technology are presented.

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