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Rheology and processing of liquid crystalline polymers

The specific aims of the project include: a scientific basis for rheological modelling and computer aided design/computer aided manufacture (CAD/CAM) analysis of the processing of liquid crystalline polymers (LCP); guidelines to predict the effect of the flow history on the resulting microstructure.

The project provides a scientific basis for dealing with processing problems of LCPs such as: development of materials, design of moulds, selection and optimisation of injection moulding. The results constitute the basic elements of a computer aided design/computer aided manufacture programme, which could be developed with the available results.

The project has generated quite complete sets of rheological data, including transient behaviour, for 2 LCPs. This provides a basis for understanding the flow behaviour of such materials and the underlying flow induced structure. These aspects have been conidered in detail in the subsequent parts of the project. For the first time systematic data on velocity profiles in LCPs have been obtained (1-dimensional and 2-dimensional flows). This indicates how the rheological data can be used to simulate flows. Deviations from predictions have been found for which explanations are suggested. For the analysis of the flow induced structures a device for SALS measurements on flowing systems has been developed. The resulting data, together with other rheooptical measurements, provided the basis for a structural interpretation of the rheological experiments, both for steady shear flow and for transients. By using rod like molecular theory, the behaviour of LCPs has been modelled in the various flow regimes, from tumbling at relatively low shear rates up to flow aligning behaviour at high ones. Based on both experiments and theory a consistent description of the complex dynamics of these materials has emerged. It has been used to develop a rheological model that was demonstrated to describe the detailed experimental results quite well, at least at the relevant high shear rates.

Reported by

Katholieke Universiteit Leuven
de Croylaan 46
3001 Leuven
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