When liquid crystalline polymers (LCP) first appeared in the 1980s it looked like the dawn of a major new class of thermoplastics. Thermotropic LCPs, mostly aromatic polyesters, have the interesting feature of retaining a degree of order in the melt phase, hence the name. This leads to low melt viscosity, quick set up on cooling and impressive mechanical properties, up to and over 300oC. Dimensional stability, favourable fire performance and notable chemical resistance are other attractive properties of the fibre filled grades.
LCPs are at their most competitive in thin walled mouldings (0.2 mm), such as edge connectors, and coping with soldering. They compete well with ceramics and thermosets, while replacement for stainless steel, in medical devices, is a promising area. An interesting diversification is cookware and, away from moulding, LCPs make excellent barrier layers in co-extruded film.
Melt-spun LCP fibres have high tenacity and low creep. This, along with heat and chemical resistance, make them candidates for technical textiles. LCPs act as excellent processing aids when blended with a range of engineering thermoplastics
With all these outstanding properties and potential markets, one might have expected LCPs to be more common. Is that due to processors having difficulty in coming to terms with the weld line peculiarities of LCPs and their anisotropic properties, associated with the significantly different shrinkages in flow and transverse directions? Or is it simply price?
Trade names: ‘Vectra’, ‘Zenite’
This Liquid Crystalline Polymers article was written by Dr.Charlie Geddes for Hardie Polymers
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Finally, more information on this topic may be available on the excellent British Plastics Federation website.
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