Liquid crystal polymers
Liquid crystal polymers (LCP) are halogen-free and inherently flame-retardant high-performance polymers with very good heat resistance for thin-walled applications with exceptionally precise and stable dimensions as well as high tensile strength and high tensile modulus.
Abbreviation
LCP
Molecular formula
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CAS no.
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General description
The variety of liquid crystal polymers enables a wide range of applications, each with properties optimised for the specific application.
While easy-flowing liquid crystal polymers are used when high precision and minimised energy input are required, fibre-reinforced LCPs are characterised by excellent mechanical properties. Galvanised or electrically shielded and conductive LCP are ideal for a wide range of applications in the electronics industry. In particular, the resistance to chemicals and gamma radiation makes liquid crystal polymers a proven high-tech material in medical technology.
LCP is the all-rounder among high-performance plastics for every situation.
Definition
Liquid Crystal Polymers (LCP) are liquid crystalline high-performance polymers that belong to the group of thermoplastics. They are free of halogens and are characterised by exceptionally precise and stable dimensions. In contrast to other semi-crystalline plastics, they have a special molecular structure. The prerequisite for the liquid crystalline properties are mesogens, which are found both in the main chain and in side chains of the polymer.
The stiff, rod-shaped macromolecules are not very flexible and form liquid crystal structures in the melt phase. LCP are characterised by extraordinary mechanical and chemical properties. They have a high tensile strength parallel to the molecular axis and a high modulus of elasticity. The distinctly anisotropic geometry ensures strong intermolecular cohesion.
Production
During the melt phase of the manufacturing process, the rigid rod-shaped macromolecules are ordered into liquid crystal structures.
The properties of the high-performance plastic can for instance be adjusted by varying the proportion of mesogens in the main or side chain and the melting point of the liquid crystal polymer. The targeted variation of the synthesis conditions allows customised production of LCP materials for specific applications. Small amounts of other thermoplastics can be added during production to reduce the directionality of LCP's properties.
Properties
The distinctly anisotropic geometry of liquid crystal polymers ensures strong intermolecular cohesion. As a result, the melting point is very high, solubility is poor and the mechanical properties are excellent. The water absorption is also very low. The combination of these properties predestines the high-performance plastic for use as a high-performance fibre as well as for the production of precision components that are resistant to water and organic solvents.
Liquid crystal polymers have very different material properties depending on the specific type. In addition to easy-flowing ones, for example, glass fibre-reinforced, carbon fibre-reinforced as well as mineral- and graphite-filled material types are also available, which are tensile and elastic. Other versions are galvanised or electrically shielded and conductive, which makes them ideal for use in the electronics industry. Flame-retardant types are available as well as grades for medical and pharmaceutical use. The LCP products are high-performance thermoplastics and meet the requirements of the FDA, as they are free of BPA and PTFE.
Chemical resistance
LCP are characterised by very good chemical and oxidation resistance and are halogen-free. Liquid crystal polymers are resistant to hydrolysis, bases and weak acids, aromatics, chlorinated hydrocarbons, alcohols, ketones and esters over a wide temperature range. The same applies to chemicals that otherwise trigger stress cracks. Exceptions are strongly oxidising acids and strong alkalis. Due to their properties, liquid crystal polymers have a high weathering stability and are resistant to gamma radiation and short waves. Liquid crystal polymers have very good barrier properties against gases and water vapour.
Processing techniques
The processing techniques suitable for LCP are:
Injection moulding
Extrusion
Coextrusion
Thermoforming
The low melting and solidification heat enable significantly lower energy consumption and short cooling times, especially when processing Vectra(R). The low viscosity of the melt at higher shear rates allows for easier injection and better flow in thin-walled parts. This maximises production efficiency. Especially in injection moulding, very short cycle times and burr-free injection moulding with very tight tolerances are possible due to the excellent properties.
The macromolecules orient themselves in shear or extensional flows. This results in a high anisotropy of the properties. The high toughness and strength (up to 240 MPa), the high modulus of elasticity (up to 40 GPa) and the low coefficients of thermal expansion are primarily in the orientation direction of the molecules.