Liquid crystal polymer
4721451
218678832
2008-06-11T18:23:58Z
Rainbow-five
6730462
{{Refimprove|date=April 2008}}
<!-- Here is a table of data; skip past it to edit the text. -->
{| border="0" cellpadding="2" cellspacing="0" align="right" style="margin-left:1em"
|-
! colspan="2" align=center bgcolor="#cccccc"|'''LCP'''
|-
| [[Specific Gravity]]
| 1.38 to 1.95
|-
| [[Modulus]] (E)
| 8530 to 17200 [[Mega|M]][[Pascal (unit)|Pa]]
|-
| [[Tensile strength]] (σ<sub>t</sub>)
| 52.8 to 185 MPa
|-
| Tensile Elongation (%)
| 0.26 to 6.2
|-
| Notched Izod Impact
| 21.0 to 82.5 [[kilo|k]][[joule|J]]/[[Metre|m]]<sup>2</sup>
|}
'''Liquid crystal polymers (LCPs)''' are a class of aromatic [[polyester]] [[polymer]]s. They are extremely [[Reactivity|unreactive]] and [[Inert#Chemistry|inert]], and highly [[Flame retardant|resistant to fire]].
==Background==
Liquid crystallinity in polymers may occur either by solving a polymer in a solvent (lyotropic liquid crystal polymers) or by heating a polymer above its glass or melting transition point (thermotropic liquid crystal polymers). The main example of lyotropic LCPs is the commercial aramid known as Kevlar. Chemical structure of this aramid consists of lineararly substituted aromatic rings linked by amide groups. In a similar way, several series of thermotropic LCPs have been commercially produced by several companies (e.g. Vectra). A high number of LCPs, produced in the 1980s, displayed order in the melt phase analogous to that exhibited by non-polymeric [[liquid crystal]]s. Processing of LCPs from liquid crystal phases (or mesophases) gives rise to fibers and injected materials having high mechanical properties as a consequence of the self-reinforcing properties derived from the macromolecular orientation in the mesophase. Today, LCPs can be melt-processed on conventional equipment at high speeds with excellent replication of mold details.
==Properties==
A unique class of partially crystalline aromatic polyesters based on [[p-hydroxybenzoic acid]] and related [[monomer]]s, liquid crystal polymers are capable of forming regions of highly ordered structure while in the liquid phase. However, the degree of order is somewhat less than that of a regular solid crystal. Typically LCPs have a high mechanical [[Strength of materials|strength]] at high temperatures, extreme chemical resistance, inherent flame retardancy, and good weatherability. Liquid crystal polymers come in a variety of forms from [[sintering|sinterable]] high temperature to [[Injection molding|injection moldable]] compounds. LCP can be welded, though the lines created by welding are a weak point in the resulting product. LCP has a high Z-axis [[coefficient of thermal expansion]].
LCPs are exceptionally inert. They resist [[Stress (physics)|stress]] cracking in the presence of most chemicals at elevated temperatures, including aromatic or [[halogenated hydrocarbon]]s, strong acids, bases, [[ketone]]s, and other aggressive industrial substances. [[hydrolysis|Hydrolytic]] stability in boiling water is excellent. Environments that deteriorate the polymers are high-temperature steam, concentrated [[sulfuric acid]], and boiling [[caustic]] materials.
==Uses==
Because of their various properties, LCPs are useful for electrical and mechanical parts, food containers, and any other applications requiring chemical inertness and high strength.
==External links==
*[http://www.ides.com/generics/LCP.htm The Plastics Web]
[[Category:Polymers]]
[[Category:Liquid crystals]]
[[Category:Thermoplastics]]
[[de:Flüssigkristallpolymer]]
[[ja:液晶高分子]]
[[pl:Polimery ciekłokrystaliczne]]
[[ru:Жидкокристаллический полимер]]