Liquid Crystalline Polymers (1990) / Chapter Skim
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3 PROPERTIES OF LIQUID CRYSTALLINE POLYMERS: CURRENT AND DESIRABLE CHARACTERISTICS
3 PROPERTIES OF LIQUID CRYSTALLINE POLYMERS: CURRENT AND DESIRABLE CHARACTERISTICS
Pages 49-70
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From page 49... ...
Not only is it costly to achieve high orientation via the various spinning and processing steps, but the extent of molecular orientation is severely limited by molecular entanglements and by premature crystallization resulting in a morphology wherein conventional polymer chains have a more random conformation i.e., extensive chain folding and variably oriented chains between crystalline lamellae. Accordingly, even after annealing to extend the crystal (care crystal)
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From page 50... ...
Table 3.2 summarizes the properties of a number of commercial and potentially commercial LCP fibers; selected Kevlar~ data and those of carbon and glass are included to facilitate comparisons. In addition to high thermal stability, LCP fibers, in common with other organic materials, have low densities relative to such inorganics as glass and metals.
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From page 51... ...
~ . 47g/cc (0.053 ~b/i n3 Air-gap wet spinning and heat treatment 23 gp]
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From page 52... ...
> 90% of modulus IS0°C (355°F) strength & modulus retained retained Chemical resistance, Resistant to most More chemically bare yarns solvents and chemicals resistant than Keviar~ but can be degraded by 49 strong acids, bases, and steam Ultraviolet stability Degrades, but degree depends on material thickness since Kevlar~ aramid is a strong absorber and is se~f screening.
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From page 53... ...
1988. Advanced Textile Materials Conference, Clemson University, Greenville, S.C., April 5-6.
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From page 55... ...
55 · ~ _ A ~ ~ a'-0 ~ ' - ~ ~ in ~ u o ~U ° £ - ~ ~ A, o >, U ~.
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From page 56... ...
56 Kevlar 49 Em Liquid Crystalline Polymer ~ I Carbon Fiber E~3 Ceramic Fiber it 3 5_ ~ 30- .
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From page 57... ...
S7 Injection Molding The properties of injection molded bars of commercially available meltprocessible LCPs as reported in the trade literature are given in Table 3.3. ICI's Victrex~ SRP-1 is believed to be a copolymer of hydroquinone (HQY, isophthalic acid (IA)
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From page 59... ...
59 TABLE 3.4 Classification of LCPs According to Thermal Behavior Polymer Type ~ i mi ted by Xydar~ (SRT-300) spectral X7G III Tm = 420°C II Tm = 280°C I T = 80-100°C .
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From page 60... ...
A particularly dramatic demonstration involved playing an intense 2000 °F torch on a plaque of Xydar~ without burn-through and with minimum transfer of heat, under conditions that cut through a s imilar size aluminum panel . Such behavior , coupled with very low smoke generation, points to utility in military and commercial aircraft.
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From page 61... ...
Extrusion _ Extrusion as a mode of processing LCPs to produce film and sheet has not been exploited to any great extent because of difficulties in producing uniform gauges and properties in practical widths. Markedly unbalanced properties, i.e., weak transverse properties relative to the machine direction result from the high orientation in the flow direction.
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From page 63... ...
of LCPs relative to alternative polymeric or inorganic materials. In some cases a clear advantage is perceived for the organic and polymeric materials, whereas, for others, various classes of inorganic materials either suffice or are superior.
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From page 64... ...
A list of requirements that would permit development of all - optical serial switching devices is given in Table 3.9 (Stegeman and Lytel, 19899. TABLE 3.9 Requirements for Optical Serial Switching Devices .
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From page 65... ...
A variety of intracavity second-harmonic-generation and frequency mixing devices have been demonstrated with miniature KTP crystals in conjunction with diode laserpumped miniature Nd:YAG rods, and these are now commercially available.
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From page 66... ...
The main reasons for considering polymeric materials for this class of applications are the potential for high nonlinear coefficients, possibly an order of magnitude larger than RIP, and the potential for integration with diode laser light sources. In discussing material properties for third-order nonlinear effects, it is convenient to follow the distinction made earlier between those used In devices for parallel processing and serial processing.
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From page 67... ...
This parameter is much more applicable to the operation of waveguided devices likely to be used in serial switching operations. It is noteworthy that PTS is close in value to the MQW structures.
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From page 68... ...
The nature of the application will dictate the degree to which environmental exposure is experienced. For example, consider an LCP-based component in an optical computer operating In an air-conditioned, temperaturecontrolled communications center, as contrasted with a Kevlar~ aramid-based composite aircraft structural element exposed to an entire spectrum of environments: from the tropics to the arctic, from ground level to 40,000 feet, etc.
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From page 69... ...
Even in those cases where an unacceptable effect is observed, it is likely that adequate protection, probably in the form of coatings, can be provided to reduce the effect to acceptable levels. Indeed, there are reports that the thermotropic polyesters themselves exhibit exceptional barrier properties (Chiou and Paul, 1987)
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From page 70... ...
1988. Generation of blue-light by intracavity frequency mixing of the laser and primp radiation of a miniature neodymium-yttrium aluminum garnet laser.
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