Liquid crystal polymer injection molding

Plummer CJG, Ziille B, Demarmels A, Kausch HH (1993) The stracture of filled and unfilled thermotropic liquid crystalline polymer injection moldings. J Appl Polym Sci 48(5) 751-766 Popa-Nita V, Gerlic I, Kralj S (2009) The influence of disorder on thermotropic nematic liquid crystals phase behavior. Int J Mol Sci 10(9) 3971-4008 Qin Y, Brydon DL, Mather RR, Wardman RH (1993) Fibres from polypropylene and liquid crystal polymer (LCP) blends 1. Effect of LCP concentration. Polymer 34(6) 1196-1201 Rath T, Kumar S, Mahaling RN, Mukherjee M, Das CK, Pandey KN, Saxena AK (2006) Flexible composite of PEEK and liquid crystalline polymer in presence of polyphosphazene. J Appl Polym Sci 104 3758-3765... 

Injection molded thermoplastic bipolar plates made of Vectra LCP (liquid crystal polymer) and Fortron PPS fabricated by Ticona Engineering Polymers, (http //www.ticona.com/redesign/ index/markets/innovation/fuel cell.htm Ticona Engineering Polymers. 2008 accessed March 2008.)... 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

Liquid Crystal Polymers Thermoplastic aromatic copolyesters with highly ordered structure. Has good tensile and flexural properties at high temperatures, chemical, radiation and fire resistance, and weatherabil-ity. Processed by sintering and injection molding. Used to substitute ceramics and metals in electrical components, electronics, chemical apparatus, and aerospace and auto parts. Also called LCP. 

In Figure 16, results of Jackson and Kuhfuss show the effect of molding temperature and polymer morphology weight on the mechanical properties for poly(ethylene terephthalate) modified with p-hydroxybenzoic acid. "The temperature at which the PHB copolyesters are injection molded affects the orientation of the liquid-crystal polymer chains and, therefore, affects the mechanical properties. 

Injection molding ABS, acetal, acrylic, alkyd, allyl, amino, cellulosics, epoxy fluorocarbons, liquid crystal polymer, nylon, phenolic, polycarbonate, polyester (thermoplastic), polyester (thermoset), polyethylene, polyphenylene oxide, polypropylene, polystyrene, polysulfone, polyurethane (thermoplastic), PVC, SAN... 

Figure 11.8 The backflow phenomenon in injection molding of a liquid crystal polymer.

Y. Ide and Z. Ophir, Injection molding of thermotropic liquid crystal polymers, Polymer Engineering Science, 23, 792-796 (1983). 

A number of liquid crystal polymers (LCPs) were produced in the 1970s which displayed order in the melt (liquid) phase analogous to that exhibited by non-polymeric liquid crystals. However, the commercial introduction of liquid crystal polymer resins did not occur until 1984, at that time liquid crystal polymers could not be injection molded. Today, liquid crystal polymers can be melt processed on conventional equipment at fast speeds with excellent replication of mold details and efficient use of regrind [11]. 

In this work, researchers extruded various formulations and then injection molded these formulations into test specimens. The matrix material used was a liquid crystal polymer, which is a thermoplastic that can be lemelted and used again. Two carbon fillers were used carbon black and synthrtic graphite. Varying amounts of single fillers (2.5 to 15 wt% carbon black and 10 to 75 wt% synthetic graphite) were added to the liquid crystal polymer. The goal of this project was to drtermine how various amounts of these single carbon fillers affected the composite thermal and electrical conductivity. 

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