Thermotropic liquid-crystalline polymers mechanical properties

Thermotropic polyesters derived from unsubstituted aromatic diols and diacids usually have melting points which approach or exceed the thermal decomposition point. Thus it is reasonable to expect that some modification in molecular structure would be required to render them melt-processable, even though some adverse effects on liquid crystallinity and mechanical properties of the polymers would result. 

Thermotropic liquid crystalline polymers have recently been a topic of scientific investigation (1-31. Because of their thermotropic liquid crystalline character from rigid structural moieties incorporated in the polymer backbone, these polymers possess outstanding melt processability and excellent mechanical properties. 

Saikrasun S, Bualek Limcharoen S, Kohjiya S, Urayama K. 2005. Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid crystalline polymer fibers revealed by biaxial deformations. J Polym Sci Part B Polym Phys 43 135 144. 

Ternary blends from a thermotropic liquid crystalline polymer, PEN, and PET were prepared by melt blending and melt spinning to fibers. The mechanical properties of ternary blend fibers could be significantly improved by annealing at 180°C for 2 h. This is attributed to the development of more ordered crystallites and to the formation of more perfect crystalline structures. The interfacial adhesion between PEN and liquid crystalline polymer phases is enhanced when the blends are processed with dibutyl-tindilaurate as a reactive catalyst to promote transesterification. 

X.-B. Yu, C. Wei, and F.-A. Zhang. Studies on the mechanical and dynamic mechanical properties of thermotropic liquid crystalline polymer/unsaturated polyester/glass fiber in situ hybrid composites. Polym. Adv. Tech., 17 534-539, 2006. 

S. Saikrasun and T. Amomsakchai. Isothermal decomposition behavior and dynamic mechanical properties of in situ-reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline polymer. / Appl. Polym. ScL, 103 917-927, 2007. 

S. Bualek-Limcharoen, 1. Samran, T. Amomsakchai, and W. Meesiri. Effect of compatibUizers on mechanical properties and morphology of in-situ composite film of thermotropic liquid crystalline polymer/polypropylene. Polym. Eng. ScL, 39 312-320, 1999. 

Gopakumar, T. G., Ronrathnam, S., Lele, A., Rajan, C. R., and Fradet, A. 1999. In situ compatibilisation of poly(phenylene sulphide)/wholly aromatic thermotropic liquid crystalline polymer blends by reactive extrusion Morphology, thermal and mechanical properties. Polymer 357-364. 

The preparation methods and the novel permselective characteristics of (polymer/LC) composite films have been extensively studied (1-3). Also, various types of (polymer/LC) composite systems have been reported as large area and flexible light-intensity controllable films (4-11). Since thermotropic liquid crystalline polymers (LCPs) with mesogenic side chain groups exhibit both inherent mesomorphic properties of LC and excellent mechanical characteristics of polymeric materials, LCPs... 

Thermotropic liquid crystalline polymers can be formulated with high concentration of glass fiber to withstand working temperatures in excess of 300"C. In processing LCP, one problem arises. LCP orients itself in the direction of shear or flow - the process which benefits many materials but makes products from pure LCP excessively anisotropic. To balance mechanical properties it has been suggested that some quantities of short glass or mineral fibers be added to LCP. 

Bose, S., Pramanik, N., Das, C.K., Ranjan, A., and Saxena, A.K. (2010) Synthesis and effect of polyphosphazenes on the thermal, mechanical and morphological properties of poly(etherimide)/ thermotropic liquid crystalline polymer blend. Mater. Des., 31,1148-1155. 

The processing of an immiscible or incompatible polymer pair in which the dispersed phase forms in situ reinforcing fibrils can result in an appropriate morphology and improvement in the mechanical properties. This can be achieved by blending thermotropic liquid crystalline polymers (TLCP) with thermoplastics. These blends are often referred to as in situ composites because in the flow fields that occur during polymer processing operations, e.g., in the advancing melt front... 

H. Wang, G. Hinrichsen (1997) Influence of processing temperature on morphological and mechanical properties of a polycarbonate/thermotropic liquid crystalline polymer (PC/TLCP) blend, Int. Polym. Proc. 12,26. 

Plummer CJG, Wu Y, Davies P, Zulle B, Demarmels A, Kausch HH (1993a) The short- and longterm mechanical properties of filled and unfilled thermotropic liquid crystalline polymer injection moldings. J Appl Polym Sci 48 731-740... 

The shear rheological properties of thermotropic liquid crystalline polymers (TLCPs) have been studied extensively whereas, the extensional behaviour of TLCPs has become the subject of very few studies (Gotsis and Odriozola 2000). The unusual orientation and structure of thermotropic liquid crystal polymers (TLCPs) can significantly affect the rheological and mechanical properties of... 

These thermotropic liquid-crystalline polymers have high melting points but can be melt processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction This is illustrated in Table 5.3 for molded specimens of a liquid-crystalline copolyester of ethylene glycol, terephthaUc acid, and p-hydroxybenzoic add. In the direction parallel to flow, the properties listed in Table 5.3 compare favorably with... 

Another interesting approach to improve mechanical properties of FDM materials is presented by Gray et who developed a composite material constimted from polypropylene (80wt.%) and a thermotropic liquid crystalline polymer (20wt.%). The composite can be processed in conventional FDM machines and exhibits significantly superior mechanical properties in comparison to commercially available materials such as ABS. Preparation of feedstock filaments involves an elaborate dual-extmsion process. 

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