Moldings, liquid crystalline

TABLE 4.3 Properties of a Molded Liquid-Crystalline Copolyester [14]... 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

Shear modulus, polyamide, 138 Sheet molding compounds (SMCs), 30 Shoe sole products, 205 Shore hardness gauge, 243 Side-chain liquid crystalline polymers, 49 Side reactions, in transition metal coupling, 477... 

Many researchers have reported the structure-thermal property correlations in LCPs from substituted hydroquinones (HQs) and dicarboxylic acids. Lenz and co-workers have investigated the liquid crystallinity of the polyarylates obtained from substituted HQs and terephthalic acid (TA) [6-10], substituted HQs and l,10-bis(phenoxy)decane-4,4/-dicarboxylic acid [8], and substituted HQs and a,oo-bis(phenoxy)alkane-4,4/-dicarboxylic acid [11], Kricherdorf and Schwarz [12] and Osman [13] reported the liquid crystallinity of the polyarylates obtained from substituted HQs and 1,4-cyclohexanedicarboxylic acid, while Krigbaum el al. [14], Heitz and co-workers [15] and Kricherdorf and Engelhardt [16] investigated the liquid crystallinity of the polyarylates synthesized from substituted HQs and substituted TAs. In addition, Jackson reported the liquid crystallinity and the moduli of fibers and injection molded specimens of the polyarylates... 

Because as-spun fibers of Me-HQ/Cl-PEC showed a higher modulus than those of Ph-HQ/Cl-PEC, the flexural modulus of injection molded specimens of Me-HQ/Cl-PEC exhibited a higher flexural modulus than those of Ph-HQ/Cl-PEC due to the liquid crystalline state. Although flexural-fractured injection molded specimens of Me-HQ/Cl-PEC exhibited highly oriented fibrils, Ph-HQ/ Cl-PEC no longer displayed fibrils because of the lack of liquid crystallinity. 

Thus, the influential factors in obtaining high moduli for injection molded specimens are as follows (1) the stability of the liquid crystalline state, (2) the rigidity of the polymer chain, and (3) the packing density of the polymer chain. 

A crystalline solid is a solid in which the atoms, ions, or molecules lie in an orderly array called a lattice (Fig. 5.19). An amorphous solid is one in which the atoms, ions, or molecules lie in a random jumble, as in butter, rubber, and glass (Fig. 5.20). They have a structure like that of a frozen instant in the life of a liquid. Crystalline solids typically have flat, well-defined planar surfaces called crystal faces, which lie at definite angles to one another. These faces are formed by orderly layers of atoms (Box 5.1). Amorphous solids do not have well-defined faces unless they have been molded or cut. 

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. 

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

Materials and Processing. Copolyesters of poly(ethylene terephtha-late) (PET) and para-oxybenzoic acid (FOB) were supplied by the Tennessee Eastman Corporation. Past work Indicates the copolyesters form thermotropic liquid crystalline phases at compositions containing more than 30 mole% POB (26,27,28). The composition of the copolyester studied here contains 60 mole% POB. Quiescent liquid crystalline films were made by compression molding the copolyester at 210, 230, 255, and 285 C, and followed by a quench Into Ice water, ambient air, or cooled In the press with the power off. Film thicknesses ranged between 0.05-0.15 mm. Another sa(q>le of the 40/60 PET/POB copolyester was melted at 270 °C In a Mettler hot stage, manually sheared between glass slides, and then ambient air cooled. 

The lowest cost process for preparing all-arcmatic liquid crystalline polyesters involves the reaction of aromatic carboxylic acids with acetates of aromatic hydroxy ocnpounds a recent history (2) describes the development of these ICP s. Because aoetic acid is evolved in the process and reaction temperatures are above 300°C, expensive corrosion-resistant reactors must be installed for ccranercial production. In cur latest paper (2) of this ICP series, we described a number of aliphatic-aromatic ICP s which can be produced in conventional polyester reactors and injection molded to give plastics with very high mechanical properties, heat-deflection temperatures (HDT s), and solvent resistance. These ICP s (la) were prepared by the reaction of the dimethyl ester of... 

Shrinkage in Parts Molded from Thermotropic Liquid-Crystalline Polymers Dependence upon Part Geometry and Filler Content... 

Liquid crystalline polymers exhibit anisotropy in extruded and molded articles as a result of preferential orientation of LCP domains or individual chains. Reference (21 highlights some of the molecular structural features of LCP s that account for their fundamental anisotropy. These include the large aspect ratio of the individual polymer chains and their tendency to form aligned, highly crystalline domains. 

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