Moldings, liquid crystalline polymer

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... 

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. 

From the beginning, poly(ester-imide)s had been developed as thermo-setting polymers. In the 1970s a development was started to use imide modification for improving the properties of thermoplastic polyesters. Later on in the patent literature liquid crystalline polymers can be found as being claimed as molding resins. 

The morphology of the fracture surfaces of both the extruded and injection-molded specimens was studied via scanning electron microscopy (SEM). Although there were many morphologies across the fracture surfaces, highly elongated liquid crystalline polymer domains parallel to the flow direction were observed for both the extruded and molded specimens. 

The low viscosity and the shear thinning effect of liquid crystalline polymers are advantageous for application. For instance, the filling of molded... 

The negative first normal stress difference under a medium shear rate, characterized by liquid crystalline polymers, makes the material avoid the Barus effect—a typical property of conventional polymer melt or concentrated solution, i.e., when a polymer spins out from a hole, or capillary, or slit, their diameter or thickness will be greater than the mold size. The liquid crystalline polymers with the spin expansion effect have an advantage in material processing. This phenomenon is verified by the Ericksen-Leslie theory. On the contrary, the first normal stress difference for the normal polymers is always positive. 

Injection-molded plaques of liquid crystalline polymers exhibit a multilayered structure through the thickness of a molding, where in each layer there is a high degree of orientation. Accordingly the fracture test methods of continuous fiber composites can be adopted for the testing of liquid crystalline polymers [176]. 

T. Ivanova, J. Zicans, 1. Elksnite, M. Kalnins, R. Maksimov, Mechanical properties of injection-molded binary blends of polyethylene with small additions of a liquid-crystalline polymer. J. Appl. Polym. Sci. 122, 3564—3568 (2011)... 

Although as-spun fiber of Me-HQ/Cl-PEC showed high modulus of 72 GPa,the modulus of the injection molded test pieces of Me-HQ/Cl-PEC was only 26 GPa.Ph-HQ/Cl-PEC and tBu-HQ/Cl-PEC showed no liquid crystallinity,but the moduli of the injection molded test were 7.5 and 15.1 GPa,respectively,which were 2-5 times higher than that of isotropic polymers.tBu-HQ/Cl-PEC showed many fibrils on the cross section of the flexural fractured test pieces as shown in Fig. 6(2).We assumed that tBu-HQ/Cl-PEC was a quasi liquid crystalline polymer which could orient at the high shear rate.Although W.B.Black reported a lyotropic quasi liquid crystalline polymer which could orient at the high shear rate,tBu-HQ/Cl-PEC is the first example of the thermotropic quasi liquid crystalline polymer(6). 

There are now numerous compositions of liquid crystalline polymers under consideration as fiber spinning and injection molding materials. However, the problems involved in processing these systems are similar. In particular, how can one process these polymers to yield desirable isotropic properties or at least have biaxial orientation how can one achieve the optimum properties from a given composition and how does the chemical composition and structure affect the properties In flexible chain systems one must quench in orientation in a time scale which is faster than the relaxation process of the molecules. Typically there is a distribution of relaxation times in which the longest relaxation time is a matter of a few seconds. This longest relaxation time also governs a number of other flow characteristics. 

The most unique aspect about the processing of liquid crystalline polymers is that the exceptional physical pr j>p rties found in the as-spun fibers or as-injection molded parts . ... 

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