Liquid crystalline polymers LCPs blends

E. Shiva Kumar, C. Das, K. Banik, and G. Mennig. Viscoelastic properties of in situ composite based on ethylene acrylic elastomer (AEM) and liquid crystalline polymer (LCP) blend. Compos. Sci. Tech., 67(6) 1202-1209, May 2007. 

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. 

This chapter provides an overview of current researches on liquid crystalline polymers (LCPs). Topics include syntheses of main-chain and side-chain LCFs, structured characterization of LCFs and LCP networks and rheology and processing. Applications of LCP/polymer blends as self-reinforced polymers and electro-optical meterials are also discussed. 

Toy et al. [1994] investigated the effect of irradiation on blends of liquid crystalline polymers (LCP) with either polyvinylidene fluoride (PVDF) or HDPE (Table 11.9) such blends are useful for making dimensionally recoverable articles. This patent contains many claims but few results. 

Specific blends, which could offer an interesting combination of properties with proper com-patibilization, include PPS/PSE, PEl/PPS, PA/PSE, PA/PEI, and PC/PPS. Patent activity has been noted for most of these blend combinations as well as other selected blends involving engineering polymers as noted in Table 17.3. A number of recent patent and published papers have discussed blends of engineering polymers with various specialty polymers including high temperature polymers, liquid crystalline polymers (LCP s), conductive polymers, and as matrix materials for molecular composites. These will be discussed in the following sections. 

New opportunities of blending polyolefin can be seen in thermotropic liquid crystalline polymer (LCP) multicomponent, automobile fuel tanks, polymer solar cells, chemical sensors, polymer membrane, and foams. 

Melt compounding is most commonly utilized for the preparation of PO/silica nanocomposites. POs and their blends, such as PP [326-337], PE [338-343], ethylene-propylene copolymer [344-354], ethylene-octene copolymer [347], thermoplastic POs [348-350], PP/ EPDM [351,352], and PP/liquid-crystalline polymer (LCP) [353-357] blends, have been used as the matrices in the preparation of PO/silica nanosystems and nanomaterials by twin-screw extrusion and injection molding or lab-scale single-screw extrusion and compression molding. 

W. Chinsirikul, T. C. Hsu, and I. R. Harrison, Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film Effects of counter-rotating die on fiber orientation and film properties, Polym. Engr. and Sci., vol. 36, No. 22, 2708-2717, November (1996). 

Keywords polymer blend, liquid crystalline polymer (LCP), morphology, compatibilization, processing, polymer reinforcement, in situ composites. 

Thermotropic, main-chain, liquid-crystalline polymers (LCPs) have attracted considerable attention as a result of their high stiffness and mechanical properties. There has been interest in combining the LCPs with other materials. In one area, LCPs are used, in relatively low concentration, to reinforce less-stiff materials. In another case, a second component is used as a solvent to increase the mobility in the LCP and form lyotropic liquid-crystalline materials. There are now two reports, from Kricheldorf s group, of blends of PCL with liquid-crystalline polyesters [156,157]. 

It has been well recognized that melt blending of a thermotropic liquid crystalline polymer (LCP) and an isotropic polymer produces a composite in which fibrous LCP domains dispersed within the blend act as a reinforcement il ). The so-called insitu composite possesses several advantages in comparison with the inorganic reinforced thermoplastic composites. Firstly, LCP lowers the blend viscosity in the actual fabrication temperature range (3-5), Hence, the enhanced processability endows moldability for fine and complex shaped products. 

It has been reported (Akinay et al. 2001,2002) that the Hartman equation works well for both polymeric solids and melts, including amorphous and crystalline polymers and their blends. Moreover, it also works well in more complicated multiphase systems, such as liquid crystalline polymers (LCPs). Use of the Hartman equation is relatively simple, and its variables can be measured experimentally. Several other equations of state are cited in the Polymer Handbook (Brandrup 1999). Some of these do not permit direct measurement of parameters or contain universal constants that complicate determination of the required parameters. Another advantage of the Hartman... 

Liquid crystalline polymers (LCPs) added to high Tg polymers can often significantly reduce the viscosity of the high Tg polymer at very low LCP addition levels [269-272]. An example of this is shown in Fig. 6.22 for polyamide/liquid crystalline polymer blends. The significant negative deviation behavior was observed with a minor amount of LCP addition. 

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... 

Shivakumar et al [46] used DMA to investigate the compatibility of ternary blends of acrylic rubber, PET and a liquid crystalline polymer (LCP). The work concentrated on evaluating the effect that the LCP content of the mixes had on the compatibility of the acrylic rubber and the PET, and the crystallinity and thermal properties of the resulting products. 

Shivakumar E, Srivastava RB, Pandey KN, Das CK. Compatibility studies of blends of acryUc rubber (ACM), poly(ethyleneterephthalate) (PET), and liquid crystalline polymer (LCP). / Macromol... 

The effect of shear on the temporal development of phase separation in thermotropic liquid crystalline polymer (LCP)/polycarbonate (PC) blends was examined. Experiments were performed using a polarized-hght microscope, equipped with a shearing hot stage. Phase separation, with and without shear, in blends containing 50 wt % TCP were analyzed. The results showed that the speed and amount of phase separation increased when shear was applied. 

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