Blends with LCPs

Seo [1997] prepared compatibilized PA blends with LCP polyesteramide (Hoechst Vectra B950) in the presence of anhydride-functionalized polyolefin. Specifically, 60 parts PA-6 was mixed with 25 parts LCP and 15 parts EPDM-g-MA in a TSE at 290°C. The blend was characterized by SEM, optical microscopy, Raman spectroscopy, mechanical properties, selective solvent extraction, and FTIR. 

Compared to most isotropic polymers, thermotropic LCPs possess outstanding mechanical properties due to their rigid rod-like backbones. It has been reported that LCPs have tensile strength in a range of 150 to 400 MPa and tensile modulus from 13 to 25 GPa, while LCP fibers have tensile strength ranging from 500 to 650 MPa and tensile modulus from 50 to 100 GPa. When LCPs are blended with thermoplastics in a process where an elongational flow field exists, the LCP phase will deform into molecularly oriented fibers that reinforce the thermoplastic matrix. So, until now, many isotropic polymers have been blended with LCPs. Table 7.5 summarizes various in situ composites reported, with their machine direction mechanical properties. 

PP was blended with LCP 2 extruders with a static mixer, to stretch LCP into microfibrils Sukhadia et al. 1991, 1992... 

The Differential Scanning Calorimeter (DSC) scans of the PAI-2 and PAI-1 and their blends with LCP are presented in Figs. 7a and 7b, respectively. The TS and STM blends both uncured and cured are conq>ared. From the scans of the uncured sanq)les, no significant difference is observed between the TS and STM sanq)les (Fig. 7a). The peak seen at 320 °C is that of PTFE v diich is a conq)onent of PAI-2. 

A TEM thin section of an unstained LCP with 5% polycarbonate is shown as an example in Fig. 5.100, as prepared by Wood [273]. Ultramicrotomy of the blend shows the typical banded texture of the LCP with the dark submicrometer isotropic polycarbonate domains uniformly dispersed in the ordered matrix. It is worth noting that although there is extensive research going on in university laboratories today there are few major commercial products which are blends with LCPs. In most cases this is due to the mismatch in thermal and rheological properties which results in materials which have physical properties that resemble the thermoplastics rather than the liquid crystalline polymers. 

Materials with totally new property combinations may be achieved by blending two or more polymers together. Through blending of thermotropic main-chain LCPs with engineering thermoplastics, the highly ordered fibrous structure and good properties of LCPs can be transferred to the more flexible matrix polymer. LCPs are blended with thermoplastics mainly in order to reinforce the matrix polymer or to improve its dimensional stability, but LCP addition may modify several... 

The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Studies with blends of LCPs and thermoplastics have shown indications that for good fibrillation to be achieved the viscosity of the dispersed LCP phase should be lower than that of the matrix [22,38-44]. 

Prior to blending, the LCP was dried at 155°C for 5 h. The melt blending of the materials was carried out with a Berstorff ZE 25 x 33D corotating twin-screw extruder at a melt temperature of 290°C, with a screw speed of 200 rpm, and an output of 6.4 kg/h. The extrudate was immediately quenched in a water bath and repelletized. 

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. 

Polarized optical photographs of the blends are shown in Figure 20.3. The spherical LCP domains are irregularly dispersed in the PEN and PET phases below 20 mol % PHB content (Figure 20.3(a)). The results observed from 30 mol % PHB reveal a continuous co-existence of the PHB phase and the PEN/PET matrix in the blended polymers (Figure 20.3(b)). However, the blend with 40 mol % PHB shows a nematic LC phase. This result is similar to that found for the copolyesters synthesized by Chen and Zachmann [26], who found... 

Most of the work to date concerns the area with the greatest potential for commercial exploitation, the blending of LCPs with conventional polymers. While a few studies of solution blending with Kevlar do exist [57-61], most of the work has centered on melt blending thermotropic copolyesters (Vectra, Xydar) with engineering thermoplastics (PET, PC, PEI, etc.). For convenience, this work may be separated into three blend regions based on LCP content, namely ... 

As sparse as the dataset describing mainchain nematic LCP blends with conventional polymers is, it is rich compared to the almost non-existent data on the blending of other types of LCPs-side chain polymers, flexible spacer polymers, smectics, etc. 

As in the case of LCP/conventional polymer blending, little data exists on the blending of LCPs of different inherent chain architecture or mesophase symmetry. Publications from the laboratories of Ringsdorf [80] and Finkelmann [81] show phase separation in blends of sidechain nematics with other similar polymers or small molecule analogs. It is now established that, in contrast to the behavior of low molecular weight LCs, LCPs are often immiscible. 

DeMeuse and Jaffe. In another chapter, Brostow et al. discuss the phase behavior of binary and ternary mixtures containing an LCP component. The kinetics of thermally induced phase separation of an HBA/PET LCP blended with poly(ether imide) are described by Zheng and Kyu. 

LCPs are a group of aromatic copolyester polymers with high physical performance properties, high levels of inertness, low flammability with excellent high temperature resistance. Use for pharmaceuticals is predicted, possibly blended with PE or... 

LCP (liquid crystal polymers) used either on their own or as blends with other materials (PE and PET)... 

Non-compatibilized blends of PS with either PEST or PEST and PMMA have been used for decorative applications or as the so-called plastic paper [Kamata et al., 1980]. Similarly, PAr blends with either SAN [Brandstetter et al, 1983], or high performance blends of LCP with thermoplastic polymers e.g., PP, PS, PC, PI) [Haghighat... 

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