A study on the ternary blends of polyphenylenesulfide,polysulfone, and liquid crystalline polyesteramide

Ternary blends of poly(p-phenylenesulfide) (PPS), thermotropic liquid crystalline polyesteramide (LCP), and polysulfone (PSF) were investigated in terms of processing characteristics, blend morphology, and physical properties. In the incompatible PPS/LCP blends, LCP imparted a nucleating effect to the crystallization of PPS. Up to 10wt% LCP content, the tensile properties of PPS/LCP blends were enhanced with increasing LCP content, but they deteriorated if the LCP content exceeded 20wt%. Addition of a third component, PSF, to the 90/10 PPS/LCP blend promoted development of rodlike or threadlike fibrillar structure and orientation of the deformed LCP domains, which led to improvement of tensile strength up to 20%.     

Mechanical properties and morphology of liquid crystalline copolyester-amide and amorphous polyamide blends

Blends of an amorphous polyamide (PA) and a liquid crystalline copolyesteramide (LCP), poly(naphthoate-aminophenoterephthalate) were prepared in a twin-screw extruder. Specimens for mechanical testing were prepared by injection molding. Morphological, thermal, mechanical, and rheological properties were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffractometry, capillary rheometry, and a tensile tester, respectively. The tensile mechanical behavior of the LCP/PA blends was found to be affected by their compositions and specimen thickness. Tensile testing revealed that the tensile mechanical behavior of the LCP/PA blends was very similar to that of polymeric composite and the tensile strength of the LCP/PA (50/50) blend was approximately two times of the value of PA homopolymer and exceeded that of pure LCP. The morphology of the LCP/PA blends was also found to be affected by their compositions. SEM studies revealed that the liquid crystalline polymer (LCP) formed finely dispersed spherical domains in the PA matrix and the inclusions were deformed into fibrils from the spherical droplets with increasing LCP content. It has been found that droplet and fiber formations lead to low and high strength material, respectively. In particular, at specific LCP content (50 wt%), the tensile strength of the LCP/PA blend exceeded that of pure LCP. The improvement in tensile properties is likely due to the reinforcement of the PA matrix by the fibrous LCP phase as observed by SEM. A distinct shell-core morphology was found to develop in the injection molded samples of these blends. This is believed to have a synergistic effect on the tensile properties of the LCP/PA blends. The rheological behavior of the LCP/PA blends was found to be very different from that of the parent polymers and significant viscosity reductions were observed for the LCP/PA (50/50) blend. Based upon DSC, these blends have shown to be incompatible in the entire range of concentrations.     

Morphology and mechanical properties of liquid crystalline copolyester and poly(ethylene 2,6-naphthalate) blends

Blends of poly(ethylene 2,6-naphthalate) (PEN) and a liquid crystalline copolyester (LCP), poly(benzoate-naphthoate), were prepared in a twin-screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology and mechanical properties were investigated by scanning electron microscopy (SEM) and an Instron tensile tester. SEM studies revealed that finely dispersed spherical domains of the liquid crystalline polymer (LCP) were formed in the PEN matrix, and the inclusions were deformed into fibrils from the spherical droplets with increasing LCP content. The morphology of the blends was found to be affected by their composition and a distinct skin-core morphology was found to develop in the injection molded samples of these blends. Mechanical properties were improved with increasing LCP content, and synergistic effects have been observed at 70 wt% LCP content whereas the elongation at break was found to be reduced drastically above 10 wt% of LCP content. This is a characteristic typical of chopped-fiber-filled composites. The improvement in mechanical properties is likely due to the reinforcement of the PEN matrix by the fibrous LCP phase as observed by scanning electron microscopy. The tensile and modulus mechanical behavior of the LCP/PEN blends was very similar to those of the polymeric composite, and the tensile strength and flexural modulus of the LCP/PEN 70/30 blend were two times the value of PEN homopolymer and exceeded those of pure LCP, suggesting LCP acts as a reinforcing agent in the blends.     

Studies on blends of a thermotropic liquid crystalline polymer and polybutylene terephthalate

Summary Structure-property relationships of blends of a thermotropic polyester-type main-chain LCP and polybutylene terephthalate (PBT) were investigated. LCP was melt blended with three different PBTs and the blends were processed by injection moulding or extrusion. Mechanical and thermal properties of the blends were determined and the blend structure was characterized by scanning electron microscopy (SEM). LCP acted as mechanical reinforcement for PBT and improved also its dimensional and thermal stability. The stiffness of PBT increased with increasing LCP content, but at the same time the blends became more brittle. In extrusion the orientation of LCP phases could be further enhanced by additional drawing, which led to significant improvements in strength and stiffness at LCP contents of 20–30 wt.-%.     

Reinforced poly(ether sulfone) materials by blending with a semiaromatic liquid crystalline copolyester

Blends based on poly(ether sulfone) (PES) and a semiaromatic liquid crystalline copolyester (R5) were obtained by injection molding across the entire composition range. The blends showed two pure amorphous phases. The fibrillar structure of the skin led to enhancements in the stiffness. The break properties, however, decreased at low LCP contents, due to the expected lack of adhesion between the phases. The increase in the modulus at increasing LCP content led to improvements in tensile strength. The notch sensitivity of PES decreased after the addition of low LCP levels, giving rise to enhancements of almost 600% in the notched impact strength. The unusually enhanced performance of the 20/80 blend, which has been seen previously in another thermoplastic/LCP blend, suggests that the dispersed PES phase in this blend may act as rubber particles do in rubber toughened thermoplastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 52–59, 2004     

In‐situ reinforcement of PBT/ABS blends with liquid crystalline polymer

Ternary in‐situ poly(butylene terephthalate) (PBT)/poly(acrylonitrile‐butadienestyrene) (ABS)/liquid crystalline polymer(LCP) blends were prepared by injection molding. The LCP used was a versatile Vectra A950, and the matrix material was PBT/ABS 60/40 by weight. Maleic anhydride (MA) copolymer and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these blends. The tensile, dynamic mechanical, impact, morphology and thermal properties of the blends were studied. Tensile tests showed that the tensile stregth of PBT/ABS/LCP blend in the longitudinal direction increased markedly with increasing LCP content. However, it decreased sharply with increasing LCP content up to 5 wt%; thereafter it decreased slowly with increasing LCP content in the transverse direction. The modulus of this blend in the longitudinal direction appeared to increase considerably with increasing LCP content, whereas the incorporation of LCP into PBT/ABS blends had little effect on the modulus in the transverse direction. The impact tests revealed that the Izod impact strength of the blends in longitudinal direction decreased with increasing LCP content up to 10 wt%; thereafter it increased slowly with increasing LCP. Dynamic mechanical analyses (DMA) and thermogravimetric measurements showed that the heat resistance and heat stability of the blends tended to increase with increasing LCP content. SEM observation, DMA, and tensile measurement indicated that the additions of epoxy and MA copolymer to PBT/ABS matrix appeared to enhance the compatibility between PBT/ABS and LCP.     

Extruded blends of a thermotropic liquid crystalline polymer with polyethylene terephthalate,polypropylene, and polyphenylene sulfide

Structure–property relationships were investigated for blends of a polyester-type thermotropic liquid crystalline polymer (LCP) with polyethylene terephthalate (PET), polypropylene (PP), and polyphenylene sulfide (PPS). The polymers were melt blended in a twin-screw extruder and the blends were extruded to strands of different draw ratios. Tensile properties of the blends were determined as a function of LCP content and draw ratio and compared with the results of morphological and rheological analyses. In general, the strength and stiffness of the matrix polymers were improved with increasing LCP content and draw ratio. At a draw ratio of 11, the blends of PET/30 wt % LCP exhibited a tensile strength about three times and an elastic modulus nearly four times that of pure PET. All blends exhibited a skin/core morphology with thin fibrils in the skin region. The formation and the sizes of the fibril-like LCP domains in the matrices were found to depend on LCP content and the viscosity ratio of the blend components.     

Structure and properties of molded polyblends containing liquid crystalline polymers

The relationship between the microstructure developed during injection molding of liquid crystalline polymers (LCPs) containing blends and their mechanical properties, was studied. A wholly aromatic copolyester LCP was melt blended in various levels with polycarbonate (PC), poly(butylene terephthalate) (PBT), Nylon 6 (N-6), and amorphous nylon (AN). In all cases the LCP was the minor component. The resulting injection molded structure had a distinct skin core morphology, where elongated fibrous LCP particles comprised the skin layer and spherical and ellipsoidal ones composed the core section. The highest elongation and the finest diameter LCP fibrils were obtained with AN/LCP system, followed by PC/LCP. PBT/LCP blends showed a coarser morphology, while N-6/LCP system did not correlate with the tensile moduli of the injection molded specimens. AN/LCP blends demonstrated the highest moduli values, consistent with the highest orientations observed using electron microscopy, followed by PC/LCP, PBT/LCP, and N-6/LCP. Finally, tensile strength levels were correlated with both orientation levels and interfacial adhesion between the polyblend components. AN/LCP that exhibited the highest orientation and good adhesion appearance gave the highest tensile strength values followed by PC/LCP, PBT/LCP, and N-6/LCP polyblends.     

Rheology,morphology and properties of LCP/Nylon 66 composite fibers

The rheology, morphology and properties of the composite systems of LCP, Vectra A^TM 950 and Nylon 66 were investigated. The viscocity ratio of LCP and matrix has strong influence on their morphology. For LCP blends, the viscosity ratio of LCP is a critical factor in determining the blend morphology. The optical micrographs show that the good fibrillation can be achieved when the viscocity of the dispersed LCP phase is less than that of the Nylon 66 matrix at 310°C. The dispersed LCP domains tend to be spherical or cluster‐like when the viscosity ratio of the disperesed LCP phase and the Nylon 66 matrix is more than 1 at 280°C. The scanning electron microscopy (SEM) and optical micrograph observations show that Nylon 66 is immiscible with LCP, and there are two distinct phases in the blends. The morphology of LCP phase changes with the composition. LCP exhibits a fine fibril dispersed phase in the Nylon 66 matrix in the low LCP concentration. With an increase in LCP concentration, the morphology of LCP phase is changed form a fine fibril dispersed phase to a perfectly aligned continuous fiber reinforced phase in the rich LCP concentration. The tensile moduli increase with LCP concentration, especially in the rich LCP concentration. The tensile strengths increase with LCP concentration only when LCP concentration is above 40 wt%. Compared to the pure Nylon 66 fiber, the 40 wt% LCP composite sample shows a 982.1% increase in tensile modulus and a 123.3% increase in tensile strength. The mechanical properties of composite fibers are below the rule of mixtures if the LCP concentration is low, but above the rule of mixtures if the LCP concentration is high.     

Structure and properties of blend fibers from poly(ethylene terephthalate) and liquid crystalline polymer

The structure and properties of the as-spun fibers of poly(ethylene terephthalate) (PET) blends with a thermotropic liquid crystalline polymer (LCP), Vectra A900, were studied in detail. The DSC results indicate that the LCP component may act as a nucleating agent promoting the crystallization of the PET matrix from the glassy state but which inhibits its crystallization from the melt due to the existence of an LCP supercooled mesophase. The effect of the drawdown ratio on the orientation of the as-spun blend fibers is highly composition-dependent, which is mainly associated with the formation of LCP fibrils during melt spinning. The modulus of the as-spun blend fibers has a significant increase as the content of LCP reaches 10%, while the tensile strength has a slightly decreasing tendency. The mechanical properties of the as-spun blend fibers could be well improved by heat treatment because of a striking increase in the crystallinity of the PET matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 217–224, 1997     

Morphology and mechanical properties of liquid crystalline copolyester and polyester elastomer blends

Blends of a polyester elastomer (PEL) having a hard segment of polyester (PBT) and soft segment of polyether (PTMG) and a liquid crystalline copolyester (LCP), poly(benzoate-naphthoate), were prepared in a twin-screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology of the LCP/PEL blends was characterized under different processing conditions. To determine what conditions were necessary for the development of a fibrillar morphology of LCP, we have studied the effect of processing method (extrusion and injection molding), injection molding temperature (below and above the melting point of LCP), and gate position in the mold (direct gate and side gate). SEM studies revealed that some extensional flow was required for the fibrillar formation of LCP and the fibrillar structure of LCP was controlled by the processing method. The morphology of the blends was found to be affected by their compositions and processing conditions. SEM studies revealed that finely dispersed spherical domains of LCP were formed in the PEL matrix and the inclusions were deformed in fibrils from the spherical droplets with increasing LCP content and injection temperature. The mechanical properties of the LCP/PEL blends were also found to be affected by their compositions and processing conditions. The mechanical properties of LCP/PEL blends were very similar to those of polymeric composite. An attempt was made to correlate the structure of the blends from the scanning electron microscope with the measured mechanical properties. All of the aspects of the morphology were possible to explain in terms of the mechanical properties of the blends. A DSC study revealed that the crystallization of PEL was accelerated by the addition of LCP in the matrix and a partial compatibility between LCP and PEL was predicted. The rheological behavior of the LCP/PEL blends was found to be very different from that of the parent polymers, and significant viscosity reductions were observed in the blend consisting of only 5 wt% of LCP.     

Strengthening of poly(butylene adipate-co-terephthalate) by melt blending with a liquid crystalline polymer

Poly(butylene adipate-co-terephthalate) (PBAT) is a soft biodegradable polymer with a low melting temperature. PBAT has been melt-blended with a liquid crystalline polymer (LCP) aiming at preparing a new biodegradable polymer blend with improved mechanical properties. The phase structure and crystalline morphologies of the PBAT/LCP blends were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). It was found that the LCP domains are precisely dispersed in the PBAT matrix and that these domains act as the nuclei for PBAT crystallization. The nonisothermal crystallization temperature from the melt was dramatically shifted from 50°C to about 95°C by the addition of 20% LCP. In addition, the tensile modulus of the prepared blends increases gradually with increasing LCP content, indicating the excellent strengthening effects of LCP on the PBAT matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high‐density polyethylene

Blends of an extrusion‐grade high‐density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4–9 vol%), whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two‐dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc‐shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%–55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%–92%) than in solubility (39%–76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra RD501 blends and relatively small for the Vectra A950 blends.     

Structure and mechanical properties of polysulfone‐based in situ composites

Composites based on the polysulfone of bisfenol A (PSF) and a liquid‐crystalline copolyester (Rodrun 5000) were obtained by two processing methods, (1) direct injection moulding (DI) and (2) extrusion followed by injection moulding (PI), across the whole composition range. The blends were immiscible and showed two pure amorphous phases. The inferior mechanical properties of PI blends, and their more difficult processing, meant that the PI procedure is not suitable in these blends. The generally linear relationship of the Young's modulus of the DI blends is due to the counteracting effects of the large orientation of the skin and its low thickness. The improvement in notched impact strength of PSF on the addition of small amounts of LCP indicated an important reduction in its notch sensibility. The tensile strength behaviour was close to linearity, with the exception of the 20/80 blend in which it was synergistic. This had been seen in previous thermoplastic/LCP blends, and depicts a behaviour reminiscent of rubber‐toughened blends. Copyright © 2004 Society of Chemical Industry     

Mechanical properties and morphology of LCP/ABS blends compatibilized with a styrene–maleic anhydride copolymer

A co‐polyester liquid crystalline polymer (LCP) was melt blended with an acrylonitrile–butadiene–styrene copolymer (ABS). LCP fibrils are formed and a distinct skin/core morphology is observed in the injection moulded samples. At higher LCP concentration (50 wt%), phase inversion occurs, where the dispersed LCP phase becomes a co‐continuous phase. While the tensile strength and Young's modulus remain unchanged with increasing LCP content up to 30 wt% LCP, a significant enhancement of the modulus at 50 wt% LCP is observed due to the formation of co‐continuous morphology. The blend modulus is lower than the values predicted by the rule of mixtures, suggesting a poor interface between the LCP droplets and ABS matrix. A copolymer of styrene and maleic anhydride (SMA) was added in the LCP/ABS blends during melt blending. It is observed that SMA has a compatibilizing effect on the blend system and an optimum SMA content exists for mechanical properties enhancement. SMA improves the interfacial adhesion, whereas excess of SMA reduces the LCP fibrillation. Copyright © 2003 Society of Chemical Industry     

Structure and properties of polyblends of a thermotropic liquid crystalline polymer with an alloy of polyamide-6 and ABS

The relationship between the microstructure and corresponding mechanical properties developed during injection molding of blends containing a liquid crystalline polymer (LCP) as the minor component and an engineering polymer system has been studied. A wholly aromatic copolyester LCP (Vectra A950) was melt blended at different compositions with a thermoplastic matrix consisting of a commercial compatibilized blend of polyamide-6 and ABS (Triax 1180). These blends were prepared under two different sets of injection molding conditions. In the first case, a higher melt temperature, higher barrel temperature, lower injection pressure, lower mold temperature, and shorter residence time in the mold were used during injection molding, as compared with the second case. The mechanical properties of the blends were superior to those of the base polymer. In the second case, the resulting injection-molded specimens had a distinct skin–core morphology where elongated fibrils of LCP constituted the skin layer. The mechanical properties of the blends processed under the second set of processing conditions were superior to those of the first, though the trends in both cases were the same. To study the effects of process variables the 15% LCP blend and the second set of processing conditions were taken as the base. Samples were injection-molded by varying one parameter at a time. It was seen that the properties of the blend were increased by maintaining a lower barrel temperature, greater injection pressure, lower injection speed, higher mold temperature, and a greater residence time in the heated mold. Thus it was found that the processing conditions played a vital role in determining the mechanical properties and morphology of the polyblends. © 1996 John Wiley & Sons, Inc.     

Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film: Effects of counter-rotating die on fiber orientation and film properties

Polyethylene blends (LLDPE:HDPE ≈ 2:1 by wt) used in NASA's balloon film applications can be effectively reinforced by addition of a small amount of liquid crystalline polymer (LCP). Cast and blown PE films containing ≈ 10% LCP show an appreciable enhancement in tensile modulus ≈400% over that of the neat PE matrix. Anisotropy in these in-situ composites was reduced by controlling LCP molecular orientation via a counter-rotating (C/R) annular die. LCP/PE blend blown films with nearly isotropic properties are obtained. Based on microscopy studies, LCP domains were generally present as fibrils with diameters of ≈ 1 to 3 µM and lengths of ≈ 100 to 300 µM. Films, produced using a C/R die, had fibrillated LCP phases and variable orientation through the film thickness. This paper describes the influence of some key process variables including temperature profile, number of extrusion cycles, degree of mixing, adapter geometry, and die counter-rotation on LCP/PE blend film morphology and mechanical properties. The structure of LCP/PE blend blown films was also evaluated using scanning electron microscope (SEM) and wide angle X-ray scattering (WAXS) techniques.     

Miscibility and mechanical properties of poly(ether imide)/poly(ether ether ketone)/liquid crystalline polymer ternary blends

This paper is concerned with a novel ternary blend composed of poly(ether imide) (PEI), poly(ether ether ketone) (PEEK) and a liquid crystalline polymer (LCP; HX4000, Du Pont). Different compositions were prepared by extrusion and injection moulding. Dynamic mechanical thermal analysis and the observation of the fracture surfaces, before and after annealing, allowed determination of the cold crystallization temperatures and miscibility behaviour of these systems. PEEK/PEI blends are known from previous studies to be miscible at all compositions. In this case it was observed that the PEEK/HX4000 blend was miscible up to 50 wt% HX4000 but partially miscible above this value. The PEI/HX4000 blends were found to be partially miscible in the whole concentration range. As a result, some ternary blend compositions exhibited only one phase, while others exhibited two phases. The measurement of the tensile properties showed that ternary blends with high modulus can be obtained at high LCP loadings, while compositions with high ultimate tensile strength can be obtained with high loadings of PEI or PEEK.     

液晶聚合物增强PC／PET共混物挤出片材的性能研究

介绍液晶聚合物对ＰＣ／ＰＥＴ共混体系的增强改性。选用了六种不同熔眯的ＬＣＰ引入到ＰＣ／ＰＥＴ共混体系中，用自制的有利于形成定向的口模，将共混物挤出成片材，并测定了拉伸强度，维卡软化点，结晶速率，结果表明：在ＰＣ／ＰＥＴ共混物中，加入少量ＬＣＰ后，拉伸强度可比原体系提高３０％左右，不同熔点的ＬＣＰ影响有差异，熔点太高的ＬＣＰ反而会使体系的拉伸强度下降，维卡软化点未见明显变化，当增大ＬＣＰ用量后，体系     

Weld lines and mechanical properties of injection molded polyethylene/polystyrene/copolymer blends

In this article, we investigate the effect of weld lines on the tensile mechanical properties of unmodified and copolymer modified high density polyethylene (HDPE) and polystyrene (PS) blends. The homopolymers were melt blended in the proportion of 20 wt% HDPE and 80 wt% PS using a twin screw extruder at a temperature of 200°C. The results show that the mechanical properties are generally lower when weld lines are present. The decrease of the mechanical properties is much more pronounced for the blends. The addition of small amounts of a commercial styrene/butadiene copolymer significantly improves the strength and the elongation at break of this blend. An optimum copolymer concentration was observed at 3 wt%. This value coincides with the interphase saturation concentration of the copolymer obtained from the analysis of the DMTA (dynamic mechanical and thermal) properties of the blends. The copolymer was also found to induce important changes in the morphology of the blend. The interdiffusion of the polymer fronts in the weld region was also improved by the presence of the copolymer. It is believed that these two aspects contribute to the enhanced properties obtained with copolymer modified blends in presence of weld lines. An important effect of the injection temperature on the tensile strength and the elongation at break of welded samples with copolymer modified blends was observed. The effect of mold temperature on these properties was less important mainly at low injection temperatures. Only a slight effect of these two parameters was observed for the tensile modulus in the range of mold and injection temperatures considered in this study.