Characterization of thermotropic liquid crystalline polyester/polysulfone blends

The morphology, rheology, and mechanical properties of blends of polysulfone (PSF) with up to 65% of a wholly aromatic liquid crystalline polymer (LCP) were investigated. In injection molded specimens a skin-core morphology was observed with the LCP minor phase oriented in the skin and globular in the core. Scanning electron microscopy of fractured surfaces showed sharp phase boundaries, suggesting low interfacial adhesion. The neat PSF and blends with low amounts of LCP exhibited a low shear Newtonian plateau not observed in the blends with high LCP levels. The addition of LCP to PSF resulted in an increase in stiffness, a small increase in tensile strength, and a significant improvement in processability.     

In situ composite: Phenolphthalein polyethersulfone—thermotropic liquid crystalline polymer blends

Phase behavior, thermal, rheological and mechanical properties plus morphology have been studied for a binary polymer blend. The blend is phenolphthalein polyethersulfone (PES-C) with a thermotropic liquid crystalline polymer (LCP), a condensation copolymer of p-hydroxybenzoic acid with ethylene terephthalate (PHB-PET). It was found that these two polymers from optically isotropic and homogeneous blends by means of a solvent casting method. The homogeneous blends undergo phase separation during heat treatment. However, melt mixed PES-C/PHB-PET blends were heterogeneous based upon DSC and DMA analysis and SEM examination. Addition of LCP in PES-C resulted in a marked reduction of melt viscosity and thus improved processability. Compared to pure PES-C, the charpy impact strength of the blend containing 2.5% LCP increased 2.5 times. Synergistic effects were also observed for the mechanical properties of blends containing < 10% LCP. Particulates, ribbons, and fibrils were found to be the typical morphological units of PHB-PET in the PES-C matrix, which depended upon the concentration of LCP and the processing conditions.     

Comparative study on phase and properties between rPET/PS and LCP/PS in situ microfibrillar-reinforced composites

Microfibrillar-reinforced composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate) (rPET), and polystyrene (PS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of LCP/PS and rPET/PS blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into PS significantly improved the processability. The potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of rPET/PS system was lower than that of LCP/PS system, most rPET domains appeared as small droplets. An addition of LCP and rPET into PS matrix improved the thermal resistance in air significantly. The obtained results suggested the high potential of rPET as a processing aid and thermally stable reinforcing-material similar to LCP. The mechanical properties of the LCP-containing blends were mostly higher than those of the corresponding rPET-containing blends when compared at the same blend composition.     

Effects on the melt rheology of systems of Nd‐Fe‐B particles suspended in a poly(phenylene sulfide) and liquid crystalline polymer blend

The melt rheology of blends of a liquid crystalline polymer (LCP) and poly(phenylene sulfide) (PPS) and their composites with ferromagnetic Nd‐Fe‐B particles (MQP) was studied. We investigated the effects of LCP concentration, Nd‐Fe‐B particle volume fraction and size, distribution, and shear rate on the rheological properties of these composites. Enthalpy of fusion changes that were observed resulted from the addition of the LCP and Nd‐Fe‐B particles to the polymer blends/composites. The shear rate and frequency dependencies of the materials revealed a viscosity reduction at low (1–3 wt%) and moderate (10–15 wt%) LCP concentrations, and strong effects on the shear‐thinning characteristics of the melt. The suspensions of polydispersed Nd‐Fe‐B particle configurations in PPS that were of lower size ratios gave better processability, which is contradictory to previously reported behavior of suspensions containing spherical particles. Specifically, the compositions with unimodal and a bimodal distribution of Nd‐Fe‐B particles gave the lowest viscosities. The experimental data were correlated with semi‐empirical viscosity model equations of Maron‐Pierce, Krieger‐Dougherty, Eilers, and Thomas and were found to be consistent with the data. The maximum packing fraction, ϕ_m, of the MQP particles was estimated to be within the range of 0.78 ϕ ≤_m ≤ 1.0 through graphical and parametric evaluation methods.     

Rheology,morphology, and mechanical characteristics of poly(etherether ketone)-liquid crystal polymer blends

This paper is in continuation of our previous paper on Poly(etherether ketone)-liquid crystal polymer (PEEK-LCP) composites. Rheological, morphological, and mechanical properties of polyetherether ketone and a thermotropic liquid crystalline polymer based on hydroxybenzoic acid/hydroxynaphthoic acid have been reported. Addition of LCP resulted in a marked reduction of viscosity and improved processability. Tensile properties improved with increase in LCP concentration. Synergistic effects have been observed at certain LCP concentrations. The elongation at break was found to reduce drastically above 10% of LCP content. This is a characteristic typical of chopped-fiber-filled composites. Morphology of injection molded and capillary extruded samples of the blends showed that the in-situ formed fibrous LCP phase was preserved in a solidified form. The improvement in tensile properties is likely due to the reinforcement of the PEEK matrix by the fibrous LCP phase as observed by scanning electron microscopy. A distinct skin-core morphology was found to develop in the injection molded samples of these blends. Mechanical properties measured in the flow and transverse direction indicated an increase in the degree of anisotropy with an increase in LCP content.     

In situ reactive compatibilized noryl/LCP blends

This article reveals that the already known improved properties of the thermoplastic–liquid crystalline polymer (LCP) blends can be further improved substantially over the corresponding noncompatibilized counterparts by using a reactive in situ type compatibilizer, the styrene–glycidyl methacrylate (SG) copolymer. This SG copolymer has been demonstrated in this article to be an effective reactive compatibilizer to improve the processability, heat deflection temperature, and mechanical properties of Noryl/LCP blends. The epoxy functional groups of the SG copolymer can react with the end groups of PPO (in Noryl) and LCP. The in situ-formed SG–g–LCP copolymer tends to reside along the interface of Noryl–LCP and reduces the interfacial tension during melt processing. The resultant LCP fibers in the Noryl matrix of the compatibilized blends have a higher aspect ratio because the fibers become finer, longer, and tend to form lamellate domains with a greater interphase contact area than those from the noncompatibilized blends. The compatibilized blends also improve the interphase adhesion between Noryl and LCP. The presence of ethyl triphenylphosphonium bromide catalyst promotes the grafting reaction to improve blend compatibilization. © 1995 John Wiley & Sons, Inc.     

Processability,morphology and mechanical properties of glass fiber reinforced poly(ether sulfone) modified by a liquid crystalline copolyester

Ternary composites based on glass fiber reinforced polyethersulfone (gPES) modified by a liquid crystalline copolyester (R5) were obtained by injection molding at different nozzle temperatures and at LCP contents up to 20%. The blends showed two pure amorphous phases. The ability of R5 to improve processing was seen mainly in the increase in the MFI of the blends on 5% LCP addition, which was more than 75% and 16% with respect to that of pure gPES and PES, respectively. The best processing temperature appeared to be 330°C, as it led to the maximum skin fibrillation and provided both the best small strain and fracture mechanical properties. The blend processed at 330°C with 5% R5 showed the best balance of properties because, besides the highest relative processability increase, it led to maximum values in all mechanical properties measured. This was due to both the overall fibrillation of the skin and to its having the highest ductility.     

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.     

Rheogoniometry of molten blends of polystyrene and styrenic ionomers

The rheological properties of the molten blends between polystyrene (PS) and styrenemethacrylic acid copolymer (S-MAA) or its metallic salts were determined with a Weissenberg rheogoniometer, and the mixed structure and the processability were discussed. Results were as follows. (1) The viscosities of the salts increased and the compliances decreased with increasing density of ionic crosslinkings. (2) The viscosities of the molten blend between PS and S-MAA or its salt increased steeply even at lower shear rate and the Newtonian flow region was not observed. (3) This shear-sensitivity of viscosity in low shear rate region increased with increasing temperature. (4) The effect of temperature on the viscosity of these blends deviated from the simple Arrhenius plot. (5) Some network structures are suggested for the blends between PS and S-MAA salts but they may be broken eventually under high shear rate or at high temperature. Therefore, the mixed structures and the flow mechanisms of these molten blends seem to change with shear or temperature.     

Phase behavior and rheology of blends containing polycarbonate and a thermotropic polyester

The phase behavior and rheology of binary blends of polycarbonate (PC) and a liquid crystalline polymer (LCP) have been investigated. The thermotropic LCP employed was a semiflexible polyester synthesized by melt condensation of t-butylhydroquinone and 4,4′ dichloroformyl-α,ω-diphenoxyhexane. It shows a distinct nematic-to-isotropic transition in the pure state and in the blends. Results of DSC and optical microscopy indicate that the LCP is solubilized in the mixture for weight fractions of LCP less than about 0.05 and shows partial miscibility with PC over the rest of the composition range. The phase separation is considered to be driven by both isotropic and anisotropic interactions between constituent chains. Dynamic oscillatory measurements show that there is some interaction between the separate isotropic and anisotropic phases, with complex viscosities of the blends being intermediate between those of pure components and showing significant deviation from a logarithmic rule-of-mixtures. © 1996 John Wiley & Sons, Inc.     

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.     

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

Blends of a poly(ethylene 2,6-naphthalate) (PEN) and a liquid crystalline copolyester (LCP), poly(benzoate-naphthoate) were prepared in a twin-screw extruder. Specimens for thermal properties were investigated by means of an instron capillary rheometer (ICR) and scanning electron microscopy (SEM). The blend viscosity showed a minimum at 10 wt% of LCP and increased with increasing LCP content above 10 wt% of LCP. Above 50% of LCP and at higher shear rate, phase inversion occured and the blend morphology was fibrous and similar to pure LCP. The ultimate fibrillar structure of LCP phase appeared to be closely related to the extrusion temperature. By employing a suitable deformation history, the LCP phase may be elongated and oriented such that a microfibrillar morphology can be retained in the solid state. Thermal properties of the LCP/PEN blends were studied using DSC and a Rheovibron viscoelastomer. These blends were shown to be incompatible in the entire range of the LCP content. For the blends, the T_g and Tm were unchanged. The half time of crystallization for the LCP/PEN blends decreased with increasing LCP content. Therefore, the LCP acted as a nucleating agent for the crystallization of PEN. The dimensional and thermal stability of the blends were increased with increasing LCP content. In studies of dynamic mechanical properties, the storage modulus (E′) was improved with increasing LCP content and synergistic effects were observed at 70 wt% of LCP content. The storage modulus for the LCP/PEN 70/30 blend is twice that of PEN matrix and exceeded pure LCP.     

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.     

Rheology and impact characteristics of compatibilized polypropylene-liquid crystalline polymer composites

Polypropylene-liquid crystalline polymer (PP/LCP) and maleic anhydride compatibilized PP/LCP blends were prepared using the extrusion technique followed by injection molding. The LCP employed was Vectra A950 which consists of 25 mol % of 2,6-hydroxynaphthoic acid and 75 mol % of p-hydroxybenzoic acid. The rheology, morphology, and impact behavior of compatibilized PP/LCP blends were investigated. The rheological measurements showed that the viscosity of LCP is significantly higher than that of the PP at 280°C. This implied that the viscosity ratio of the LCP to the polymer matrix is much larger than unity. Scanning electron microscopy (SEM) observations revealed that the LCP domains are dispersed mainly into elongated ellipsoids in the PP/LCP blends. However, fine fibrils with large aspect ratios were formed in the compatibilized PP/LCP blends containing LCP content ≥ 10 wt %. The development of fine fibrillar morphology in the compatibilized PP/LCP blends had a large influence on the mechanical properties. The Izod impact strength of the PP/LCP blends showed little dependence on the LCP concentrations. On the other hand, the impact strength of the compatibilized PP/LCP blends was dependent on the LCP concentrations. The correlation between the LCP fibrillar morphology and spherulitic structure with the impact properties of the compatibilized PP/LCP blends is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 521–530, 1998     

Mechanical and Rheological Properties of Poly(ethylene terephthalate)/ Polypropylene Blends

Poly(ethylene terephthalate) and polypropylene (PET/PP) were compounded and pelletized with a single-screw extruder. Standard ASTM tensile test specimens were made by injection moulding. The blends are stronger and stiffer than the plain PP specimens. The addition of a compatibilizer, EPOLENE E-43, is found to improve the strength and stiffness of the blends at loadings of 50% and 70% PET. At 10% PET loading, E-43 has the opposite effect of slightly reducing the tensile properties. All the blends are more brittle relative to either plain PET or PP. The addition of E-43 results in negligible improvement in the elongation at break. E-43 is also found to be an effective lubricant in improving the processability of the blends. The blends with E-43 added have lower viscosities and less shear-thinning characteristics than those without E-43. © 1997 SCI.     

Effect of LCP and rPET as reinforcing materials on rheology,morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

Microfibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of interactions on the mechanical,morphological and thermal properties of in situ ternary composites based on fluorocarbon elastomer,acrylic elastomer and liquid crystalline polymer blends

The mechanical, morphological and thermal properties of the binary and ternary blends of a fluorocarbon elastomer (FKM), an acrylic elastomer (ACM) and a liquid crystalline polymer (LCP) were investigated. The ternary blends were prepared by varying the amount of the LCP but fixing the ratio of the FKM and ACM. Addition of a third component, a polyacrylic rubber which interacted with the LCP, facilitated the structural development of the LCP phase by acting at the interface. The mechanical properties of the ternary blends were substantially improved because of both the fibril generation and adhesion of rubber particles on the LCP fibrils, which were attributed to the ACM interaction. Morphological investigations suggest that the fine fibrillation of the LCP domains is more apparent in the ternary blends than in the binary blends of FKM and LCP prepared under the same processing conditions. Thermogravimetric analysis (TGA) revealed an improved thermal stability of the FKM in the presence of the LCP for the binary blends, but a lower thermal stability for the ternary blends. Copyright © 2005 Society of Chemical Industry     

Rheology and morphology of some thermoplastic blends with a liquid crystalline copolyester

Liquid crystalline polymers (LCPs) are known for their high performance properties. However, owing to their high cost, research efforts are much oriented to their use as reinforcements for different thermoplastics. In this study, we investigated the morphology, mechanical and dynamic rheological properties of blends of a 60/40 para hydroxybenzoic acid–ethylene terephthalate copolyester LCP (PHB/PET) with poly(butylene terephthalate) (PBT), poly(hexamethylene terphthalate) (PHMT), and polycarbonate (PC). Addition of up to 30 wt% of LCP to the different thermoplastics was performed in a Haake Rheomix mixer at 300°C. The dynamic rheological properties of the blends showed significant changes upon the addition of LCP, but no improvement in the mechanical properties was observed. The rheological properties of the blends below the nematic transition temperature of the LCP (210°C) were similar to those of solid filled thermoplastics. At 270°C, at which the LCP is in the nematic phase, the viscosity of LCP blends with PC blends decreased, whereas that obtained with PBT blends was increased. This is interpreted as being due to the differences in viscosity and interfacial tension between the components and to a possible reaction between the LCP and the thermoplastics.     

Effect of a filler on the rheological and mechanical properties of the liquid‐crystalline polyester–poly(methyl methacrylate) blends

The rheological and mechanical properties of the blends of liquid‐crystalline polyester (LCP) and poly(methyl methacrylate) (PMMA) filled with aluminum borate whiskers have been studied. It was established the combined action of reinforcing LCP and filler onto the property of PMMA matrix leads to marked reinforcing of PMMA. At 10% of filler and 30% of LCP, the tensile strength of PMMA increases by 30% and elasticity modulus by 110%, the processability being no worse. The viscosity of the blend PMMA + 30% LCP + 10% filler practically is the same as the PMMA melt viscosity at 220°C. With increasing concentration of LCP up to 30%, the filler effect in binary matrix becomes more essential. The possible reason is the preferential adsorption of LCP at the filler interface (surface segregation) and additional ordering of LCP near the surface, possible, due to additional stretching of nematic phase in the convergent flow zone. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 993–999, 2000     

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.-%.