The dynamic properties,temperature transitions,and thermal stability of poly (etherether ketone)-thermotropic liquid crystalline polymer blends

Differential scanning calorimetry, dynamic mechanical measurements, and thermal gravimetric analysis techniques have been used to thermally characterize blends of poly(etherether ketone)-thermotropic liquid crystalline polymer (LCP) based on hydroxybenzoic and hydroxynaphthoic acid (HBA/HNA). Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentration. For these blends the glass transition temperature of both components does not change much with composition. Dynamic mechanical measurements performed under torsional and flexural modes of testing and different samples geometries indicate that the dynamic properties depend a lot on the above two factors. Anisotropy in these blends was studied by performing dynamic measurements in flow and transverse directions. The effect of orientation is found to be predominant. Dynamic mechanical properties tend to improve in the flow direction, whereas in the transverse direction they are found to decrease with increasing LCP concentration.     

Thermal and mechanical properties of injection molded liquid crystalline polymer/amorphous polymer blends

Injection molded samples of binary blends of Vectra (LCP) and the three amorphous polymers polyethersulfone (PES), polycarbonate (PC), and aromatic poly(ester carbonate) (APEC) have been subjected to morphological and rheological characterization, and coefficients of linear thermal expansion and Young's moduli have been determined. The Young's modulus of the PES/LCP blends exhibited a near lower-bound behavior that could be predicted by the one-adjustable-parameter equations of Halpin-Tsai (ζ = 0.18) and Takayanaga (b = 0.23), whereas the coefficients of linear thermal expansion followed the Takayanaga equation with a value of b = 0.50. The chain orientation of the LCP component was essentially constant in all PES/LCP blends with a Herman's orientation parameter of 0.39 ± 0.03. Transesterification reactions led to randomization of the constituents of the PC/LCP and APEC/LCP blends. The effect was more pronounced in the PC/LCP blends. The introduction of the LCP into the PC/LCP blends led to no reduction in melt viscosity and no self-reinforcement. APEC/LCP exhibited self-reinforcement in blends with a content greater than 27 vol% LCP, and especially the blend with 67 vol% LCP. The self-reinforcement was caused by the presence of an oriented LCP phase, confirmed by X-ray diffraction, and by improved interfacial bonding, presumably resulting from the transesterification reactions occurring at the phase boundaries.     

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     

Ternary blends of acrylic rubber,poly(butylene terephthalate), and liquid crystalline polymer: Influence of interactions on thermal and dynamic mechanical properties

The ternary blends of acrylate rubber (ACM), poly(butylene terephthalate) (PBT), and liquid crystalline polymer (LCP) were prepared by varying the amount of LCP but fixing the ratio of ACM and PBT, using melt mixing procedure. The influence of interactions on thermal and dynamic mechanical properties of the blends was investigated over the complete composition range. The techniques applied were Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), and dynamic mechanical analysis (DMA). The FTIR spectroscopy analysis showed reduction in the intensity of the peak corresponding to epoxy groups of ACM with increasing heating time at 290°C. This implies that there is a chemical reaction between the epoxy and end groups of PBT and LCP. Glass transition temperature (T_g) and melting temperature (T_m) of the blends were affected depending on the LCP weight percent in the ACM/PBT blend, respectively. This further suggests the strong interfacial interactions between the blend components. In presence of ACM, the nucleating effect of LCP was more pronounced for the PBT phase. The thermogravimetric study showed improved thermal stability for the blends with the increasing LCP content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3904–3912, 2006     

Viscoelastic properties of ternary in situ elastomer composites based on fluorocarbon, acrylic elastomers and thermotropic liquid crystalline polymer blends

Dynamic mechanical analysis was performed to characterize the viscoelastic properties of binary and ternary blends of fluorocarbon elastomer (FKM), acrylic elastomer (ACM) and liquid crystalline polymer (LCP). The results showed that the storage and loss modulus of all the blends increased significantly with the weight percentage of the LCP. The glass transition temperature evaluated at the loss modulus peak, were in the range of −10-+5 °C for all the blends. The time temperature superposition principle was applied for the FKM/ACM and 20% LCP filled FKM/ACM blend in order to evaluate the changes in the viscoelastic properties of FKM/ACM blend by the addition of LCP. The Arrhenius and William-Landel-Ferry (WLF) equations were used to quantify the viscoelastic behaviour at the glass transition region. Both the blends exhibited a single relaxation, which is glass transition, observed as a peek in the loss modulus at 1 Hz. The glassy moduli of these two systems were found to be comparable, but the rubbery moduli of the LCP filled FKM/ACM was much higher than the LCP unfilled system. However, the viscoelastic behaviour of these two systems and their sensitivity to time temperature may be considered to be quite similar.     

Structure and mechanical properties of blends of an amorphous polyamide and a liquid crystalline polymer

The structure and the mechanical properties of blends of an amorphous polyamide (PA) and a thermotropic copoly(ester‐amide) (VB) obtained both by direct injection molding (DI) and also by extrusion and subsequent injection molding (EI) have been studied. Besides the usual fibrillar morphology of the skin, fibrillation was also observed in the core of most of the blends. The important synergisms in the modulus of elasticity (20% positive deviations in both blends with 30% and 40% VB contents) and also in the tensile strength (30% and 55% positive deviations in the EI blends at the same compositions) were obtained without the presence of compatibilizer.     

Molecular orientation and mechanical properties of polymer blends of PBT and a liquid crystalline polyester

A thermotropic liquid crystalline polyester (LCP) based on 4-hydroxyacetophenone azine and sebacoyl dichloride was synthesized via a low-temperature solution route. The liquid crystalline polymer was characterized by ¹H-NMR, DSC, GPC, and polarizing microscopy experiments. The LCP was melt-blended with poly(butylene terephthalate) (PBT), followed by the melt-spinning process at take-up speeds ranging from 14 to 50 m/min. We analyzed the molecular orientational order of LCP and PBT in as-spun fibers of the LCP/PBT blends by the attenuated total reflection (ATR) FTIR dichroism technique and WAXS. The order parameter (S), representing the molecular orientational order, of LCP in the polyblend fibers increased as the employed LCP amounts and the draw ratio increased. Moreover, the order parameter of PBT in the blends increased dramatically when sufficiently large amounts of LCP (over 50 wt %) were employed, especially for highly drawn fibers, which suggested a considerable miscibility between LCP and PBT. The thermal behavior of the blends investigated by DSC also indicated that the synthesized LCP was miscible, at least partially, with PBT. All these results correlated with the enhancement of mechanical properties observed for higher concentrations of LCP in the blends and for highly drawn samples. © 1996 John Wiley & Sons, Inc.     

Structural,rheological, and mechanical properties of ternary blends of PEN,PET, and liquid crystalline polymer

Structural, rheological, and mechanical properties of ternary blends of a liquid crystalline copolyester (LCP) composed of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, poly(ehtylene naphthalate)(PEN), and poly(ethylene terephtalate) (PET) were investigated using capillary rheometry, tensile testing, scanning electron microscopy, and X-ray diffraction. Viscosity-shear rate behavior of the ternary blends is very similar to that of pure polymers and their binary blends. The activation energy of flows of the ternary blends was smaller than those of PEN and PET. Tensile modulus and strength of extruded strands of the blends increased with increasing LCP content. The extruded strands of the blends consist of a crystalline and oriented LCP phase and an amorphous and unoriented PEN/PET blended phase. Tensile mechanical properties and structures of the ternary blends were discussed.     

Mechanical performance of blends of thermotropic liquid crystalline polymer spheres‐dispersed polycarbonate

Liquid crystalline polymer (LCP) blends with a thermotropic LCP dispersed in the form of microspheres is studied to show the role of LCP spheres. Polycarbonate (PC), p‐hydroxybenzoic acid–poly(ethylene terephthalate) copolyester, and random styrene–maleic anhydride copolymer are used as the matrix, the dispersed phase, and the compatibilizer, respectively. A scanning electron microscopy observation shows the formation of LCP spheres with improved interfacial adhesion in the injection‐molded samples via compatibilization. The mechanical tests show increased modulus, elongation at break, and fracture‐absorbed energy of blends of LCP spheres‐dispersed PC. This shows an optimistic potential for the dispersed LCP phase, in spite of its morphology in the form of fibrils for reinforcing the matrix or in the form of microspheres for toughening the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1493–1499, 2003     

Engineering properties of compatibilized polypropylene/liquid crystalline polymer blends

Polypropylene (PP) and Vectra A950, a thermotropic liquid crystalline polymer (LCP), blends were prepared in a single‐screw extruder with the variation in Vectra A950 content in presence of fixed amount (2%, with respect to PP and LCP mixture as a whole) of ethylene‐acrylic acid (EAA) copolymer as a compatibilizer. Mechanical analysis of the compatibilized blends within the range of LCP incorporations under study (2–10%) indicated pronounced improvement in the moduli, ultimate tensile strength (UTS), and hardness. Fourier transform infrared (FTIR) spectroscopy studies revealed the presence of strong interaction through H‐bonding between the segments of Vectra A950 and the compatibilizer EAA. Morphological studies performed by scanning electron microscopy (SEM) manifested the development of fine fibrillar morphology in the compatibilized PP/Vectra A950 blends, which had large influence on the mechanical properties. Differential scanning calorimetry studies showed an initial drop of the melting point of PP in the presence of EAA followed by enhancement of the same in presence of Vectra A950. TGA showed an increase in the thermal stability for all blends with respect to matrix polymer PP. Rheological studies showed that a very small quantity of Vectra A 950 was capable of reducing the melt viscosity of PP particularly in the lower shear rate region and hence facilitated processibility of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of self-reinforced polypropylene/liquid crystalline polymer blends

The mechanical properties of self-reinforced liquid crystalline polymer/polypropylene (LCP/PP) blends strongly depend on the viscosity ratio of the blend components in the melt. This ratio was determined for PP blends with different commercial LCPs (Vectra A950 and Vectra B950), by means of capillary rheometry, under conditions representative for the blending process during extrusion. It was found that optimal mechanical properties were achieved when the LCP/PP viscosity ratio at 285°C ranges between 2 and 4 at a shear rate of 800–1000s⁻¹. The LCP/PP viscosity ratio appears to be shear stress dependent. This creates the option of fine tuning the LCP droplet deformation process by means of the extrusion rate. This shear stress dependence is more pronounced for PP blends with Vectra B950 than for blends with Vectra A950.     

The morphology and mechanical properties of phenoxy/liquid crystalline polymer blends and the effect of transesterification

Morphological, rheological, and mechanical properties of poly(hydroxy ether of bisphenol A) (phenoxy) and a Vectra liquid crystalline copolyester (LCP) blends were investigated. Scanning electron micrographs of fracture surfaces of injection-molded samples show that the LCP forms an elongated fibrous dispersion in the phenoxy matrix. As the mixing time increases, the tensile strength and modulus increase while the elongation at break remains almost constant. These improvements are attributed to the formation of LCP-grafted phenoxy by the interchange reaction between phenoxy and LCP. The interchange reaction was identified by DSC, a rheometer, and a FTIR spectrometer. The graft copolymer gives better adhesion between the two phases and thus improves mechanical properties of the blends. © 1995 John Wiley & Sons, Inc.     

A dynamic mechanical and thermal study of various rubber–bitumen blends

Blends of a Nynas 100 penetration‐grade bitumen with a cis‐polybutadiene, a butyl rubber, three polyisobutylenes of different molecular weights, a chlorinated‐polyethylene, polychloroprene in latex form, and a polyurethane rubber (scrap Lycra) were prepared using a Z‐blade masticator mixer at a temperature of about 180°C. The blends contained between 10 and 40 pph (i.e., 9 and 29%) by weight of rubber. They were characterized by fluorescence optical microscopy, differential scanning calorimetry, and dynamic mechanical thermal analysis. The bitumen‐rich phases provided the matrix in most of these systems, polymer‐rich extensive phases being formed with butyl rubber, and low‐ and moderate‐molecular‐weight poly(isobutylenes) when the proportion rose above 30 pph, and for the poly(cis‐butadiene) and chlorinated polyethylene system only when the proportion rose above 40 pph, according to the tan δ plots. Only glass transitions were associated with polymer‐rich phases, and there were some melting transitions from paraffinic wax components ejected from the bitumen‐rich phases. Below room temperature the modulus of blends of polybutadiene, chlorinated polyethylene, and the polyurethane rubber were similar to that of the bitumen; but those of the other polymers were stiffer by a factor of 50, perhaps because of a rearrangement of the asphaltenes. The softer blends, particularly the first two named above, had loss processes (with tan δ > 0.5) ranging over 200°C or more. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 586–601, 2000     

Morphology,mechanical properties,and thermal stability of polyurethane–epoxide resin interpenetrating polymer network rigid foams

A series of rigid interpenetrating network foams (IPNFs) based on a rosin‐based polyurethane (PU) and a crosslinked epoxide resin (ER) were prepared by a simultaneous polymerization technique. The morphology, mechanical properties, thermal stability, and changes in the chemical structure during the thermal degradation process of the rigid IPNFs were investigated by scanning electron microscopy (SEM), compressive testing, thermogravimetric analysis (TGA), and Fourier‐transform infrared spectroscopy (FTIR). The SEM micrographs showed that the cell structure of the rigid IPNFs became less homogeneous with increasing ER content. The brittleness of the cell walls increased as the ER content and the cure time of the rigid IPNFs increased. The compressive strength of the rigid PU/ER IPNFs increased to a maximum value and then decreased with further increase in the ER content. Similar behavior was observed for the elastic modulus. This behavior was related to the nonhomogeneous cells and more brittle cell walls for the rigid IPNFs with high ER content. The TGA data showed that the thermal stability of the rigid PU foam increased with the addition of increasing levels of ER, due to the better thermal stability of the ER compared to that of the PU. With the exception of the ER alone, a two‐stage weight‐loss process was observed for all these rigid IPNFs and for the PU foam alone. The FTIR analysis suggested that the first stage of weight loss was due to the degradation of the polyol–derived blocks of the PU, and the second weight loss stage was governed by both the degradation of the ER component and that of the isocyanate‐derived blocks of the PU. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 406–416, 2000     

PP–elastomer–filler hybrids. I. Processing,microstructure, and mechanical properties

Three-component systems with a polypropylene (PP) matrix consisting of polar elastomer (ethylene–propylene rubber and styrene–ethylene–butylene–styrene grafted with maleic anhydride) or of polar PP (PP grafted with maleic anhydride) and filler were investigated. Three microstructures of PP–elastomer–filler hybrids were obtained by processing control and elastomer or PP modification with the maleic anhydride: fillers and rubber particles were separated in the PP matrix, rubber particles with filler core were distributed in the PP matrix, and mixed microstructures of the first and second. A study of mechanical properties showed that the elastic modulus increased in the first microstructure and impact strength increased in the second microstructure. Mechanisms for the relationships between microstructure, processing, and mechanical properties are discussed. © 1996 John Wiley & Sons, Inc.     

Thermal properties,structure and morphology of PEEK/thermotropic liquid crystalline polymer blends

The dynamic crystallization and subsequent melting behaviour of poly(aryl ether ether ketone), PEEK, and its blends with a thermotropic liquid crystalline polymer, Vectra^®, have been studied using differential scanning calorimetry, optical microscopy and wide‐angle and small‐angle X‐ray diffraction (WAXS and SAXS) techniques in a wide compositional range. Differences in crystallization rates and crystallinities were related to the structural and morphological characteristics of the blends measured by simultaneous real‐time WAXS and SAXS experiments using synchrotron radiation and optical microscopy. The crystallization process of PEEK in the blends takes place in the presence of the nematic phase of Vectra and leads to the formation of two different crystalline families. The addition of Vectra reduces the crystallization rate of PEEK, depending on composition, and more perfect crystals are formed. An increase in the long period of PEEK during heating was generally observed in the blends at all cooling rates. Copyright © 2003 Society of Chemical Industry     

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 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.     

Impact strength and dynamic mechanical properties correlation in elastomer‐modified polypropylene

This article describes the impact and dynamic mechanical properties of rubber‐modified binary blends of polypropylene (PP). Two conventional elastomers [viz. ethylene vinyl acetate copolymer (EVA) and ethylene propylene diene terpolymer (EPDM)] were used as an impact modifier for PP. It is clearly indicated by the results that EPDM is better than EVA as an impact modifier of PP. Analysis of data of dynamic mechanical properties and impact properties at various compositions of the blends revealed a direct correlation between impact properties and dynamic mechanical loss tangent. The energy dissipation due to viscoelastic relaxation is therefore suggested as a mechanism of impact toughening of PP, in addition to the other commonly known mechanisms of toughening (viz. shear yielding and crazing induced by deformation of rubber‐phase domains). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 962–971, 2000     

Studies on morphology,mechanical, thermal,and dynamic mechanical behavior of extrusion blended polypropylene and thermotropic liquid crystalline polymer in presence of compatibilizer

Polypropylene was melt blended in a single screw extruder with thermo tropic Vectra B‐950 liquid crystalline polymer (copolyester amide) in different proportions in presence of 2% of EAA, ethylene‐acrylic acid copolymer (based on PP) as a compatibilizer. The mechanical properties of such compatibilized blends were evaluated and compared in respect of their Young's Modulii, Ultimate tensile strength, percent elongation at break, and toughness to those of Pure PP. The Morphology was studied by using a polarizing light microscope (PLM) and Scanning electron microscope (SEM). The Thermal characterization of these blends were carried out by differential scanning calorimeter (DSC).The mechanical properties under dynamic conditions of such compatibilized blends and pure PP were studied by dynamic mechanical analyzer (DMA). Mechanical analysis (Tensile properties) of the compatibilized blends displayed improvements in Modulii and ultimate tensile strength (UTS) of PP matrix with the incorporation of 2–10% of LCP incorporation. The development of fine fibrillar morphology in the compatibilized PP/LCP blends had large influence on the mechanical properties. Differential scanning calorimeter (DSC) studies indicated no remarkable changes in the crystalline melting temperature of the blends with respect to that of pure PP. However, an increase in the softening range of the blends over that of PP was observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009