The Effect of Compatibilization of Maleated Polypropylene on a Blend of Polyamide-6 and Liquid Crystalline Copolyester

Blends of polyamide-6 (PA6) and thermotropic liquid crystalline polymer (LCP) compatibilized with various maleic-anhydride-grafted polypropylene (MAP) contents were injection-moulded. The effect of compatibilization on the mechanical properties of the blends was investigated by means of tensile testing, drop weight Charpy impact measurement and dynamic mechanical analysis. The static tensile measurement showed that the strain-at-break depends strongly on the MAP content. The impact test also indicated that the critical strain energy release rate (G_IC) is dependent on the MAP concentration. These results revealed that the 80%PA6/MAP(86/14)–20%LCP blend exhibits the highest strain-at-break and G_IC values. Moreover, the tensile ductility and impact toughness tended to decrease dramatically with increasing MAP content. This was attributed to the chemical and thermal decomposition of PA6 during blending for the LCP/PA6 blends containing higher MAP concentration. © of SCI.     

Fracture toughness and morphology of phenolphthalein poly(ether sulfone)–thermotropic liquid crystalline polymer blends

Blends of a new phenolphthalein poly(ether sulfone) (PES-C) and a thermotropic liquid crystalline polymer (LCP) were prepared by melt-blending in a twin-screw extruder. Rheological properties, fracture toughness, K_IC, and morphology of the blends were studied. It was found that the addition of LCP could reduce the melting viscosity and improve the fracture toughness of the PES-C matrix. The morphology of the LCP phase for the fractured section changed with increasing LCP content in the blend from dropletlike to fibrillar and layered structure. Strong interfacial adhesion could be observed at a lower content of LCP. The toughening mechanisms by blending LCP were also discussed. © 1994 John Wiley & Sons, Inc.     

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.     

Thermal and mechanical properties of PPO filled epoxy resins compatibilized by triallylisocyanurate

A series of blends has been prepared by adding a poly(phenylene oxide) (PPO), in varying proportions, to an epoxy resin cured with dicyandiamide. All the materials show two‐phase morphology when characterized by SEM and DMA. SEM and DMA indicate that partial mixing exists in all the blends especially with high PPO content. This implies that the epoxy oligomer or low crosslinking density epoxy exists in the PPO phase after curing. The tensile strength and modulus of these blends are nearly independent of the PPO content, while the fracture toughness (G_IC) is improved by PPO. However, the two‐phase particulate morphology is not uniform. In order to improve the uniformity and miscibility, triallylisocyanurate (TAIC) has been used as an in situ compatibilizer for the polymer blends of epoxy and PPO. SEM and DMA reveal improvement of miscibility and solvent resistance for this system. The fracture toughness of these TAIC‐modified systems are also improved by adding TAIC (0–20 phr). © 2000 Society of Chemical Industry     

Blends of a bottle grade polyethylene terephthalate copolymer and a liquid crystalline polymer. Part I: Injection molding morphology and rheological properties

Blends of a bottle grade polyethylene terephthalate copolymer (PET) with a liquid crystalline polymer (LCP) were prepared by injection molding. The thermal transitions, the morphology and the rheological properties of the pure components and of the blends were measured by dynamic mechanical analysis (DMTA), scanning electron microscopy (SEM) and capillary and parallel plates rheometry, respectively. The blends displayed only one T_g; the B60 and B80 compositions showed the highest LCP β‐transition, which has been correlated to good barrier properties. In all the blends a “skin‐core” type morphology was observed; the core region had two phases while the skin region showed only one fibrillar phase. The viscosity measurements gave an indication that the interface was strong, probably due to transterifications reactions that occurred during the tests. On creep recovery, the increasing addition of the LCP to the PET increased the blends elastic recovery. On stress growth, the highest stress overshoot was displayed by the pure LCP; this polymer actually presented two overshoots that were also observed in some of the blends at high shear rates.     

Rheological and physical properties of polyarylate/LCP blend systems

A polyarylate Unitika U-Polymer 100 (PAR) was melt blended with a thermotropic liquid crystalline polymer (LCP) Vectra A950, and the processingmorphology-properties relations were investigated. Inclusion of LCP slightly reduced T_g of PAR. The PAR/LCP blend with the LCP content higher than 50 wt% exhibited a noticeable yield stress, particularly in the vicinity of crystal-to-nematic transition temperature (T_cn). LCP lowered the blend viscosity above T_cn and seemed to play a role as processing aid. The tensile strength of the blends was increased with increasing spin draw ratio and level of LCP, and the spinning temperature influenced tensile strength. The relaxation behavior under dynamic shear and resultant blend morphology based on WAXD and SEM analyses are discussed as well.     

Compatibilizing effect of styrene–maleic anhydride copolymer on the properties of polyamide‐6/liquid crystalline copolyester composites

Liquid crystalline polymer–polyamide‐6 (LCP/PA6) composites containing 20 wt % LCP content were compatibilized by a random styrene–maleic anhydride copolymer (RSMA). The blending was performed via extrusion followed by injection molding. The LCP employed was a commercial copolyester, Vectra A950. The dynamic mechanical (DMA), rheological, thermal, and mechanical properties as well as the morphology of the composites were studied. The DMA and rheological results showed that RSMA is an effective compatibilizer for LCP/PA6 blends. The mechanical measurements showed that the stiffness, tensile strength, and toughness of the in situ composites are generally improved with increasing RSMA content. However, these mechanical properties deteriorated considerably when RSMA content was above 10 wt %. The drop‐weight dart impact test was also applied to analyze the toughening behavior of these composites. The results show that the maximum impact force (F_max) and crack‐initiation energy (E_init) tend to increase with increasing RSMA content. From these results, it appeared that RSMA prolongs the crack‐initiation time and increases the energies for crack initiation and impact fracture, thereby leading to toughening of LCP/PA6 in situ composites. Finally, the correlation between the mechanical properties and morphology of the blends is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1964–1974, 2000     

Post extrusion hot drawing of polycarbonate/liquid crystalline polymer blends

The post extrusion hot drawing of polycarbonate/liquid crystalline polymer (PC/LCP) blends, over the entire composition range, was studied. The extruded filament morphology and elastic modulus were followed as a function of blends composition, initial phase morphology, and draw ratio (DR). Hot drawing was found to cause further orientation to the already existing partially oriented LCP phase at the die exit, as reflected by the increased blends modulus. The additional orientation depends on the initial filaments structure, the blend composition, and the DR. Moreover, the orientability of the LCP phase is much higher, similar to that of neat LCP, for blends in which the LCP forms the continuous phase. In low LCP content blends, a critical DR was identified, beyond which the LCP fibrils undergo fragmentation and voids at the fibrils/matrix interface are formed, resulting in a decrease in the drawn filament modulus.     

Study on in situ reinforcing and toughening of a semiflexible thermotropic copolyesteramide in PBT/PA66 blends

Ternary in situ composites based on poly(butylene terephthalate) (PBT), polyamide 66 (PA66), and semixflexible liquid crystalline polymer (LCP) were systematically investigated. The LCP used was an ABA30/PET liquid crystalline copolyesteramide based on 30 mol % of p‐aminobenzoic acid (ABA) and 70 mol % of poly(ethylene terephthalate) (PET). The specimens for thermal and rheological measurements were prepared by batch mixing, while samples for mechanical tests were prepared by injection molding. The results showed that the melting temperatures of the PBT and PA66 phases tend to decrease with increasing LCP addition. They also shifted toward each other due to the compatibilization of the LCP. The torque measurements showed that the ternary blends exhibited an apparent maximum near 2.5–5 wt % LCP. Thereafter, the viscosity of the blends decreased dramatically at higher LCP concentrations. Furthermore, the torque curves versus the PA66 composition showed that the binary PBT/PA66 blends can be classified as negative deviation blends (NDBs). The PBT/PA66/LCP blends containing up to 15 wt % LCP were termed as positive deviation blends (PDBs), while the blends with the LCP ≥25 wt % exhibited an NDB behavior. Finally, the tensile tests showed that the stiffness and tensile strength of ternary in situ composites were generally improved with increasing LCP content. The impact strength of ternary composites initially increased by the LCP addition, then deteriorated when the LCP content was higher than 10 wt %. The correlation between the mechanical properties and morphology of the blends is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1975–1988, 2000     

Blends of phenolphthalein poly(ether ether ketone) and a thermotropic liquid crystalline copolyester

Blends of phenolphthalein poly(ether ether ketone) (PEK-C) and a thermotropic liquid crystalline copolyester (LCP), poly[(1-phenylethyl-p-phenylene terephthalate)-co-(1-cumyl-p-phenylene terephthalate)], was prepared via melt mixing. The studies of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) indicate that the PEK-C/LCP blends display two glass transition temperatures which correspond to those of PEK-C- and LCP-rich phases, respectively. The PEK-C/LCP blends were judged to be partially miscible. Scanning electron microscopy (SEM) was employed to examine the morphology of the blends, and it was observed that all the PEK-C/LCP blends displayed a phase-separated structure. The interface between the PEK-C- and LCP-rich phases is poor. The Young's modulus of the PEK-C/LCP blends was found to increase with LCP content due to the high modulus of the LCP. However, the tensile strength and the elongation at break of the blends greatly decreases with increase of LCP content, owing to the poor interfacial adhesion. From the thermogravity analysis (TGA), it was observed that all the blends exhibited a two-step weight loss mechanism, and the thermal degradation onset temperature of the blends was lowered with the addition of LCP content. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1923–1931, 1998     

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     

Crystallization kinetics of a PEEK/LCP blend

The crystallization kinetics of a polyetheretherketone (PEEK)/liquid crystalline polymer (LCP) blend was studied by using differential scanning calorimetry. Nonisothermal runnings were performed on heating and on cooling at different rates. Isothermal crystallization experiments at 315, 312, 310, and 307°C, from the melt state (380°C) were performed in order to calculate the Avrami parameters n and k and the fold surface free energy, σ_e. Polarized light optical micrographs were also obtained to confirm the Avrami predictions. It was observed that the LCP retarded the PEEK crystallization process and that the PEEK melting temperature decreased with the amount of LCP, but the LCP melting temperature increased with the amount of PEEK. Probably the PEEK improves the perfection of the LCP crystalline domains. A spherulitic morphology in pure PEEK and its blends was predicted by the Avrami analysis; however this morphology was only observed for pure PEEK and for the 80/20 composition. The other compositions presented a droplet and fibrillar-like morphology. The overall crystallization rate was observed to decrease with the crystallization temperature for all compositions. Finally, σ_e was found to decrease with the increase of LCP in the blends, having unrealistic negative values. Thus, calculations were made assuming σ_e constant at all compositions. It was observed that δ, the interfacial lateral free energy, decreased but still remained positive. It was concluded that in these blends neither σ_e nor σ could be considered constant. © 1995 John Wiley & Sons, Inc.     

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     

Mechanical,dynamic mechanical properties and thermal stability of fluorocarbon elastomer–liquid crystalline polymer blends

Blends of fluorocarbon elastomer (FKM) and liquid crystalline polymer (LCP) have been prepared by the melt mixing technique. Processing studies indicated the increase in viscosity with the addition of LCP. The tensile strength, tear strength, and modulus of the elastomer are greatly improved by the addition of the LCP. Dynamic mechanical analysis (DMA) results showed that the shift in the glass transition temperature (T_g) of the elastomer with the addition of LCP and the storage modulus of the blends increased above the T_g of FKM, whereas decreases below the T_g of the elastomer were seen with up to 20 wt% LCP; this suggests that the LCP acts as an effective reinforcing agent above the T_g of FKM. From the thermogravimetric analysis (TGA) and differential thermogravimetry (DTG), we found that the thermal stability of the elastomer enhances by blending with the LCP. The weight loss and the weight loss rate of the FKM decrease enormously with the addition of LCP. From the X‐ray diffraction (XRD) study, it has been observed that the LCP acts as a nucleating agent by increasing the crystallinity of the blend. The failure mechanism of the blends was studied using a scanning electron microscope (SEM). It suggested that the failure occurred in the blends; mainly due to the pull out of the fibrils from the matrix phase and due to lower interfacial adhesion between the LCP phase and the elastomer. POLYM. COMPOS. 26:306–315, 2005. © 2005 Society of Plastics Engineers     

Polymer blends of polyethersulfone with all aromatic liquid crystalline co-polyester

Polymer blends of polyethersulfone (PES) with an all aromatic liquid crystalline co-polyester (LCP) were investigated. In addition, PES oligomers with the reactive functions end groups (?ONa) were added as a third component to the above blends in order to improve their properties. Flexural properties, such as modulus and strength, and dynamic viscoelastic properties, such as dynamic storage elasticity (E′) and loss tangent (tan δ), of the blends were measured. The morphology of blends was characterized using a differential scanning calorimeter (DSC) and a scanning electron microscope (SEM). Of the flexural properties, the modulus of PES increased almost linearly with increasing LCP content. However, strength decreased as LCP content increased to 20 wt%. In contrast, the addition of the PES oligomers had little effect on modulus, but strength was clearly improved. Regarding dynamic viscoelastic properties, the oligomer-containing blends exhibited complex behavior. Regarding morphologies, SEM analysis revealed that the LCP was not fibrous in the core of the blend containing 40 wt% or less, but the addition of the PES oligomers made LCP fibrous even in blends with low LCP content. It was concluded that the PES oligomers with reactive functional groups acted as a compatibilizer in polymer blends of PES/LCP.     

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.     

Rheology and physical properties of ternary blends containing a thermotropic liquid crystalline copolyester

Ternary blends of polyarylate (PAR) U-Polymer 100, thermotropic liquid crystalline copolyester (LCP) Vectra A950, and a block copolyesterether Hytrel 7246 were investigated in terms of rheological properties, morphology, and mechanical properties. The PAR/Hytrel blend exhibited melting point depression and gave a unique single T_g over the entire range of blend compositions. Addition of Hytrel to the PAR/LCP blend decreased both dynamic viscosity and storage modulus over the normal processing temperature range. Further, it notably reduced the voids between the LCP domains and the matrix, and improved the mechanical properties. The optimum usage level of Hytrel proved to be 2 phr.     

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.     

Dynamic rheological properties of polyetherimide/polyetheretherketone/liquid crystalline polymer ternary blends

The dynamic rheological properties of poly(etherimide)/poly(etheretherketone)/liquid crystalline polymer (LCP) ternary blends were measured in order to correlate these properties with the morphology obtained after extrusion. The viscosity radio, η_d/η_m, where η_d = disperse phase viscosity and η_m = matrix viscosity, had to be redefined. Below 50 wt% LCP, η_d = η_LCP, η_m = η_PEEK+PEI and η_d/η_m < 1. Above 50 wt% LCP, η_d = η_PEEK+PEI, η_m = η_LCP and η_d/η_m > 1. Fibrillar morphologies were obtained in both cases, except below a concentration of 20 wt% LCP. At low concentrations of LCP the ternary blends had lower viscosities than the component polymers, showing a flow promotion effect of the LCP on the PEI- and PEEK-rich phases.     

Fiber reinforcement and fracture resistance of PC/PBT/LCP ternary in situ composite

The microstructures, mechanical properties, and fracture toughness of LCP (Vectra B950) reinforced PC/PBT blend with a 60/40 weight ratio have been studied. LCP of varying concentrations were investigated as rigid fillers in matrices of multiphase polymer blends. In this study, differences in microstructures and morphology between samples of two thicknesses (4 mm thick and 6 mm thick) and two geometries (dumbbell and rectangular) were compared using scanning electron microscopy (SEM). Given identical processing conditions, fibrous LCP structures were evident in the 4-mm-thick injection molded, dumbbell-shaped samples, whereas the 6-mm-thick rectangular samples displayed spherical dispersion of LCP aggregates that embrittled the preblended ductile matrix. Tensile properties of the dumbbell specimens showed superior strengthening and stiffening whereby the tensile strength increased twofold and the modulus increased fourfold. Plane strain fracture toughness was slightly enhanced as the LCP content increased because of the fiber strengthening effect but the overall fracture performance of the in situ composites was relatively poor compared with PC/PBT. Experimental results were compared with those predicted in composite theory. Simplified micromechanics equations were developed to describe the tensile moduli of injection molded LCP reinforced blends that exhibited a strong skin-core morphology.