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.     

Rheological and physical properties of in situ composite based on liquid crystalline polymer and poly(ethylene 2,6‐naphthalate) blends

The in situ composites based on poly(ethylene 2,6‐naphthalate) (PEN) and liquid crystalline polymer (LCP) were investigated in terms of thermal, rheological, and mechanical properties, and morphology. Inclusion of LCP enhanced the crystallization rate and tensile modulus of the PEN matrix, although it decreased the tensile strength in the PEN‐rich phase. The orientation effect of this blend system was composition and spin draw ratio dependent, which was examined by Instron tensile test. Further, the addition of dibutyltindilaurate (DBTDL) as a reaction catalyst was found to increase the viscosity of the blends, enhance its adhesion between the dispersed LCP phases and matrix, and led to an increase of mechanical properties of two immiscible blends. Hence DBTDL is helpful in producing a reactive compatibilizer by reactive extrusion at the interface of this LCP reinforced polyester blend system. The optimum catalyst amount turned out to be about 500 ppm, when the reaction proceeded in the 75/25 PEN/LCP blend system. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2448–2456, 1999     

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.     

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%.     

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.     

Uniaxial orientation and tensile properties of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) blends

Amorphous films of poly(ethylene terephthalate)/poly(ethylene-2,6-naphthalate) (PET/PEN) blends with different blend ratios were uniaxially drawn by solid-state coextrusion and the structure development during solid state deformation was studied. As-prepared blends showed two T_gs. The lower T_g was ∼72 °C, independent of the blend ratio. In contrast, the higher T_g increased with increasing PEN content. Thus, the coextrusion was carried out around the higher T_g of the sample. At a given draw ratio of 5, which was close to the achievable maximum draw ratio, the tensile strength of the drawn samples from the initially amorphous state increased gradually with increasing PEN content. On the other hand, the tensile modulus was found to decrease initially, reaching a minimum at 40-60 wt% PEN, and then increased as the PEN content increased. The results indicate that we can get the drawn films with a moderate tensile modulus and a high tensile strength. The drawn samples from the blends containing 40-60 wt% of PEN showed a maximum elongation at break, and a maximum thermal shrinkage around 100 °C. Also, the degree of stress-induced crystallinity showed a broad minimum around the blend ratio of 50% of PEN. These morphological characteristics explained well the effects of blend ratio on the tensile modulus and strength of drawn PET/PEN blend films.     

Morphology and properties of poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through melt mixing. The morphology, rheology, crystallization behavior, mechanical properties, dynamic mechanical properties and thermal properties of the PVDF/SR blends were investigated. The blend with 9 wt % of SR showed spherical shape of disperse phase whereas the blend with 27 wt % of SR resulted in irregular shape of rubber phase. The rheology showed that the complex viscosity and storage modulus of the blends decreased with increasing the SR content. The mechanical properties of the blends were decreased with increasing the SR content but that were significantly improved after dynamical vulcanization. The crystallization temperature of PVDF phase in PVDF/SR blends was increased. The incorporation of SR improved the thermal stability of PVDF/SR blends, and the temperature at 10% mass loss of the blends increased to about 489°C compared with 478°C of the pure PVDF. The mass of residual char in experiment of the blends was lower than that obtained in theory. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39945.     

Mechanical,morphological, and thermal properties of poly(ethylene 2,6-naphthalate) and copolyester LCP blends

Binary blends of a liquid crystalline polymer (LCP) and poly(ethylene 2,6-naphthalate) (PEN) were melt blended and injection molded. The mechanical properties were studied as a function of LCP content. Both the ultimate tensile strength and Young's modulus are higher than the theoretical values predicted by the rule of mixtures and they display a synergistic behavior at 70 wt % LCP content. However, the tensile strength decreases with LCP content and Young's modulus remained unchanged at lower LCP contents (10 to 30 wt %). The poor mechanical property is attributed to the immiscibility between PEN and LCP and the fibrillation behavior of LCP as revealed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) results. However, LCP and PEN are found to be partially miscible at higher LCP content, ascertained by DSC and dynamic mechanical analysis (DMA). This is attributed to the transesterification reaction between PEN and PET moiety in the LCP molecules. SEM micrographs reveal a skin/core morphology in the tensile bars, that is, the LCP is better oriented in the skin than in the core region. At lower LCP content, the dispersed LCP phase is spherical in the core and ellipsoidal in the skin, with long axes oriented in the flow direction. DSC studies show that the crystallization rate is significantly enhanced by the presence of LCP up to 50 wt %, where the LCP acts as a nucleating agent for PEN crystallization. The melting temperature decreases with LCP content, probably as a result of imperfect crystals formed in the presence of LCP heterogeneous nucleating centers and the increasing miscibility between LCP and PEN. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 477–488, 2001     

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.     

Effect of composition and molecular structure on the LC phase of PHB-PEN-PET ternary blend

Poly(p-hydroxybenzoic acid) (PHB)–poly(ethylene terephthalate) (PET) 8/2 thermotropic liquid crystalline copolyester, poly(ethylene 2,6-naphthalate) (PEN), and PET were mechanically blended to pursue the liquid crystalline (LC) phase of ternary blends. The torque values of blends with increasing PHB content abruptly decreased above 40 wt % of PHB content because the melt viscosity of ternary blends dropped. Glass transition temperature and melting temperature of blends increased with increasing PHB content. The tensile strength and initial modulus of blends were low at 10 and 20 wt % PHB. However, the blends containing above 30 wt % PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 20 wt % PHB formed irregularly dispersed spherical domains, and the blends of 30–40 wt % PHB showed LCP ellipsoidal domains and fibrils. In the polarized optical photographs, the blends of 40 wt % PHB showed pseudo LC phases. The degree of transesterification and randomness of blends were increased with blending time. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1065–1073, 1998     

Crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were investigated by DSC as functions of crystallization temperature, blend composition, and PET and PEN source. Isothermal crystallization kinetics were evaluated in terms of the Avrami equation. The Avrami exponent (n) is different for PET, PEN, and the blends, indicating different crystallization mechanisms occurring in blends than those in pure PET and PEN. Activation energies of crystallization were calculated from the rate constants, using an Arrhenius‐type expression. Regime theory was used to elucidate the crystallization course of PET/PEN blends as well as that of unblended PET and PEN. The transition from regime II to regime III was clearly observed for each blend sample as the crystallization temperature was decreased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 23–37, 2001     

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     

On the interrelationship of transreaction with viscoelastic properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends in the presence of nanoclay

An attempt was made to explore the effects of the interchange reactions on the viscoelastic behavior of binary blends based on poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) and their nanocomposites. It was seen that with an increase in the number of extrusion runs and mixing temperature, the extent of reaction (X) and degree of randomness (RD) both increased, whereas the average sequence block lengths values were decreased. On the contrary, the blend composition did not play a significant role on X and RD values. Addition of nanoclay inhibited the transreactions in PET/PEN blends. The absence of crystallization peaks implied that the crystalline structure was destroyed as a result of blending and an amorphous system was created possibly due to the transreactions simultaneously with the formation of random copolymers inhibiting the crystallization process. The rheological investigations showed that the addition of PEN into the PEN/PET blends enhanced the storage modulus, loss modulus, and complex viscosity. The viscosity upswing observed at low‐frequency region in the case of nanocomposite systems evidently confirmed the occurrence of transreactions. Nonetheless, a significant increment in the viscoelastic properties was perceived in the presence of nanoclay corroborating the proper nanoclay distribution throughout the PET/PEN blend system. POLYM. ENG. SCI., 53:2556–2567, 2013. © 2013 Society of Plastics Engineers     

Dynamic rheological behavior and mechanical properties of PVC/ACS blends

In order to increase the processability and mechanical properties of poly(vinyl chloride) (PVC), the terpolymer of acrylonitrile-chlorinated polyethylene-styrene (ACS) is used to modify the PVC. The plasticizing, rheological, and dynamic mechanical properties of PVC/ACS blends are investigated by means of torque rheometer, oscillation rheometer, and dynamic mechanical analyzer. The measurements of torque rheometer showed that both plasticizing time and stabilization torque are decreased with increasing ACS content. The PVC/ACS melts displayed larger dynamic storage modulus (G′), loss modulus (G′′), and complex viscosity (η*) than that of pure PVC, and these values reached maximum for the blend with 10 wt% ACS. When ACS content was below 10 wt%, PVC and ACS showed good compatibility in the blends by displaying a single T _g; however, when ACS content was more than 15 wt%, the phase separation phenomena occurred in the blends. PVC/ACS blends showed larger storage modulus (E′) and loss modulus (E′′) than that of pure PVC, but these values decreased with increasing ACS content. ACS can enhance both tensile and impact strength of PVC, and the impact strength reached maximum with 15 wt% ACS content which is higher 2.5 kJ/m² than the pure PVC. These results suggested that ACS is an efficient processing aid and toughening modifier for PVC at appropriate content.     

Compatibility of poly(ethylene 2,6-naphthalate) and poly(butylene 2,6-naphthalate) blends

Blends prepared from poly(ethylene 2,6-naphthalate) (PEN) and poly(butylene 2,6-naphthalate) (PBN) show only partial miscibility judged from their glass transition temperatures. Two distinct mechanical behaviors are observed: brittle for the blends < 20 wt% of PBN, while ductile > 20 wt% of PBN. The experimental modulus and strength values of the blends are within the predicted values according to Kleiner and Paul models, respectively. This means that PEN/PBN blends are somewhat compatible based on their tensile properties. Especially for 20 wt% of PBN blend, the high modulus and strength are observed. The viscosity of the blend is high, which may imply a somewhat entangled morphology in the amorphous state.     

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.     

Crystallization, hydrolytic degradation, and mechanical properties of poly (trimethylene terephthalate)/poly(lactic acid) blends

Crystallization, melting, hydrolytic degradation, and mechanical properties of poly(trimentylene terephthalate)/poly(lactic acid) (PTT/PLA) blends have been investigated. The blends show a single and composition-dependent glass-transition temperature (T _g) over the entire composition range, implying that these blends are fully miscible in the amorphous state. The observed T _g is found to increase with increasing PLA content and fitted well with the Gordon–Taylor equation, with the fitting parameter k being 0.91. The cold-crystallization peak temperature increases, while the melt-crystallization peak decreases with increasing the PLA content. Both the pure PTT and PTT/PLA blends cannot accomplish the crystallization during the cooling procedure and the recrystallization occurs again on the second heating. Therefore, on the thermogram recorded, there is exothermal peak followed by endothermal peak with a shoulder. However, to pure PLA, no crystallization takes place during cooling from the melt, therefore, no melting endothermic peak is found on the second heating curve. WAXD analysis indicates PLA and PTT components do not co-crystallize and the crystalline phase of the blends is that of their enriched pure component. With increasing PLA content, the hydrolytic degradation of the blend films increases, while both the tensile strength and the elongation at break of the blend films decrease. That is to say, the hydrolytic degradation of the PTT/PLA blends increases with the introduction of PLA at the cost of the decrease of the flexibility of PTT.     

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.     

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     

Injection molding of PC/PBT/LCP ternary in situ composite

A liquid crystalline polymer (LCP), Vectra B950, reinforced polycarbonate (PC) 60 wt%/polybutylene terephthalate (PBT) 40 wt% blend was studied using the injection molding process. Morphology and mechanical properties of ternary in situ LCP composites were investigated and compared with binary polycarbonate/Vectra B950 LCP composites. Good in situ fibrillation of LCP was observed in the direct injection-molded LCP composites. Preliminary results of this work indicate that addition of PBT improves skin-core distribution of LCP microfibrils in the matrix and also enhances adhesion between the matrix and Vectra B950, which contains terephthalic acid. The PC/PBT/LCP ternary system also exhibits lower viscosity than the PC/PBT blend and pure LCP. In a ternary system with 30 wt% of Vectra B950, tensile modulus and strength increase approximately threefold and twofold, respectively. The rule of mixtures (ROM) for continuous reinforcement can accurately represent the strengthening effects for the ternary LCP in situ composites. Generally, LCP reduces the ductility and impact strength of the thermoplastic blends; however, the relative loss is less in the ternary system than in the binary system.