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.     

Reactive extrusion of in-situ composite based on PET and LCP blends

The “in-situ” compatibilization for a PET/LCP blend via transesterification reactions in a twin-screw extruder having a very short residence time is investigated through thermal, rheological, and mechanical studies. Inclusion of a small amount of liquid crystalline polymer (LCP) enhanced the crystallization rate of the poly(ethylene terephthalate) (PET) matrix. It acted as a nucleating agent. LCP lowered the blend viscosity above T_cn (crystalline-nematic transition temperature), working as a processing aid. However, the addition of dibutyltindilaurate (DBTDL) as a reaction catalyst was found to increase the viscosity of the blends, diminish the size of the dispersed phase, enhance its adhesion with the matrix, and lead to an increase of mechanical properties of two immiscible phases. Hence DBTDL is helpful in producing a reactive compatibilizer by reactive extrusion at the interface of this polyester blend system. The optimum catalyst amount turned out to be about 500 ppm when the reaction proceeds in 90/10 PET/LCP polyester blend systems. Its effect on the mechanical properties is discussed in detail. The structural change of reactive blend was identified by H¹ NMR and wide angle X-ray diffraction patterns.     

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     

Determination of the phase diagram of HBA‐HNA liquid crystalline polymer/polycarbonate blends

The phase diagram of blends of liquid crystalline polymer (LCP) and polycarbonate (PC) was constructed. The effect of temperature on morphological development in melt‐blended samples was examined with a polarized light microscope, in conjunction with a heating stage. Phase separation in the blend was observed as the temperature was increased. For a particular LCP/PC blend composition, two‐phase separation temperatures (T_sp1 and T_sp2) were determined. Consequently, the corresponding phase diagram relating to phase separation was constructed. It was divided into three regions. No phase separation occurred when the blend was below T_sp1. However, a slight phase separation was detected when the temperature was between T_sp1 and T_sp2. Moreover, pronounced phase separation was observed when the blend was at a temperature above T_sp2. The phase‐separated structure varied according to the initial composition of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Solid state NMR analysis of poly(L‐lactide) random copolymer with poly(ε‐caprolactone) and its reactive extrusion process

A random copolymer based on poly(L ‐lactide) (PLA) with poly(ε‐caprolactone) (PCL) was prepared and characterized by mechanical testing and solid state NMR, compared with a polymer blend. For a monofilament sample consisting of PLA/PCL random copolymer, there were negative correlations between the CL content and the mechanical properties: tensile strength, tensile elastic modulus, flexural rigidity, and flexural hysteresis decreased with increasing CL content. In contrast, the mechanical properties of the polymer blend were only slightly changed by addition of the CL unit. For the random copolymer, the addition of a small amount of CL reduced relaxation times, T₁C and T_1ρH, gradually. The T₁C and T_1ρH values correlated closely with the tensile elastic modulus and the tensile strength, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

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.     

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.     

Poly(para‐dioxanone)/poly(D,L‐lactide) blends compatibilized with poly(D,L‐lactide‐co‐para‐dioxanone)

The effect of poly(D ,L ‐lactide‐co‐para‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the T_g was composition dependent; when 5% PLADO was added into blend, the T_g distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Poly(butylene terephthalate)/poly(ethylene glycol) blends with compatibilizers

Polymer blend systems offer a versatile approach for tailoring the properties of polymer materials for specific applications. In this study, we investigated the compatibility of polybutylene terephthalate (PBT) and poly(ethylene glycol) (PEG) blends processed using a twin-screw extruder, with the aim of enhancing their compatibility. Phthalic anhydride (PAn) and phthalic acid (PAc) were used as potential compatibilizers at different concentrations to improve interfacial interactions between PBT and PEG. Blend morphologies were characterized using scanning electron microscopy, which revealed improved interfacial compatibility and reduced phase separation with the incorporation of small amounts of PAn and PAc. Differential scanning calorimetry analysis indicated changes in the melting temperature (T_m) and glass transition temperature (T_g) of the blends owing to the compatibilizing effects of PAn and PAc. Dynamic mechanical analysis further corroborated the influence of the compatibilizers on the T_g and viscoelastic behavior. Thermogravimetric analysis demonstrated enhanced thermal stability with the addition of either PAn or PAc. Rheological measurements indicated an increase in complex viscosity with increasing compatibilizer content, indicating improved compatibility. The degradation point (T_d) of PBT/PEG blend increased from 158 to 200 and 319°C with the incorporation of 5 phr PAn and 2 phr PAc, respectively. Mechanical properties, including tensile strength, Young's modulus, and Izod impact strength, were evaluated. For instance, the tensile strength of PBT/PEG blend was enhanced from 43.5 to 48.7 and 49.7 MPa by incorporating 5 phr PAn and 2 phr PAc, respectively. However, the impact strength of PBT/PEG blend increased from 3.0 to 4.3 and 4.2 kJ/m² with the addition of 1 phr PAn and 1 phr PAc, respectively. The findings demonstrated that adding 5 phr PAn or 2 phr PAc to the PBT/PEG blends was advantageous, achieving a harmony of performance benefits and compromises. Rheological observations contributed significantly to the mechanical and thermal properties. Overall, the study highlights the significance of utilizing PAn and PAc as effective compatibilizers for enhancing the properties of PBT/PEG blends, making them potential candidates for various applications.     

Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in-situ composite

Fibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the fibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal-nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp diffraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in-situ composite have increased by 7.3 times and 1.4 times, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.     

液晶聚合物增强PC／PET共混物挤出片材的性能研究

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

Manufacturing and characterisation of microfibrillar reinforced composites from liquid crystalline polymers and poly(phenylene ether)

Abstract

The purpose of the present study was to investigate the fibrillisation process of liquid crystalline polymers (LCPs) in an amorphous poly(phenylene ether) (PPE) matrix during melt blending and a subsequent drawing operation, as well as to analyse the relationship between morphology and mechanical properties of the fibrillar reinforced LCP/PPE blends. In order to understand the effect of the compatibility between the blend partners, an additional set of LCP/PEE blends, containing different amounts of a compatibiliser, was studied too. The processing steps included: (i) melt extrusion and continuous hot stretching for fibrillisation of the LCP component in the different LCP/PPE blends, and (ii) compression (CM) or injection moulding (IM) of the drawn blends at temperatures below the melting temperature (T_m) of the LCPs. Samples from each processing stage were characterised by means of scanning electron microscopy (SEM), wide and small angle X-ray scattering (WAXS and SAXS), and mechanical testing. SEM and WAXS showed that the as extruded blends were isotropic, but after hot stretching the LCP components became highly oriented, with a high aspect ratio and a diameter of the fibrils between 0·4 and 3 μm. The fibrillated structure of the LCPs in the blends could be preserved after the compression and injection moulding only at temperatures below T_m of the LCPs. Addition of a compatibiliser to the LCP/PPE blend did not remarkably improve the adhesion between the components, as a result of the large difference between the coefficients of thermal expansion of the blend partners, which leads to different shrinkage conditions of the LCP fibrils and the PPE matrix. The flexural modulus (E) of all IM blends increased stepwise with an increase in the weight (wt) fraction of the LCP. At the same time, the highest values for the flexural strength (σ) were obtained for the LCP/PPE blends containing 5 wt-% LCP.     

Improvement of the processability of poly(ether ketone ketone) by the addition of a thermotropic liquid crystalline polymer

The addition of a thermotropic liquid crystalline, wholly aromatic copolyester, TLCP, improved the melt processability of poly(ether ketone ketone), PEKK. The tensile strength and modulus of the blends also improved with increasing TLCP, but the elongation at break decreased significantly. The blends were phase‐separated, but the polymers were partially miscible as evident from shifts of the glass transition temperature (T_g) of each component towards that of the other component in the blend. Similarly, the melting points (T_m) of both components were depressed by blending. When the crystallization temperature was above T_m of the TLCP, the PEKK crystallization rate in the blend was slower than for the pure material, while crystallization was faster when the temperature was below T_m of the TLCP. Polym. Eng. Sci. 44:541–547, 2004. © 2004 Society of Plastics Engineers.     

Influences of ethylene–butylacrylate–glycidyl methacrylate on morphology and mechanical properties of poly(butylene terephthalate)/polyolefin elastomer blends

Elastomer ethylene–butylacrylate–glycidyl methacrylate (PTW) containing epoxy groups were chosen as toughening modifier for poly(butylene terephthalate) (PBT)/polyolefin elastomer (POE) blend. The morphology, thermal, and mechanical properties of the PBT/POE/PTW blend were studied. The infrared spectra of the blends proved that small parts of epoxy groups of PTW reacted with carboxylic acid or hydroxyl groups in PBT during melt blending, resulting in a grafted structure which tended to increase the viscosity and interfere with the crystallization process of the blend. The morphology observed by scanning electron microscopy revealed the dispersed POE particles were well distributed and the interaction between POE and PBT increased in the PBT/POE/PTW blends. Mechanical properties showed the addition of PTW could lead to a remarkable increase about 10‐times in impact strength with a small reduction in tensile strength of PBT/POE blends. Differential scanning calorimetry results showed with increasing PTW, the crystallization temperature (T_c) and crystallinity (X_c) decreased while the melting point (T_m) slightly increased. Dynamic mechanical thermal analysis spectra indicated that the presence of PTW could improve the compatibility of PBT/POE blends. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40660.     

Influence of carbon nanotubes with different functional groups on the morphology and properties of PPO/PA6 blends

Carbon nanotubes with different functional groups were prepared and then incorporated into the poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6) blend via melt blending. The influence of different carbon nanotubes on the morphology and properties of the blend was studied. The results show that addition of pristine CNTs, CNTs‐OH, CNTs‐NH₂ leads to the evolution of the phase structure of PPO/PA6 (mass ratio: 60/40) blend from sea‐island to cocontinuous, whereas incorporation of CNTs‐COOH does not change the blend morphology due to serious aggregation of the carbon nanotubes. Incorporating different CNTs into PPO/PA6 blend increases the tensile modulus and storage modulus of the blends, whereas decreases slightly the tensile strength. At the same time, the glass transition temperatures (T_g) of PA6 and PPO are enhanced. ΔT_g, the gap between the T_g of PA6 and PPO, decreases with the addition of carbon nanotubes due to the stronger interaction of carbon nanotubes with PA6 than PPO. A similar tendency was found in the storage modulus (G′) and complex viscosity (η*) of the composites. The dispersion state of different carbon nanotubes and their interaction with polymer components are different, which causes the different confinement effect to the macromolecular chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The phase behavior,mechanical, and rheological characteristics of blends containing nitrile polymers and poly(ethylene-co-maleic anhydride)

The phase behavior of binary blends of acrylonitrile/methyl acrylate/butadiene terpolymer (B210) and poly(ethylene-co-maleic anhydride) (PEMA) was examined based on thermal analysis and optical microscopy. Miscibility of these polymer blends was recognized over a wide range of compositions. The appearance of phase separation during subsequent heatings above the glass transition temperature (T_g) of these blends was associated with a lower critical solution temperature (LCST) behavior. Rheological characteristics such as shear storage modulus (G′), loss modulus (G″) and complex viscosity have been shown to depend on the amount of PEMA in the blend. Mechanical properties including the tensile strength and flexural modulus also were found to be related to the composition of the blend. © 1993 John Wiley & Sons, Inc.     

Curing of a tetrafluoroethylene–propylene elastomer with high-vinyl polybutadiene rubber and peroxide

A cocuring agent is necessary for tetrafluoroethylene–propylene elastomer (FEPM), which cannot be cured by peroxide alone. We observed that high-vinyl polybutadiene rubber (HVBR) could be used as a cocuring agent for FEPM. The structure and properties of FEPM–HVBR blend vulcanizates were investigated by ¹³C-NMR, differential scanning calorimetry, swelling tests, tensile tests, dynamic mechanical analysis, and thermogravimetric analysis. This research showed that HVBR significantly improved FEPM by conferring a high crosslink degree to the FEPM–HVBR blends. When the HVBR concentration was 25% without any filler reinforcement, the tensile strength of the FEPM–HVBR blend vulcanizate reached 11.6 MPa, and the crosslinking density reached 171 μmol/cm³. In addition, HVBR improved the thermal stability of FEPM and changed the glass-transition temperature (T _g) of the blend; as the HVBR content increased, the T _g of the blend also increased. ¹³C-NMR analysis confirmed that crosslinks existed between the HVBR and FEPM macromolecules. When the blends contained trace amounts of HVBR, free-radical reaction was more preferred between FEPM and HVBR, whereas when HVBR was 15% or more, crosslinking between HVBR was predominant. These findings expand the choices for the curing of FEPM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47836.     

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     

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

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