Formation,stability, and properties of in-situ composites based on blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer

This paper describes the preparation and properties of in-situ composites based on polymers with no overlap in processing temperatures. The polymers used were Vectra A900, a thermotropic liquid crystalline copolyester (TLCP), and Arnitel em630, a thermoplastic elastomer. Blends were generated by feeding the two components from separate extruders into a Ross static mixer. Different morphologies were obtained by varying the number of mixing elements of the static mixer. Using 8 mixing elements led to a stratified morphology of Vectra layers in Arnitel, using 11 mixing elements resulted in the desired continuous fiber/matrix morphology whereas a pronounced skin-core morphology was obtained with 14 mixing elements. It is argued that in-situ composites can be generated by a distributive mixing process without the formation of an intermediate droplet/matrix morphology as occurs in common dispersive blending equipment. Tensile modulus and strength of all blends increased with extrudate draw ratio as a result of increased molecular orientation of the TLCP phase. The level of reinforcement, however, was lower than expected, probably due to the low temperature of drawing. Annealing and capillary instability experiments showed that above the melting point of the TLCP the fiber/matrix morphology rapidly breaks up into a droplet/matrix morphology. This process takes just a few seconds for fibers of thickness ∼ 1 μm. It is shown to be the probable cause of the skin-core morphology obtained in case of 14 mixing elements.     

Self‐reinforcing elastomer composites based on polyolefinic thermoplastic elastomer and thermotropic liquid crystalline polymer

In situ reinforcing elastomer composites based on Santoprene thermoplastic elastomer, a polymerized polyolefin compound of ethylene–propylene–diene monomer/polypropylene, and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a single‐screw extruder. The rheological behavior, morphology, mechanical, and thermal properties of the blends containing various LC3000 contents were investigated. All neat components and their blends exhibited shear thinning behavior. With increasing TLCP content, processability became easier because of the decrease in melt viscosity of the blends. Despite the viscosity ratio of dispersed phase to the matrix phase for the blend system is lower than 0.14, most of TLCP domains in the blends containing 5–10 wt % LC3000 appeared as droplets. At 20 wt % LC3000 or more, the domain size of TLCP became larger because of the coalescence of liquid TLCP threads that occurred during extrusion. The addition of LC3000 into the elastomer matrix enhanced the initial tensile modulus considerably whereas the extensibility of the blends remarkably decreased with addition of high TLCP level (>.20 wt %). The incorporation of LC3000 into Santoprene slightly improved the thermal resistance both in nitrogen and in air. Dynamic mechanical analysis results clearly showed an enhancement in dynamic moduli for the blends with 20–30 wt % LC3000. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix

This study investigates deformation of a thermotropic liquid crystalline polymer (TLCP) in different die geometries. Blends of aTLCP with a thermiplastic elastomer of EPDM were made in a twin-screw extruder. Morphological observation of the extruded blends demonstrates the complimentary effect of shear in the die exit on dispersed phase deformation and fibril formation. Shear strain can affect fibril formation for a relatively large dispersed phase in the region close to the die wall. However, the main role of shearing is in breaking up the larger particles and initial polydomain structure. A strong elongational deformation on the blended melt after the die exit is required, and fine microfibrils normally obnserved in in situ composites were not easily formed by shear deformation only in the die.     

Blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer. I: Mechanical properties and morphology

Blends of a thermotropic liquid crystalline polymer (LCP), Vectra A900, and a thermoplastic elastomer, Kraton G1650, were made on a single screw extruder. During extrusion, fibers of the LCP are formed under influence of shearing and elongating forces. The stiffness and tensile strength of the elastomer are greatly improved by the addition of the LCP. The modulus of elasticity of blends containing up to 20% LCP can be described well with the Halpin-Tsai equation. Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) measurements show that the polymers are immiscible, but the DMTA results show a shift of the glass transition temperature of the elastomeric block of the Kraton polymer. This shift may be attributed to a layer of elastomer adsorbed on the LCP particles.     

Studies on blends of a thermotropic liquid crystalline polymer and polybutylene terephthalate

Summary Structure-property relationships of blends of a thermotropic polyester-type main-chain LCP and polybutylene terephthalate (PBT) were investigated. LCP was melt blended with three different PBTs and the blends were processed by injection moulding or extrusion. Mechanical and thermal properties of the blends were determined and the blend structure was characterized by scanning electron microscopy (SEM). LCP acted as mechanical reinforcement for PBT and improved also its dimensional and thermal stability. The stiffness of PBT increased with increasing LCP content, but at the same time the blends became more brittle. In extrusion the orientation of LCP phases could be further enhanced by additional drawing, which led to significant improvements in strength and stiffness at LCP contents of 20–30 wt.-%.     

Stability of blends of thermotropic liquid crystalline polymers with thermoplastic polymers

Breakup of fibers of a thermotropic liquid crystalline polymer (TLCP) above the melting temperature in various ordinary polymers has been studied by capillary instability experiments on single TLCP fibers and by annealing experiments on extruded TLCP/thermoplast blends. The TLCP was an aromatic copolyester, Vectra A900, the matrix polymers were PP, PS, PC, PEL PES, and PEBT. Both types of experiments show that the fiber/matrix morphology is, in general, highly unstable in the molten state. The TLCP fibers break up into droplets by a combination of Rayleigh distortions, end-pinching and retraction, depending on the system and shape of the fiber. Fibers of a thickness of ～1 μm can break up in a few seconds. Breakup times of fibrous blends and individual fibers are in agreement provided size effects are accounted for. Rayleigh distortions develop exponentially in time up to relative distortions of 0.5 to 0.6. Breakup occurs within a range of wave numbers rather than at one distinct dominant wave number, which is shown to be the consequence of relatively large initial distortions. Apparent values for the interfacial tensions calculated with Tomotika's theory turned out to be of the correct order of magnitude, ranging from 7 mN/m for Vectra/PES to 24 mN/m for Vectra/PP and to yield correct values of the interfacial tensions of PP/PS, PP/PC, and PS/PC using Antonow's rule.     

Fibers from blends of PET and thermotropic liquid crystalline polymer

Blends of poly(ethylene terephthalate-Co-p-oxybenzoate), PET/PHB, with poly(ethylene terephthalate), PET, have been studied in the form of as-spun and drawn fibers. DSC melting and crystallization results show that the PET is compatible with LCP and the crystallization of PET decreases by the addition of LCP in the matrix. Upon heating above the crystal melting temperature of PET, the blend shows good dispersion of LCP in the PET matrix. Wide angle X-ray diffraction of drawn blended fibers show the possible formation of LCP oriented domains. The mechanical properties of drawn fiber up to 10 wt% LCP composition exhibit significant improvement in tensile modulus and tensile strength with values of 17.7 GPa and 1.0 GPa, respectively. Values of modulus are compared with prediction from composite theory, assuming the blend system as nematic domains of LCP. dispersed in PET matrix.     

Studies on compatibilization of blends of polypropylene and a thermotropic liquid crystalline polymer

Thermotropic liquid crystalline polymers, LCPs, are frequently blended with thermoplastics to achieve an in situ composite structure. Significant mechanical reinforcement is obtained for the matrix polymer in the direction of the LCP fibers, but the transversal properties are often inferior because of the incompatibility of the components. Blends of LCP with polypropylene, and with three related matrix polymers, and PP/LCP blends with added potential compatibilizers were prepared and studied for their mechanical properties and morphology. A notable improvement in impact strength was achieved when a small amount of ethylene-based terpolymer was added as compatibilizer. © 1993 John Wiley & Sons, Inc.     

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.     

Morphology and mechanical properties of thermoplastic composites containing a thermotropic liquid crystalline polymer

Blends of two thermotropic liquid crystalline polymers (TLCPs), with brittle and ductile matrix materials were both injection molded and spun into fibers, in order to investigate the mechanism of in-situ mechanical reinforcement. In the injection molded samples, the TLCP was only moderately elongated into fibrils, and the mechanical properties were below predictions of the rule of mixtures. Fibers spun out of the blends contained numerous fine fibrils with nearly infinite aspect ratio, and as expected, the modulus increased linearly with the TLCP volume fraction, obeying the Tsai-Halpin equation for transversely isotropic composites. Wide angle X-ray diffraction measurements, as well as determination of the fiber-moduli, revealed that during spinning not only a macroscopic elongation of the fibrils was achieved, but also a considerable molecular orientation within the TLCP domains.     

Phase behavior of thermotropic liquid crystalline/conducting polymer blends

Summary Liquid crystalline/conducting polymer blends have been prepared. The conductingpolymer [poly(2,5-dimethoxyphenylene vinylene)] retards the liquid crystallinity of the liquid crystalline polymer (hydroxypropyl cellulose), while the liquid crystalline polymer reduces the conductivity of the conducting polymer. However, blends with 17% conducting polymer were both liquid crystalline and conductive. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

Rheology of blends of a thermotropic liquid crystalline polymer with polyphenylene sulfide

Blends of thermotropic liquid crystalline polymer (LCP) and polyphenylene sulfide (PPS) were studied over the entire composition range using Rheometrics Stress Rheometer, capillary rheometer, and differential scanning calorimeter. There is no molecular scale mixing or chemical reaction between the components, as evidenced by melting and crystallization points in the PPS phase. From the strain scaling transients test at low‐rate, LCP and the blends require approximately 60 strain units to obtain steady stale shearing results. The large recoveries in the strain recovery test, magnitude 3 to 3.3 strain unit, are likely the results of texture present in LCPs. With increasing PPS content in LCP/PPS blends, the total recovery declines. Scaling of the transient strain rate remains, but the magnitude of the transients is reduced. At low‐rate, when the LCP is added to the PPS, the pure melts have similar visosity: 500 Pa · s for LCP and 600 Pa · s for PPS, but the viscosity of the blends goes through a maximum with concentration that is nearly three times the viscosity of the individual melts. At high‐rate, a significant depression of the viscosity is observed in the PPS‐rich compositions and this may be due to the fibrous structure of the LCP at high shear rates.     

Novel reinforced polymers based on blends of polystyrene and a thermotropic liquid crystalline polymer

A thermotropic liquid crystalline polymer (LCP), when added to polystyrene (PS), can function as both a processing aid and a reinforcing filler. Thermal, rheological, and mechanical properties of the pure components and blends containing up to 10 percent LCP are reported. The LCP used is immiscible with PS, and when an extensional component of flow is present during processing, the LCP forms an elongated fibrous phase oriented in the flow direction. This oriented phase lubricates the melt, substantially lowering the viscosity. When the processed blend is cooled, the dispersed fibrous LCP phase is preserved in the solidified material. The LCP microfibers behave like short reinforcing fibers to improve the mechanical properties of the blend; for example, at an LCP concentration of 4.5 percent, the modulus is increased about 40 percent vs. pure PS.     

Properties of films from polypropylene and thermotropic liquid crystalline polymer blends

In this paper the effect of the inclusion of two different thermotropic liquid crystalline polymers, namely Rodrun 3000 and Vectra A950, in a PP matrix is analyzed with particular attention to the gas transport and mechanical properties of the extruded blend films. The experiments, conducted on PP/Rodrun 3000 and PP/Vectra A950 films, have shown that the presence of TLCPs, also at low percentages, modify the properties of the thermoplastic matrix in a manner depending on the degree of compability and interfacial adhesion between the two components of the blends. Moreover, the effect of a maleic anhydride grafted PP (MAP), used as compatibilizing agent, on the properties and morphology of the PP/Rodrun 3000 system was examined. It was found that the addition of the MAP determines an increase in the barrier properties and in toughness of the films compared to those without MAP.     

Processing and properties of polyimide melt blends containing a thermotropic liquid crystalline polymer

Several polymer blend compositions of LaRC-TPI 1500 and New TPI 450 (Mitsui Toatsu) with Xydar SRT 900 LCP (Amoco Performance Products) were extrusion processed. In addition to binary blends containing one TPI with an LCP, ternary blends consisting of an alloy containing both TPIs as the matrix were also processed. By varying the ratio of the polyimides in the matrix, the blends' thermal behavior could be tailored. This paper addresses both processing issues and film properties of these blends. Rheological and thermal studies were conducted on both blends made in a torque rheometer and on biaxially oriented film produced with a counter-rotating annular die. These biaxial blend films were further characterized by measuring tensile and electrical properties. For 70/30 New TPI/Xydar equal biaxial films of 50 μm thickness, a modulus of 3.8 GPa and a stress at break of 100 MPa were measured. For near uniaxial blend films (±3°) a modulus of 14.5 GPa and a strength of 220 MPa in the machine direction (MD) were measured. The transverse direction (TD) properties were still higher than the neat New TPI. The electrical properties of these blends were outstanding. The dissipation factor was typically less than 0.01 for most blend compositions. Similarly, the dielectric constant was typically less than 3 up to temperatures as high as 300°C.     

Shape memory thermoplastic elastomer from maleated polyolefin elastomer and nylon 12 blends

Semicrystalline maleated polyolefin elastomer (mPOE) and nylon 12 were melt blended in an internal mixer at 200 °C with proportions of 90/10, 80/20, and 70/30 wt/wt, respectively. Molau test, melt viscosity measurement, differential scanning calorimetry, dynamic mechanical analysis and tensile testing were conducted to characterize the structure and properties of the blends. The results revealed that POE-graft-nylon 12 copolymer was formed during the mixing, and the blends show two melting transitions at 57–60 and 174–178 °C attributed to mPOE and nylon 12, respectively, which are dependent on the blend composition. The blends exhibit typical thermoplastic elastomeric behavior and their tensile modulus, strength and hardness increase with increasing nylon content. It was also observed that the blends form a physically crosslinked structure until the melting transition of nylon 12. The blends exhibit excellent thermally triggered shape memory effect, i.e., almost 100 % shape fixity rate and 100 % shape recovery rate, and the recovery occurs in a few seconds when the temporarily fixed shaped sample is heated just above the T _m of mPOE phase in the blends.     

Enhanced wear performance of nylon 6/organoclay nanocomposite by blending with a thermotropic liquid crystalline polymer

A new approach for improving the wear performances of nylon 6 (PA6)/clay nanocomposites was examined in this study. Two hybrid nanocomposites were prepared by melt blending a thermotropic liquid crystalline polymer (TLCP) and a well‐dispersed PA6/clay nanocomposite, but with and without the incorporation of maleic‐anhydride grafted polypropylene (MAPP) as compatibilizer. The addition of MAPP improved the compatibility between TLCP and matrix and thus enhanced the fibrillation of dispersed TLCP phase. Wear‐testing results revealed that the wear resistance of the compatibilized hybrid nanocomposite could be improved effectively, as indicated by the low values of specific wear rate and frictional coefficient, especially under high‐normal load (i.e., 80 N). Based on the characterization on the worn damage and the debris, it was suggested that abrasive wear was the main‐damage mechanism for all the materials under investigation, except for the compatibilized hybrid nanocomposite. For this system, the wear damage was caused by a combination of abrasive and adhesive wearing because of the formation of transfer film on the counter pin surface from the wear debris. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Compatibilization of nylon 6/liquid crystalline polymer blends with three types of compatibilizers

Polyblends of nylon 6 and liquid crystalline polymer (LCP) (Vectra A 950) are immiscible and highly incompatible, with resultant poor interfacial adhesion, large phase domains, and poor mechanical properties. In the present work, compatibilizing strategies are put forward for blends containing nylon and LCP. Effects of three types of compatibilizers, including ionomer Zn–sulfonated polystyrene (SPS), reactive copolymer styrene–maleic anhydride (SMA), functional grafted copolymers—polypropylene grafted glycidyl methacrylate (PP‐g‐GMA) and polypropylene grafted maleic anhydride (PP‐g‐MAH)—are studied in the aspects of morphology and dynamic mechanical behavior. The addition of compatibilizers decreases the domain size of the dispersed phase and results in improved interfacial adhesion between LCP and matrix. The compatibilization mechanism is discussed by way of diffuse reflectance Fourier transform spectroscopy (DRIFT), showing the reaction between compatibilizers and matrix nylon 6. Mechanical properties are improved by good interfacial adhesion. The contribution of SMA to mechanical properties is more obvious than that of Zn‐SPS and grafted PPs used. The blending procedure is correlated with the improvement of mechanical properties by the addition of compatibilizer. Two‐step blending is demonstrated as an optimum method to obtain composites with better mechanical properties as a result of a greater chance for LCP to contact the compatibilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1452–1461, 2003     

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%.