Thermotropic Liquid Crystalline Polymer Content Research Articles

Study on the Isothermal Crystallization Behaviors of PEN/TLCP Blends

Abstract: The isothermal crystallization behaviors of blends of poly(ethylene naphthalate) (PEN) and a thermotropic liquidcrystalline polymer (TLCP) were investigated by differential scanning calorimetry (DSC) as functions of crystallization tem-perature and blend composition. Avrami analyses were applied to obtain information on the crystal growth geometry andthe factors controlling the rate of crystallization. The crystallization kinetics of the PEN/TLCP blends followed the Avramiequation up to a high degree of crystallization, regardless of crystallization temperature. The calculated Avrami exponentsfor PEN/TLCP revealed three-dimensional growth of the crystalline region in each blend. The crystallization rate of eachblend increased as the crystallization temperature decreased, and decreased as the TLCP content increased. The crystalli-zation of PEN in the blend was affected by the addition of TLCP, which acts as a nucleating agent.Keywords: Avrami equation, isothermal crystallization kinetics, nucleating agent, PEN/TLCP blend

Nucleation Effect of Thermotropic Liquid Crystalline Polymer on the Crystallization of Poly(ε-Caprolactone)

Poly(ε-caprolactone) (PCL) has attracted much attention in recent years due to its good biodegradability and biocompatibility. As a semicrystalline polymer, the final properties of PCL strongly depend on its bulk crystallization level. However, PCL shows a lower crystallization temperature and rate than other aliphatic polyesters, which restricts its range of applications. To improve the crystallization is hence a key problem to enhance the performance of PCL materials. In this work, a thermotropic liquid crystalline polymer (TLCP) was used as a nucleating agent to improve the crystallization of PCL. The PCL/TLCP blend with the maximum TLCP content of 10 wt.% was prepared by melt mixing. The nonisothermal crystallization behaviour of the PCL matrix was studied using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), and the crystallization kinetics was then further analysed by methods including the Avrami, Ozawa, Mo, Ziabicki, Lauritzen-Hoffman and Kissinger models. The results showed that the presence of the solid TLCP particles could enhance crystallization temperature of the PCL matrix evidently at very small content levels (1 wt.%). Although the mobility of the PCL chain segments decreased with increasing TLCP content, heterogeneous nucleation by TLCP particles always played a dominant role in the overall crystallization. Therefore the blends showed higher crystallization rates and ability than those of pure PCL. The kinetic analysis and the data obtained in this work could be useful to optimize the processing conditions and to improve the crystallization of PCL.

Viscoelastic properties of polyarylene ether nitriles/thermotropic liquid crystalline polymer blend

Polyarylene ether nitriles (PEN)/thermotropic liquid crystalline polymer (TLCP) blend was prepared via melt mixing. The immiscible phase morphologies, linear and nonlinear, as well as transient viscoelastic properties of the blend were studied using SEM, rheometer, and DMA. The linear dynamic viscoelastic behavior of the blend shows temperature dependence due to further evolution of the immiscible morphology and, as a result, the principle of time-temperature superposition (TTS) is invalid. In the steady shear flow, the discrete TLCP phase is difficult to be broken up because of the high viscosity ratio of the blend systems, while is easy to be coarsened and followed by elongation, and finally, to form fibrous morphology at high TLCP content and high shear level. During this morphological evolution process, the transient stress response presents step increase and nonzero residual relaxation behavior, leading to increase of the dynamic viscoelastic responses after steady preshear. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

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

AbstractIn 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

In Situ Reinforcing Elastomer Composite 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 (EPDM)/polypropylene (PP), 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 due to 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 (>20wt%). The results obtained from thermogravimetric analysis suggested that the incorporation of LC3000 into Santoprene slightly improved the thermal resistance both in nitrogen and in air.

Studies on the mechanical and dynamic mechanical properties of thermotropic liquid crystalline polymer/unsaturated polyester/glass fiber in situ hybrid composites

AbstractIn situ hybrid composites of thermotropic liquid‐crystalline polymer (TLCP), unsaturated polyester (UP) and glass fiber (GF) have been successfully prepared by melt mixing technology. The mechanical properties and dynamic mechanical properties and the morphologies of these in situ hybrid composites have been studied by static mechanics analysis, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The static mechanical test results showed that the impact strength and the bending strength, bending modulus, specific strength and specific modulus of the in situ hybrid composites tend to increase with the increase of TLCP content for the composites containing TLCP content below 5%. DMA results indicate that the microstructure of curing network, glass transition temperature and obdurability of composites with TLCP content below 5% have been improved. Scanning electron microscope observations revealed that the interfacial adhesion between matrix and fiber had been improved with the addition of TLCP. Copyright © 2006 John Wiley & Sons, Ltd.

Thermotropic liquid‐crystalline copolyester (Rodrun LC3000)/thermoplastic elastomer (SEBS) in situ composites: II. Mechanical properties and morphology of monofilaments in comparison with extruded strands

AbstractMonofilaments of in situ composites were prepared from an immiscible blend of a thermotropic liquid‐crystalline polymer (TLCP), Rodrun LC3000, and a thermoplastic elastomer, styrene–(ethylene butylene)–styrene (SEBS), by a melt spinning process. Mechanical properties and the morphology of the composite monofilaments were investigated and compared with those of the extruded strands previously reported. The stresses at all tensile strains of the composite monofilaments were much higher than those of the extruded strands. The tensile strengths of both extruded strands and monofilaments were comparable, but the elongation at break of monofilaments dropped considerably. The tension sets of composite monofilaments were slightly higher than those of extruded strands. All composite monofilaments with TLCP content of ≤15 wt % exhibited good elastic recovery under the applied strain up to 200%. The dynamic mechanical storage modulus at 25°C of 10 wt % TLCP composite monofilament increased fourfold compared with that of the composite extruded strand and fivefold compared with that of the neat SEBS monofilament. The dramatic enhancement in the mechanical properties of in situ composite monofilaments is due to the formation of finer and longer TLCP fibrils (length‐to‐width ratio > 100) than those formed in the extruded strands. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 518–524, 2003

Determination of orientation parameters in drawn films of thermotropic liquid crystalline polymer/polypropylene blends using WAXS

The effects of composition and compatibilizers on the molecular orientation in thermotropic liquid crystalline polymer (TLCP)/PP in situ composite films have been investigated using wide angle X-ray scattering (WAXS) techniques. The degree of preferred orientation for each component was evaluated using a novel separation technique based on a description of the scattering through spherical harmonic functions. The evaluated orientation parameters 〈P2〉 and 〈P4〉 of TLCP phase were found to increase up to 0.76 and 0.53, respectively, with increasing TLCP content and film draw ratio. In contrast, the PP component in all films exhibits a very low orientation (〈P2〉 ∼0.01) i.e. essentially isotropic. The PP component exhibits the so-called smectic phase which can be transformed to the more stable crystalline phase (α-form) by annealing at 110 °C for 2 h, with a small increase in the level of preferred orientation. The inclusion of particular polystyrene-based compatibilizers was observed to have a substantial effect on the modulus of the composite and in some cases this is reflected in the level of preferred orientation in the TLCP. We deduce that the orientation parameters are largely insensitive to the fibril morphology once a certain aspect ratio has been exceeded.

Thermotropic liquid crystalline polymer (Rodrun LC5000)/polypropylene in situ composite films: rheology, morphology, molecular orientation and tensile properties

In situ composite films were prepared by a two-step method. First, polypropylene and thermotropic liquid crystalline polymer (TLCP), Rodrun LC5000 (80 mol% p-hydroxy benzoic acid (HBA)/20 mol% polyethylene terephthalate (PET)), were melt blended in a twin-screw extruder and then fabricated by extrusion through a mini-extruder as cast film. Rheological behavior of the blends, morphology of the extruded strands and films, and tensile properties of the in situ composite films were investigated. Rheological behavior of the blends at 295 °C studied using a plate-and-plate rheometer revealed a substantial reduction of the complex viscosity with increasing TLCP content, and all specimens exhibited shear thinning behavior. Over the angular frequency range of 0.6–200 rad/s, the viscosity ratio (dispersed phase to matrix phase) was found to be very low, in the range of 0.03–0.07. Morphologies of the fracture surfaces of the blend extrudates and the film surfaces etched in permanganic solution were investigated by scanning electron microscope (SEM). The TLCP droplets in the extruded strands were seen with a progressive deformation into fibrillar structure when TLCP content was increased up to 30 wt%. In the extruded films, TLCP fibrils with increasing aspect ratio (length to width) were observed with increasing TLCP concentration. Orientation functions of each component were determined by X-ray diffraction using a novel separation technique. It was observed that the Young's modulus in machine direction of the extruded film was greatly improved with increasing TLCP loading, due to the increase in fiber aspect ratio and also molecular orientation.

Fabrication of continuous fiber-reinforced thermoplastic composites with structural gradient from sheath-core type bicomponent fibers

Sheath-core type bicomponent fibers of polypropylene (PP) as a sheath component and thermotropic liquid crystalline polymer (TLCP) as a core component were prepared by the highspeed melt spinning process. Continuous fiber reinforced thermoplastic composites, in which TLCP acts as a reinforcing fiber and PP as a matrix polymer, were fabricated by the compression molding of these fibers. In the melt spinning, the attainable highest take-up velocity of TLCP was improved by co-processing with PP. Tensile modulus and strength of the TLCP component in the PP/TLCP bicomponent fibers increased with an increase in the take-up velocity. Comparison of wide-angle X-ray diffraction patterns of starting bicomponent fibers and fabricated composites indicated that the orientation relaxation of TLCP did not occur in the compression molding process. Accordingly, the tensile modulus and strength of the PP/TLCP composites were similar to those of the bicomponent fibers. Continuous fiber reinforced thermoplastic composites with various types of fiber content distributions were fabricated from the bicomponent fibers in which sheath-core composition was changed gradually in the spinning process. In the three-point bending test, the composites with two different types of symmetric structural gradients, one with higher TLCP fiber content near the surfaces than in the center and the other with higher TLCP content in the center than near the surfaces, exhibited different flexural moduli even though the overall TLCP contents were comparable. In the three-point bending test of a composite with asymmetric structural gradient, the yielding behavior and maximum flexural load varied depending on the direction of load application although the initial flexural moduli were similar.

Morphology and properties of fibers based on polycarbonate/liquid crystalline polymer blends

AbstractPolycarbonate‐triad‐4–co‐polybutylene terephthalate liquid crystalline blends were prepared and spun into fibers. It has been shown that fibrillation of the thermotropic liquid crystalline polymer (TLCP) takes place at the given spinning conditions, forming thus “in situ” reinforcement. Continuous fibrils are formed at concentrations between 2.5 and 5% LCP. A degree of miscibility between two phases was observed. The moduli of both as‐spun and cold drawn fibers increase almost linearly with increasing concentration of TLCP. Tensile strength was found to decrease and elongation at break to increase with increasing TLCP content. The structure of the cold drawn fibers was not stable with time, causing a relaxation in the observed properties.

Characterization and processing of blends of poly(ether imide) with thermotropic liquid crystalline polymer

We investigated thermal, rheological, morphological and mechanical properties of an in situ composite of poly(ether imide) (PEI) and thermotropic liquid crystalline polymer (TLCP). Ultem 1000 was used as a matrix and Vectra B950 was used as the in situ reinforcing TLCP. Fibre-spinning of the blends was performed on a capillary rheometer. Differential scanning calorimetry thermograms of extruded fibres indicated that the thermal properties of PEI did not change noticeably with the amount of TLCP but thermogravimetric analysis showed that thermal stability of the blend was decreased with the amount of TLCP. Immiscibility was checked with thermal data. The rheological properties of the blends changed remarkably with temperature and composition. The tensile strength and modulus of blend fibre increased with TLCP content and spin draw ratio. The increase of tensile strength was more striking for the fibre of the blend containing more TLCP. Wide angle X-ray patterns suggested that the increase in tensile strength was due to the enhanced molecular orientation and resultant fibrillation of TLCP. A modified Tsai-Halpin equation was used to predict the aspect ratio of microfibrils for these blends. Morphology of the blend showed that PEI/TLCP fibres contained fine fibrils of almost infinite aspect ratio and nearly perfect orientation in the flow direction. The draw ratio effect on the mechanical properties was remarkable at low draw ratio, but levelled off soon. The amount of TLCP influenced the fibril formation. Morphological observation showed the effect of thermal history of the blend and its effect on mechanical performance. The blend showed maximum aspect ratio and aspect ratio change when TLCP content was 25 wt%. TLCP orientation and its steric effect seem to induce the optimum TLCP amount for fibril formation.

Rheology and Physical Properties of Polysulfone in-situ Reinforced with a Thermotropic Liquid-Crystalline Polyester

Blending Amoco polysulfone Udel P-1700 and Hoechst Celanese thermotropic liquid-crystalline polymer (TLCP) Vectra A-950 in a twin-screw extruder produced in-situ composites. An inclusion of TLCP did not notably change the thermal properties of polysulfone but the rheological properties were notably changed depending on the measured temperature and blend composition. In the vicinity of crystal-nematic transition temperature, an incorporation of TLCP into polysulfone increased the melt viscosity and gave rise to a large yield stress. Above the crystal-nematic transition temperature, however, TLCP dramatically decreased the melt viscosity and the resultant yield stress was very small. The tensile strength and modulus of as-spun polysulfone/TLCP fibers were increased as the TLCP content and spin draw ratio were increased. The increase in tensile strength with spin draw ratio was more noticed with the polysulfone/TLCP fiber containing higher TLCP content. Wide angle X-ray diffraction patterns suggested that the increase in tensile strength is ascribable to the enhanced molecular orientation and resultant fibrillation of TLCP. The compositional moduli of as-spun blend fibers were well fitted to the additivity rule of mixtures, viz., the Tsai-Halpin equation for the reinforcement of infinite aspect ratio.