Liquid Crystalline Polymer Content Research Articles

Tribological enhancement effect of main-chain thermotropic liquid crystalline polymer

Although main-chain thermotropic liquid crystalline polymer (LCP) has been extensively investigated as self-reinforcing composites, tribological application is rarely reported. This paper explores tribological enhancement effect of LCP on representative matrix poly (vinylidene fluoride) (PVDF). Moreover, structures of PVDF/LCP blends are assessed in detail. Due to immiscibility, LCP in blends is uniformly dispersed in the form of particles or microfibrils, dependent on LCP content. Besides, LCP improves storage modulus of PVDF. Most importantly, tribological performance of PVDF is obviously promoted. Compared with neat PVDF, the wear rate, coefficient of friction and oscillation amplitude of blend containing 20 wt% LCP simultaneously decrease by 97.7%, 80.7% and 80.2%, respectively. In particular, frequency-enhancement phenomenon is observed. By probing worn PVDF domains with nanoindentation test and atomic force microscopy (AFM), preliminary tribological enhancement mechanism of LCP is unveiled. Overall, this finding provides a new, but promising lubrication route of polymer.

Morphology, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer blends

The miscibility, crystallization and melting behaviour of poly(trimethylene terephthalate)/thermotropic liquid crystalline polymer (LCP) blends were studied using differential scanning calorimetry. The blends were found to form primarily an immiscible system. The addition of LCP accelerated the overall rate of crystallization and caused a depression in equilibrium melting temperature, especially at low LCP content. Lauritzen–Hoffman analysis showed that the addition of LCP caused a reduction in the fold surface energy and increased the regime II to III transition temperature.

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

AbstractThermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Strengthening of poly(butylene adipate‐co‐terephthalate) by melt blending with a liquid crystalline polymer

AbstractPoly(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

Crystallization Behaviors of Poly(ethylene 2,6-naphthalate) in the Presence of Liquid Crystalline Polymer

The crystallization behaviors and morphology of poly(ethylene 2,6-naphthalate) (PEN) in the presence of liquid crystalline polymer (LCP) Vectra RD501 have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), atomic force microscopy (AFM), and wide-angle X-ray diffraction (WAXD). It was found that the LCP in PEN/LCP blends accelerates the crystallization rate of PEN at both higher and low crystallization temperatures, which indicates that LCP acts as both nucleating agent and nucleation promoter for PEN crystallization. The crystallization of PEN was effectively improved with increasing LCP content up to 1 wt %, and then tended to level off with increasing LCP. The Avrami exponent n changed from 2.0-2.7 for pure PEN to <2 for PEN in the presence of LCP, which indicated that the nucleation mechanism of PEN crystallization was changed. The size of the PEN spherulitic crystals became smaller in the presence of LCP, but WAXD has shown that there is no change in the crystal modifications of PEN.

Molecular orientation of extruded PET/LCP blend films. II. X‐ray pole figures

AbstractThe crystalline uniaxial molecular orientation of two liquid crystalline polymers (LCPs), Vectra®A950, and Rodrun®LC5000, blended with poly(ethylene terephthalate) (PET) was obtained from wide angle X‐ray pole figures. The blends films were produced by extrusion using a twin screw extruder with a slit die. The molecular orientation was evaluated along the transverse section of the films and as a function of the blends composition. The influence of a compatibilizer agent on the LCPs orientation was also analyzed. It was found that the orientation of both LCPs in the pure LCP films was high, highest in the draw direction but variable along the transverse section of the extruded films; in this last case, it was higher at the position where the shear rate was maximum. However, a drastic orientation decrease in both LCP's phases was observed in the films made of PET/LCPs blends. The maximum orientation effects were observed for the blend with 5 wt % of LCP content and also at the position where the shear rate was the highest. The Vectra®A950 LCP, as a pure material and in the blend with PET, orient more effectively than the Rodrun®LC5000 LCP in the films produced at the same processing conditions. The results showed that the use of a compatibilizer agent decreased the LCP orientation and were in accordance with previous studies using polarized infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Effects of the addition of small amounts of a thermotropic liquid crystalline polymer on the processing characteristics of polyphenylene oxide–polyamide alloys

AbstractThe possibility of improving the processing characteristics of a high‐viscosity engineering polymer alloy (PPO‐PA6,6) was explored through the addition of small amounts of a thermotropic liquid crystalline polymer (LCP). The thermal and rheological characteristics were examined for LCP contents up to 5 wt%. Inclusion of even a small amount of LCP (1 wt%) has resulted in a substantial decrease in the melt viscosity (∼50%) and in the possible lowering of the processing temperature of the PPO–PA alloy. Numerical simulation and experimental tests for the injection molding of a fairly complex component have shown that cavity filling occurs more rapidly when small amounts of LCP are added to the blend. Together with morphological examinations, these results have confirmed that LCP is thoroughly dispersed in the blend and acts as a true viscosity depressant, rather than behaving as an external lubricant. The resulting improvements in processing characteristics were also evident from the increase in the onset degradation temperature and the reduction in thermal expansion coefficient of the blends. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:109–120, 2007; Published online in Wiley InterScience www.interscience.wiley.com). DOI 10.1002/adv.20089

Viscoelastic properties of in situ composite based on ethylene acrylic elastomer (AEM) and liquid crystalline polymer (LCP) blend

Viscoelastic properties of in situ ethylene acrylic elastomer composites containing 10 and 20 wt.% of liquid crystalline polymer (LCP) were measured in dynamic mechanical experiments. The results show the significant improvement in the storage modulus of the composites with increasing LCP content. All the composites exhibits a single relaxation, which is glass to rubber transition, observed as a peak in the loss modulus at 1 Hz. The time–temperature superposition principle was applied for the pure ethylene acrylic elastomer (AEM) and its composites, in order to evaluate the changes in the viscoelastic properties of AEM by the addition of LCP. Temperature dependence of the shift factors were described using both the Arrhenius and William–Landel–Ferry (WLF) model at the glass transition region. The activation energies of the shift factors are increases with increasing temperature due to complexicity in the motions of the polymer chains, which is further confirmed by the large activation entropies. The principle of time–temperature superposition is used to study changes in the relaxation spectra of in situ AEM system. It is suggested that the change in the viscoelastic behavior, in the case of LCP reinforced AEM, is due to altered molecular mobility of the polymer chain segments in the vicinity of the LCP phase.

Binary Blends of Polytetrafluoroethylene and Liquid Crystalline Polymer

Blends of polytetrafluoroethylene (PTFE) and liquid crystalline polymer (LCP) were prepared by varying the amount of LCP when using a melt mixing technique. The rheological, morphological, thermal, and dynamic mechanical properties of the blends were investigated. The viscosity of the blends was decreased with the increasing LCP content in the blends up to 20% of LCP. With further loadings of LCP a slight improvement in viscosity was observed. This decrease in the viscosity was attributed to be the interlayer slip of the polymers due to formation of the elongated fibrils of LCP, whereas at higher amounts of LCP the fibril nature of LCP was not apparent, which is revealed by the scanning electron microscopic study. The differential scanning calorimetry (DSC) results showed a shift in the melting temperature (Tm) of PTFE with the addition of LCP. This shift in the Tm of PTFE is due to increasing crystallinity. This is further supported by the X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) studies.

Molecular orientation of extruded PET/LCP blend films. Part I: Polarized infrared spectroscopy

AbstractThe polarized infrared (IR) spectroscopy technique was used to evaluate the surface uniaxial molecular orientation of films of poly(ethylene terephthalate) (PET), two thermotropic liquid crystalline polymers (LCPs), Vectra®A950 and Rodrun®LC5000, and their blends obtained by extrusion. The molecular orientation of the LCP and of the crystalline and amorphous PET phases in the draw direction was evaluated along the transverse section of the films and as a function of the blend composition. A compatibilizer agent was used to improve the interfacial adhesion between the PET and LCPs. The results showed that the surface molecular orientation of both LCPs was very high along the draw direction. However, when blended, the orientation of the LCP phase decreased drastically, it was dependent of its content and varied along the transverse section of the extruded films. The maximum orientation was observed in the blend with 5 wt % LCP content and at the position where the shear rate was maxima. The LCP Vectra®A950 showed higher orientation than the Rodrun®LC5000, as a pure material and as blended. For the PET phases, an alignment of the amorphous phase in the draw direction due to the presence of LCP and compatibilizer agent was observed. The crystalline phase of PET, however, showed no significant orientation in the draw direction. The compatibilizer agent proved efficient for both PET/LCP systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2241–2248, 2006

Phase Diagram for Predicting In Situ Fibrillation of LCP During Molding

ABSTRACT The present work represents an important attempt at constructing a phase diagram for predicting the type and extent of fibrillation of the liquid crystalline polymer (LCP) phase in LCP-based polymer blends. A polycarbonate (PC)/LCP polymer blend was utilized in the current study. The combined effects of three factors, namely, the shear rate, the LCP content in the blend, and interfacial adhesion between the LCP phase and the matrix polymer (PC) were considered. In contrast, work in reported literature has usually considered the individual effect of only one or at most two of these three factors. A thermotropic liquid crystalline polymer, LC5000, consisting of 80/20 of hydroxybenzoic acid and poly(terephthalate) was employed. The effect of interfacial adhesion between the LCP and the PC matrix on fibrillation was considered by using a compatibilizer for the PC/LCP blend. It was demonstrated that the constructed phase diagram could successfully be used to predict and illustrate the conditions under which in situ fibrillation of the LCP phase would occur in the LCP-based blend.

Ternary blends of acrylic rubber, poly(butylene terephthalate), and liquid crystalline polymer: Influence of interactions on thermal and dynamic mechanical properties

AbstractThe 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 (Tg) and melting temperature (Tm) 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

Effect of viscosity ratio of the components of thermoplastic and liquid-crystalline polymer blends on the properties

The effects of viscosity ratio on the rheological and mechanical properties of the blends of four thermoplastics of low viscosity and a liquid crystalline polymer (LCP) were studied. A polyamide of reduced crystallinity (amorphous PA), a polycarbonate (PC), a polyethylene-terephthalate (PET), and a cyclic polyolefin (COC) were investigated with the copolymer of 2-hydroxy-6-naphthoic acid (HNA) and 4-hydroxybenzoic acid (HBA) (Vectra A type LCP). The LCP content changed in the range of 0–50 w/w%. The mechanical properties were determined by tensile tests on injection molded test bars in parallel and perpendicular directions to the flow. Except for the PC/LCP blends, the viscosity decreased with increasing LCP content, the tensile strength increased significantly in the parallel and decreased in the perpendicular direction indicating formation of fibrillar phase morphology. In the case of PC/LCP blends, a reinforcing effect was observed at low LCP contents, but above 20 w/w% the viscosity increased and the parallel tensile strength dropped to the value measured in the perpendicular direction. The loss of the reinforcing effect might originate from chemical reactions of the two polymers.

Evolution of the morphological and rheological properties along the extruder length for compatibilized blends of a commercial liquid‐crystalline polymer and polypropylene

AbstractIn a previous article, we reported on the evolution of the morphological and rheological properties along the length extruder for blends of a liquid‐crystalline polymer (LCP), Rodrun LC3000, and polypropylene (PP). In this work, we extended this study to compatibilized PP/Rodrun LC3000 blends, containing 10 wt % LCP and different compatibilizers, to determine the influence of the addition of a compatibilizer during the processing and, consequently, on the final properties of such systems. The results revealed that the addition of compatibilizers led to a decrease in the mean diameters of the LCP structures, in comparison with those presented by the noncompatibilized blend containing the same LCP content. This phenomenon occurred more quickly for those blends in which compatibilization was carried out in an efficient way. Linear oscillatory shear was mainly sensitive to the type of morphology present in the blends, whereas nonlinear oscillatory shear was more sensitive to the evolution in the droplet/fibril size and along the extruder length. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 347–359, 2006

Self-Reinforcing Composites of Polyacrylic Elastomers and Liquid Crystalline Polymer: Mechanical, Thermal, and Dynamic Mechanical Properties

In order to study the effect of liquid crystalline polymers (LCP) as reinforcing agents for polyacrylic elastomer (ACM), blends of ACM and a liquid crystalline polymer were prepared. These blends were cured with ammonium benzoate and Diak-4, 4,4'-methylen ebis(cyclohexylamine) carbamate in order to understand the curing behaviour of ACM in presence of LCP. A rheometric study of the blends indicated an improved state of cure in presence of Diak-4, but a deteriorated state of cure in presence of ammonium benzoate. All the blends showed substantial improvement in modulus and tear strength with the increasing amounts of LCP however; this improvement was predominant when Diak-4 was used as a curing agent. The tensile strength of the blends decreased with increasing LCP content, attributed to lack of interfacial adhesion between ACM and LCP, which was confirmed by scanning electron microscopy (SEM). It was found from the X-rd measurements that LCP acts as a nucleating agent by increasing the crystallinity of the blend. The degradation temperatures and heats of degradation deduced from the thermal analysis suggested that ACM had reduced thermal stability when in presence of LCP. A dynamic mechanical analysis (DMA) study revealed the improved storage modulus of the blends with increasing LCP content.

Self-Reinforcing Composite Based on Ethylene Acrylic Elastomer (AEM)/Liquid Crystalline Polymer (LCP) Blend

Blends of ethylene acrylic elastomer (AEM) and thermotropic liquid crystalline polymer (TLCP) have been prepared by melt mixing technique. Processing studies indicated a decrease in the viscosity of the blends with the addition of liquid crystalline polymer (LCP). At lower level of LCP the tensile strength and tear strength increased. However, at higher level of LCP tensile strength values decreased due to insufficient adhesion between two phases. The modulus of the samples increased with the LCP content. The degree of crystallinity increased with increasing LCP content. This improvement in crystallinity is associated with the increase in crystallite size. For the blends, thermal studies indicated, the endothermic signals which were more prominent at all the peak temperatures. The heat of degradation values increased with the LCP content. Scanning electron microscope (SEM) study suggested the fibril formation, which affected the failure mechanism under DMA studies. Storage modulus and loss modulus of the blends increased with increasing LCP content. At above glass transition temperature (Tg) improvement in storage modulus is nearly five times higher than that of the pure AEM.

In-situ elastomer composite based on fluorocarbon elastomer/liquid crystalline polymer blend

Blends of fluorocarbon elastomer (FKM) and liquid crystalline polymer (LCP) have been prepared by melt mixing technique. Processing studies indicated the decrease in the viscosity and the state of cure with the addition of 10 wt% LCP, and then increased at a higher rate with the addition of more LCP to the blend. The tensile strength values decreased at lower level of LCP. However, the modulus and tear strength values increased with higher increment of LCP content. From the X-ray diffraction measurements it has been observed that the crystalline structure of the FKM is greatly affected by the addition of LCP. The degradation temperatures from thermogravimetric analysis (TGA) suggested improved thermal stability of the fluorocarbon-LCP blends. From the dynamic mechanical analysis (DMA), it has been found that the glass transition temperature (T g) of the blends increased with increase in LCP content. For the compositions of 10 wt% and 20 wt% LCP blends, enhancement in storage modulus is found above the glass transition of FKM. Under dynamic conditions the increase of LCP content restricts the matrix flow and hence cracks developed at the interface of the LCP fibrils and matrix.

Effects of Compositions and Processing Variables on Barrier and Mechanical Properties of Liquid Crystalline Polymer/Polyethylene Blend Films

AbstractCast films of liquid crystalline polymer (LCP) and low density polyethylene (LDPE) blends have been produced and investigated. Effects of LCP content and processing parameters, i.e., processing temperature profile, screw speed, and post‐die drawing, on morphology and O2 barrier property are presented. Increasing processing temperature and LCP content tend to enhance aspect ratios (L/D) of the LCP dispersed phase and at the same time influencing LCP structure. These effects are clearly observed when LCP content is increased from 10 % to 30 % by wt. At high temperature profiles, LCP morphologies are presented in a more or less ‘ribbon’ or ‘tape’ like structure together with a common LCP fibrillar structure. Films of 10% and 30% LCP produced at two optimum temperature profiles show a noticeable proportion of LCP tape‐like structure and interestingly high barrier properties of ∼1.6 and 5.5 times that of the neat LDPE films. High barrier characteristics of such LCP/PE blend films are indicated by low oxygen transmission rate values. Apart from processing temperature effect, increases of screw speed result in films having smaller aspect ratios for both LCP fibers and ribbons; films also exhibit poorer barrier and mechanical properties. However, post‐die drawing clearly demonstrates a positive effect in improving aspect ratios of the LCP domains and the resulting films' moduli. Effects of post‐die drawing on enhancing films' barrier properties become more pronounced at high LCP content. By comparing with the neat LDPE film (30 μm thick) having modulus of ∼180 MPa and OTR of ∼11000 cc/m2.day, the developed LCP/PE films containing 30 wt% LCP show remarkably high modulus values of ∼1100 MPa with low OTR of ∼2000 cc/m2.day.

Structural Characterization and Related Properties of EP/LCP Blends

Blends of (ethylene-co-propylene) and a thermotropic liquid crystalline polymer (LCP) have been prepared by melt mixing technique. Microstructure of the blends has been studied by XRD and SEM. Thermal properties and dynamic behavior of the composites have been analyzed by DSC/TGA and DMTA respectively. The crystallinity decreases with the increase in LCP content. At lower level of LCP in composites (up to 20%), a growth in crystallinity is favored. From DMTA it has been observed that at higher loading of LCP, the relaxation peaks shift to a higher temperature. The changes of storage modulus, loss modulus and stiffness as a function of blend ratio have suggested the phase inversion at the 50% level of LCP in the blend. From DSC it has been shown that thermal stability increases with increasing LCP content in the composites. The decreasing heat of fusion supports the finding of a change in crystallinity of the blends. Under dynamic conditions the matrix flow was restricted with the increase of LCP content and hence cracks developed at the interface of the glass fibre and matrix.

Performance characteristics of compatibilized ternary Nylon 6/ABS/LCP in-situ composites

Ternary Nylon 6/poly(acrylonitrile-butadiene-styrene)(ABS)/liquid crystalline polymer (LCP) blends compatibilized by the maleic anhydride-grafted polypropylene (MAP) and solid epoxy resin (bisphenol type-A) were injection molded. Thermoplastic matrix consisting of Nylon 6/ABS (60/40) (wt%) was melt blended with various LCP (Vectra A950) contents. The effects of compatibilizer additions on the structure-mechanical property relationship of the in-situ composites reinforced with LCP were investigated. SEM observation revealed that the additions of epoxy and MAP compatibilizers to the Nylon 6/ABS/LCP blend were very effective to enhance the interfacial adhesion of its phase components. Consequently, extended long and fine LCP fibrils were formed in the skin section of in-situ composites. Tensile measurements revealed that uncompatibilized Nylon 6/ABS/LCP blend exhibited lower strength, stiffness and impact toughness. However, the incorporation of MAP and epoxy resin compatibilizers into Nylon 6/ABS/LCP blend improved its tensile strength, stiffness and impact toughness considerably. This was due to the compatibilizers effectively promoted stress transfer at the interfacial phase regions of ternary in-situ composites. The compatibilized composites exhibited mechanical anisotropy, especially for the tensile strength. Thermogravimetric measurements showed that the heat resistance and heat stability of the in-situ composites tended to increase with increasing LCP content.