LCP Content Research Articles

Study on modification of ZnNb2O6/PTFE microwave composites with LCP fiber

For polymer matrix microwave composites, the agglomeration of ceramic particles at a high filling ratio will cause the microwave dielectric properties, mechanical properties and thermal conductivity of the materials to deteriorate sharply. This paper examines the reinforcement effect of LCP A950 fibers on PTFE and ZnNb 2 O 6 /PTFE composites to prevent this phenomenon. SEM, DMA, and other analysis methods showed that the incorporation of a small amount of LCP can promote the crystallization of PTFE and the mechanical strength of composites. When the volume fraction of the ZnNb 2 O 6 /PTFE/LCP three-phase is 50/45/5, the composites have a medium dielectric constant ( ε r = 6.46), extremely low loss ( t a n δ = 7.54 × 10 −4 ) and a near-zero temperature coefficient of the dielectric constant ( τ ε = +2.25 ppm/°C). Under the same conditions, the linear expansion coefficient of the material is 45.4 ppm/°C, which is 30.5% lower than that before doping with LCP, and the flexural strength is 37.8 MPa, which is an increase of 17% com、pared to the previous value. The LCP-reinforced composites have excellent overall properties, but when the LCP content is too high, its reinforcement effect on the composites is gradually weakened.

Experimental results for the rheological and rheo‐optical behavior of poly(ethylene terephthalate)/liquid‐crystalline polymer blends

AbstractThe use of thermoplastic/liquid‐crystalline polymer (LCP) blends is recognized as a good strategy for reducing viscosity and improving mechanical properties relative to pure thermoplastics. This improvement, however, is only noticeable if the LCP fibrillates, in situ, during processing and the fibrils are kept in the solid state. In this article, we report a morphological, rheological, and rheo‐optics study performed with two blends of poly(ethylene terephthalate) with a LCP, Rodrun LC3000 (10 and 25 wt % LCP content), and we show that the obtained droplet‐shape relaxation time (the time the deformed droplet took to regain its spherical form after the cessation of flow) allowed for the explanation of the morphological observations. In fact, the droplet‐shape relaxation time was higher for the blend with higher LCP content, for the higher experimentally accessible shear rates, and still increased at the highest shear rate, which explained the fibrils of the LCP dispersed phase observed in this blend, whereas for the lower LCP content blend, the droplet‐shape relaxation time reached a low‐value plateau for higher shear rates, which explained the absence of fibrillation in this blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Optimisation of Rodrun LC3000/PP Compatibilised Blends: Influence of the Compatibiliser and LCP Contents on the Rheological, Morphological and Mechanical Properties

The present study focuses on the optimisation of LCP/TP compatibilised systems. This study was essentially devoted to the influence of different LCP and compatibiliser contents on the final morphological, rheological and mechanical properties of the blends. Rheologically, we used both standard small amplitude oscillatory shear and large amplitude oscillatory shear (LAOS) experiments in order to improve the understanding of the mechanisms behind the mechanical reinforcement that might be helpful in the optimisation of liquid crystalline polymer and thermoplastic blends. The results revealed that LAOS, in particular, is highly sensitive to different morphologies and may be correlated with the effectiveness of compatibilisers, which is not surprising since the flow behaviour of LCPs is highly complex and non-linear, with lower non-linear characters obtained for those blends that showed a higher fibrillar formation and better mechanical properties.

Rheology of LCP/PET Blends at Solid and Molten States of LCP

Abstract Liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having different volume fractions of constituent polymers. Shear stress, shear viscosity, first normal stress difference at different shear rates under steady state conditions of these blends were evaluated at two different temperatures 265 and 285˚C. The LCP was in solid state at 265˚C and in melt state at 285˚C and was dispersed in molten matrix of PET at both temperatures. Shear viscosity of blend increased with addition of LCP in PET matrix. A maxima was observed in viscosity versus composition plot. Blends containing more than 50 vol. % of LCP in the blend show higher viscosity as compared to the constituent polymers. First normal stress difference, N1, increased with LCP content in the blend at 285˚C when ploted against shear stress whereas at 265˚C this trend was opposite. The increased value of N1 with shear rate was explained assuming a tendency of asymmetric particles to rotate under velocity gradient of suspending medium. At 285˚C N1 varied with shear stress in two stages. First stage was characterized with high sensitivity of N1 with shear stress, which reduced in second stage on plastic deformation of LCP droplets.

A Study of Rodrun LC3000/PP Blends Under Different Stationary and Non-Stationary Shear Conditions: The Influence of LCP Content and Processing Temperature

Blends containing liquid crystalline polymers and thermoplastics have been a topic of great interest for the scientific community due to their excellent performance and properties and thus, promising use in industrial applications. For that reason, from the eighties until today, these systems were widely studied and characterized in terms of their mechanical, morphological, and rheological properties under stationary conditions but not under non-stationary ones which are, in fact, those most relevant to processing sequences. Thus, despite all the published work on this subject, there is still a need to study the response of the materials under the latter conditions. The transient shear measurements performed on the blends of Rodrun LC3000 and PP showed an overshoot for the transient stress, the magnitude of which increases with increasing LCP content. This overshoot is attributed to the orientation and deformation of the LCP structures. The results obtained for the blends by Large Amplitude Oscillatory Shear, LAOS, were revealed to be highly sensitive (compared with those observed in steady shear measurements) not only to the LCP content, but also to the processing temperature. From the rheological point of view an unusual behavior was observed for these systems, which was characterized by an increase of the viscosity and storage modulus with the increase of the LCP content at low frequencies, but a decrease at high frequencies. The traditional and well-known decrease of steady shear viscosity and mechanical improvement, induced by the addition of liquid crystalline polymer to the thermoplastic, was also observed.

Tensile behavior and morphology studies of glass‐fiber‐reinforced polymeric in situ hybrid composites

AbstractThe morphology and tensile behavior of an in situ hybrid composite system, based on E‐glass‐fibers, liquid‐crystalline polymers, and Noryl (a modified polyphenylene ether/polystyrene blend) with a hierarchical microstructure containing reinforcements with an order‐of‐magnitude difference in size, were studied. The primary reinforcement was short E‐glass fibers, and the secondary reinforcement was formed by LCP inclusions with submicrometer dimensions generated in situ during fabrication. With an increase in the LCP content, both the geometry and dimensions of the LCP phase in the composites changed, from spherical droplets to ellipsoidal droplets and then to fibrils or lamellar structures. The orientation of the short E‐glass fibers was influenced by this change, and the breakage of the glass fibers during processing was less intensive. The tensile strength of the composites increased moderately with the addition of LCPs and the reduction of the glass‐fiber content. The elastic modulus of the composites did not follow rule‐of‐mixture predictions. This more complicated hybrid effect was attributed to several competing mechanisms. Tensile fractography analysis indicated that the tensile fracture of the composites was dominated by fiber/matrix‐interface failure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 211–221, 2004

PP/LCP Blends: Influence of the LCP Content on the Mechanical, Rheological and Morphological Properties

PP/LCP Blends: Influence of the LCP Content on the Mechanical, Rheological and Morphological Properties

Speciality Polymer Blends of Polybutylene Terephthalate and Glass-Filled Liquid Crystalline Polymer

The blends of polybutylene terephthalate (PBT) with glass-filled thermotropic liquid crystalline polymer (LCP-g) was prepared by a melt mixing technique. The rheological, crystalline, thermal, dynamic mechanical, and morphological characteristics of these blends were investigated. The viscosity of the blends was higher than PBT in the whole shear rate range. At low shear rate, the viscosity of blends decreased with LCP concentration. Higher percent crystallinity was observed with increasing LCP-g content in the blend with PBT. The thermal stability increased with LCP-g content in the blend with PBT. The relaxation phenomenon as observed from DMTA analysis was changing depending on the blend ratio. The variation of stiffness and storage modulus as a function of LCP-g concentration at various temperatures suggested the phase inversion occurred at 40% LCP-g present in the blend. The orientation of the LCP-g molecules probably play a major role in determining the surface morphology rather than the surface free energy difference.

Processability, morphology and mechanical properties of glass fiber reinforced poly(ether sulfone) modified by a liquid crystalline copolyester

AbstractTernary composites based on glass fiber reinforced polyethersulfone (gPES) modified by a liquid crystalline copolyester (R5) were obtained by injection molding at different nozzle temperatures and at LCP contents up to 20%. The blends showed two pure amorphous phases. The ability of R5 to improve processing was seen mainly in the increase in the MFI of the blends on 5% LCP addition, which was more than 75% and 16% with respect to that of pure gPES and PES, respectively. The best processing temperature appeared to be 330°C, as it led to the maximum skin fibrillation and provided both the best small strain and fracture mechanical properties. The blend processed at 330°C with 5% R5 showed the best balance of properties because, besides the highest relative processability increase, it led to maximum values in all mechanical properties measured. This was due to both the overall fibrillation of the skin and to its having the highest ductility.

Reinforced poly(ether sulfone) materials by blending with a semiaromatic liquid crystalline copolyester

AbstractBlends based on poly(ether sulfone) (PES) and a semiaromatic liquid crystalline copolyester (R5) were obtained by injection molding across the entire composition range. The blends showed two pure amorphous phases. The fibrillar structure of the skin led to enhancements in the stiffness. The break properties, however, decreased at low LCP contents, due to the expected lack of adhesion between the phases. The increase in the modulus at increasing LCP content led to improvements in tensile strength. The notch sensitivity of PES decreased after the addition of low LCP levels, giving rise to enhancements of almost 600% in the notched impact strength. The unusually enhanced performance of the 20/80 blend, which has been seen previously in another thermoplastic/LCP blend, suggests that the dispersed PES phase in this blend may act as rubber particles do in rubber toughened thermoplastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 52–59, 2004

Long chain polyunsaturate supplementation does not induce excess lipid peroxidation of piglet tissues.

Addition of highly polyunsaturated fatty acids to infant formulas raises the possibility of increased lipid peroxidation. We determined the effects of increasing levels of dietary docosahexaenoic acid (DHA) and arachidonic acid (AA) on lipid peroxidation and peroxidative potential in piglet tissues. Four groups of piglets (n = 6) were bottle-fed a formula containing one of four treatments: no long chain fatty acid (Diet 0) and three different levels of DHA/AA at 1-fold (0.3 %/0.6% FA; Diet 1) 2-fold (0.6 %/1.2% FA; Diet 2) and 5-fold (1.5%/3% FA; Diet 5) concentration used in some human infant formulas, and all with equal amount of vitamin E (5.7 IU/ 100 kcal formula) for four weeks. There were no significant differences between the groups in conjugated diene and glutathione (GSH) levels in the liver, and thiobarbituric acid-reactive substance (TBARS) in plasma. TBARS levels of the erythrocyte membranes increased in a dose-dependent manner when in vitro oxidation was induced with 10 mM hydrogen peroxide (H(2)O(2)) for 30 minutes. The TBARS levels of the liver homogenates of the Diet 5 and Diet 2 groups were significantly different than those of the membranes of the Diet 0 group when the in vitro oxidation was induced with H(2)O(2). The results show that dietary vitamin E effectively prevented lipid peroxidation at the LCP concentrations investigated and suggest that levels presently in infant formulas are sufficient.

Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high‐density polyethylene

AbstractBlends of an extrusion‐grade high‐density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4–9 vol%), whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two‐dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc‐shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%–55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%–92%) than in solubility (39%–76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra RD501 blends and relatively small for the Vectra A950 blends.

Flow Properties and Morphology of PC/LCP Blends Affected by the Addition of Glass Fiber and Resulted Mutual Influences

Abstract In-situ hybrid composites containing matrix polycarbonate, glass fiber and LCP are prepared. The morphology of LCP and the rheological behavior of the composites are described. The relationship between flowability and morphology is discussed. It is interesting to find that in some hybrid systems, composites containing more glass fiber have better flowability than composites containing less glass fiber. Glass fiber aspect ratio is an important factor that determines the flowability. Materials with short glass fiber have lower viscosities than the materials with long glass fiber. LCP morphology is another important parameter that determines the flowability of the composites. If LCP forms fibrils, the composites have better flowability. If spheres dominate the morphology of LCP, the materials have larger viscosity. The addition of glass fiber brings about new factors that influence the morphology of LCP. The LCP morphology is not only affected by LCP content, but also by glass fiber content and glass fiber length. LCP fibrils are promoted in some in-situ hybrid composites. A model is proposed to describe how fibrillation of LCP is promoted due to the addition of glass fiber.

Arachidonic acid status during pregnancy is associated with polychlorinated biphenyl exposure

Seafood is an important source of long-chain polyunsaturated fatty acids (LCPs), which are essential for normal growth and development. However, the nutritional benefits could be limited by polychlorinated biphenyl (PCB) contamination. In particular, inhibition of desaturase activities by PCBs may affect the maintenance of arachidonic acid (AA) status during development. The aim was to evaluate AA status in a birth cohort from a fishing community with a high seafood intake and a wide range of PCB exposures. We measured LCP concentrations in paired mother and umbilical cord serum samples obtained from 182 consecutive births in the Faroe Islands, where PCB-contaminated whale blubber forms part of the diet. PCB exposure was determined from maternal concentrations. Serum phospholipid AA concentrations averaged 9.14% and 16.5% (by wt) in maternal and cord serum, respectively. After adjustment for gestational age and concentrations of linoleic, alpha-linolenic, and eicosapentaenoic acids, a decrease in AA concentrations of 0.17% (by wt) (95% CI: 0.03%, 0.31%) and 0.31% (by wt) (95% CI: 0.10%, 0.52%) was seen in maternal and cord serum, respectively, for each doubling of PCB exposure. Increased PCB exposure was associated with a modest decrease in serum AA concentrations, which is in accordance with the experimental evidence of desaturase inhibition by PCBs. Such interference with LCP utilization could attenuate the beneficial effects of the essential lipids contained in seafood. Because AA is of key importance for growth and development, these results suggest that this possible mechanism for PCB toxicity deserves to be explored.

Processability of LCP‐nylon‐glass hybrid composites

AbstractA hybrid composite consisting of rubber toughened nylon 6,6, short glass fibers and thermotropic LCP was investigated by varying the content of LCP. It was found that a hybrid composite offered better processability over the glass fiber reinforced polymers alone. The total torque in melt mixing increased with short glass fiber addition but decreased with an increase in LCP content. The thermal stability of the glass fiber reinforced composite was improved by blending with LCP. However, a minimum of 15 wt% LCP was required to realize reinforcement effect from the hybrid composite. The fracture morphology was examined using SEM techniques. Some LCP fibrils could be observed on the tensile fracture surface.

SELF REINFORCING COMPOSITE BASED ON EPR/LCP BLEND

Blends of ethylene propylene rubber (EPR) and thermotropic liquid crystalline polymer (TLCP) have been prepared by melt-mixing technique. Processing studies indicated the decrease in the viscosity of the blends with the addition of LCP. The mechanical properties like tensile strength and modulus increased up to 10% of LCP and then decreased. The crystallinity increased with an increase in the LCP content. At higher levels of LCP, crystal growth is favored. Thermal studies indicated the endothermic signals that were more prominent at all the peak temperatures. The surface degradation increases with an increase in elastomer (EPR) content in the blend. The relaxation phenomena, as observed from Dynamic Mechanical Thermal Analysis (DMTA) analysis, are changing depending on the blend ratio. The dynamic modulus and stiffness increased with the addition of LCP in the blend. Under dynamic application, at higher levels of LCP, it was observed from scanning electron microscope that there were no cracks at the interface between the EPR and the glass fibers suggesting the better wetting of the fibers by the EPR.

Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites

AbstractLiquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (Fmax), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.

Flory-huggins interaction parameters of LCP/thermoplastic blends measured by DSC analysis

Liquid crystalline polymer/polyamide 66 (LCP/PA66) and LCP/poly(butyl terephthalate) (LCP/PBT) blends were compounded using a Brabender Plasticorder equipped with a mixing chamber. The LCP employed was a semi-flexible liquid crystalline copolyesteramide based on 30 mol% of p-amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The Flory-Huggins interaction parameters (χ12) of the LCP/ PA66 and LCP/PBT blends are estimated by melting point depression from DSC measurement. The results indicate that c12 values all are negative for LCP/PA66 and LCP/PBT blends, and when the LCP content in these blends is more than 10 mass%, the absolute value of χ12 decreases. Thereby, we can conclude that LCP/PA66 and LCP/PBT blends are fully miscible in the molten state, the molecular interaction between the LCP and PA66 is stronger than that between LCP and PBT. As the LCP content in LCP/PA66 and LCP/PBT blends is more than 10 mass%, the molecular interaction between LCP and matrix polymer decreases.

THERMAL TRANSITIONS AND MORPHOLOGICAL BEHAVIOR OF POLYETHER ETHER KETONE AND LIQUID CRYSTALLINE POLYMER BLENDS

Polyether ether ketone (PEEK) and thermotropic liquid crystalline polymer (TLCP) based on hydroxy benzoic acid and hydroxy naphthoic acid (HBA/HNA) were prepared on a single-screw extruder with rotor speed 45 rpm at 350°C. Thermal analysis data, especially the glass transition temperature (T g), indicated that the blends were incompatible in the entire range of concentration. Melting temperature (T m) of the blends was found to be close to melting temperature of pure PEEK. Thermogravimetric analysis data show the poor thermal stability of the blends compared to the parent material. The percent weight loss increased with increasing LCP concentration. Analysis with a scanning electron microscope clearly indicated that a distinctive fibrous morphology was developed in the extruded samples at the low concentration of LCP, but the adhesion of the fiber to the PEEK matrix was poor, with circular voids around the LCP phase at higher concentration.

Effect of LCP Addition Content on the Microstructure and Fatigue Property of PP/LCP Polymer Blends.

The effect of LCP content on the microstructure and fatigue fracture property of PP/LCP blend materials with easily recycle was investigated in this study. The results are following as : (1) PP/LCP blend is an immiscible two-phase material. While LCP content was below 40%, it would be easily formed fiber. (2) Because the thermal expansion coefficient of PP is large, LCP is a nonexpansion material. Thus, the mechanics joining strength of the interphase between PP and LCP phase would be improved when the PP content was more than 60%. (3) According to the tensile testing results, PP was a ductile material, but LCP is a typical brittle material. For those blend materials companion with the increase in the addition content of LCP, the tensile strength was increased, but the stretch would largely decreased. (4) E´would decrease and tan δ would increase on the recycling fatigue of PP single phase, because the specimen producing heating itself happened ductile fracture. Companion to the increase in the addition content of LCP on the fatigue process, the trend degree of the decrease in E´and increase in tan δ would lower, the specimen lifetime would become larger, the fracture would also change to the brittle property.