Liquid Crystalline Polymer Fibrils Research Articles

Effect of Aspect Ratio of Whisker on the Fibrillation of Liquid Crystalline Polymer in Polysulfone Matrix

AbstractThe influence of content and aspect ratio of whiskers, calcium carbonate and aluminum borate, on the morphology evolution of liquid crystalline polymer (LCP) was investigated in polysulfone (PSF) matrix. The study showed that the deformation of LCP droplets was significantly promoted by adding whiskers into PSF/LCP blends, and the longer whisker produced a more pronounced fibrillation effect. The analysis of flow field and elasticity of system showed that the addition of longer whiskers increased the elasticity of materials more efficiently and enhanced the vortex in the converging flow area at the entry of capillary, which resulted in an increase of the elongational stress and promoted the formation of longer LCP fibrils in PSF/whisker system.

Modification of CNT and its effect on thermo mechanical, morphological as well as rheological properties of Polyether Imide (PEI)/Liquid Crystalline Polymer (LCP) blend system

This work analysed the effect of physical and chemical interactions between the modified mutiwalled carbon nanotubes (MWCNTs) and the Polyetherimide/Liquid crystalline polymer (PEI/LCP) blend matrix, on the dispersion of MWCNTs and deformation of LCP particles. Silicon Carbide (SiC) and TiO2 coated MWCNTs were prepared from polycarbosilane and titanium (IV) n- butoxide precursors, respectively, by sol–gel process to improve their dispersion in the polymer matrix. Formation of both was confirmed by X-Ray diffraction (XRD), Transmission Electron Microscope (TEM) and X-Ray photoelectron Spectroscopy (XPS) studies. Polyetherimide (PEI)/liquid crystalline polymer (LCP) blends with unmodified and modified MWCNTs were prepared by melt blending. TEM and Field Electron Scanning Electron microscope (FESEM) studies revealed better dispersion of modified MWCNT in the polymer matrix than the unmodified one. Rheological analysis of hybrid composite systems containing modified and unmodified MWCNT revealed that nano composite containing TiO2 coated MWCNT has the lowest viscosity and this is due to fibrillation of LCP. Superior thermal stability of modified MWCNT added composites was confirmed from thermo-gravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA) and Differential Scanning Calorimetry (DSC) studies showed the variation in glass transition temperature (Tg) of the composites in presence of pure and modified MWCNT. Mechanical properties of nanocomposites with TiO2 coated MWCNTs were found to be higher than that of pure MWCNTs added nanocomposite.

Effect of nanosilica and polyphosphazene elastomer on the in situ fibrillation of liquid crystalline polymer (LCP) and thermo-mechanical properties of polybutylene terephthalate (PBT)/LCP blend system

Nanocomposites of polybutylene terephthalate (PBT) and liquid crystalline polymer (LCP) with either polyphosphazene or nanosilica, or in combination of both were prepared by melt blending. The compatibility between the polymeric phases (PBT&LCP) was observed to be increased by the addition of polyphosphazene while the nanosilica promoted the LCP domain deformation from spherical to ellipsoidal shape. LCP fibres were produced in presence of both polyphosphazene and nanosilica due to the compatibilization of polyphosphazene and bridging effect of nanosilica through hydrogen bonding. All these above structural changes were confirmed by scanning electron microscope (SEM). Transmission electron microscope (TEM) images showed better dispersion of nanosilica in presence of polyphosphazene than nanosilica alone. There is remarkable increase in storage modulus with the addition of nanosilica, individually and in combination with polyphosphazene. Percentages of crystallinity for the concerned nanocomposites were calculated through X-ray diffraction study (XRD). Tensile strength and Young modulus were increased with addition of nanosilica and polyphosphazene but percentage of elongation at break was higher for polyphosphazene added nanocomposite. This is due to flexible compatibilizing effect of polyphosphazene, which delays the detachment of liquid crystalline polymer (LCP) domain from the polybutylene terephthalate (PBT) matrix and thus detains the fracture.

Potential Use of Recycled PET in Comparison with Liquid Crystalline Polyester as a Dual Functional Additive for Enhancing Heat Stability and Reinforcement for High Density Polyethylene Composite Fibers

The recycle poly(ethylene terephthalate) (rPET) used as an alternative reinforcing material for in situ microfibrillar-reinforced composite, compared with liquid crystalline polymer (LCP), was investigated. The PE-LCP and PE-rPET composites were prepared as fiber using hot drawing process. The effects of draw ratios and compatibilizer (styrene-ethylene butylene-styrene-grafted maleic anhydride, SEBS-g-MA) loading on morphology, tensile properties, thermal stability and dynamic mechanical characteristics of the LCP- and rPET-composite systems were studied. In as-spun samples containing compatibilizer, the fibrillation of LCP domains was observed whereas rPET domains appeared as droplets. After drawing, good fibrillation of LCP and rPET domains is remarkably observed especially in the composite fibers with compatibilizer loading. The mechanical properties of the composite fibers were strongly depended on the fibrillation of the dispersed phases which directly related the levels of draw ratio and compatibilizer loading. The mechanical properties enhanced by SEBS-g-MA were more pronounced in the rPET than LCP systems. The presence of rPET in the composite fibers alone or with the compatibilizer clearly improved the thermal resistance of PE whereas no significant change in thermal stability for the LCP-containing composite fibers with and without compatibilizer loading. The results from dynamic mechanical analysis revealed that an improvement in dynamic mechanical properties of the composite fibers could be achieved by drawing with optimum draw ratio together with optimum compatibilizer dosage. All obtained results suggested the high potential of rPET minor blend-component as a good reinforcing and thermal resistant materials for the thermoplastic composite fiber, in replacing the more expensive LCP.

Effect of polyphosphazene and modified carbon nanotubes on the morphological and thermo-mechanical properties of polyphenylene sulfide and liquid crystalline polymer blend system

Ternary blends of polyphenylene sulfide (PPS) and liquid crystalline polymer (LCP) with either polyphosphazene, unmodified multiwall carbon nanotubes (MWCNTs) or SiC-coated MWCNTs, were prepared by melt blending. While polyphosphazene improved the compatibility between the PPS and LCP, unmodified MWCNTs promoted LCP domain deformation, from spherical to ellipsoidal. Long LCP fibers were formed in presence of SiC-coated MWCNTs due to the bridging effect of modified MWCNTs at the interface of PPS and LCP. This bridging effect was confirmed by field emission scanning electron microscopy (FESEM). The better dispersion of SiC-coated MWCNTs was confirmed by both FESEM and transmission electron microscopy analysis. The superior mechanical properties of SiC-coated MWCNTs added blend system can be attributed to the fibrillation of LCP and better dispersion of SiC-coated MWCNTs. Polyphosphazene containing blend system showed lowest thermal stability while blend with SiC-coated MWCNTs was found to be highest, among all the blend systems.

Rheological hybrid effect in dually filled polycarbonate melt containing liquid crystalline polymer

Polycarbonate (PC)/liquid crystalline polymer (LCP) blends dually filled with glass fiber and nano-SiO2 were prepared by melt blending, with the use of a commercial Vectra A130 as the source of LCP and glass fiber. In these dually filled PC/LCP melts, rheological hybrid effect occurred, confirmed by the melt viscosity of the quadruple polymer blends decreased with increasing nano-silica loading, influenced by the minor LCP phase in the blend. The drastic viscosity reduction closely correlates with the deformation and fibrillation of LCP droplets in the system. The LCP fibrillation was controlled jointly by the thermodynamic and hydrodynamic driving forces. Finally, the dually filled PC/LCP melt had decreased viscosity lower than those of pure PC, silica-filled PC, and PC/Vectra A130 blends, and furthermore had decreased glass fiber breakage, shown by larger average aspect ratio than that in PC/Vectra A130 blends. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Effect of SiC coated MWCNTs on the thermal and mechanical properties of PEI/LCP blend

Multiwalled carbon nanotubes (MWCNTs) were modified by polycarbosilane derived β-SiC particle to improve its dispersion in the polymer matrix. Formation of β-SiC particle onto MWCNTs was conformed by XRD study. Polyetherimide (PEI)/liquid crystalline polymer (LCP) blends with unmodified and modified MWCNTs were prepared by melt blending and the dispersion of the nanofillers in the polymer blend was studied by high resolution transmission electron microscopy, which showed improved dispersion of modified MWCNTs compared to pure MWCNTs. Viscosity of ternary blend with modified MWCNTs was found to be lower than the ternary blend with pure MWCNTs. Incorporation of modified MWCNTs improved the fibrillation of LCP in ternary blend as compared to pure MWCNTs. Thermal analysis revealed the higher thermal stability of the modified MWCNTs added nanocomposites compared to unmodified MWCNTs. Mechanical properties of nanocomposites with SiC coated MWCNTs were found to be higher than that of pure MWCNTs added nanocomposites.

Studies on the engineering properties of LCP-Vectra B 950/PP blends with the variations of EAA content

Polypropylene (PP) was melt blended with Vectra B-950 [a thermotropic liquid crystalline polymer (LCP)], in a single screw extruder in presence of different doses of ethylene acrylic acid (EAA) copolymer, as modifier. The effect of incorporation in different proportions of EAA at a fixed dose of 5% LCP, on mechanical, thermal, morphological, and rheological properties of such blends was studied and the same were compared with that of pure PP and amongst themselves. Mechanical analysis (tensile properties) of the prepared blends exhibited improvements in ultimate tensile strength (UTS), modulus, toughness, hardness, and impact strength of PP matrix with the incorporation of EAA. The improvement in mechanical properties is associated with the formation of LCP fibrils as evidenced by scanning electron microscopy (SEM). A strong interaction through H-bonding between the segments of Vectra B-950 and EAA was established by FTIR study. Differential scanning calorimetry (DSC) studies indicated substantial increase in melting point of the blends, and thermogravimetric analysis (TGA) showed that the thermal stability of PP was improved with the addition of LCP and EAA. Rheological properties showed that LCP and EAA drop down the melt viscosity of PP and thus facilitate processibility of blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Improvement of the properties of PC/LCP blends in the presence of carbon nanotubes

Polycarbonate (PC)/liquid crystalline polymer (LCP)/Multiwall carbon nanotube (MWNTs) nanocomposites containing as-received and modified (COOH-MWNT) carbon nanotubes were prepared through melt process in extruder and then compression molded. The chemical modification of MWCNT enhances the compatibility as well as miscibility between Polycarbonate and LCP in the concerned composites. Incorporation of functionalized MWCNTs improves the thermal, mechanical dynamic mechanical and electrical properties of the composites. Storage modulus and glass transition temperature increases in a remarkable fashion due to the enhanced interfacial adhesion between the PC/LCP/COOH-MWCNT. Field emission microscopy (FESEM) and HRTEM exhibit LCP fibrillation and fine dispersion of COOH-MWCNT throughout the matrix highlighting the miscibility between LCP and PC matrix.

Rheological Hybrid Effect and its Conditions in Filled Polymer Melts

AbstractIn contrast to usually increased viscosity of filled polymer melts with increasing filler content, some filled polymer melts showed decreased melt viscosity in the presence of thermotropic (main chain) liquid crystalline polymer (LCP) with increasing filler content. This phenomenon was termed as rheological hybrid effect and found correlated well with the fibrillation of LCP melt droplets. Investigation of this LCP fibrillation in matrix polymers, with fillers of various shapes at micro‐ and nano‐meter scales, showed that LCP fibrillation was promoted by the filler addition, depending upon thermodynamic and hydrodynamic driving forces involved.

In situ reinforcement of poly(butylene terephthalate) and butyl rubber by liquid crystalline polymer

AbstractTernary in situ butyl rubber (IIR)/poly(butylene terephthalate) (PBT) and liquid crystalline polymer (LCP) blends were prepared by compression molding. The LCP used was a versatile Vectra A950, and the matrix material was IIR/PBT 50/50 by weight. Morphological, thermal, and mechanical properties of blends were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry, and thermogravimetric analysis (TGA). Microscopy study (SEM) showed that formation of fibers is increasing with the increasing amount of LCP A950. Microscopic examination of the fractured surface confirmed the presence of a polymer coating on LCP fibrils. This can be attributed to some interactions including both chemical and physical one. The increased compatibility in polymer blends, consisting of IIR/PBT, by the presence of LCP A950 may be explained by the adsorption phenomena of the polymer chains onto the LCP fibrils. SEM and AFM images provided the evidence of the interaction between IIR/PBT and the LCP. Dynamic mechanical analyses (DMA) and TGA measurements showed that the composites possessed a remarkably higher modulus and heat stability than the unfilled system. Storage modulus for the ternary blend containing 50 wt% of LCP exhibits about 94% increment compared with binary blend of IIR/PBT. From the above results, it is suggested that the LCP A950 can act as reinforcement agent in the blends. Moreover, the fine dispersion of LCP was observed with no extensional forces applied during mixing, indicating the importance of interfacial adhesion for the fibril formation. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Fibrillation of liquid crystalline polymer in polysulfone promoted by increased system elasticity via adding nano-silica

Ternary blends composed of a liquid crystalline polymer (LCP), nano-SiO 2 and polysulfone (PSF) were prepared by melt blending. Very long and perfectly oriented LCP fibrils were in situ formed in capillary flows by adding 5 vol% of nano-SiO 2 to binary PSF/LCP blend. Dynamic rheology analysis indicated that the sharp increase of elasticity was caused by higher content of nano-SiO 2. Then the entrance angle was decreased and elongational stress increased when the polymer melt flowed through the abrupt contraction, which resulted in the fibrillation of LCP in PSF/LCP/nano-SiO 2 system.

Effect of Aspect Ratio of Whisker on the Fibrillation of Liquid Crystalline Polymer in Polysulfone Matrix

Abstract The influence of content and aspect ratio of whiskers, calcium carbonate and aluminum borate, on the morphology evolution of liquid crystalline polymer (LCP) was investigated in polysulfone (PSF) matrix. The study showed that the deformation of LCP droplets was significantly promoted by adding whiskers into PSF/LCP blends, and the longer whisker produced a more pronounced fibrillation effect. The analysis of flow field and elasticity of system showed that the addition of longer whiskers increased the elasticity of materials more efficiently and enhanced the vortex in the converging flow area at the entry of capillary, which resulted in an increase of the elongational stress and promoted the formation of longer LCP fibrils in PSF/whisker system.

Enhanced fibrillation of LCP by CaCO3 whisker in polysulfone matrix through increasing elongational stress

Induced by different fillers, various hydrodynamic effects enhance the fibrillation of liquid crystalline polymer (LCP) in in situ hybrid composites. Through choosing CaCO3 whisker as the filler and polysulfone (PSF) as the matrix, the effect of the filler size and the affinity between components on the morphological evolution of LCP droplets has been investigated. In contrast to the spherical or ellipsoidal droplets of LCP formed in binary PSF/LCP blends, the fibrillation of LCP was promoted by the introduction of whisker particles in all ternary blends at shear rates studied. The analysis of the flow field indicated that the predominant factors promoting the fibrillation of LCP were the vortex enhanced and elongational stress increased by the whisker in the converging flow area at the entrance of capillary, rather than the viscosity ratio and capillary number.

Factors that Affect Fibrillation of the Liquid Crystalline Polymer (LCP)Phase in an Injection Moulded Polycarbonate / LCP Blend

The effects of compatibilization and mould geometry on the fibrillation of liquid crystalline polymer were investigated in this study. The blend is composed of polycarbonate (PC) and LC5000, a thermotropic liquid crystalline polymer consisting of 80/20 wt% of hydroxybenzoic acid and poly(terephthalate). The effect of compatibilization was investigated by studying the morphological properties of injection moulded plaques and significant enhancement in the fibrillation of LCP was observed in the moulded samples after addition of the compatibilizer. The effect of mould geometry was studied by comparing results obtained from three types of specimens, namely, specimens cut from large rectangular plaques, moulded rectangular bar specimens and molded dog-bone specimens. It was found that mould geometry had a direct influence on the magnitude of the elongational and shear stresses in the melt during molding and thus affected the degree of LCP fibrillation. Moreover, it was observed that the constriction at the “neck” of the dogbone geometry actually facilitated development of LCP fibre in the blend by increasing shear stress during moulding and promoting LCP fibre coalescence.

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.

Rheology–morphology relationships in nylon–LCP hybrid composites

Rheological behaviors of hybrid composite systems consisting of liquid crystalline polymer (LCP), short glass fibers and toughened nylon 66 were characterized with capillary rheometry. The results were compared with the rheological behavior of untoughened nylon/glass fiber/LCP hybrid composites to establish the role of elastomers and glass fibers on LCP fibrillation. Results showed that, compatibilization of nylon and LCP in the presence of MA-grafted elastomer and glass fibers is the primary factor promoting LCP fibrillation in toughened glass fiber filled hybrid composites. Glass fibers serve as inert fillers modifying the interfacial interaction between the toughened nylon 66 and LCP phases. Morphology of the rheometer extrudates observed with scanning electron microscopy was consistent with the predictions from rheological results. The influence of rheology and morphology on the mechanical properties was also examined. It was found that tensile strength of toughened hybrid composites improved with the addition of glass fibers and on the other hand the strength of untoughened hybrid composites deteriorated with the glass fiber addition.

Effect of glass bead packing on the fibrillation of liquid‐crystalline polymer in polycarbonate

AbstractPolycarbonate (PC) was melt blended with small amount of liquid‐crystalline polymer (LCP) and various contents of glass beads (GB) having different diameters. The rheological measurements indicated that the GB addition increased the viscosity ratio and seemed unfavorable to the LCP fibrillation. However, the morphological observation showed that the LCP fibrillation was promoted by the GB addition and varied with the GB packing. With the increased GB packing by increasing the GB content and/or decreasing the GB diameter, LCP deformed from spheres and ellipsoids into stretched ellipsoids at lower shear rates and into long fibrils at higher shear rates. Although higher content of smaller GB jammed into the larger LCP droplets and inhibited the LCP fibrillation, very long LCP fibrils formed at higher shear rates at a high enough packing of GB. The relationship between GB packing and LCP fibrillation revealed two kinds of hydrodynamic effects of GB promoting the LCP fibrillation: at lower GB packing, the shear flow was enhanced by the high local shear between GB, in quantity; and for a high enough GB packing, the shear flow was changed, in quality, into elongational flow, which was more effective for the LCP fibrillation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1020–1030, 2006

Morphology evolution of a liquid crystalline polymer in polycarbonate matrix enhanced by the addition of glass beads

Polycarbonate (PC)/liquid crystalline polymer (LCP)/glass bead (GB) composites filled with various volume fractions of GB were melt blended and characterized with rheological measurements and morphological observation. The study showed that the morphology evolution of LCP droplets from spheres and ellipsoids to long fibrils during the flow was enhanced by the addition of GB. Increasing shear rate also promoted the fibrillation of LCP. At the first glimpse, increasing the apparent shear rate significantly decreased the viscosity ratio ( p) and increased the capillary number ( Ca), which facilitated the deformation and fibrillation of LCP, while adding GB affected these parameters less. But a 5% incorporation of GB produced a more pronounced fibrillation effect than an 8-time increase of the apparent shear rate. Image analysis and model establishment were conducted to demonstrate that a high local shear, existing between the closely nearby rotating spheres, increased Ca effectively and promoted the LCP fibrillation even at lower apparent shear rates.

Uniaxial extensional flow behavior of immiscible and compatibilized polypropylene/liquid crystalline polymer blends

In this work liquid crystalline polymer (LCP) and thermoplastic (TP) blends with and without compatibilizer were studied with respect to their elongational flow behavior, under uniaxial extensional flow. This knowledge is important because in processes involving dominantly extensional deformations, like the case of the formation of the LCP fibrillation, transient extensional flow properties become more important than transient or steady-shear properties. In systems characterized by disperse phase morphologies (10 and 20 wt%) the LCP acts as a plasticizer, decreasing the viscosity of the system and increasing its durability with respect to that of the matrix. On the other hand, for a system in which a co-continuous morphology is present (40 wt% LCP) fibrils and droplets deformation occurs simultaneously, leading to a much higher strain hardening and durability. Moreover, the addition of compatibilizers to the blends gives rise to an increase of the strain hardening and to a decrease of the durability, which is in accordance with the mechanical properties, namely a higher Young’s modulus and lower elongation at break, in comparison with noncompatibilized systems.