Liquid Crystalline Polymer Blends Research Articles

Improvement of compatibility, thermal stability and mechanical properties of poly (phenylene oxide) (PPO) and liquid crystalline polymer (LCPA950) blends with epoxy containing acrylate rubber (ACM) as a compatibilizer

This paper proposes a new approach for improving the compatibility of liquid crystalline polymers with engineering thermoplastics. To improve compatibility and mechanical performance of poly (phenylene oxide) (PPO)/liquid crystalline polymer (LCP) A950 blends, a third component compatibilizer is incorporated into the processing step. In this work, epoxy containing acrylate rubber (ACM) is used for the compatibilization of PPO/LCPA950 blends through the chemical reaction of epoxy functional groups of the acrylate rubber with terminated carboxylic acids or hydroxyl end groups of the two phases. The compatibilization effect on the properties of PPO/LCPA950 blends is investigated by adjusting the amount of acrylate rubber. Fourier transform infrared (FTIR) spectroscopy and melt-rheological analysis were used to study the compatibilization mechanism of acrylate rubber, and the results demonstrate that acrylate rubber is capable of reacting with PPO/LCPA950 to form a chemical bonding interface. The electron microscopic images revealed a well-compatibilized microstructure of PPO/LCPA950 blends in presence of acrylate rubber with submicron-sized liquid crystalline polymer domains in the continuous poly (phenylene oxide) matrix phase, which could not be detected for immiscible PPO/LCPA950 blend. The dynamic mechanical analysis shows that PPO/LCPA950 blend with acrylate rubber exhibit greater elastic storage moduli. It was observed that blends of PPO/LCPA950 compatible with acrylate rubber showed significant increases in tensile strength as well as notched impact strength. These blends can be used in automotive industry.

Lignin-Assisted Stabilization of an Oriented Liquid Crystalline Cellulosic Mesophase, Part B: Toward the Molecular Origin and Mechanism.

Lignin valorization has been scarcely considered in the form of liquid crystalline polymer blends. Recently, a stabilizing effect of organosolv lignin (OSL) on the oriented mesophase of hydroxypropyl cellulose (HPC) was observed and related to drastic improvements in tensile properties of the blends. With a view to elucidating this relaxation phenomenon, different molecular weight fractions and derivatives of organosolv lignin are synthesized, blended in solution with the liquid crystalline cellulosic polymer and analyzed in regard to their effect on the microstructural evolution of shear-aligned HPC chains. The rheological and rheo-optical investigations suggest a crucial contribution of the lower molecular weight oligomers and the phenolic hydroxy functionalities to the stabilization of the oriented cellulosic mesophase. The results provide an indication of the molecular origin and mechanism and might be of special interest for the production of anisotropic materials from liquid crystalline cellulosic polymers.

Lignin-Assisted Stabilization of an Oriented Liquid Crystalline Cellulosic Mesophase, Part A: Observation of Microstructural and Mechanical Behavior.

Liquid crystalline polymer blends containing lignin have been scarcely studied in the literature, albeit demonstrating potential for the design of high-performance lignin-based materials. In this study, organosolv lignin is blended in solution with hydroxypropyl cellulose (HPC), a lyotropic cellulose derivative, and its impact on the dynamics of the cellulosic liquid crystalline mesophase is investigated. Rheological measurements and rheo-optical investigations under crossed polarizers reveal that lignin enhances the persistence of the shear-induced orientation of the cellulosic macromolecules. In shear-cast films, the retention of the microstructural organization or band texture entails a drastic increase of the mechanical anisotropy and properties with lignin content. For the origin of the textural stabilization, we propose a specific "jacketing"-like effect of lignin on HPC. This study indicates the possibility of a beneficial impact of lignin on the relaxation behavior of liquid crystalline cellulosic polymers.

Investigation into the morphology, crystallization and melting behaviour of nylon 6,6/LCP blends

The morphology, isothermal crystallization and melting behaviour of melt-mixed nylon 6,6/Vectra A950 liquid crystalline polymer (LCP) blends were investigated. The blends formed an immiscible system for all compositions, and the inclusion of LCP, especially at low content, accelerated the bulk crystallization rate of the matrix. The addition of LCP was also found to decrease the crystallite size in the growth direction. The effect of thermal history on the triple melting behaviour and the equilibrium melting temperature was discussed. The equilibrium meting temperature was determined to be lower in the blends. Lauritzen-Hoffman analysis on the crystallization data revealed an apparent regime I to II transition in all the samples. The blends showed lower fold surface energy and work of chain folding as compared to nylon 6,6.

Study of Compatibilized Liquid Crystalline Polymer/Cyclic Olefin Copolymer Blends

ABSTRACTThe technology to produce compatibilized blends of liquid crystalline polymer and highly amorphous cyclic olefin copolymers through two novel approaches were studied. The first approach was to use silane-functionalized halloysite nanotube as nonspecific compatibilizer and the second method was reactive compatibilization. The study of blends and their resulting microstructure; their thermal, mechanical, and viscoelastic properties were investigated. The kinetic study of blends compatibilized through both routes was performed.

Nonisothermal crystallization kinetics of nylon 66/LCP blends

The non isothermal crystallization kinetics and melting behaviour of nylon 66/thermotropic liquid crystalline polymer (LCP) blends was investigated using differential scanning calorimetry (DSC). In the blends, LCP, at low concentrations, accelerated the bulk crystallization rates of the matrix. However, at high concentrations, it posed a hindrance to the crystallization process. The Avrami, modified Avrami, Ozawa and Mo models were used to fit the experimental data. The effective energy barrier was estimated using Friedman method. The inclusion of LCP had led to lowered energy barrier to crystallization and increased nucleation activity. Moreover, application of Lauritzen Hoffman surface nucleation theory revealed that the addition of LCP, in low concentrations, reduced the work of chain folding and increased the regime I to II transition temperature.

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.

In situ composites based on blends of PEEK and thermotropic liquid crystalline polymer

ABSTRACTA series of blends were prepared by mixing pellets of the thermotropic liquid crystalline polymers (TLCP) with poly (ether ether ketone)(PEEK) in the dry state under injection mouldingmolding conditions. The mechanical properties of blends were measured, and it is proved that the mechanical properties of blends are better than those of their matrix. Compared with the thermoplastic matrix, the tensile modulus and strength of the blends increased obviously, with the addition of only 2 wt% LCP. At the same time, the addition of TLCP decreased the melt viscosity of the blends.

Optical Behaviors of Cholesteric Liquid-Crystalline Polyester Composites with Various Chiral Photochromic Dopants.

New developments in the field of chiral nematic liquid crystals, such as color displays, are now being widely proposed. This article describes the tunable incident reflection band based on composite materials of low-molecular-weight chiroptical dopants and polymeric networks. These materials have advantages including easily manageable color according to a change in the helical pitch of the cholesteric liquid crystal upon exposure to light. A series of novel chiral dopants of isosorbide derivatives containing photochromic groups and three new main-chain liquid crystalline polyesters were synthesized and identified using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and elemental analyses. The phase-transition temperatures and the liquid-crystal phase determination of the synthesized polymers were estimated using DSC, WAXD, and POM analyses. The influence of the dopant concentrations and the solubility in a liquid crystalline polymer blend were also studied. The reflection band of the cholesteric liquid crystalline composites could be adjusted and tuned with a wide range of color variation across the entire visible region. A real image recording of the chiral photochromic liquid crystalline polymer blend was achieved by exposing it to UV light through a mask.

Dual Effect of Polyphosphazene and Halloysite Nanotubes in the Blends of Poly(Phenylene Oxide)/Liquid Crystalline Polymer

The present study investigates the effect of polyphosphazene elastomer and halloysite nano tubular fillers in the blend of poly(phenylene oxide) and liquid crystalline polymer. Fabricated materials were extensively investigated with field emission scanning electron microscope, high resolution transmission electron microscope, thermogravimetric analyzer, rheometer, universal testing machine, and dynamic mechanical thermal analyzer. Significant changes in morphology were observed when fillers were added along with the compatibilizing agent polyphosphazene. Filler-matrix adhesion improves in the presence of polyphosphazene that results in the reduction in the average domain sizes of the dispersed phase where the interfacial phenomena controls the size of the dispersed phase.

Investigation on crystallinity, performance and processability of naturally occurring halloysite nanotubes compatibilized sPS/LCP thermoplastic nanocomposites

This article deals with the analyses of the effect of halloysite nanotubes (HNTs) and modified HNTs (mH) with minimal loading on the properties of syndiotactic polystyrene (sPS)/liquid crystalline polymer (LCPs) blends. Modification of HNTs with N-(β-aminoethyl)-γ-aminopropyl-trimethoxysilane (APTMS) is confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) studies. Intensification of crystallinity of the thermoplastic blends due to induced nucleation by the halloysite nanotubes are corroborated by XRD as well as Differential Scanning Calorimetry (DSC). Due to favorable LCP fibrillations, nanocomposites exhibited higher dynamic mechanical properties than the matrix polymer as observed from the Dynamic Mechanical Analysis (DMA). Rheological properties of the blends were upgraded whereas; the chain orientations along with their alignments were highly influenced by both unmodified and modified HNTs. Modification of HNTs brings compatibility in between the blend partners revealing improved crystallization, morphological, rheological, and thermo-mechanical properties relative to that of pure matrix.

Incompatible blends of liquid crystalline polymers and engineering thermoplastic

The increasing demand of the high technology market for new applications in the aerospace industry has led to research on high performance thermoplastics as composite matrices. The inclusion of solid fibres in this class of materials during manufacturing may result in processing conditions that are too demanding. High temperature and pressure in stamping or injecting tools may result in thermal degradation of the organic matrix. Moreover, the load transfer through the fibre–matrix interface produces fibres breaking into fragments shorter than the critical length, affecting their aspect ratio, and consequently reducing the final performance of the product. The possibility of producing the reinforcing filler during the cooling cycle of the composite processing has suggested the definition of 'in situ' composite. In this paper the addition of thermotropic liquid crystalline polymer to engineering thermoplastics has been investigated. X–ray diffraction techniques have been used to evaluate the molecular orientation of the dispersed phase. The rheology and the mechanical properties of the in situ composites is related to the morphology of the material and to the processing operations.

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 Mixing Sequence of Polymer and Nanofillers on Thermo Mechanical as well as Morphological Property of the Nanocomposites

Blends of polybutylene terephthalate (PBT) and thermo tropic liquid crystalline polymer (LCP) and blend of PBT, LCP and nanosilica have been prepared by melt mixing technique. Polymer composites made by engineering thermoplastic PBT and reinforcing polymer LCP has been extruded in presence of nanosilica in different mixing sequence. Here the mixing sequence of PBT, LCP and nanosilica has been picked out so as to study the different changes that can be observed in the characteristics in each of the system. The resultant mixtures are then compression moulded in high temperature range. Microstructures of the blends have been studied by Field Emission Scanning Electron Microscope (FESEM). Thermal properties and dynamic behaviour of the composites have been analyzed by Thermo gravimetric Analysis (TGA) and Dynamic Mechanical Thermal Analyser (DMTA), respectively. From the TGA analysis it is evident that PNL has superior thermal stability than the other nanocomposites. FESEM analysis revealed that the nanosilica prefers the low viscous LCP phase than the high viscous PBT. PNL has the highest tensile modulus among all the nano composites due to migration of nanosilica from high viscous PBT to low viscous LCP phase. There is a remarkable enhancement in storage modulus value is observed in case of PNL system than the other nano composites.

Processing and characterization of TLCP fibers reinforced by 1 wt% MWCNT

A thermotropic liquid crystalline polymer (TLCP) blend with 1 wt% multiwall carbon nanotubes (MWCNTs) was prepared by melt compounding. Morphological observations of the blend show that the chemical-treated MWCNTs were well dispersed in the TLCP matrix with a good interface. MWCNTs have little effects on the thermal and rheological properties of pure TLCP. TLCP fibers with and without MWCNTs were prepared at certain drawing ratios by a melt spinning method. The degree of orientation of TLCP chains is enhanced by MWCNT micro-clusters during the fiber formation. The mechanical properties of TLCP/MWCNT fibers are significantly increased by 34.5 % for tensile strength and 38.0 % for tensile modulus in comparison with those of pristine TLCP fibers, due to the synergistic effects of MWCNT and TLCP.

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.

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.

Molecular Interaction and Properties of Poly(Ether Ether Ketone)/Liquid Crystalline Polymer Blends Incorporated with Functionalized Carbon Nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a carboxyl group (-COOH) to achieve better interfacial adhesions with both phases of the poly(ether ether ketone) (PEEK) and liquid crystalline polymer (LCP) in their blend. These strong interfacial interactions among the functionalized MWCNTs, PEEK and LCP improved the mechanical properties of the polymer blend. Three different weight percentages (0.6%, 1.2% and 1.8%) of acid modified CNTs were used with PEEK-LCP blend, for the preparation of nanocomposites. In PEEK-LCP blend, the ratio of PEEK and LCP was maintained as 10:6 respectively. The tensile strength and modulus of the composites were improved by 51% and 73% respectively with the incorporation of only 1.2% of MWCNT-COOH as compared to the unfilled PEEK/LCP blend. Moreover, careful studies of the molecular interaction, morphological, dynamic mechanical and thermal properties confirmed that a better miscibility between PEEK and LCP had been constituted in the presence of MWCNT-COOH. Therefore, it was found that the functionalized MWCNTs not only played the traditional role as reinforcing filler, but also performed a novel role as a compatibilizer for the PEEK/LCP blends.

Compatibilizing effect of functionalized polyphosphazene on the properties of poly(phenylene oxide)/vectra a blend system

AbstractThe effect of functionalized polyphosphazene on the thermal, rheological, and morphological properties of PPO (poly(phenylene oxide))/liquid crystalline polymer (Vectra A) blend has been investigated by means of the capillary rheometry, mechanical testing, and scanning electron microscopy (SEM) in this study. The rheological measurements show that compatibilized blends exhibit substantial rise in viscosity in comparison to uncompatilized blend especially pronounced at lower shear rates which results in improved interfacial adhesion. DMA study highlights that polyphosphazene could be used as an effective compatibilizer for the concerned blend system. SEM study reveals fine fibrillation of liquid crystalline polymers in presence of compatibilizer and the fibers are oriented in the direction of flow field. The mechanical properties of the ternary blends are increased when a proper amount of polyphosphazene is added. This is attributed to fine strand generation induced via the addition of polyphosphazene. Enhanced adhesion at the interface invokes better elongation in the ternary blends. However, mechanical properties deteriorate considerably when polyphosphazene content is 5 wt %. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

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.