Thermomechanical properties of a magnetically and mechanically oriented liquid crystalline copolyester,xydar

Elastic moduli and linear coefficients of thermal expansion (CTE) of a random thermotropic liquid crystalline copolyester, oriented in a magnetic field and by mechanical methods were measured in the directions parallel and perpendicular to the orientation direction. The axial elastic modulus of the magnetically oriented film was lower than that of the uniaxially stretched film. The elastic modulus measured in the transverse direction was higher for the magnetically oriented film. In the axial direction, both the mechanically stretched and magnetically oriented films exhibited shrinkage at low temperatures (CTE ≈ -2 · 10^?5 K^?1) and exhibited expansion at elevated temperatures. In the transverse direction, expansion was observed except for the biaxially stretched film at low temperatures. The magnetically oriented film showed the lowest axial CTE at elevated temperatures.     

Elastic moduli of liquid crystalline copolymers

Dynamic tensile and shear moduli measurements have been carried out on highly oriented thermotropic liquid crystalline copolymers formed by random copolymerization of 2-hydroxy-6-naphthoic acid, terephthalic acid and p-aminophenol. This liquid crystalline copolymer is known as HNATA. Application of the aggregate model of units of structure gives rise to an estimation of the orientation angle θ = 5° and a chain modulus E_c = 230 GPa. The fall in tensile modulus with increasing temperature is related to two factors: a decrease in the intrinsic chain modulus and a reduction in the shear modulus.     

Effects of molecular weight and monomer composition on tensile properties of thermotropic liquid crystalline poly(p-oxybenzoate-co-ethylene terephthalate)s

Summary Relations between molecular structure and mechanical properties of as-spun filaments of thermotropic liquid crystalline poly(p-oxybenzoate-co-ethylene terephthalate)s have been investigated. The tensile modulus is independent of molecular weight, which suggests that the flow-induced orientation is not affected by molecular weight. On the other hand, the tensile breaking strength is inversely proportional to the reciprocal of molecular weight with the critical molecular weight of approximately 6000. The modulus and a balance between tensile strength and processability are enhanced with increasing the content of a rigid p-oxybenzoate unit in the copolyester.     

Static tensile and dynamic mechanical properties of hydroxypropylcellulose films prepared under various conditions

The films of hydroxypropyl cellulose (HPC), which is a lyotropic and thermotropic liquid crystal, were cast under various conditions of temperature and concentration. The effects of the casting conditions on the static tensile and dynamic mechanical properties of the cast films were determined, and the results were compared with those of films prepared by means of hot compression. The tensile properties of the films prepared by both processes (cast and hot compression) were unsatisfactory in comparison with other liquid crystalline polymers, and this was partly due to water absorbed during the test. In dynamic properties, two distinct transitions were detected. The higher one, around 110°C, was associated with the rotation of an unhydroglucose ring and the lower one, around 25°C, was associated with the T_g. There were no marked differences in the properties between cast films and hot-compressed films, except the disappearance of the T_g for hot-compressed film prepared at a relatively higher temperature. The basis for defining the liquid crystalline structure in cast and hot-compressed films are not directly given in this preliminary paper. However, judging from the dynamic mechanical properties and refractive index data for films prepared by both processes, it appears that dimethylacetamide-cast films and films compressed at 180 and 200°C may have some structures related to liquid crystalline phase and that inter- and intramolecular hydrogen bonding play an important role in lyotropic and thermotropic liquid crystalline behavior for HPC.     

A comparative study of structure–property relationships in highly oriented thermoplastic and thermotropic polyesters with different chemical structures

Structure and properties of commercially available fully oriented thermoplastic and thermotropic polyester fibers have been investigated using optical birefringence, infrared spectroscopy, wide‐angle X‐ray diffraction and tensile testing methods. The effect of the replacement of p‐phenylene ring in poly(ethylene terephthalate) (PET) with stiffer and bulkier naphthalene ring in Poly(ethylene 2,6‐naphthalate) (PEN) structure to result in an enhanced birefringence and tensile modulus values is shown. There exists a similar case with the replacement of linear flexible ethylene units in PET and PEN fibers with fully aromatic rigid rings in thermotropic polyesters. Infrared spectroscopy is used in the determination of crystallinity values through the estimation of trans conformer contents in the crystalline phase. The analysis of results obtained from infrared spectroscopy data of highly oriented PET and PEN fibers suggests that trans conformers in the crystalline phase are more highly oriented than gauche conformers in the amorphous phase. Analysis of X‐ray diffraction traces and infrared spectra shows the presence of polymorphic structure consisting of α‐ and β‐phase structures in the fully oriented PEN fiber. The results suggest that the trans conformers in the β‐phase is more highly oriented than the α‐phase. X‐ray analysis of Vectran® MK fiber suggests a lateral organization arising from high temperature modification of poly(p‐oxybenzoate) structure, whereas the structure of Vectran® HS fiber contains regions adopting lateral chain packing similar to the room temperature modification of poly(p‐oxybenzoate). Both fibers are shown by X‐ray diffraction and infrared analyses to consist of predominantly oriented noncrystalline (63–64%) structure together with smaller proportion of oriented crystalline (22–24%) and unoriented noncrystalline (12–15%) structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 142–160, 2006     

Impact of different die draw ratio on crystalline and oriented properties of polypropylene cast films and annealed films

Four kinds of polypropylene (PP) cast films with different die draw ratios (DDR) were prepared. The impact of different DDR on the crystalline and oriented properties of PP cast films and annealed films was explored herein. Wide angle X-ray diffraction (WAXD) and fourier transform infrared (FTIR) methods were adopted to examine the orientation degree of crystalline and amorphous phases. Long period distance (L_p) of the crystalline structure was tested by small angle X-ray scattering (SAXS). Crystallization was determined by differential scanning calorimeter (DSC). The oriented and crystalline behaviors of the samples were carried out by the elastic recovery (ER) testing. Then, samples after being annealed were examined by the same methods. The influence of annealing process on the films’ structures and properties was explored. Besides, the final stretched microporous membranes manufactured via stretching the annealed films along machine direction were examined by scanning electronic microscope (SEM). No matter for cast films or for annealed films, it is found that the films’ orientation degree of crystalline and amorphous phases, as well as L_p and crystallinity are larger at higher DDR and relatively lower at lower DDR. When the DDR is overly high (DDR?=?170), both the oriented and crystalline properties will decline. Elastic recovery testing indicates that a film with better orientation of the crystalline and the amorphous phases as well as with higher crystallinity can be obtained at an appropriate DDR. SEM images show that stretched membranes with better microporous structure can be obtained when the precursor film is prepared at a proper DDR.     

Process for the formation of biaxially oriented films of poly(p-phenylene terephthalamide) from liquid crystalline solutions

A new process for making equal biaxially oriented films from liquid crystalline solutions of poly(p-phenylene terephthalamide) (PPD-T) is described. The process involves extruding solutions of PPD-T/H₂SO₄ through an annular die and over an oil-coated mandrel into a coagulation bath. The films were studied using wide angle X-ray diffraction (WAXS) and scanning electron microscopy (SEM). Tensile stress–strain properties were obtained on samples cut at various directions in the plane of the film. Biaxially oriented films which possess equal properties in the various directions in the plane of the film were produced. Moduli of 2.3 × 10⁹ Pa and tensile strengths of 9.6 × 10⁷ Pa were obtained in the plane of the film. Films with unequal biaxial orientation were also produced. These tend to have higher modulus/tensile strength in the direction of major orientation, the machine direction (up to 8.3 × 10⁹ Pa/2.5 × 10⁸ Pa), but become brittle in the transverse direction.     

Structural,mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester

Structural, Mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester containing p-hydroxybenzoic acid and 2-hydroxynaphthoic acid were investigated using X-ray diffraction measurements, differential scanning calorimetry, rheovibron measurements, and scanning electron microscopic observation. The extruded sheets of the thermotropic copolyester are composed of layered structures containing skin and core layers. A skin layer comprises fine fibrils oriented almost parallel to the extrusion direction. A core layer contains poorly oriented thicker fibrils or platelike structures. The orientation function of sheets and their tensile dynamic modulus parallel to the extrusion direction increase with increasing draw-down ratio of the sheet. Annealing of the sheet caused the increases in the temperature and the heat of crystal—mesophase transition, the heat-resistance to the mechanical tensiles properties, and the inherent viscosity of the polymer. The effect of annealing on the structural properties of the extruded sheet was discussed. © 1993 John Wiley & Sons, Inc.     

Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m‐hydroxybenzoic acid units

Fibers of fully aromatic thermotropic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a high‐temperature melt‐spinning technique. Two types of the copolyesters were prepared by a high‐temperature melt polycondensation reaction using 33 mol % of kink (m‐ABA) and 67 mol % linear monomer units (p‐ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase‐separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well‐developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p‐ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2580–2587, 2002     

Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in-situ composite

Fibers (strands) with various draw ratios were spun from the liquid crystalline state of a pure aromatic liquid crystalline copoly(ester amide) and the melts of its blend with polycarbonate. Scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed to investigate the structure and properties of the resulting fibers. Mechanical properties of the fibers were also evaluated. It was found that both the crystallite size and heat of fusion of the liquid crystalline polymer (LCP) increase steadily with draw ratio. However, the crystal-nematic transition temperature of the LCP is virtually unaffected by drawing. Moreover, heat of fusion of LCP is much smaller than that of isotropic condensation polymers despite the presence of very sharp diffraction peaks in WAXS measurements. These results are ascribed to the (semi)rigid rod nature of the LCP chains and the persistence of an ordered structure in the LCP melt, i.e., entropy effect. It was further observed that tensile modulus and tensile strength along fiber axis rise with draw ratio for the composite fibers. The elastic modulus of the composite fibers were found to be as high as 19 GPa and tensile strength reached 146 MPa with draw ratios below 40 and an LCP content of 30 wt%. Compared with the thermoplastic matrix, the elastic modulus and tensile strength of the in-situ composite have increased by 7.3 times and 1.4 times, respectively, with the addition of only 30 wt% LCP. This improvement in mechanical properties is attributed to fibrillation of the LCP phase in the blend and the increasing orientation of the LCP chains along the fiber axis during drawing.     

Polymorphism and mechanical properties of syndiotactic polystyrene films

The dynamic-mechanical behaviour and the tensile moduli of unstretched and stretched semicrystalline s-PS films, presenting different polymorphic forms (α, γ, δ and clathrate) but similar crystallinity and orientation, have been compared. The main aim is to elucidate the possible influence of different crystalline phases, being largely different in chain conformation and density, on mechanical properties of s-PS semicrystalline samples. For unstretched films presenting a preferential perpendicular orientation of the chain axes, the highest elastic modulus is observed for films with the high density γ phase while for uniaxially oriented films the highest modulus is observed for films with the trans-planar α phase. As for the clathrate films, the guest molecules when only included into the crystalline clathrate phase, have no plasticizing effect.     

Functionalized graphene nanoplatelets as a barrier enhancing filler in organic photovoltaic encapsulant

This research work has concerned the development of polymer films, reinforced with graphene nanoplatelets (GNP) for use as encapsulating films for organic photovoltaic (OPV) cells. The aim of this work was to investigate the effects of concentrations and orientations of GNP on mechanical, optical, and barrier properties of polymer composite films. In this regard, the neat GNP was modified with Fe₃O₄ prior to mixing with acrylate-based monomers. The mixture was then cured by photo-polymerization with and without the application of magnetic fields. Changes in orientation of the functionalized GNP with the direction of applied magnetic fields were analyzed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. From the results, it was found that by inducing the orientation of functionalized GNP to the horizontal direction (with respect to the OPV cell), the great enhancement in tensile and barrier properties of the polymer composite films was achieved. This led to the longer performance of the OPV cell encapsulated with the nanocomposite film with 0.1 phr of the horizontally oriented GNP in comparison with the OPV cell encapsulated with the film reinforced with randomly oriented GNP at the same content.     

Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film: Effects of counter-rotating die on fiber orientation and film properties

Polyethylene blends (LLDPE:HDPE ≈ 2:1 by wt) used in NASA's balloon film applications can be effectively reinforced by addition of a small amount of liquid crystalline polymer (LCP). Cast and blown PE films containing ≈ 10% LCP show an appreciable enhancement in tensile modulus ≈400% over that of the neat PE matrix. Anisotropy in these in-situ composites was reduced by controlling LCP molecular orientation via a counter-rotating (C/R) annular die. LCP/PE blend blown films with nearly isotropic properties are obtained. Based on microscopy studies, LCP domains were generally present as fibrils with diameters of ≈ 1 to 3 µM and lengths of ≈ 100 to 300 µM. Films, produced using a C/R die, had fibrillated LCP phases and variable orientation through the film thickness. This paper describes the influence of some key process variables including temperature profile, number of extrusion cycles, degree of mixing, adapter geometry, and die counter-rotation on LCP/PE blend film morphology and mechanical properties. The structure of LCP/PE blend blown films was also evaluated using scanning electron microscope (SEM) and wide angle X-ray scattering (WAXS) techniques.     

Effect of composition and molecular structure on the LC phase of PHB-PEN-PET ternary blend

Poly(p-hydroxybenzoic acid) (PHB)–poly(ethylene terephthalate) (PET) 8/2 thermotropic liquid crystalline copolyester, poly(ethylene 2,6-naphthalate) (PEN), and PET were mechanically blended to pursue the liquid crystalline (LC) phase of ternary blends. The torque values of blends with increasing PHB content abruptly decreased above 40 wt % of PHB content because the melt viscosity of ternary blends dropped. Glass transition temperature and melting temperature of blends increased with increasing PHB content. The tensile strength and initial modulus of blends were low at 10 and 20 wt % PHB. However, the blends containing above 30 wt % PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 20 wt % PHB formed irregularly dispersed spherical domains, and the blends of 30–40 wt % PHB showed LCP ellipsoidal domains and fibrils. In the polarized optical photographs, the blends of 40 wt % PHB showed pseudo LC phases. The degree of transesterification and randomness of blends were increased with blending time. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1065–1073, 1998     

Structure of liquid crystalline copolyesters from two acetoxybenzoic acids and polyethylene terephthalate

The molecular and supermolecular structures of thermotropic liquid crystalline copolyesters from p-acetoxybenzoic acid (B), polyethylene terephthalate (E), and m-acetoxybenzoic acid (M) were studied by Fourier transform infrared spectrometer, 200-MHz ¹H-nuclear magnetic resonance (NMR), and wide-angle X-ray diffraction methods. The assignments of resonance peaks in NMR spectra are given and the effect of B/E/M molar ratio on the NMR spectra and number-average degree of polymerization of the copolyesters are discussed. The equatorial, meridional, and azimuthal scans, and their dependency on monomer mole ratio for the copolymers, are elaborated. The persistence length and orientation of the copolymer ribbons were found to increase with an increase in p-oxybenzoate unit content from 60 to 75 mol % at a fixed m-oxybenzoate unit content of 5 mol %. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2921–2925, 1999     

Effects of Magnetic Fields on Polymer Liquid Crystals

Abstract

The effects of magnetic fields on polymer liquid crystals (PLCs) are analyzed, dealing in turn with isotropic solutions, lyotropic LCs (including polypeptides, polyribonucleotides and DNA) and thermotropic PLCs (including polyesters and polypeptides). Looking for a common denominator in LC behavior, living systems are also analyzed, including viruses, biological membranes, sperm nuclei, rhodopsin and fibrinogen. Magnetropism is discussed, as are applications of PLC oriented in magnetic fields for the purpose of producing ultra-high modulus materials.     

Controlled direction of electrical and mechanical properties in nickel tethered graphene polyimide nanocomposites using magnetic field

Oriented hybrid nickel tethered graphene polyimide resin nanocomposites with different degrees of orientation were prepared by in-situ magnetic field solvent casting method. Magnetization of the hybrid Ni-graphene polyimide nanocomposites exhibited a maximum in the magnetic field direction and a minimum perpendicular to the magnetic field direction indicating the orientation of the superparamagnetic nickel nanoparticles. In-plane dc electrical conductivity of the 1.3 vol.% Ni-graphene was 2.5 times higher when cast in a high magnetic field compared to films cast without an applied magnetic field. The through-plane dc conductivity of the 1.3 vol.% oriented Ni-graphene polyimide nanocomposites decreased with increasing magnetic field strength and reached insulation (10⁻¹² S/cm) for the films cast in high magnetic field. The in-plane tensile modulus of the polyimide exhibited a 35% increase when 0.16 vol.% Ni-graphene was added to the polyimide and cast in a low-strength magnetic field. Further addition of Ni-graphene, up to 1.3 vol.%, to the polyimide resulted in nearly constant tensile moduli. Tensile strength of nickel graphene nanocomposites showed up to 2-fold increase compared to the neat polyimide. Scanning electron microscopy (SEM) revealed that the Ni-graphene nanosheets were oriented in the magnetic field direction.     

Mechanically adaptive thermoplastic polyurethane/cellulose nanocrystal composites: Process-driven structure–property relationships

To enable filament extrusion additive manufacturing of mechanically adaptive nanocomposites, the effect of melt extrusion on the tensile modulus and mechanical adaptiveness of cellulose nanocrystal (CNC)/thermoplastic polyurethane (TPU) composites was investigated. TPU (Texin RxT70A) was processed with 10 wt % CNC in multiple formats, including solvent-cast films and melt extrusion-produced filaments. CNC orientation is characterized by polarized Raman spectroscopy and small-angle X-ray scattering (SAXS) and found to be uniaxially oriented in extruded filaments, and randomly oriented in solvent-cast films. Dynamic mechanical analysis results show the addition of 10 wt % CNC increases the pure TPU storage modulus from 10 to 60–70 MPa in the dry state for solvent-cast and extruded nanocomposites. Following water saturation, all CNC-containing samples reach a similar wet storage modulus of approximately 26 MPa, regardless of CNC orientation and thermal history. Fickian diffusion scaling factors (6.8 to 11.6) scale closely to the time-dependent empirical scaling factors (4.9 to 7.2), confirming the rate of mechanical adaptivity is driven by water diffusion through sample thickness. Our results suggest that mechanical adaptivity is retained following processing, enabling use as a feedstock for extrusion-based additive manufacturing of CNC/TPU composites for mechanically adaptive parts. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46992.     

Structures and properties of injection moldings of crystallization nucleator-added polypropylenes. I. Structure–property relationships

Flexural test specimens were injection-molded from polypropylenes added with 0.5 wt % of calcium carbonate, talc, p-tert- dibutyl-benzoic acid monohydroxy aluminum, or p-di-methyl-benzylidene sorbitol under cylinder temperatures of 200–;320°C. Properties such as flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, hardness, and mold shrinkage and higher-order structures such as crystalline texture, crystallinity, a^*-axis-oriented component fraction, and degree of crystalline orientation were measured and structure–property relationships were studied. By the addition of crystallization nucleators, the flexural modulus, flexural strength, heat distortion temperature, hardness, and mold shrinkage were increased and Izod impact strength was decreased. The degrees of crystalline orientation such as the orientation fraction OF and c-axis orientation function f_c were increased by the addition of nucleators. The degree of the increase was higher as the crystallization temperature was higher. Close relationships were observed between some properties and the degrees of crystalline orientation.