Addition Of Liquid Crystalline Polymer Research Articles

Miscibility and morphology of poly p-phenylene sulphide–liquid crystal polymer blends

Blends of poly p-phenylene sulphide (PPS) and a liquid crystalline polymer (LCP) were made by two methods: (i) mixing and capillary extrusion (samples A), and (ii) injection moulding (samples B). To study miscibility in the melt and solid states and the resulting morphology, techniques like polarized light optical microscopy, capillary rheometry, dynamic mechanical thermal analysis and scanning electron microscopy with X-ray microanalysis were used. It was observed that the miscibility of the amorphous fractions of both polymers increased with increasing intensity (rates and stresses) of deformational flow (shear and elongational). Samples A had a morphology composed of fibrils of both polymers, but a matrix made of only one polymer i.e. PPS. Samples B had a mainly fibrillar morphology, with no observable matrix, made of both polymers. Formation of pure LCP fibrils was not observed neither in the extruded blends nor in the injection moulded samples. The addition of LCP to PPS improved its mechanical properties. At a molecular level, these blends can be considered to be “molecular composites”.

Study on the Morphology and Mechanical Properties of Binary and Ternary Blends of Semiaromatic LCP/PP/PC

The morphology and the mechanical properties of injection-molded binary and ternary blends of semiaromatic liquid-crystalline polymers (LCP) (Unitika Rodrun LC-5000 LCP), polypropylene (PP), and polycarbonate (PC) were investigated. It was found that the addition of LCP in the PP matrix resulted in an increase in tensile modulus but a decrease in tensile strength. The addition of a maleic-anhydride-grafted PP (MAGPP), a compatibilizer, in the binary blend of LCP/PP was not effective in improving the tensile strength. PC was then introduced into the binary system of LCP/PP. The ternary blends of LCP/PP/PC exhibited that there was a significant improvement in tensile property. Finally, scanning electron micrographs revealed that semiaromatic LCP phase was deformed to lamella structure in the ternary system, whereas it was fibril structure in the binary system.

Poly(p-phenylene sulfide)/liquid crystalline polymer blends. II. Crystallization kinetics

The crystallization kinetics of blends made of poly(p-phenylene sulfide) (PPS), with a liquid crystalline polymer (LCP) was studied. The blends were found to be immiscible by dynamic mechanical thermal analysis (DMTA). Results of non-isothermal and isothermal crystallization experiments made by differential scanning calorimetry (DSC) showed that both components had their crystallization temperatures increased ; also the LCP melting temperature was found to increase in the blends. It was concluded that the addition of LCP to the PPS increased the PPS overall crystallization rate due to heterogeneous nucleation. The fold interfacial free energy, σ e , of the PPS in the blends was observed not to vary with composition.

Mechanical properties of injection moulded blends of polypropylene with thermotropic liquid crystalline polymer

Blends of a thermotropic liquid crystalline polymer (LCP) with polypropylene (PP) were injection moulded. The LCP exhibited a higher viscosity than that of PP. Static and dynamic mechanical measurements, Izod impact tests, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were performed on these blends. The static tensile tests show that the tensile modulus and strength of PP are improved with the addition of LCP. The improvement in mechanical properties is associated with the formation of LCP fibrils as evidenced by SEM observations. Dynamic studies on these blends show an increase in the storage modulus but a decrease in loss factor with the addition of LCP. Furthermore, TGA measurements show that the thermal stability of PP is improved substantially with the addition of LCP.

In situ composite: Phenolphthalein polyethersulfone—thermotropic liquid crystalline polymer blends

AbstractPhase behavior, thermal, rheological and mechanical properties plus morphology have been studied for a binary polymer blend. The blend is phenolphthalein polyethersulfone (PES‐C) with a thermotropic liquid crystalline polymer (LCP), a condensation copolymer of p‐hydroxybenzoic acid with ethylene terephthalate (PHB‐PET). It was found that these two polymers from optically isotropic and homogeneous blends by means of a solvent casting method. The homogeneous blends undergo phase separation during heat treatment. However, melt mixed PES‐C/PHB‐PET blends were heterogeneous based upon DSC and DMA analysis and SEM examination. Addition of LCP in PES‐C resulted in a marked reduction of melt viscosity and thus improved processability. Compared to pure PES‐C, the charpy impact strength of the blend containing 2.5% LCP increased 2.5 times. Synergistic effects were also observed for the mechanical properties of blends containing < 10% LCP. Particulates, ribbons, and fibrils were found to be the typical morphological units of PHB‐PET in the PES‐C matrix, which depended upon the concentration of LCP and the processing conditions.

Effects of Chemical Reactions on the Properties of Copolyesters Made from Poly(ethylene terephthalate) Prepolymer and Liquid Crystalline Polymer

Copolyesters were prepared by melt-phase polycondensation of poly(ethylene terephthalate) (PET) prepolymer and a thermotropic liquid crystalline polymer (LCP), 60 mol% p-hydroxybenzoic acid and 40 mol % poly(ethylene terephthalate) (PHB60/PET40). The copolyesters were characterized using gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), thermal analysis, and wide angle X-ray diffraction measurement. The molecular weights of final copolyesters decreased with the addition of LCP. GPC results indicate that chain scission reaction of LCP occurs accompanied by chain-growing reaction of PET. From NMR analysis, LCP added underwent transesterification resulting in statistical reorganization of chain sequence with producing ether type by-products responsible for limiting the chain growth of copolyesters. It was observed that the crystallization of PET was delayed and melting temperature decreased with increasing LCP content in copolyesters. The resulting thermal properties and structural regularities of copolyester can be modified by exchange reactions during preparation.

Structure and mechanical properties of the extruded blends of a liquid crystalline polymer with polypropylene

Blends of a thermoplastic, isotatic polypropylene (PP) and a liquid-crystalline polymer (LCP) based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid, were extruded. The LCP exhibited a higher viscosity than that of the PP under the extrusion conditions. Calorimetric, microscopic, static and dynamic mechanical tests were performed on these blends. Differential scanning calorimetry thermograms indicated that the crystallization temperature of PP increases slightly with increasing LCP content. Scanning electron microscopy examinations revealed that the LCP phase was elongated into microfibrils in the blends investigated. However, some undeformed spherical droplets were dispersed in the PP matrix in addition to microfibrils for the blends containing high LCP concentrations. Static tensile tests showed that the addition of LCP to PP results in an increase of the modulus of elasticity but a decrease in tensile strength. The storage modulus of the extruded blends was found to increase with the addition of LCP.

Modulation of supramolecular structure of linear polyurethane systems by addition of liquid-crystalline polymers in the molecular miscibility range

The peculiarities of domain structure of segmented polyurethane-urea/liquid-crystalline polyester (PU/LCP) blends were studied in the LCP concentration range of 1–10%, with different lengths of the flexible moiety. Small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry were used. The position of the SAXS maximum changes discontinuously with increasing LCP concentration. We suggest that the rigid fragments of the LCP tend to be incorporated into the rigid domains of the PU component with the restriction that only each third or fourth fragment is involved. The part of the LCP molecule that fits in the space between rigid PU domains is stretched and determines the interdomain distance.

Miscibility and viscoelastic properties of blends of a liquid-crystalline polymer and poly(ethylene terephthalate)

A thermotropic liquid-crystalline polymer (LCP) was found to be miscible with poly(ethylene terephthalate) (PET) for LCP contents up to 35 wt% and immiscible at higher LCP contents. The melts of the miscible blends are isotropic under the polarizing microscope. They crystallize with a single transition during rheological cooling measurements. In the solid state, the miscible blends showed a single glass transition, as represented by a single peak of loss modulus G″ versus temperature, which decreased linearly with LCP content. Addition of a small quantity of LCP has a dramatic effect on rheology. For example, addition of 2 wt% LCP reduces the viscosity by about 60%. This effect is most pronounced for PET of higher molar masses. The melt viscosity decreases exponentially with the LCP content in the range of composition where the blends are miscible, but there is no significant further reduction of viscosity when the LCP content exceeds 50 wt% as the phase separation appeared. Addition of LCP also changes the distribution of the relaxation times of PET and broadens the zero-shear viscosity regime.

Characterization of thermotropic liquid crystalline polyester/polysulfone blends

AbstractThe morphology, rheology, and mechanical properties of blends of polysulfone (PSF) with up to 65% of a wholly aromatic liquid crystalline polymer (LCP) were investigated. In injection molded specimens a skin‐core morphology was observed with the LCP minor phase oriented in the skin and globular in the core. Scanning electron microscopy of fractured surfaces showed sharp phase boundaries, suggesting low interfacial adhesion. The neat PSF and blends with low amounts of LCP exhibited a low shear Newtonian plateau not observed in the blends with high LCP levels. The addition of LCP to PSF resulted in an increase in stiffness, a small increase in tensile strength, and a significant improvement in processability.

Blends of a liquid crystalline polymer with polyether ether ketone

AbstractBlends of Polyether ether ketone (PEEK) and a thermotropic liquid crystalline Polymer (LCP) based on paraoxy‐benzoyl and oxy‐biphenylene terepthaloyl units were prepared using a static mixer attached to a single screw extruder at 420°C. Rheological studies indicated an increase in the viscosity of the blends upon the addition of LCP. Thermal studies on these blends demonstrated their poor thermal stability compared to the parent materials. The mechanical properties indicated improvement in Young's tensile and flexural modulus but no improvement in the break strength with the addition of the LCP. Morphological studies indicated the formation of ellipsoids of LCP at low LCP concentration in the matrix of PEEK, with extended ellipsoids being observable at 25 percent LCP composition. Phase inversion was noticeable at higher LCP content blends with the formation of PEEK fibrils in the matrix of the LCP. Dynamic studies on these blends showed an increase in the storage modulus with the addition of LCP.

Blends of a thermotropic liquid-crystal polyester with poly(phenylene sulphide)

Blends of a thermotropic liquid-crystalline polymer (LCP), based on a copolyester of hydroxynaphthoic acid and hydroxybenzoic acid, with an engineering thermoplastic, poly(phenylene sulphide) (PPS), were prepared using a co-rotating twin-screw extruder. The blends were subsequently injection moulded to study their mechanical, dynamic, impact and morphological characteristics. Rheological studies have indicated a higher shear viscosity of the LCP as compared to PPS, with the shear viscosity of some of the blends being higher than that of the LCP. Dynamic and thermal studies have indicated overlapping temperature transitions of the pure components. Therefore, based on these measurements it is not possible to make a conclusion about the compatibility of the blends. Thermogravimetric studies have indicated the poor thermal stability of the blends when compared to the pure materials. The tensile and impact properties of these blends were found to increase with the addition of LCP. However, the pure LCP exhibits the highest properties. The morphology of the blends has indicated their incompatibility and the formation of LCP droplets in the matrix of PPS at nearly all concentrations of LCP, with the formation of the skin-core morphology being clearly visible at LCP content greater than 25%.