Effect of ethylene/propylene ratio on reinforcing characteristics of liquid crystalline polymer (LCP) in EPDM-LCP composites

Abstract

Two ethylene/propylene diene monomer (EPDM) polymers were blended with a liquid crystalline polymer (LCP) at concentrations of 10, 20, 30 and 40 wt-%. The effects of ethylene/propylene (EP) ratio on the in situ fibrillation, and hence the reinforcing characteristics, of the LCP in EPDM-LCP blends were studied. The fibre forming capacity of the LCP depended on the viscosity of the EPDM rubber. Under high temperature processing conditions (at 300°C), the high EP ratio EPDM, which had the higher viscosity, facilitated the fibrillation of the LCP. Further melt processing at 100°C, followed by curing at 150°C, decreased the reinforcing effects of the LCP owing to breakage of the fibrils under the high shear stresses developed in the high viscosity matrix. However, this degradation of fibre lengths depended on the LCP concentration. After curing, the more viscous EPDM formed blends with higher stiffnesses and strengths than those obtained from the low viscosity EPDM. Both the nucleation and growth of crystal domains in the EPDM matrix were promoted by small amounts of LCP. Again the effects were more pronounced in the EPDM with the higher EP ratio.     

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.     

Energy‐based predictive criterion for LCP fibrillation in LCP/thermoplastic polymer blends under shear

This article relates the fibrillation of liquid crystalline polymer (LCP) under shear in its blend with a thermoplastic polymer (TP) to the relative rate of energy utilization in the LCP and TP phases. The development of a criterion based on the energy relationship for predicting LCP fibrillation in the blend is discussed. The formation of LCP fibers in the blends of LCP with polycarbonate (PC), polyethylene naphthalate (PEN), high‐density polyethylene (HDPE), polypropylene (PP), and silica‐filled polypropylene (PP) was studied to validate the criterion and to demonstrate its applicability. For all the blends, viscosity data were obtained by using a capillary rheometer, which was subsequently used to estimate the rate of energy utilization in the LCP and the matrix phases. The predictions based on the proposed criterion were verified through the morphological investigations carried out on the extrudates obtained from the same capillary experiments. The energy‐based criterion was easy to implement, could account for the effect of variable LCP concentration and fillers in the blend, and could provide reliable predictions for a variety of LCP/TP blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3314–3324, 2003     

Factors influencing microstructure formation in polyblends containing liquid crystalline polymers

Four isotropic polymers, poly(butylene terephthalate) (PBT), polycarbonate (PC), polyethersulfone (PES) and polysulfone (PSU), were blended by extrusion with a thermotropic liquid crystalline polymer (LCP) at different temperatures. The morphology of extrudates was observed by means of scanning electron microscopy and the intrinsic aspect ratio of LCP fibrils and particles separated from matrix resin was measured with an image analysis. Special attention was paid to the LCP fibrillation in these four matrices in a wide temperature range from 270 to 360°C and the internal relations among the effects of processing parameters, such as viscosity ratio, extrusion temperature, and LCP concentration. The results show that the viscosity ratio of the dispersed LCP phase to the continuous phase is a decisive factor determining the formation of LCP fibrils, but its effect closely relates with the LCP content. In the range of viscosity ratios investigated, 0.004 to 6.9, and lower LCP content of 10%, significant fibrillation took place only at viscosity ratios below 0.01. It is predicted that the upper limit of the viscosity ratio for LCP fibrillation will increase with increasing LCP content. A comparison of the morphologies of LCP/PES blends with different LCP concentrations reveals that the LCP phase becomes continuous at a concentration of less than 50%, and high LCP content does not always favor the formation of long and uniform LCP fibrils. The extrusion temperature has a marked effect on the size of the minor LCP domains. For fibril forming systems, the percentage of LCP fibrils with larger aspect ratios increases with increasing extrusion temperatures. All these results are explained by the combined role of deformation and coalescence of the LCP disperesed phase in the blend.     

Preparation and properties of self-reinforced polypropylene/liquid crystalline polymer blends

The mechanical properties of self-reinforced liquid crystalline polymer/polypropylene (LCP/PP) blends strongly depend on the viscosity ratio of the blend components in the melt. This ratio was determined for PP blends with different commercial LCPs (Vectra A950 and Vectra B950), by means of capillary rheometry, under conditions representative for the blending process during extrusion. It was found that optimal mechanical properties were achieved when the LCP/PP viscosity ratio at 285°C ranges between 2 and 4 at a shear rate of 800–1000s⁻¹. The LCP/PP viscosity ratio appears to be shear stress dependent. This creates the option of fine tuning the LCP droplet deformation process by means of the extrusion rate. This shear stress dependence is more pronounced for PP blends with Vectra B950 than for blends with Vectra A950.     

Comparative study on phase and properties between rPET/PS and LCP/PS in situ microfibrillar-reinforced composites

Microfibrillar-reinforced composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate) (rPET), and polystyrene (PS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of LCP/PS and rPET/PS blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into PS significantly improved the processability. The potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as-extruded strand. Although the viscosity ratio of rPET/PS system was lower than that of LCP/PS system, most rPET domains appeared as small droplets. An addition of LCP and rPET into PS matrix improved the thermal resistance in air significantly. The obtained results suggested the high potential of rPET as a processing aid and thermally stable reinforcing-material similar to LCP. The mechanical properties of the LCP-containing blends were mostly higher than those of the corresponding rPET-containing blends when compared at the same blend composition.     

Characterization of liquid crystalline polyester polycarbonate blends

Mechanical and rheological properties of blends of a thermotropic liquid crystalline polyester with a polycarbonate have been investigated. The blends are fibrillar in character and exhibit great hardness and toughness due to high degree of molecular orientation which develops during the melt blending and processing steps. Increases of the Young modulus by 100 percent are observed for blends containing only 10 percent of liquid crystalline polymer, LCP. Time-dependent behavior of the blends was investigated by performing solid state relaxation measurements and the relaxation modulus was also found to increase by the addition of LCP. The effect is relatively small in the glassy zone of viscoelastic response, but increases through the transition and viscous flow regions. The melt viscosity of the polycarbonate is slightly shear thinning whereas that of the unblended LCP increases rapidly with decreasing shear rate at low shear rate. This suggests the presence of yield stresses as confirmed by measurements on the Rheometics RSR in the stress sweep mode. The melt viscosity of the blends was found to be similar to that of the unblended polycarbonate, but more shear-thinning and less viscous. Preliminary results of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) are also presented.     

Physical properties of blends of polycarbonate and a liquid crystalline copolyester

Blends of polycarbonate (PC) and poly(ethylene terephthalate-co-p-oxybenzoate) (PET/PHB60) were prepared by melt-blending. Physical and/or chemical interactions between the two phases of the system were studied by thermal analysis and infrared spectroscopy. Rheological measurements in shear flow were carried out both in the low and high shear rate regions in the temperature range of the existence of the mesophase. At low liquid crystalline polymer (LCP) content, the blends showed flow curves similar to those of the unfilled PC, while at higher LCP percentages the rheological behavior of the pure LCP was resembled. Moreover, in the whole shear range, the viscosity values of such blends were in between those of the pure polymers. The influence of the addition of 10% LCP on the mechanical properties of the PC was investigated. Fiber-spinning was performed under different experimental conditions, and it was found that opportune drawing conditions are necessary to improve the modulus of the matrix. Morphological analyses of the pure LCP and of the blends were related to the rheological and mechanical behavior of these systems. While the LCP exhibited an elevated dimensional stability, the inclusion of the LCP in PC matrix did not improve the dimensional stability of the blends.     

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 LCP and rPET as reinforcing materials on rheology,morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

Microfibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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

The 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     

Electrical conductivity of polymer blends containing liquid crystalline polymer and carbon black

This paper presents results of a study of melt‐processed immiscible polymer blends of high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and carbon black (CB). Relationships between composition, electrical resistivity and morphology of the blends produced by Brabender mixing followed by compression molding, extrusion through a capillary rheometer, extrusion through a single‐screw extruder and injection molding were investigated. The LCP phase morphology in the blends was found sensitive to the processing conditions. A blend composition of at least 20 wt% LCP and 2 phr CB is necessary to preserve the conductivity of filaments produced over a wide range of shear rates. Enhancement of conductivity of blends containing CB and 30 wt% or more LCP was observed, under processing at 270°C and increasing levels of shear rate. An important role of the skin region in determining the resisitivy of injection molded samples was found. A good agreement between resistivity values of extruded or injection molded blends with resistivity values of filaments produced at similar conditions by a capillary rheometer was shown. Hence, the study of shear rate effect on resistivity of capillary rheometer filaments may serve as a predictor of resistivity behavior in real processing procedures. Polym. Eng. Sci. 44:528–540, 2004. © 2004 Society of Plastics Engineers.     

Novel approach to fibrillation of LCP in an LCP/PP blend

A novel concept of improving shear‐induced fibrillation of liquid crystalline polymer (LCP) in LCP/thermoplastic blend systems was introduced. Silica fillers (SiO₂) were added to an LCP/polypropylene (PP) system to serve as a viscosity thickening agent and to improve the fibrillation of the LCP phase. The formation of LCP fibrils was found to enhance with the incorporation of 5–15 wt % of fillers. The presence of LCP fibrils improved the flow properties of the LCP/PP/SiO₂ composites. It was evident from the rheological and morphological studies that the addition of silica led to an increase of the aspect ratio of the LCP fibrils, which, in turn, should improve their effectiveness as reinforcements and/or toughening agents. Substantial improvement in LCP aspect ratio was achieved by the introduction of hydrophobic SiO₂ fillers in the PP/LCP blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2070–2078, 2002     

The morphology and rheology of polymer blends containing a liquid crystalline copolyester

The morphology of blends of polycarbonate and nylon 6,6 with a copolyester of 60 mole percent p-hydroxybenzoic acid/40 mole percent poly(ethylene terephthalate) was characterized under different processing conditions. In particular, single-screw extrusion, steady simple shear flow, and flow through a capillary were studied to determine what conditions were necessary for the development of a fibrillar morphology of the liquid crystalline polymer (LCP). Results indicate that some extensional flow is required for the coalescence and extension of the particulate LCP phase. The viscosity of the blends was determined both in a cone-and-plate geometry of a Rheometrics Mechanical Spectrometer at low shear rates and in the Instron Capillary Rheometer at higher rates. In general, only a small (10 or 30 percent) weight fraction of LCP was required to reduce the viscosity of the thermoplastics to that of the polymeric liquid crystal. An attempt was made to correlate the structure of the blends seen under the scanning electron microscope with the observed rheology. Not all aspects of the morphology were possible to explain in terms of the viscous properties of the blends.     

Liquid crystal polymer/polyethylene blends for thin film applications

A series of liquid crystal polymer/polyethylene (LCP/PE) blends have been studied to determine the potential of such a system to produce a high modulus film material which retains fabrication and low temperature characteristics of some current PE films. The subject of liquid crystalline polymer blends has been the focus of significant attention for the last decade due to the novel rheological and mechanical properties of this class of polymers. It has been demonstrated that if an LCP blend is processed under elongational flow conditions, the partially ordered LCP meso-phase intermediate allows the development of an oriented fibrillar morphology which is retained upon solidification. In this study, blown films of blends of 5 and 15% LCP in PE have been produced which show an enhancement in modulus over the neat PE matrix. These results are discussed in terms of processing conditions, LCP reinforcement aspect ratio, fibril diameter, and LCP/PE modulus ratio.     

Effects of the addition of a liquid crystalline copolyester to polystyrenes on blending torque and mechanical properties of blends

Blending of polystyrenes (PS) with a thermotropic liquid crystalline polymer (LCP) was performed by using a continuous corotating twin screw extruder. The influence of LCP content on the blending process was studied by changing the barrel heater temperature and the screw speed. The torque of screw shafts, generated during the blending process, was influenced by LCP content and its influence was not simple. The torque generated during the blending process was not directly related to the apparent melt viscosity of blends. Further, the effects of the matrix viscosity on the morphology and mechanical properties of the PS/LCP blends were studied using three grades of PS as matrix resins. It was found that the size of the LCP dispersed phase decreased with increasing matrix viscosity. Consequently, the mechanical properties of the PS/LCP blend were improved. © 1993 John Wiley & Sons, Inc.     

The effect of composition on thermal,mechanical, and morphological properties of thermotropic liquid crystalline polyester with alkyl side-group and polycarbonate blends

A thermotropic liquid crystalline polymer (LCP) with an alkyl side-group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases.     

Rheological and physical properties of polyarylate/LCP blend systems

A polyarylate Unitika U-Polymer 100 (PAR) was melt blended with a thermotropic liquid crystalline polymer (LCP) Vectra A950, and the processingmorphology-properties relations were investigated. Inclusion of LCP slightly reduced T_g of PAR. The PAR/LCP blend with the LCP content higher than 50 wt% exhibited a noticeable yield stress, particularly in the vicinity of crystal-to-nematic transition temperature (T_cn). LCP lowered the blend viscosity above T_cn and seemed to play a role as processing aid. The tensile strength of the blends was increased with increasing spin draw ratio and level of LCP, and the spinning temperature influenced tensile strength. The relaxation behavior under dynamic shear and resultant blend morphology based on WAXD and SEM analyses are discussed as well.     

Effect of viscosity ratio and processing conditions on the morphology of blends of liquid crystalline polymer and polypropylene

The effect of viscosity ratio and processing conditions on LCP/PP blend morphology was studied. The viscosity ratio (η_LCP/η_PP) was varied from 0.1 to 3.6 by using five different polypropylene grades as the matrix and two LCPs as the dispersed phase (20 wt %). The most spontaneous fiber formation was achieved when the viscosity ratio was between 0.5 and 1. In addition to shear forces, elongational forces are important in achieving a highly fibrillar structure and significant mechanical reinforcement. The lubricating effect induced by the low viscosity of LCP was most pronounced for the blends exhibiting a fibrillar morphology. The morphologies of blends produced by different mixing equipment differed only slightly. The greatest variation in the mixing efficiency was found for blends whose components had totally dissimilar melt viscosities. The slight differences in morphology due to melt blending in dissimilar equipment were decreased after injection molding, whereas the differences in morphology due to dissimilar viscosity ratios were still evident in the injection molded blends. Thus, the viscosity ratio at processing in the actual processing conditions is of great importance. © 1994 John Wiley & Sons, Inc.     

Blends of thermotropic polyester with poly(phenylene oxide)

A thermotropic liquid crystalline polymer (LCP) based on wholly aromatic copolyesters based on hydroxynaphthoic and hydroxybenzoic acid was melt-blended with a thermoplastic poly(phenylene oxide) by corotating twin screw extruder. Rheological properties, temperature transitions, dynamic and mechanical properties, and electron microscopy study have been performed. Rheological study indicated significant viscosity reductions with increasing LCP content leading to ease of processing. From the differential scanning calorimeter (DSC) and dynamic mechanical thermal analyzer results, these blends showed incompatibility for the whole range of concentrations. Mechanical properties were found to be slightly improved at low LCP and dramatically improved at above 50% LCP contents. In addition, impact strength was significantly increased up to two times after adding 10% LCP into the matrix. The morphology of blends was affected by composition. Droplets and stubby fibrils structures caused lower tensile strength, whereas fibrillar structure improved this property.