Studies on morphology, mechanical, thermal, and rheological behavior of extrusion-blended polypropylene and thermotropic liquid crystalline polymer (original) (raw)
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Journal of Applied Polymer Science, 1996
The effect of the viscosity ratio of the dispersed LCP phase to the polystyrene/ poly(pheny1ene oxide) (PS/PPO) thermoplastic matrix on the rheological, morphological, and resultant mechanical properties of the LCP blends was investigated. The viscosity of PS/PPO is largely dependent on the blend composition, so that different levels of viscosity ratios of dispersed LCP phase to PS/PPO thermoplastic matrix are obtained by using PSI PPO premixtures of different blend ratios as a thermoplastic matrix. When the viscosity of the LCP dispersed phase is lower than that of the thermoplastic matrix, finely distributed fibril structure of LCP is obtained. Tensile modulus of injection molded specimens show a positive deviation from the additive rule when the viscosity ratio (vLcP/vmatrix) is smaller than unity. These improvements in tensile modulus are attributed to the formation of finely distributed LCP fibrils. 0 1996 John Wiley & Sons, Inc.
Journal of Applied Polymer Science, 2006
The main aim of this work is to study the morphological and rheological evolution during extrusion of blends of polypropylene and a commercial liquid crystalline polymer, Rodrun LC3000. This study was performed for blends with 10, 20 and 40 wt% LCP, processed at 220 and 240 8C. For this purpose, a special collecting device was used that allows the removal of samples at different locations along the extruder length. The results of the morphological study revealed that the mean diameter of the LCP structures decrease as they proceed along the extruder axis. The rheological properties were also studied ex situ both in the linear and in the non-linear regime. From the results obtained in oscillatory shear it was observed that the elastic modulus and the complex viscosity decreases from the beginning to the end of the extrusion process, reaching a minimum for the final extrudate. FT rheology was used to study the non-linear viscoelastic behavior and the results also show marked difference between samples collected at various stages of the process, the ratio Ið3v 1 Þ=Iðv 1 Þ decreasing along the extruder. q
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 rheooptics 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 dropletshape 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 observa-tions. 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.
Chemical Engineering Science, 2009
Blends of a long-chain branched polypropylene (LCB-PP) and four linear polypropylenes (L-PP) having different molecular weights were prepared using a twin screw extruder. The linear viscoelastic properties suggested the immiscibility of the high molecular weight L-PP based blends, and the miscibility of the low molecular weight L-PP based blends. In addition, the Palierne emulsion model showed good predictions of the linear viscoelastic properties for both miscible and immiscible PP blends. However, as expected, the low-frequency results showed a clear effect of the interfacial tension on the elastic modulus of the blends for the high molecular weight L-PP based blends. A successful application of time-temperature superposition (TTS) was found for the blends and neat components. Uniaxial elongational properties were obtained using a SER unit mounted on an ARES rheometer. A significant strain hardening was observed for the neat LCB-PP as well as for all the blends. The influence of adding LCB-PP on the crystallinity, crystallization temperature, melting point, and rate of crystallization were studied using differential scanning calorimetry (DSC). It was found that the melting point and degree of crystallinity of the blends first increased by adding up to 20 wt% of the branched component but decreased by further addition. Adding a small amount of LCB-PP caused significant increase of the crystallization temperature while no dramatic changes were observed for blends containing 10 wt% LCB-PP and more. Furthermore, the crystalline morphology during and after crystallization of the various samples was monitored using polarized optical microscopy (POM). Compared to the neat linear polymers, finer and numerous spherulites were observed for the blends and LCB-PP. Dynamic mechanical (DMA) data of the blends and pure components were also analyzed and positive deviations from the Fox equation for the glass transition temperature, T g , were observed for the blends.
Polymer, 2003
In situ composite films were prepared by a two-step method. First, polypropylene and thermotropic liquid crystalline polymer (TLCP), Rodrun LC5000 (80 mol% p-hydroxy benzoic acid (HBA)/20 mol% polyethylene terephthalate (PET)), were melt blended in a twin-screw extruder and then fabricated by extrusion through a mini-extruder as cast film. Rheological behavior of the blends, morphology of the extruded strands and films, and tensile properties of the in situ composite films were investigated. Rheological behavior of the blends at 295 8C studied using a plate-and-plate rheometer revealed a substantial reduction of the complex viscosity with increasing TLCP content, and all specimens exhibited shear thinning behavior. Over the angular frequency range of 0.6-200 rad/s, the viscosity ratio (dispersed phase to matrix phase) was found to be very low, in the range of 0.03-0.07. Morphologies of the fracture surfaces of the blend extrudates and the film surfaces etched in permanganic solution were investigated by scanning electron microscope (SEM). The TLCP droplets in the extruded strands were seen with a progressive deformation into fibrillar structure when TLCP content was increased up to 30 wt%. In the extruded films, TLCP fibrils with increasing aspect ratio (length to width) were observed with increasing TLCP concentration. Orientation functions of each component were determined by X-ray diffraction using a novel separation technique. It was observed that the Young's modulus in machine direction of the extruded film was greatly improved with increasing TLCP loading, due to the increase in fiber aspect ratio and also molecular orientation. q
Rheologica Acta, 2000
An immiscible blend of a thermotropic liquid crystalline polymer (TLCP) with a thermoplastic resulted in a ®berreinforced thermoplastic called an in situ composite, the term coined by . Such composites arise due to the formation of a ®brillar TLCP phase during extensional melt¯ow. They are interesting because they have several outstanding features. In addition to the improvement on physical and dimensional stability of the matrix, the incorporation of TLCP also enhances the ease of processing, resulting from the reduced overall melt viscosity of the system. Processing conditions including temperature and the shear and elongational forces strongly aect the molecular orientation of the TLCP phase as well as the ®ber aspect ratio which determines the ®nal physical properties of the composite.
Mechanical properties of blends of liquid crystalline copolyesters with polyprophylene
Mechanics of Composite Materials, 1995
As new composites produced in the form of blends of thermotropic liquid crystals (LCP) with less expensive engineering thermoplastics became very popular recently, increased interest about the production and investigations of these materials is noted during the last few years [1-5]. First, the addition of the LCP permits us to essentially decrease the viscosity of certain engineering thermoplastics and therefore to facilitate the processing considerably. Second, during injection molding the drops of the LCP, as a dispersed phase, are lengthening out themselves into aniso-diametrical, thread-like forms, finally reinforcing the isotropic thermoplastic matrix. It allows us to obtain reinforced composites with improved physicomechanical properties directly during processing. To optimize the selection and the composition of the components as well as the processing conditions, investigations of the melt rheological properties and the mechanical and physical properties of the products are necessary. The main purpose of our work was to determine the mechanical properties of the blend of the LCP with polypropylene and the anisotropy of mechanical properties produced as a result of processing by injection molding. EXPERIMENTAL Material. The isotactic polypropylene (PP), VB 65 11B, produced by NESTE, Finland, and the liquid crystalline copolyester (LCP) of 40% polyethylene terephthalate with 60% p-hydroxybenzoic acid (40 PET/60 PHB), LC-3000, produced by Unitika Ltd., Kyoto, were used in our investigations. Binary blends with LCP content of 0%, 5%, 10%, 15%, and 20% were prepared. Sample Preparation. To exclude the possible degradation of macromolecule chains by hydration, the 40 PET/60 PHB copolyester was dried for 8 h at 130~ the blending was done using a single screw extruder Goettfert ~ = 20 mm (the length/diameter ratio L/D = 20) with a 3 mm cylindrical die. The extruded rods were granulated using a palletizing trait. The temperatures of the heating zones of the barrel were 210~ 200~ and 230~ The screw rotation speed was 55 rpm. Plates with a length of 160 mm, width of 100 ram, and thickness of 2 mm were prepared by injection molding. This was conducted at a rather high temperature to assure the processing of the blend in the liquid crystalline phase and to form the LC-rich regions in the thermoplastic matrix. The machine used was the injection press BILLION with a clamping force of 90 tons. The following injection parameters were applied: temperature of the barrel 170~176176 and 245~ the mold temperature was 20~ filling pressure 530 bars, packing pressure 270 bars, packing time 5 sec, and the cooling time in the mould was 15 sec. To determine the anisotropy of the mechanical properties by tensile test, samples in the form of a dog-bone were cut in the flow direction (MD) (direction of injection) and in the transversal direction (TD) (perpendicular to the flow direction). The dimensions of MD specimens were: thickness 2 turn, length 150 ram, the length of the narrow section 60 ram, and the distance between the clamps 90 mm. For TD specimens, the corresponding dimensions were: 100 ram, 40 mm, and 60 mm.
Polymer Journal, 1996
The effects of the viscosity ratio of dispersed phase to matrix on the rheological, morphological, and mechanical properties of blends of polystyrene and two rheologically different liquid crystalline polymers (LCPs) were investigated. Two different rheological behaviors are obtained by blending polystyrene (PS) and two different LCPs: one is the case that the viscosity of dispersed phase is lower than that of matrix phase as observed in PSIRodrun blends, and another one is the case that the viscosity of dispersed phase is higher than that of matrix phase as observed in PSIVectra blends. Scanning electron micrographs of fracture surfaces of injection-molded samples show that the finely distributed LCP fibril structure is observed for PSIRodrun blends where the viscosity of the dispersed LCP phase is lower than that of the polystyrene matrix phase, whereas dispersed LCP phase in PSIVectra blends show the spherical form of LCP domains. Mechanical properties of injection molded specimens show that the modulus of PSIRodrun blends shows a strong positive deviation from the simple additive rule, whereas the modulus ofPSIVectra blends follows the simple additive rule of mixture. These mechanical properties are well consistent with the morphological characteristics of the PSILCP blends.
Polymers for Advanced Technologies, 2009
In this study, the potential of recycled poly(ethylene terepthalate) (rPET) as a well-defined reinforcing material for the in situ microfibrillar-reinforced composite (iMFC) was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with high density polyethylene (PE) by using extrusion process. The rheological behavior, morphology, and the thermal stability of LCP/PE and rPET/PE 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 LCP or rPET into PE significantly improved the processability. A 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 the rPET/PE system was lower than that of the LCP/PE blend system, most rPET domains appeared as small droplets. An addition of LCP and rPET into the PE matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and good thermally resistant material similar to LCP.