Characterization and processing of blends of polyethylene terephthalate with several liquid crystalline polymers

Blends of an engineering thermoplastic, poly(ethylene terephthalate) (PET), and two liquid crystalline polymers (LCPs) viz., copolyesters of PET and parahydrox-ybenzoic acid (PHB) in 40/60 mole percent (LCP60) and in 20/80 mole percent (LCP80) were prepared. A blend of LCP60 and LCP80 in 50/50 weight percent (LCP60-80) was blended with PET. Both flat films and rods were extruded and their properties examined. The morphology of the films investigated using Scanning Electron Microscopy (SEM) revealed that the LCP phase remained as dispersed droplets in the PET matrix. In spite of the lack of fibrillation in these films, the mechanical properties were enhanced to some extent with a maximum at 10 weight percent of the LCP phase. However, in the case of the rods thin fibrils of the LCP phase of the order of 1 μm in diameter were observed provided the composition of the LCP was 20 weight percent or greater. This success In achieving fibrillation is through to be due to the extensional flow fields present at the entrance of the capillary die and the fact that a short L/D ratio die was used. Differential Scanning Calorimetry (DSC) thermograms of the extruded films indicated that the LCP phase may act as a nucleating agent for the crystallization of PET. Rheology of the blends revealed that the complex viscosity of the blends is not much different from that of pure PET. This is attributed to the partial miscibility of the two components. Based on the DSC results and residence times in the extruder, it is concluded that no significant transesterification reactions appear to have: taken place in the blends. The rheology is studied further with respect to the cooling behavior of the pure components and factors important to the fibrillation of the LCP phase and the formation of in-situ reinforced composites are discussed.     

Thermomechanical properties of radiation-modified blends of polyethylene with liquid crystalline copolyester

The results of investigation of gamma irradiated blends of high-density polyethylene (PE) with thermotropic polymer liquid crystal (PLC) are presented. The PLC used was a copolyester of 40% poly(ethylene terephthalate) with 60% p-(hydroxy-benzoic acid). The PLC content in the blends was 0, 5, and 10 wt%. The constituents were blended with the use of a single screw extruder. The specimens were prepared by compression molding. The irradiation of the samples was performed by a Co⁶⁰ γ-radiation source in inert atmosphere (argon) up to absorbed relatively low doses (up to 200 kGy; 1 Mrad = 10 kGy). The morphological, thermal, and mechanical properties were investigated for irradiated and unirradiated samples. The influence of gamma irradiation and addition of PLC on the temperature dependence of the elastic modulus as well as the effect of a “form memory” of the materials examined are discussed. It was found that an addition of the PLC affects substantially the stress-strain relationship in tension at temperatures above the melting point of PE for the irradiated samples. The features of thermomechanical behavior of the PE + PLC blends, previously irradiated and oriented, at isometrical heating and cooling were also established. The results obtained testify that the addition of PLC to PE makes it possible to improve considerably the thermosetting properties of the heat-shrinkable polymeric products.     

Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high‐density polyethylene

Blends of an extrusion‐grade high‐density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4–9 vol%), whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two‐dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc‐shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%–55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%–92%) than in solubility (39%–76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra RD501 blends and relatively small for the Vectra A950 blends.     

Mechanical properties of in-situ composites based on partially miscible blends of glass-filled polyetherimide and liquid crystalline polymers

The use of inorganic (glass) fiber reinforcement to enhance the mechanical properties and reduce the anisotropy of in situ composites based on blends of liquid crystalline polymers (LCPs) with polyetherimide (PEI) is discussed. It was found that the tensile and flexural moduli are increased and the anisotropy is reduced with increasing grass content (when compared at equivalent LCP weight fractions). The creep compliance of the PEI/LCP composites is reduced upon the addition of glass fibers. However, the disadvantage is that the processability worsens upon addition of glass fibers to the PEI/LCP in situ composites. The effect of adding glass reinforcement on the ultimate tensile strength is less clear, because the data do not show any consistent trend. Similarly, the elongation at break and toughness do not show any consistent improvement upon addition of glass reinforcement. Morphological studies show that there is considerable difference between the size and texture of the reinforcing glass fibers and LCP microfibrils.     

Mechanical properties of in situ composites based on partially miscible blends of polyetherimide and liquid crystalline polymers

Results related to the mechanical properties of in situ composites based on partially miscible blends of polyetherimide (Ultem) and liquid crystalline polymers (HX1000 and HX4000) are discussed. It is observed that, at least in terms of the tensile and flexural modulus, there is a positive deviation from the law of mixtures. These results are analyzed and an attempt is made to explain the origin of this synergistic behavior based upon morphological data. The behavior of these partially miscible systems is compared to that of an immiscible system (Ultem/Vectra) and also that of glass-reinforced Ultem. Using blends subjected to two passes through a single screw extruder, and thereby increasing the mixing history of the Ultem/HX4000 blend, led to improved dispersion but did not lead to any measurable improvement, within experimental error, in the tensile modulus or ultimate strength (though the toughness was enhanced). The dynamic creep compliance was measured and the creep behavior with composition and temperature is discussed. The data seem to suggest that a number of factors (including partial miscibility, the properties of the specific LCP chosen as the reinforcement and the final blend morphology) all interact in a complex and as yet undetermined manner to produce the enhanced mechanical properties.     

Morphology and properties of blends of polyethylene with a semiflexible liquid crystalline polymer

Blends of three polyethylene (PE) samples (two HDPE grades and LLDPE) with an experimental sample of a semiflexible liquid crystalline polymer (SBH 1:1:2 by Eniricerche) have been prepared in a Brabender compounder. The processing-aid effect of the LCP has been demonstrated by the decreased energy required for extruding the blends, as compared to that needed for neat PE. The thermal properties, as studied by differential scanning calorimetry (DSC), have shown that the two components of the blends are immiscible. However, the dispersed SBH phase has been found to act as a nucleating agent for the crystallization of LLDPE, whereas no such effect was observed for HDPE. This has been taken as an indication that the phase interactions of SBH with LLDPE are more pronounced than with HDPE. The morphological study of the blends, done by scanning electron microscopy (SEM), has confirmed this conclusion. In fact, the SBH particles show a much better dispersion and a narrower size distribution in the LLDPE/SBH blends. The mechanical properties of the blends have been studied on compression-molded specimens. The results indicate that the reinforcing effect of SBH is practically none for both HDPE grades. In fact, the elongation at break decreases to very low values, and the tensile strength is also reduced, when the LCP concentration increases beyond 5–10%, whereas the tensile modulus does not vary appreciably, over the whole (0–20%) LCP range investigated. On the contrary, the tensile modulus of the LLDPE/SBH blends increases up to ca. 50%, and the elongation at break decreases more smoothly, on increasing the SBH content up to 20%. © 1995 John Wiley & Sons, Inc.     

Novel reinforced polymers based on blends of polystyrene and a thermotropic liquid crystalline polymer

A thermotropic liquid crystalline polymer (LCP), when added to polystyrene (PS), can function as both a processing aid and a reinforcing filler. Thermal, rheological, and mechanical properties of the pure components and blends containing up to 10 percent LCP are reported. The LCP used is immiscible with PS, and when an extensional component of flow is present during processing, the LCP forms an elongated fibrous phase oriented in the flow direction. This oriented phase lubricates the melt, substantially lowering the viscosity. When the processed blend is cooled, the dispersed fibrous LCP phase is preserved in the solidified material. The LCP microfibers behave like short reinforcing fibers to improve the mechanical properties of the blend; for example, at an LCP concentration of 4.5 percent, the modulus is increased about 40 percent vs. pure PS.     

Stability of blends of thermotropic liquid crystalline polymers with thermoplastic polymers

Breakup of fibers of a thermotropic liquid crystalline polymer (TLCP) above the melting temperature in various ordinary polymers has been studied by capillary instability experiments on single TLCP fibers and by annealing experiments on extruded TLCP/thermoplast blends. The TLCP was an aromatic copolyester, Vectra A900, the matrix polymers were PP, PS, PC, PEL PES, and PEBT. Both types of experiments show that the fiber/matrix morphology is, in general, highly unstable in the molten state. The TLCP fibers break up into droplets by a combination of Rayleigh distortions, end-pinching and retraction, depending on the system and shape of the fiber. Fibers of a thickness of ～1 μm can break up in a few seconds. Breakup times of fibrous blends and individual fibers are in agreement provided size effects are accounted for. Rayleigh distortions develop exponentially in time up to relative distortions of 0.5 to 0.6. Breakup occurs within a range of wave numbers rather than at one distinct dominant wave number, which is shown to be the consequence of relatively large initial distortions. Apparent values for the interfacial tensions calculated with Tomotika's theory turned out to be of the correct order of magnitude, ranging from 7 mN/m for Vectra/PES to 24 mN/m for Vectra/PP and to yield correct values of the interfacial tensions of PP/PS, PP/PC, and PS/PC using Antonow's rule.     

Nonisothermal elongational behavior of blends with liquid crystalline polymers

Measurements of melt strength and breaking stretching ratio of several blends of thermoplastic polymers with liquid crystalline polymers are presented. The melt strength behavior depends not only on the viscosity of the blends but also on the temperature dependence of the viscosity. In particular, even if the viscosities of the blends are, at the extrusion temperature, lower than that of the thermoplastic matrices, the melt strength can be larger than that of the pure thermoplastics if its viscosity-temperature curve exceeds that of the matrices far from the solidification temperature. This behavior allows one to spin or film blow these blends despite the low viscosity.     

乙烯基对苯二甲酸类甲壳型液晶高分子的形状记忆性能

通过自由基聚合合成了四种基于乙烯基对苯二甲酸类甲壳型液晶高分子（PBPCS,PMPCS,PDCHVT,PbiPCS）。TGA和DMA表征结果表明,这四种甲壳型液晶高分子均具有较好的热稳定性,其侧基末端基团刚性越大,相对应的片材在30～80℃温度区间刚性越大。形状记忆弯角回复测试表明：四种聚合物热压成型的片材都具有很好的形状记忆固定率,均接近100%。形状记忆回复效果与聚合物侧基的末端基团有关,侧基末端基团分别为对丁氧基苯基和环己基（对应聚合物分别为PBPCS和PDCHVT）时,片材显示出较好的形状记忆性能,形状记忆回复率分别为87%和100%。将PDCHVT通过熔融纺丝制成纤维,采用形状记忆循环DMA测试表征其形状记忆性能,结果表明PDCHVT纤维具有稳定的优异的形状记忆性能。     

The effect of mixing shear rate on the properties of liquid crystalline polymer/polyethylene terephthalate blends

The effect of mixing speed of a batch mixer on the properties of liquid crystalline polymer/polyethylene terepthalate (LCP/PET) blends is investigated through two techniques: scanning electron micrographs to examine morphological changes, and tensile testing to determine the mechanical property dependence of the degree of mixing. The results of the two methodologies are well correlated, indicating that the increased degree of mixing of the blend, which is a function of the mixing speed, can be related directly to improved mechanical properties. The results are discussed in the light of existing theories on polymer mixing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1783–1787, 2000     

Barrier properties of polyamide-6/high density polyethylene blends

SUMMARY The barrier properties of Polyamide-6 (PA6)/High Density Polyethylene (HDPE) blends with and without compatibilizer prepared by ribbon extrusion were studied. The results show that the toluene diffusivity was improved by the addition of an interfacial agent and by inducing orientation of the polymer chains. The presence of PA-6 in the blend results in a decrease of the toluene diffusivity. This reduction is even larger for the case of the interfacial modified system. However, the most important reduction of the toluene diffusivity is observed for pure HDPE when stretched. A six-fold decrease is observed when the draw ratio is increased two fold. In the case of the permeability of different solvents through blends a gravimetric permeation cell was used. The results show that the permeability decreases with increasing size of the penetrant molecules (CH₂Cl₂, CHCl₃ and CCl₄) and this decrease is more important for a compatibilized blend. Received: 1 December 2000/Revised version: 21 March 2001/Accepted: 21 March 2001     

Studies on blends of melt‐processable liquid crystalline polymers and thermoplastics. I. Blend of polyesteramide with polyethylene

The processability characteristics, physicomechanical properties, and thermal decomposition characteristics of blends of low‐density polyethylene (LDPE) and polyesteramide (PEA), a thermotropic liquid crystalline polymer, were studied using various analytical techniques. Studies on a Brabender Plasticorder at temperatures ranging from 170 to 230°C showed good melt processability for the blends. The melt rheology of the blends containing 0–15% of PEA at 170°C was studied using a capillary rheometer (Goettfert) fitted with a circular die (L/D = 30/1) at apparent shear rates ranging from 12 to 2300 s⁻¹. The samples containing PEA showed a comparatively lower die swell at high shear rates. X‐ray diffraction measurements showed a reduction in crystallinity of LDPE in the presence of 2–4% of PEA. Scanning electron microscopic evaluation of the morphology of the fractured surface of the blend showed some degree of orientation, but not to the level typical of LCPs. However, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated significant improvement in the resistance to thermooxidative decomposition of LDPE modified with PEA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1811–1817, 2000     

Synthesis,structure and properties of liquid crystalline polymers

The following is an extended abstract of a paper presented at the conference on Liquid Crystalline Polymers in Leeds, 1980, summarising the principles of the synthesis of thermotropic liquid crystalline polymers, their structure dependant phase behaviour and their orientation in electric and magnetic fields.     

In situ composites based on blends of a polyetherimide and thermotropic liquid crystalline polymers subjected to shearfree deformations

The effects of shearfree elongational flows on the morphology and mechanical properties of blends of a polyetherimide (PEI) with thermotropic liquid crystalline polymers (TLCP) have been investigated. Extruded sheets and injection molded plaques of PEI/Vectra A and PEI/HX1000 blends, with a TLCP concentration of ≤30 wt%, were subjected to uniaxial elongation, planar and biaxial deformations at 240°C, above the glass transition temperature of the PEI, and at 265°C, which is below the melting point of the TLCPs. Experimental results revealed that each particular mode of shearfree deformation had a distinct effect on the morphology and properties of the blends. For instance, TLCP droplets were deformed into elongated fibrils by application of uniaxial elongation, deformed into elongated ribbon-like structures after planar deformation, and deformed into a disc-like shape by application of equibiaxial flow. Regarding mechanical properties, it was observed that the tensile modulus and strength of molded plaques of PEI/HX1000 80/20 wt% increased to about twice their initial values (from 5.13 to 10.40 GPa and from 105 to 198 MPa, respectively) after a strain of 0.75 was applied in a direction parallel to the initial direction of the TLCP fibers. In addition, samples exhibiting equal values of flow and transverse direction tensile modulus of ∼5.0 GPa were obtained when molded plaques of PEI/HX1000 80/20 wt% were subjected to planar stretching in a direction transverse to the initial direction of the fibers. Thus, by subjecting injection molded plaques to planar stretching, it was possible to obtain a sample exhibiting balanced flow and transverse direction mechanical properties and, consequently, reduced anisotropy.     

Thermal and morphological properties of main chain liquid crystalline polymers

Temperature modulated differential scanning calorimetry (TMDSC), variable heating rate DSC, and tapping atomic force microscopy (AFM) were used to study semi-crystalline liquid crystalline polymers (LCPs). Main chain LCPs included a random copolyester (Vectra® A950) and an azomethine alternating copolymer. For the azomethine LCP the TMDSC non-reversing signal detected broad exothermic transitions associated with melting and recrystallization as the slow DSC heating scan induced surprisingly large morphological changes. Non-isothermally crystallized Vectra® and some isothermally crystallized samples at lower temperatures exhibited different levels of DSC scan induced crystal reorganization. Such crystal metastability was also studied by variable heating rate DSC and an independent technique for estimating the melting point at very rapid heating rates. The TMDSC characterization of the scan induced crystal perfection in Vectra® was substantially different than for the other polymers studied. In most cases even though crystal perfection was occurring, no clear exotherm was detected in the non-reversing signal. High temperature annealing for long times resulted in degrees of crystal perfection which could be studied by DSC with minimal scan induced reorganization. High resolution tapping AFM was used to elucidate details of crystal morphology for mechanically oriented and non-oriented Vectra® before and after annealing. Structures resembling lamellae were found to be oriented perpendicular to the chain direction in the oriented Vectra®. In the non-oriented film broad and sometimes curved ‘lamellae’ were detected. They were about 1000 nm long and between 20 and 35 nm wide, with the width increasing slightly as a function of increased annealing time at 260 °C melt crystallization conditions. Substructure of the lamellae in both oriented and non-oriented Vectra® consisted of smaller stacked crystallites which are detected by AFM studies of these surfaces.     

Synthesis and properties of dimesogenic liquid crystalline side group polymers

Summary Liquid crystalline polymalonates with side groups consisting of two different mesogenic units separated by alkylene spacers from each other and from the polyester backbone have been prepared. According to microscopic observations, DSC measurements and X-ray studies, all polymers display smectic phases.     

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.     

Structure and properties of molded polyblends containing liquid crystalline polymers

The relationship between the microstructure developed during injection molding of liquid crystalline polymers (LCPs) containing blends and their mechanical properties, was studied. A wholly aromatic copolyester LCP was melt blended in various levels with polycarbonate (PC), poly(butylene terephthalate) (PBT), Nylon 6 (N-6), and amorphous nylon (AN). In all cases the LCP was the minor component. The resulting injection molded structure had a distinct skin core morphology, where elongated fibrous LCP particles comprised the skin layer and spherical and ellipsoidal ones composed the core section. The highest elongation and the finest diameter LCP fibrils were obtained with AN/LCP system, followed by PC/LCP. PBT/LCP blends showed a coarser morphology, while N-6/LCP system did not correlate with the tensile moduli of the injection molded specimens. AN/LCP blends demonstrated the highest moduli values, consistent with the highest orientations observed using electron microscopy, followed by PC/LCP, PBT/LCP, and N-6/LCP. Finally, tensile strength levels were correlated with both orientation levels and interfacial adhesion between the polyblend components. AN/LCP that exhibited the highest orientation and good adhesion appearance gave the highest tensile strength values followed by PC/LCP, PBT/LCP, and N-6/LCP polyblends.     

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.