Hierarchical structure in LCP/PET blends

The structural hierarchy in injection molded blends of poly(ethylene terephthalate) (PET) and a commercial liquid crystal polymer (LCP), two immiscible polymers, was characterized at various blend compositions. The macroscopic core and skin have a gradient structure and are subdivided into ordered and disordered layers. The sublayers consist of rodlike domains at 25% LCP. The domains become thinner, longer, and more fibril-like with increasing LCP concentration. The interconnection between the LCP domains also becomes more significant at higher LCP concentrations. The highest degree of orientation in the injection direction is at the mold surface and the lowest at the sample center. The LCP orientation reflects the elongational and fountain flow in the mold and increases with increasing LCP concentration. Schematic structural models were used to illustrate the levels of structure in these blends. A minimum exists in the tensile strength, elongation at break, and impact strength with varying blend composition at approximately 50% LCP. The tensile strength of the LCP-rich blends is significantly lowered by the presence of a weldline or an angle between the stress and orientation directions. The unique mechanical properties of the LCP depend on the formation of a highly oriented and highly connected hierarchical structure that does not exist in blends with 75% or less LCP.     

In situ reactive compatibilized noryl/LCP blends

This article reveals that the already known improved properties of the thermoplastic–liquid crystalline polymer (LCP) blends can be further improved substantially over the corresponding noncompatibilized counterparts by using a reactive in situ type compatibilizer, the styrene–glycidyl methacrylate (SG) copolymer. This SG copolymer has been demonstrated in this article to be an effective reactive compatibilizer to improve the processability, heat deflection temperature, and mechanical properties of Noryl/LCP blends. The epoxy functional groups of the SG copolymer can react with the end groups of PPO (in Noryl) and LCP. The in situ-formed SG–g–LCP copolymer tends to reside along the interface of Noryl–LCP and reduces the interfacial tension during melt processing. The resultant LCP fibers in the Noryl matrix of the compatibilized blends have a higher aspect ratio because the fibers become finer, longer, and tend to form lamellate domains with a greater interphase contact area than those from the noncompatibilized blends. The compatibilized blends also improve the interphase adhesion between Noryl and LCP. The presence of ethyl triphenylphosphonium bromide catalyst promotes the grafting reaction to improve blend compatibilization. © 1995 John Wiley & Sons, Inc.     

GF增强PPS/LCP复合材料的结晶行为和力学性能

液晶聚合物(LCP)的低熔接线强度是限制LCP应用的重要因素。为了提升LCP材料的力学性能,利用熔融加工方式制备不同LCP含量的聚苯硫醚(PPS)/LCP复合材料。DSC测试结果显示,当复合材料中LCP质量分数小于30%时,LCP的异相成核作用可提升PPS的结晶温度;随着LCP含量的进一步增加,PPS的结晶被抑制,复合材料的结晶温度逐渐降低。对于玻璃纤维(GF)增强PPS/LCP复合材料,随着LCP含量的增加,复合材料的拉伸强度和弯曲强度逐渐降低,弯曲弹性模量逐渐升高;而复合材料的熔接线拉伸强度随着LCP含量增加呈现出先降低后增加的趋势。微观结构观察显示,GF增强PPS/LCP复合材料的性能与PPS/LCP两相界面结合以及树脂/GF之间的界面结合作用较差有关。进一步利用乙烯-丙烯酸甲酯-甲基丙烯酸缩水甘油酯无规三元共聚物和环氧树脂提升GF增强PPS/LCP复合材料的界面相互作用,结果显示,环氧树脂可以显著提升复合材料的力学性能,同时复合材料的熔接线拉伸强度由31 MPa提升至70 MPa。     

Compatibilization of PPO/LCP blends by semi‐interpenetrating liquid crystalline polymer networks LCP/PS

A new approach for enhancing the compatibility of liquid crystalline polymers (LCPs) with engineering thermoplastics is developed in this paper. By adding a new type of compatibilizer to poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO)/LCP blends (semi‐interpenetrating LCP network (ILCPN) comprising the liquid crystalline polymer poly‐(ethylene terephthalate)/p‐hydroxybenzoic acid (PET/60PHB) and crosslinked polystyrene), a well‐compatibilized PPO/LCP composite with considerably improved mechanical properties was obtained. Compared with the uncompatibilized PPO/LCP blend, the bending strength and the Izod impact strength of the compatibilized sample with 5% semi‐ILCPN increase more than 2 and 4 times, respectively.     

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     

In situ compatibilized SAN/LCP blends through reactive copolymers

Styrene–acrylonitrile–glycidyl methacrylate (SAG) copolymers with various contents of glycidyl methacrylate (GMA) were used to compatibilize the incompatible blends of styrene–acrylonitrile (SAN) and a liquid crystalline polymer (LCP). These SAG copolymers contain reactive glycidyl groups that are able to react with the carboxylic acid and/or hydroxyl end groups of the LCP to form the SAG‐g‐LCP copolymers during melt processing. The in situ–formed graft copolymers tend to reside along the interface to reduce the interfacial tension and to increase the interface adhesion. The morphologies of the SAN/LCP blends were examined by using scanning electron microscopy (SEM), where the compatibilized SAN/LCP blends were observed with greater numbers and finer fibrils than those of the corresponding uncompatibilized blends. The mechanical properties of the blends increased after compatibilization. The presence of a small amount (200 ppm) of ethyl triphenylphosphonium bromide (ETPB) catalyst further promotes the graft reaction and improves the compatibilization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3321–3332, 2001     

In situ compatibilization of PEN/LCP blends by ultrasonic extrusion

In situ compatibilization of immiscible blends of PEN and thermotropic LCP was achieved by the ultrasonically‐aided extrusion process. Ultrasonically‐treated PEN underwent degradation, leading to a decrease of its viscosity. Viscosity of LCP was unaffected by ultrasonic treatment. Because of reduced viscosity ratio of PEN to LCP at high amplitude of ultrasonic treatment, larger LCP domains were observed in molding of the blends. LCP acted as a nucleating agent, promoting higher crystallinity in PEN/LCP blends. Ultrasonically‐induced copolymer formation was detected by MALDI‐TOF mass spectrometry in the blends. Ultrasonic treatment of 90/10 PEN/LCP blends improved interfacial adhesion in fibers spun at intermediate draw down ratios (DDR), improving their ductility. The lack of improvement in the mechanical properties of fibers spun at high DDR after ultrasonic treatment was attributed to the disturbance of interfacial copolymer by high elongation stresses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Synthesis of PP–LCP graft copolymers and their compatibilizing activity for PP/LCP blends

The aim of this work was the synthesis of new graft copolymers consisting of polypropylene (PP) backbones and liquid crystalline polymer (LCP) branches, to be used as compatibilizing agents for PP/LCP blends. The PP-g-LCP copolymers have been prepared by polycondensation of the monomers of a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2), that is, sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the mole ratio of 1 : 1 : 2, carried out in the presence of appropriate amounts of a commercial acrylic-acid-functionalized polypropylene (PPAA). The polycondensation products, referred to as COPP50 and COPP70, having a calculated PPAA concentration of 50 and 70 wt %, respectively, have been fractionated with boiling toluene and xylene, and the soluble and insoluble fractions have been characterized by Fourier transform infrared and nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry, and X-ray diffraction. All analytical characterizations have concordantly shown that the products are formed by intricate mixtures of unreacted PPAA and SBH together with PP-g-SBH copolymers of different composition. Exploratory experiments carried out by adding small amounts of COPP50 or COPP70 into binary mixtures of isotactic polypropylene (iPP) and SBH while blending have demonstrated that this practice leads to an appreciable improvement of the dispersion of the minor LCP phase, as well as to an increase of the crystallization rate of iPP. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 391–403, 1998     

Microstrcture development during the injection molding of PET/LCP blends

A liquid crystal polymer (LCP) was blended polethylene terephthalate (PET) in different concetrations to improve the barrier properties of PET in injection stretch blow molded bottles. The improvement depends on the microstructure developed at various stages of the process.In this work, the emphasis is on the injection molding stage of the preform. The characteristics and number of morphological layers were directly related to the amount and type of LCP in the blend and the loction within the perform. It was found that at 10% LCP, three morphological layers were found across the thickness of the part, while at 30% LCP, five morphological layers could be identified. The LCP structure can be classified into four types: droplets, thick rods, thin fibrils and ribbons. Each morphological layer is made up of one or more types of structures. The evolution of on type structure to another depends on the particular flow regime ongoing at various locations in the mold. This microstructure development, during the flow, was examined in detail.     

Manipulating the phase morphology in PPS/PA66 blends using clay

By adding a small amount of clay into poly(p‐phenylene sulfide) (PPS)/polyamide 66 blends, the morphology was found to change gradually from sea–island into cocontinuity and lamellar supramolecular structure, as increasing of clay content. Clay was selectively located in the PA66 phase, and the exfoliated clay layers formed an edge‐contacted network. The change of morphology is not caused by the change of volume ratio and viscosity ratio but can be well explained by the dynamic interplay of phase separation between PPS and PA66 through preferential adsorption of PA66 onto the clay layers and through layer–layer repulsion. This provides a means of manipulating the phase morphology for the immiscible polymer blends. The mechanical and tribological properties of PPS/PA66 blends with different phase morphologies (different clay contents) were studied. Both tensile and impact strength of the blends were found obviously increased by the addition of clay. The antiwear property was greatly improved for the blends with cocontinuous phase form. Our work indicates that the phase‐separating behavior of polymer blends contained interacting clay can be exploited to create a rich diversity of new structures and useful nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

PVC／LPA6／LCP共混物的制备与性能研究

采用低熔点尼龙6（LPA6）／液晶高分子（LCP）复合物对PVC进行共混改性,研究了LPA6／LCP含量对PVC／LPA6／LcP共混物力学性能及维卡软化温度的影响。结果表明：加入质量分数为10％以下的LPA6／LCP,可明显提高共混物的弯曲强度及弯曲模量;加入质量分数为30％以下的LPA6／LcP,可明显提高共混物的...     

Use of epoxy reactivity for compatibilization of PP/PBT and PP/LCP blends

Binary blends of a reactive ethylene-based terpolymer with polybutylene terephthalate (PBT) and with a liquid crystalline polyester (LCP) were studied to clarify the possible interactions between the blended polymers. The aim was to determine the suitability of the reactive terpolymer containing epoxy reactivity as a compatibilizer in blends of polypropylene (PP) and these two polyesters. The binary blends exhibited increased viscosity during blending, changes in the crystallization of the PBT phase, and an intimate contact between the blended polymers, which pointed to strong interactions or chemical reactions between the compatibilizer and both PBT and LCP. FTIR analysis confirmed the reaction of the epoxide and formation of new esters. Most probably the carboxyl end groups of the polyesters reacted with the epoxy group of the compatibilizer. In the second part of the work the same terpolymer was shown to act as a compatibilizer in PP/PBT and PP/LCP blends. This behavior was based on good mixing with the PP phase and on the chemical reactivity or strong interactions with the polyesters demonstrated in the investigations on binary blends. Addition of 5 wt% of the compatibilizer improved the impact strength, especially in PP/PBT blends where synergistic behavior was found at compositions of 80/20 and 20/80. In PP/LCP blends, the compatibilizer significantly improved the impact strength of unnotched samples at 20 wt % LCP content. In both blends, the compatibilizer reduced the size of the dispersed domains and caused them to attach better in the matrix. © 1995 John Wiley & Sons, Inc.     

On the use of PET-LCP copolymers as compatibilizers for PET/LCP blends

Copolyesters of poly(ethylene terephthalate) (PET) with a liquid crystalline polymer (LCP), SBH 1:1:2, have been synthesized by the polycondensation, carried out in the melt at temperatures up to 300°C of sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the presence of PET. The PET-SBH copolyesters have been characterized by differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, etc., and the relationships between properties and preparation conditions are discussed. The copolyesters show a biphasic nature, which is more evident for the products synthesized with a thermal profile comprising relatively lower temperatures (220–230°C) in the initial stages of the polycondensation. Another procedure, whereby the addition of PET to the monomer charge was made at a later stage of the reaction, has also been devised to prepare copolyesters with enhanced blockiness. The compatibilizing effect of the PET-SBH copolymers toward PET/SBH blends has been investigated. PET/SBH blends (75/25, w/w) have been prepared in a Brabender mixer at 270°C and 30 rpm, with and without the addition of appropriate amounts (2.5, 5, and 10%, w/w) of 50-50 PET-SBH copolyesters. Different blending techniques have been used according to whether the three components were fed into the mixer at the same time, or one of them was added at a later stage. The effect of the type and the amount of added copolyester has been studied through morphological, thermal, and mechanical characterizations. The results show that the addition of small amounts ∼5 wt% of copolyesters leads to improved dispersion and adhesion of the minor SBH phase. Moreover, while the tensile modulus of the blends is practically unaffected by the addition of the copolymer, a substantial increase of both tensile strength and elongation to break is found for a concentration of added copolyester of ∼5wt%. Slightly better results were apparently obtained by the use of a block copolyester.     

Shear rate dependence of viscosity and first normal stress difference of LCP/PET blends at solid and molten states of LCP

The liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having 20, 40, 60, 80, and 100 wt % of LCP. Morphology of these samples was studied using scanning electron microscopy. The steady state shear viscosity (η), dynamic complex viscosity (η*) and first normal stress difference (N₁) were evaluated and compared at two temperatures: 265°C, at which LCP was in solid state, and 285°C, at which LCP was in molten state. The PET was in molten state at both the temperatures. The shear viscosity of the studied blends displayed its dependence on composition and shear rate. A maxima was observed in viscosity versus composition plot corresponding to 80/20 LCP/PET blend. The N₁ increased with LCP loading in PET and with the increased asymmetry of LCP droplets. The N₁ also varied with the shear stress in two stages; the first stage demonstrated elastic deformation, whereas second stage displayed dominant plastic deformation of LCP droplets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2212–2218, 2007     

Morphology and rheology of HDPE/LCP blends compatibilized by a novel PE-g-LCP copolymer

A novel graft copolymer (PE-g-LCP) consisting of polyethylene (PE) backbones and liquid crystalline polymer (LCP) branches was synthesized via reactive blending of an acrylic acid-functionalized PE (Escor 5000 by Exxon) with a semiflexible LCP (SBH 1 : 1 : 2 by Eniricerche S.p.A.). The crude reactive blending product (COP) was shown by investigation of the fractions soluble in boiling toluene and xylene and of the residue to contain unreacted Escor and SBH, together with the graft copolymer forming the interphase. The compatibilizing activity of COP for PE/SBH blends, compared to that of pure Escor, was investigated using two PE grades. The COP addition into 80/20 PE/SBH blends caused a much stronger reduction of the SBH droplet dimensions and morphology stabilization than did that of pure Escor. The rheological behavior of the samples showed that COP leads to a slight increase of interfacial adhesion in the melt as well and that the effect is more pronounced when lower molar mass PE grade is used as the blend matrix. Melt-spinning tests demonstrated that deformation of the SBH droplets into highly oriented fibrils can be obtained for the blends of lower molar mass PE, compatibilized with small amounts of the novel PE-g-SBH copolymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2069–2077, 1999     

Influence of processing conditions on the morphological and mechanical properties of compatibilized PP/LCP blends

The main aim of this work is to study the influence of the application of different processing conditions on the morphological and mechanical properties of thermoplastic/LCP blends, in which the viscosity ratios are inferior to unity and decrease with increasing temperature. The way the microstructure evolves along the extruder determines the final morphology and thus, the mechanical performance of the systems. In the present case, the mechanical properties are related with the degree of fibrillation in the final composites. The best degree of fibrillation was obtained for low screw speeds and temperatures and for intermediate outputs. The use of high screw speeds and processing temperatures results in a decrease of the viscosity ratio, in the former case via an increase in the viscous dissipation, at the regions of higher shear rates (kneading‐elements). The application of a lower processing temperature is advantageous for deformation, break‐up, and fibrillar formation because of the higher viscosity ratios and higher shear stresses involved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Clay locked phase morphology in the PPS/PA66/clay blends during compounding in an internal mixer

In this communication, we will demonstrate, by using poly(p-phenylene sulfide) (PPS)/polyamide66 (PA66) blends as an example, the clay can not only affect the phase morphology in immiscible polymer blends, but also frozen in the phase inversion. By adjusting the processing method, an inversed phase, where the minor component PA66 forms the continue phase and the major component PPS forms the dispersed phase, is observed for the first time. This is explained as due to the locking effects of clay layers on the phase development. The result is interesting and also very important, which provides a new way to control the phase morphology and phase inversion in immiscible polymer blends by using clay.     

Reactive extrusion of in-situ composite based on PET and LCP blends

The “in-situ” compatibilization for a PET/LCP blend via transesterification reactions in a twin-screw extruder having a very short residence time is investigated through thermal, rheological, and mechanical studies. Inclusion of a small amount of liquid crystalline polymer (LCP) enhanced the crystallization rate of the poly(ethylene terephthalate) (PET) matrix. It acted as a nucleating agent. LCP lowered the blend viscosity above T_cn (crystalline-nematic transition temperature), working as a processing aid. However, the addition of dibutyltindilaurate (DBTDL) as a reaction catalyst was found to increase the viscosity of the blends, diminish the size of the dispersed phase, enhance its adhesion with the matrix, and lead to an increase of mechanical properties of two immiscible phases. Hence DBTDL is helpful in producing a reactive compatibilizer by reactive extrusion at the interface of this polyester blend system. The optimum catalyst amount turned out to be about 500 ppm when the reaction proceeds in 90/10 PET/LCP polyester blend systems. Its effect on the mechanical properties is discussed in detail. The structural change of reactive blend was identified by H¹ NMR and wide angle X-ray diffraction patterns.     

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