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.     

Reactive extrusion of polyolefin ternary blends

Reactive extrusion of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM)/high-density polyethylene (PE) (80/10/10 by weight) blends were carried out using a corotating twin-screw extruder. The effects of peroxide and coagent concentrations and extruder rpm were studied in terms of rheological, morphological, thermal, and mechanical properties of the blends. Melt viscosity of the peroxide-treated blend increased and decreased over the untreated one depending on the amount of a coagent. Morphologically, interfaces blur with only a peroxide treatment, and significant domain reduction was obtained when peroxide and a coagent were used together. Both T_m (crystalline melting temperature) and T_g (glass transition temperature) of PP increased in the blend, whereas those of PE slightly decreased. © 1996 John Wiley & Sons, Inc.     

Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

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.     

Reactive extrusion of PP/natural rubber blends

Reactive extrusion of polypropylene (PP)/natural rubber (NR) (90/10) blends was conducted in the presence of a peroxide [1,3-bis(t-butylperoxy)benzene] and coagent (trimethylolpropanetriacrylate, TMPTA). Effects of peroxide and coagent content were studied in terms of melt index (MI), melt viscosity, morphology, thermal, and mechanical properties. At a constant content of the coagent, melt viscosity increased at a low and decreased at a high content of the peroxide. On the other hand, melt viscosity increased monotonically with the coagent concentration at constant peroxide content. The increase and decrease of viscosity were interpreted in terms of crosslinking and chain scission of PP, which governed the rubber domain size and mechanical properties of the reactive blends. © 1995 John Wiley & Sons, Inc.     

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.     

Reactive compatibilization of PET and PPE blends by epoxy couplers

A commercially available tetrafunctional epoxy monomer was demonstrated to be an effective reactive compatibilizer for blends of poly(ethylene terephthalate) (PET) and polyphenylene ether (PPE). It requires about 10–20% by weight of a conventional reactive compatibilizer to achieve the same level of compatibilization in terms of domain size reduction and mechanical property improvement. This epoxy monomer is able to contact and react with PET and PPE simultaneously during high shear extruder blending to form the desirable PET–epoxy–PPE mixed copolymer. This mixed copolymer contains PET and PPE segments that tend to anchor at the interface to act as an efficient compatibilizer of the PET and PPE blends. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 739–753, 1997     

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.     

Through-thickness distribution of LCP in PPS/LCP blends

Through-thickness distribution of liquid crystalline polymer (LCP) of blends containing polyphenylene sulfide (PPS) and LCP was investigated using differential scanning calorimetry and scanning electron microscopy. The effect of the LCP distribution on the mechanical test was checked through bending testing of the various compositions of the injection molded samples. These studies showed a nonuniform distribution of LCP in the PPS-rich region where the LCP content in the skin layer was higher than in the core layer or boundary between the two layers. The LCP component was uniformly distributed in the LCP-rich region. The increase of bending modulus with increasing LCP content was attributed to the reinforcing nature of the LCP fibrils in the skin layer. © 1994 John Wiley & Sons, Inc.     

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     

Fast in situ copolymerization of PET/PEN blends by ultrasonically-aided extrusion

An ultrasonically-aided extrusion process was developed for fast in situ compatibilization of immiscible polymer blends. PET, PEN, and their 50/50 blend were ultrasonically extruded at various amplitudes. PET underwent homopolymerization and degradation, respectively, at ultrasonic amplitudes of 7.5 and 10 μm, while PEN underwent degradation at amplitudes of 5, 7.5, and 10 μm. MALDI-TOF mass spectrometry revealed greater amounts of hydroxyl and carboxyl terminated oligomers in ultrasonically treated PET and PEN, indicating their greater reactivity. Ultrasonic treatment at short residence time led to the enhancement of transesterification reaction in the PEN/PET blend, as shown by ¹H NMR and MALDI-TOF, indicating greater randomization with ultrasonic treatment. The latter was also observed through a shift in T_g that closely follows Gibbs-DiMarzio relation and an increase in viscosity of blend with treatment at an amplitude of 10 μm. No crystallinity was observed in the blend due to the already high level of transesterification introduced by extrusion without treatment. Accordingly, crystallinity, mechanical properties, oxygen permeability, and optical clarity of the blend were not influenced by ultrasonic treatment.     

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     

Customized blends of polypropylene for extrusion based additive manufacturing

Filament-based material extrusion (MatEx) additive manufacturing has garnered great interest due to its simplicity, customizability, and cost-effectiveness. However, MatEx of semicrystalline polymers is still largely relegated to prototyping applications. Major issues involving volumetric shrinkage and warpage of the printed parts must be addressed in order to employ them for printing functional parts. Moreover, the crystallization behavior and rheology of the polymer are dependent on the MatEx processing conditions. In the current work, the printability of blends of isotactic polypropylene with a soft, low crystallinity propylene based homopolymer is evaluated. Addition of the homopolymer resulted in an increase in the crystallization window of the blends by ~6°C that had a profound impact on the interlayer adhesion and residual stress state. The shear-dependent melt flow behavior inside the printing nozzle as well as the interlayer chain diffusion and interlayer welding on the print bed were investigated. Rheological characterizations also indicate sufficient dispersion and miscibility of the homopolymer in the neat polypropylene matrix. The incorporation of the homopolymer as an additive significantly improved the dimensional accuracy of the printed parts through better dissipation of the entrapped residual stresses during MatEx. Moreover, the degree of mechanical anisotropy of the parts was significantly lower than that obtained using many 3D printable grade polymers. The findings from this study can be leveraged in toolpath planning, process parameter optimization, and new feedstock development, highlighting current limitations as well as providing valuable insights into necessary processing modifications in order to enable MatEx of next generation semicrystalline polymers.     

Processing of thermotropic liquid crystalline polymers and their blends—analysis of an in-situ LCP composite system

Thermotropic LCP/LCP fiber blends were prepared by a combination of meltblending and hot-drawing, using a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman). Morphological evidence, including scanning electron (SEM) and transmission electron microscopy (TEM), showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 μm diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic LCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. The fiber blends were characterized using dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), gas chromotography/mass spectroscopy (GC/MS), and rheological measurements. It appears that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two LCP components during the melt blending process. Differential scanning calorimetry (DSC) thermograms as well as nuclear magnetic resonance (NMR) spectra of the extracted fraction from the mixture of 30 wt% K161/70 wt% PET(PHB60) confirmed the chemical interaction between the two thermotropic liquid crystalline polymers.     

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     

GMA对高分子共混体系的反应增容

介绍了甲基丙烯酯缩水甘油酯类大分子增容剂制备的方法及原理,甲基丙烯酯缩水甘油酯对聚酰胺合金、聚酯合金、聚烯烃合金、生物降解高分子合金及高分子复合材料等的反应增容及原理。综述了相关的研究进展。     

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...     

反应挤出合成聚乳酸技术研究

本文主要介绍了反应挤出合成聚乳酸的技术特点和脱挥技术应用,分析了反应挤出合成过程中脱挥处理的关键点和影响因素。     

Reactive extrusion of zein with glyoxal

Cross‐linked zein has been produced using glyoxal (GLY) as the cross‐linking reagent via reactive extrusion for the first time in a twin screw extruder using dilute sodium hydroxide as catalyst. Tri(ethylene glycol) was used as a plasticizer for various items. The extrudate was then ground and processed using either compression or injection molding. At the highest level of GLY (6%), tri(ethylene glycol) was used at 10% as a plasticizer to allow further processing to take place. With this formulation, samples could be obtained from the injection mold, however, the samples did not hold their molded shape due to the elasticity of the sample at the mold temperature. When lower levels of GLY were used, injection molded sample bars of similar quality to control were obtained. The physical properties of these samples were similar to control. At GLY levels of 1.75% and higher, the samples were resistant to dissolution by acetic acid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009