Effect of compatibilizers on mechanical properties and morphology of in-situ composite film of thermotropic liquid crystalline polymer/polypropylene

An in-situ composite film of a thermotropic liquid crystalline polymer (LC3000)/polypropylene (TLCP/PP) was produced using the extrusion cast film technique. The compatibilizing effect of thermoplastic elastomers, styrene-ethylene butylene-styrene (SEBS), maleic anhydride grafted SEBS (MA-SEBS), and maleic anhydride grafted polypropylene (MA-PP) on the mechanical properties and morphology of the TLCP/PP composite films was investigated. It was found that SEBS provided a higher value of tensile modulus than MA-SEBS, which in turn was higher than MA-PP, despite the expected stronger interaction between the MA chain and TLCP. The observation of the morphology under optical and scanning electron microscopes suggested that all three compatibilizers helped improve the dispersion of the TLCP fibers and increased the fiber aspect ratio to a different extent. The fractured surface of the specimens showed more fiber breakage than pull-out when a compatibilizer was added, which suggested the improvement of interfacial adhesion. The surface roughness of fibers with an added elastomeric compatibilizermay also provide mechanical interlocking at the interface. It is suggested that the increase in the viscosity ratio of TLCP/PP due to the added elastomeric compatibilizer, SEBS and MA-SEBS, compared with the thermoplastic compatibilizer, MA-PP, is more effective in improving the composite mechanical properties.     

热致性液晶与聚丙烯原位复合材料的相容性研究

在热致液晶共聚酯（ＬＣＰ）与聚丙烯（ＰＰ）的共混体系中引入相容剂（接枝共聚物ＭＡＨ—ｇ－ＰＰ），借助热台偏光显微镜、扫描电镜、差示扫描量热仪、流变仪等方法研究了相容剂对ＰＰ／ＬＣＰ原位复合材料的微观结构和界面性能、结晶行为、流变行为以及力学性能的影响．结果表明：添加相容剂后，基体中的ＬＣＰ微纤分散更均匀，ＬＣＰ微纤长径比Ｌ／Ｄ增大．ＰＰ和ＬＣＰ两相之间有较好的粘连，促进了共混体的结晶，改善了ＰＰ／ＬＣＰ原位复合材料的力学性能．     

Effects of processing conditions on the mechanical performance of maleic anhydride compatibilized in-situ composites of polypropylene with liquid crystalline polymer

Maleic anhydride compatibilized blends of isotactic polypropylene (PP) and thermotropic liquid crystaline polymer (LCP) were prepared either by the direct injection molding (one-step process), or by twin-screw extrusion blending, after which specimens were injection molded (two-step process). The morphology and mechanical properties of these injection molded in situ LCP composites were studied by means of scanning electron microscopy (SEM), Izod impact testing, static tensile, and dynamic mechanical measurements. SEM observations showed that fine and elongated LCP fibrils are formed in the maleic anhydride compatibilized in situ composites fabricated by means of the one-step process. The tensile strength and modulus of these composites were considerably close to those predicted from the rule of mixtures. Furthermore, the impact behavior of LCP fibril reinforced composites was similar to that of the glass fiber reinforced polymer composites. On the other hand, the maleic anhydride compatibilized blends prepared from the two-step process showed lower mechanical performance, which was attributed to the poorer processing behavior leading to the degradation of PP. The effects of the processing steps, temperatures, and compatibilizer addition on the mechanical properties of the PP/LCP blends are discussed.     

Studies on compatibilization of blends of polypropylene and a thermotropic liquid crystalline polymer

Thermotropic liquid crystalline polymers, LCPs, are frequently blended with thermoplastics to achieve an in situ composite structure. Significant mechanical reinforcement is obtained for the matrix polymer in the direction of the LCP fibers, but the transversal properties are often inferior because of the incompatibility of the components. Blends of LCP with polypropylene, and with three related matrix polymers, and PP/LCP blends with added potential compatibilizers were prepared and studied for their mechanical properties and morphology. A notable improvement in impact strength was achieved when a small amount of ethylene-based terpolymer was added as compatibilizer. © 1993 John Wiley & Sons, Inc.     

Compatibilizers for thermotropic liquid crystalline polymer/polyethylene blends prepared by reactive mixing

This paper describes the effects of composition and processing conditions on the efficiency of the compatibilizer prepared from a thermotropic liquid crystalline polymer (TLCP) and the sodium salt of a poly(ethylene‐co‐r‐acrylic acid) ionomer (EAA‐Na) in TLCP/low‐density polyethylene (LDPE) blends and TLCP/high‐density polyethylene (HDPE) blends. The TLCP‐ionomer graft copolymer formed by a melt acidolysis reaction effectively reduced the interfacial tension between TLCP and polyethylene, which improved impact strength and toughness of the compatibilized blends. Higher processing temperatures for the reactive extrusion produced a more efficient compatibilizer, presumably due to increased graft‐copolymer formation, but the reaction temperature had little effect on the impact strength of compatibilized blends for temperatures above 300°C. The addition of the compatibilizer to TLCP/LDPE blends significantly increased the melt viscosity due to increased interfacial adhesion. The TLCP/EAA‐Na ratio used to prepare the compatibilizer had little effect on the performance of the compatibilizer. Although the compatibilizer can be prepared in situ by blending and extruding a ternary blend of TLCP/EAA‐Na/polyethylene, pre‐reacting the compatibilizer resulted in blends with improved toughness and elongation.     

Thermal properties of biaxially deformed in situ composites

The thermal properties of biaxially blown poly(etherimide) (PEI) films containing a thermotropic liquid crystalline polymer (TLCP) were studied using differential scanning calorimetry, thermogravimetric analysis, wide‐angle X‐ray diffraction and dynamic mechanical thermal analysis. The effects of the compatibilizer and thermal annealing on the thermal properties of biaxially oriented TLCP films were investigated. Though the compatibilizer (poly(ester imide)) improved deformation of the TLCP phase (poly ester amide) and adhesion between the matrix and the TLCP phase, which improved mechanical properties, it did not significantly affect the thermal properties of the in situ composite films. The film degradation behavior corroborated the role of the compatibilizer. Since a relatively small amount of TLCP (10 wt%) was added to the matrix and the matrix PEI was amorphous, the effect of annealing on the TLCP structure was not obvious. By the same token, while the effect of the deformation in the circumferential direction (a change in the blow‐up ratio) was manifest in mechanical property improvements, its effect on the thermal properties was not obvious. All films showed similar thermal expansion behaviors, regardless of the thermal history and of the compatibilizer addition. Thus, there is an optimum amount of the compatibilizer required to obtain optimal mechanical properties for in situ composite films without causing a deterioration of their thermal properties. Polym. Eng. Sci. 44:1419–1428, 2004. © 2004 Society of Plastics Engineers.     

Impact-modified blends of compatibilized polyamide-6 with liquid crystalline copolyester

Compatibilized blends of polyamide-6 (PA6) and thermotropic liquid crystalline polymer (LCP) modified with various high-impact polypropylene (HIPP) contents were injection-molded. These blends were compatibilized with maleic anhydride-grafted polypropylene (MAP). The effects of impact modification on the morphology, impact, static, and dynamic mechanical properties were investigated. The results showed that the HIPP addition leads to an improvement of the Izod impact strength of the blends significantly while it reduced the tensile strength and stiffness properties. An attempt was made to correlate the structure of the PA6(MAP)/HIPP/LCP blends from the scanning electron microscopic observations with the measured mechanical properties. This work provides a way to produce a tough in situ composite. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1611–1619, 1998     

聚苯硫醚／热致液晶高分子共混体系的结构与性能研究

本文研究了聚苯硫醚(PPS)与两种热致型液晶聚合物(TLCP)共混体系的热性能、力学性能及形态。结果表明,TLCP的加入对于PPS的结晶性及热稳定性都有一定影响。当半芳聚酯类液晶用量少于5份时,共混体系的力学性能优于纯PPS。形态表明,共混物中的TLCP多以取向度较小的椭球体形式存在。     

Effect of a compatibilizer on the structural development of a thermotropic liquid crystalline polymer/polystyrene blend

A fine fibril structure of a thermotropic liquid crystalline polymer (TLCP, a poly(ester amide)) can be developed in a shear flow field of a thermoplastic matrix (polystyrene, PS). Addition of a third component, a poly(styrene‐co‐maleic anhydride) (SMA), that interacts with the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP phase by acting at the interface. Moreover, it brings about good adhesion at the interface and enables the dispersed liquid crystalline polymer phase to be deformed in shear flow without strong elongation even though the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties were substantially improved because of both the good adhesion at the interface and fibril generation, which were ascribed to the SMA interaction. These results have important implications in that they provide a means to produce strong and tough in‐situ composites when the viscosity of the matrix polymer is lower than that of the dispersed liquid crystalline polymer which is immiscible with the matrix polymer. Morphological observations determined the significance of the third component (SMA) in immiscible polymer blends, and an optimum amount of SMA exists for best mechanical performance.     

Self‐reinforcing elastomer composites based on polyolefinic thermoplastic elastomer and thermotropic liquid crystalline polymer

In situ reinforcing elastomer composites based on Santoprene thermoplastic elastomer, a polymerized polyolefin compound of ethylene–propylene–diene monomer/polypropylene, and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a single‐screw extruder. The rheological behavior, morphology, mechanical, and thermal properties of the blends containing various LC3000 contents were investigated. All neat components and their blends exhibited shear thinning behavior. With increasing TLCP content, processability became easier because of the decrease in melt viscosity of the blends. Despite the viscosity ratio of dispersed phase to the matrix phase for the blend system is lower than 0.14, most of TLCP domains in the blends containing 5–10 wt % LC3000 appeared as droplets. At 20 wt % LC3000 or more, the domain size of TLCP became larger because of the coalescence of liquid TLCP threads that occurred during extrusion. The addition of LC3000 into the elastomer matrix enhanced the initial tensile modulus considerably whereas the extensibility of the blends remarkably decreased with addition of high TLCP level (>.20 wt %). The incorporation of LC3000 into Santoprene slightly improved the thermal resistance both in nitrogen and in air. Dynamic mechanical analysis results clearly showed an enhancement in dynamic moduli for the blends with 20–30 wt % LC3000. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Separation of a thermotropic liquid crystalline polymer from polypropylene composites

This work is concerned with determining how to effectively recycle wholly thermoplastic composites comprised of a polypropylene (PP) matrix reinforced with a thermotropic liquid crystalline polymer (TLCP). A novel reclamation process was developed in which the TLCP could be recovered from the PP matrix. Reactive extrusion was used to reduce the molecular weight of the PP (Montell 6523) and to facilitate phase separation. The melt was then extruded into a heated mineral oil bath, which separated the TLCP (DuPont HX8000) from the matrix by dissolving the PP. It was found that greater than 70 wt% of the TLCP could be reclaimed from the PP matrix at a purity of greater than 96 wt%. In order to determine the ability to reuse the reclaimed HX8000, injection molded in situ composites were generated and their mechanical properties were determined. When the neat HX8000 component was partially replaced with reclaimed HX8000, the injection molded TLCP/PP composites showed no discernible difference in mechanical properties.     

Engineering properties of compatibilized polypropylene/liquid crystalline polymer blends

Polypropylene (PP) and Vectra A950, a thermotropic liquid crystalline polymer (LCP), blends were prepared in a single‐screw extruder with the variation in Vectra A950 content in presence of fixed amount (2%, with respect to PP and LCP mixture as a whole) of ethylene‐acrylic acid (EAA) copolymer as a compatibilizer. Mechanical analysis of the compatibilized blends within the range of LCP incorporations under study (2–10%) indicated pronounced improvement in the moduli, ultimate tensile strength (UTS), and hardness. Fourier transform infrared (FTIR) spectroscopy studies revealed the presence of strong interaction through H‐bonding between the segments of Vectra A950 and the compatibilizer EAA. Morphological studies performed by scanning electron microscopy (SEM) manifested the development of fine fibrillar morphology in the compatibilized PP/Vectra A950 blends, which had large influence on the mechanical properties. Differential scanning calorimetry studies showed an initial drop of the melting point of PP in the presence of EAA followed by enhancement of the same in presence of Vectra A950. TGA showed an increase in the thermal stability for all blends with respect to matrix polymer PP. Rheological studies showed that a very small quantity of Vectra A 950 was capable of reducing the melt viscosity of PP particularly in the lower shear rate region and hence facilitated processibility of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Extrusion blow molding of microcomposites based on thermotropic liquid crystalline polymers and polypropylene

This work is concerned with the extrusion blow molding of bottles from pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur in polymer processing operations and to determine if TLCP reinforced bottles could be produced by extrusion blow molding of microcomposites. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of TLCP concentration and in situ composite strand properties on the mechanical properties and anisotropy of bottles made from microcomposites. Specifically, strands having three different draw ratios are used to produce bottles at 10 and 20 wt% TLCP. Increasing the in situ composite strand modulus is shown to cause an increase in both the machine and transverse direction moduli of the composite bottles. The mechanical properties of the bottles increase with increasing TLCP composition. Finally, the machine and transverse direction properties are not balanced in the composite bottles produced in this study (degrees of anisotropy ranging from 1.5 to 1.8). The mechanical anisotropy is probably the result of a low blow up ratio (2) in the bottles and the TLCP fibers being oriented primarily in the machine direction due to the shear flow in the die.     

Compatibilizers for thermotropic liquid crystalline polymer/polyolefin blends prepared by reactive mixing: The effect of processing conditions

The effect of processing conditions on the melt formation of a graft‐copolymer compatibilizer for blends of a thermotropic liquid crystalline polymer (TLCP) and polyolefins was investigated. The compatibilizer was formed by a melt acidolysis reaction of a 50/50 (w/w) blend of TLCP and the sodium salt of a poly(ethylene‐coacrylic acid) ionomer. The effects of various processing conditions in a batch mixer and a single‐screw extruder on the extent of reaction were assessed. The extent of graft‐copolymer formation and the efficacy of the product as a compatibilizer for TLCP/polyethylene blends were affected by the processing temperature and the screw (or rotor) speed.     

In situ composite fibers: Blends of liquid crystalline polymer and poly (ethylene terephthalate)

To augment the concept of in situ composites as alternatives to fiber-reinforced composites, polyblends of a thermotropic liquid crystalline polymer (LCP) and poly(ethylene terephthalate) (PET) were prepared. Fiber-spinning of the blends was performed on a piston-driven plastorneter. Blends of LCP and a low-intrinsic-viscosity PET resin showed poor mechanical performance, which was attributed to their processing behavior. Blends of LCP and a high intrinsicviscosity PET manifested an almost additive behavior with regard to tensile modulus and strength. Elongation of the blends, however, displayed a radical decline, which is reminiscent of fiber-reinforced composites. Heat treatment of the blend fibers modestly increased the tensile properties of the LCP-rich compositions. Blend fibers from PET-rich compositions exhibit a moderate decline in tensile properties owing to thermal relaxation of PET. The data demonstrate that in situ composites or blends of thermotropic LCPs and isotropic polymers present challenging alternatives to fiber-reinforced composite systems because of their ease of processing.     

Synthesis of multi‐block copolymer and its compatibilization to the blends of poly(ether ether ketone) with thermotropic liquid crystalline polymer

A multiblock copolymer (BCP) containing amorphous poly(aryl ether ketone) (PAEK) and thermotropic liquid crystalline polymer (TLCP) segments was synthesized. The chemical structure and properties of BCP were characterized by fourier‐transform infrared spectrometer (FTIR), differential scanning calorimeter (DSC), gel permeation chromatograms (GPC), thermogravimetry analysis, polar light microscope (PLM), and solubility test respectively. BCP can dissolve in chloroform because of soluble PAEK block bonded with TLCP block, which was insoluble. The peak of the original PAEK oligomer was no more present in the GPC traces of the block copolymer. These facts indicated that polymer synthesized should be copolymers of the two components rather than blends. A single T_g at 138.1°C and broad melting endotherm at 315.7°C can be observed. The liquid crystalline texture of BCP showed uniformity in the view after heat treated for 10 min above its T_m under PLM. Ternary blends of poly(ether ether ketone) (PEEK)/TLCP/BCP were prepared by extrusion and characterized by DSC. DSC results showed that the crystallization temperature of PEEK phase in the blends shifted higher with the addition of TLCP. Wide angle X‐ray diffraction investigations indicated that the crystalline structure of PEEK was not disturbed by blending or compatibilizing. Scanning electron microscope and mechanical tests confirmed the compatibilizing effect of BCP. Reduction in dispersed phase TLCP size was observed when 2 phr by weight of compatibilizer was added to the blend. Measurement of the tensile properties showed increased elongation as well as improved modulus and strength to some extent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dynamic reaction inside co‐rotating twin screw extruder. II. Waste ground rubber tire powder/polypropylene blends

In this article, dynamic reaction of waste ground rubber tire powder/PP blends with compatibilizers is extended to commercially available waste rubber Viz. Ground rubber tire and PP for the possibility of getting recycled material with good mechanical properties. In the first part of the article it was shown that the compatibility of model material/PP blends has greatly improved. In this article, extensive studies have been carried out to study the effect of compatibilizers, in‐situ compatibilization of immiscible waste ground rubber tire (WGRT) powder/polyolefin blends of various concentrations was investigated by means of extrusion process using a co‐rotating twin screw extruder. It was observed that addition of small amounts of compatibilizers like SEBS‐g‐MA to the blends of WGRT and PP‐g‐MA can result in better mechanical properties than the blends with isotactic PP. The blends of WGRT powder and PP‐g‐MA with compatibilizer have better adhesion than those of isotactic PP blends as revealed by the morphological studies using AFM and SEM. The betterment in properties can be attributed to the presence of functional group, maleic anhydride in PP‐g‐MA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Extruded blends of a thermotropic liquid crystalline polymer with polyethylene terephthalate,polypropylene, and polyphenylene sulfide

Structure–property relationships were investigated for blends of a polyester-type thermotropic liquid crystalline polymer (LCP) with polyethylene terephthalate (PET), polypropylene (PP), and polyphenylene sulfide (PPS). The polymers were melt blended in a twin-screw extruder and the blends were extruded to strands of different draw ratios. Tensile properties of the blends were determined as a function of LCP content and draw ratio and compared with the results of morphological and rheological analyses. In general, the strength and stiffness of the matrix polymers were improved with increasing LCP content and draw ratio. At a draw ratio of 11, the blends of PET/30 wt % LCP exhibited a tensile strength about three times and an elastic modulus nearly four times that of pure PET. All blends exhibited a skin/core morphology with thin fibrils in the skin region. The formation and the sizes of the fibril-like LCP domains in the matrices were found to depend on LCP content and the viscosity ratio of the blend components.     

Effect of the compatibilizer on the physical properties of biaxially deformed in situ composites

The effect of a compatibilizer (poly(ester imide), PE^sI) on the biaxial deformation of a thermotropic liquid crystalline polymer (TLCP, poly(ester amide)) in a poly(ether imide) and the properties of biaxially deformed in situ composites were studied. The compatibilizer improved dispersion of the TLCP and the adhesion between TLCP and the matrix. The properties of blown films were affected by the amount of the compatibilizer used. The morphology evidently shows that ca. 0.6 wt% PEsI provides the best morphology when 10 wt% VB phase is included. The mechanical properties, especially in the hoop direction, were significantly improved for the compatibilized films compared to uncompatibilized one. The impact strength of a compatibilized blend film with 0.6 wt% PEsI was almost twice that of an uncompatibilized blend film.     

Compatibilization of nylon 6/liquid crystalline polymer blends with three types of compatibilizers

Polyblends of nylon 6 and liquid crystalline polymer (LCP) (Vectra A 950) are immiscible and highly incompatible, with resultant poor interfacial adhesion, large phase domains, and poor mechanical properties. In the present work, compatibilizing strategies are put forward for blends containing nylon and LCP. Effects of three types of compatibilizers, including ionomer Zn–sulfonated polystyrene (SPS), reactive copolymer styrene–maleic anhydride (SMA), functional grafted copolymers—polypropylene grafted glycidyl methacrylate (PP‐g‐GMA) and polypropylene grafted maleic anhydride (PP‐g‐MAH)—are studied in the aspects of morphology and dynamic mechanical behavior. The addition of compatibilizers decreases the domain size of the dispersed phase and results in improved interfacial adhesion between LCP and matrix. The compatibilization mechanism is discussed by way of diffuse reflectance Fourier transform spectroscopy (DRIFT), showing the reaction between compatibilizers and matrix nylon 6. Mechanical properties are improved by good interfacial adhesion. The contribution of SMA to mechanical properties is more obvious than that of Zn‐SPS and grafted PPs used. The blending procedure is correlated with the improvement of mechanical properties by the addition of compatibilizer. Two‐step blending is demonstrated as an optimum method to obtain composites with better mechanical properties as a result of a greater chance for LCP to contact the compatibilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1452–1461, 2003