Blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer. I: Mechanical properties and morphology

Blends of a thermotropic liquid crystalline polymer (LCP), Vectra A900, and a thermoplastic elastomer, Kraton G1650, were made on a single screw extruder. During extrusion, fibers of the LCP are formed under influence of shearing and elongating forces. The stiffness and tensile strength of the elastomer are greatly improved by the addition of the LCP. The modulus of elasticity of blends containing up to 20% LCP can be described well with the Halpin-Tsai equation. Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) measurements show that the polymers are immiscible, but the DMTA results show a shift of the glass transition temperature of the elastomeric block of the Kraton polymer. This shift may be attributed to a layer of elastomer adsorbed on the LCP particles.     

Formation,stability, and properties of in-situ composites based on blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer

This paper describes the preparation and properties of in-situ composites based on polymers with no overlap in processing temperatures. The polymers used were Vectra A900, a thermotropic liquid crystalline copolyester (TLCP), and Arnitel em630, a thermoplastic elastomer. Blends were generated by feeding the two components from separate extruders into a Ross static mixer. Different morphologies were obtained by varying the number of mixing elements of the static mixer. Using 8 mixing elements led to a stratified morphology of Vectra layers in Arnitel, using 11 mixing elements resulted in the desired continuous fiber/matrix morphology whereas a pronounced skin-core morphology was obtained with 14 mixing elements. It is argued that in-situ composites can be generated by a distributive mixing process without the formation of an intermediate droplet/matrix morphology as occurs in common dispersive blending equipment. Tensile modulus and strength of all blends increased with extrudate draw ratio as a result of increased molecular orientation of the TLCP phase. The level of reinforcement, however, was lower than expected, probably due to the low temperature of drawing. Annealing and capillary instability experiments showed that above the melting point of the TLCP the fiber/matrix morphology rapidly breaks up into a droplet/matrix morphology. This process takes just a few seconds for fibers of thickness ∼ 1 μm. It is shown to be the probable cause of the skin-core morphology obtained in case of 14 mixing elements.     

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     

Prepregs and laminates of polyetherimide-reinforced by a thermotropic LCP

Unidirectional sheets (prepregs) of blends of polyetherimide (PEI) with a liquid crystalline polymer (LCP) are prepared. The mechanical properties of prepregs at directions of 0°, 45°, and 90° to the machine direction are investigated as a function of draw ratio and LCP concentration. The results show that drawing significantly increases the tensile strength and modulus of prepregs in the machine direction and only slightly decreases these properties in the transverse direction. An increase in the LCP content greatly enhances the tensile strength and modulus in the machine direction but decreases these properties in the 45° and 90° directions. The strain at break of prepregs decreases with LCP content in all directions tested. An abrupt drop in the tensile strength, modulus, and strain at break of prepregs occurs in the 45° and 90° directions when LCP content reaches 40%. Prepregs are used to manufacture unidirectional and quasi-isotropic laminates. Unidirectional laminates show mechanical properties close to those of the corresponding prepregs. The tensile modulus of quasi-isotropic laminates exhibits a continuous increase with increasing LCP content while the tensile strength increases with an LCP content up to 30%, then it decreases rapidly. The morphology of LCP in prepregs is observed to change from disperse to continuous at LCP contents of 40 and 50%. This effect is found to be responsible for the large decrease in tensile strength of prepregs in the 45° and 90° directions and quasi-isotropic laminates at higher LCP concentration. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:329–340, 1997     

Blends of thermoplastic polyurethane and polypropylene. II. Thermal and morphological behavior

Neat thermoplastic polyurethane (TPU), polypropylene (PP), and TPU/PP blends with different weight ratios that were prepared in a twin‐screw extruder were investigated with differential scanning calorimetry and light and scanning electron microscopy. The results confirmed PP matrix to TPU matrix phase inversion in the concentration region between 60/40 and 80/20 TPU/PP blends. The total degree of crystallinity of the blends and the crystallization temperature of PP decreased with increasing TPU content. On the other hand, the addition of elastomeric TPU to PP significantly increased the spherulite size of PP. The TPU melt islands in the PP matrix prolonged the crystallization of PP during solidification, and this enhanced the growth of spherulites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix

This study investigates deformation of a thermotropic liquid crystalline polymer (TLCP) in different die geometries. Blends of aTLCP with a thermiplastic elastomer of EPDM were made in a twin-screw extruder. Morphological observation of the extruded blends demonstrates the complimentary effect of shear in the die exit on dispersed phase deformation and fibril formation. Shear strain can affect fibril formation for a relatively large dispersed phase in the region close to the die wall. However, the main role of shearing is in breaking up the larger particles and initial polydomain structure. A strong elongational deformation on the blended melt after the die exit is required, and fine microfibrils normally obnserved in in situ composites were not easily formed by shear deformation only in the die.     

A study on the ternary blends of nylon 6, a thermotropic liquid crystalline polymer,and a thermoplastic elastomer

Reactive extrusions were performed with blends of nylon 6 and a liquid crystalline copolyesteramide (LCP) including a functionalized elastomer (maleic anhydride grafted ethylene-propylene-diene terpolymer). The functionalized elastomer acts as a compatibilizer at the interface. The thermal behavior of the blends suggests partial compatibility of the components endowed by the produced graftcopolymer. A finer dispersion was observed for the compatibilized blends. Fine fibrils were also observed even when no extensional force was applied, indicating the importance of interfacial adhesion for the dispersed phase deformation. The shear viscosity of the ternary blend was lower than those of the neat polymers. The mechanical properties of the compatibilized blends, however, were not significantly improved except when an optimum amount of compatibilizer was added. Explanations for the compatibilizing action of the elastomer and mechanical performance of the ternary blends are presented.     

Existence of microdomain orientation in thermoplastic elastomer through a case study of SEBS electrospun fibers

Although the microdomains of polymeric systems including the thermoplastic elastomers in the as-spun electrospun fiber were reported, the orientation of microdomains has not yet been well clarified. The present work shows an existence of microdomain orientation through a case study of a well-aligned electrospun fibers of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) obtained from an electrospinning unit equipped with a rotational disk fiber-collector. Two-dimensional small-angle X-ray scattering (2D-SAXS) patterns of the as-spun electrospining SEBS fibers show elliptical and four-point patterns suggesting an orientation of distorted and fragmented lamellar microdomains. The electrospun fibers obtained from a low rotational disk collector speed (31.5 m/min) exhibits a significant microdomain distortion whereas the fibers obtained from high take-up velocities (310 m/min, 620 m/min, and 1240 m/min) show higher fragmented-microdomain stretching. By annealing the electrospun fibers, the fibers develop an isotropic SAXS pattern with traces of the remained anisotropic orientation. Based on the above mentioned evidences in SEBS, the present work, for the first time, clarifies that the as-spun thermoplastic elastomers fibers show not just a simple microdomain as used to be observed by transmission electron microscope (TEM) but rather with orientation which can be confirmed by SAXS.     

Blends of polylactic acid with thermoplastic copolyester elastomer: Effect of functionalized terpolymer type on reactive toughening

This study is an attempt to explore the effectiveness of thermoplastic copolyester elastomer (TPCE) as a toughening agent for improving the impact strength of PLA. Biobased Hytrel^® thermoplastic copolyester of polyether glycol and polybutylene terephthalate was selected as the TPCE of choice for this study. Blends of PLA/Hytrel at varying weight ratios were prepared using extrusion followed by injection molding technique. Optimal synergies of two polymers were found in the PLA/Hytrel (70/30) blend, showing impact strength of 234 J/m, a sixfold increase compared to neat PLA. In order to obtain further enhancement in toughness, different functionalized terpolymers were added to accomplish reactive compatibilization. A series of functionalized terpolymers, ethylene methyle acrylate‐glycidyl methacrylate (EMA‐GMA), ethylene butyl acrylate‐glycidyl methacrylate (EBA‐GMA), ethylene methyl acrylate‐maleic anhydride (EMA‐MaH), and ethylene butyl acrylate‐maleic anhydride (EBA‐MaH) were selected. Comparing PLA ternary blends with different terpolymers, GMA containing terpolymers showed better impact toughness compared to MaH terpolymer blends. Unique fracture surface morphology showing debonding cavitation and massive shear yielding in the ternary blends containing EMA‐GMA resulted in super toughened blends. Highest zero shear viscosity and storage modulus was also observed for ternary blends with EMA‐GMA. Under the processing conditions and blend ratio investigated, EMA‐GMA showed better efficiency in improving the toughness of the PLA blends. POLYM. ENG. SCI., 58:280–290, 2018. © 2017 Society of Plastics Engineers     

Studies on thermal stability and behaviour of polyacetal and thermoplastic polyurethane elastomer blends

The influence of thermoplastic polyurethane (TPU) elastomer on the rigidity of polyacetal (polyoxymethylene, POM) was studied by determining heat deflection temperature (HDT). The higher the content of TPU in the POM/TPU blend, the lower the HDT of the blend, as would be expected. A comparative study of the recycle capability of POM and the blends was carried out by measuring melt flow index (MFI) on each successive extrusion. Stress-strain behaviour of the virgin material and that obtained after fourth-time extrusion was analysed for POM and the blends. The effect of γ-radiation on the mechanical behaviour of the blends was investigated. The kinetics of thermal degradation of POM, TPU and their blends was studied. The kinetic parameters, viz. activation energy and the order of reaction, were established. The values of the activation energy of the blends were found to be higher than those of the POM and TPU, indicating improved stability of the resultant blends.     

Use of wood fibers in thermoplastic composites II: Polyethylene

Wood fibers of aspen in the form of chemithermomechanical pulp (CTMP) has been used as reinforcement in polyethylene (PE). The secant modulus, tensile strength, energy, and elongation at yield were measured. It was found that the mechanical properties of the composite were higher than those of PE by a factor of 2.6 for modulus, 2.3 for stress, and 2.1 for energy at yield. Compared to glass fiber composites, the CTMP composites showed higher elongation, about 100 percent higher energy, 106 percent higher stress, and 75 percent higher modulus. Note that the cost of treated wood fibers is several times lower than that of treated glass fibers.     

Mechanical hysteresis of a polyether polyurethane thermoplastic elastomer

The mechanical hysteresis of a polyether polyurethane thermoplastic elastomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature, T_g of the polymer where the material did not formally yield. At temperatures above the T_g of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crosslinks. At elevated temperatures, percent hysteresis increased as the hydrogen-bonded hard segment domains weakened. When mechanical hysteresis was considered on the basis of constant deformation energies, hysteresis values reached a maximum in the vicinity of the T_g of the polymer. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the increase in the resistance of that glass to undergo deformations sufficient to cause plastic flow. Finally, a hysteresis response surface constructed as a function of deformation energy and temperature was found to be sensitive to both the strain-induced crystallization of the rubbery soft segment matrix and to the strain-induced yielding of the glassy soft segment matrix.     

Blends of PBT with rigid thermotropic LCP having flexible side groups: Comparison of their tensile properties with semirigid main-chain TLCP blends

Two new thermotropic liquid crystalline polymers (LCPs) were synthesized. One is a di-mesogenic LCP having a flexible hexamethylene spacer in the main chain, the other is a rigid-type main-chain LCP having alkoxy side groups on the terephthaloyl moiety of the polymer. Blends of LCP with poly(butylene) terephthalate were melt-spun at different LCP contents and different draw ratios to produce a monofilament. Maximum enhancement in the ultimate tensile strength was observed for the blends containing 5% LCP at any draw ratio, and decreased with further increase in LCP content. The initial modulus monotonically increased with increasing LCP content. The tensile properties of the rigid-type LCP blends were higher than those of the flexible main-chain LCP blends. © 1996 John Wiley & Sons, Inc.     

一种新型TPE的合成与表征

采用己内酰胺、4,4'-二苯基甲烷二异氰酸酯(MDI)、四氢呋喃聚醚(PTMC)和己二酸合成聚酰胺(PA)6-MDI/PTMG热甥性弹性体.通过红外光谱、差示扫描量热法、热重分析等表征聚合物的化学结构和物理性能.随着软段PTMG含量的增加,聚合物的硬度、拉伸强度下降,拉伸断裂应变和韧性提高.从扫描电子显微镜照片中发现,...     

苯乙烯类热塑性弹性体的生产现状及发展趋势

苯乙烯与二烯烃嵌段共聚物类热塑性弹性体因性能优良而得到迅速发展,其产量已位居各类热塑性弹性体之首,消耗量占热塑性弹性体的５０％以上,预计今后产量将以年均约８％的速度递增。通过对其改性技术的研究,提高产品质量,降低生产成本,如开发高透明度,等性能优良或用途特殊的新产品。     

聚烯烃弹性体/聚丙烯热塑性弹性体的制备及力学性能

以过氧化物为硫化剂,用动态硫化法制备了聚烯烃弹性体(POE)/聚丙烯(PP)热塑性弹性体,研究了硫化剂用量、填料种类和加工次数对体系力学性能的影响。结果表明,增加硫化剂用量可以提高体系的拉伸强度,降低拉伸永久变形和压缩永久变形。碳酸钙和滑石粉对POE/PP体系无明显增强作用,炭黑的增强作用较此二者明显一些,这三种填料加入后都会使体系的扯断伸长率降低而硬度增大。加入石蜡油会使体系的扯断伸长率和压缩永久变形增大、硬度和拉伸强度降低。加工次数对POE/PP体系的力学性能无明显影响,说明体系具有较好的重复加工性能。     

The essential work of fracture of a thermoplastic elastomer

This paper presents the fracture behaviour of a thermoplastic elastomer, HYTREL 5556. Since with this material it is not possible to successfully apply the LEFM nor the EPFM, it has been studied by following the ESIS protocol for determining the essential work of fracture in plane stress and extended for mixed-mode conditions, which should give a material constant, independent of the sample geometry. DDENT specimens were used in two different thickness, and results showed that the essential works of fracture in plane stress and mixed-mode were the same for both thickness for this material. Received: 24 March 1997/Revised: 30 May 1997/Accepted: 30 May 1997     

Phase behavior and properties of in situ‐reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline copolyester

In situ reinforcing composites based on two elastomer matrices very different in melt viscosity, styrene–(ethylene butylene)–styrene triblock copolymer (Kraton G1650) and styrene–(ethylene propylene) diblock copolymer (Kraton G1701), and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a twin‐screw extruder. The rheological behavior, morphology, mechanical and thermal properties of the blends containing various LC3000 contents were investigated. G1650 was found to have much higher shear viscosity than G1701. All neat components and their blends exhibited shear thinning behavior. Melt viscosity of the blends gradually decreased with increasing LC3000 contents. Despite a large difference in melt viscosity of the two matrices, the results showed that the fibrillar morphology was obtained for both as‐extruded strands of LC3000/G1650 and LC3000/G1701 with up to 30 wt % LC3000. At 40 wt % LC3000 or more, the lamellar structure was observed for both types of blends because of the coalescence of liquid TLCP threads that occurred during extrusion. The addition of LC3000 into both elastomer matrices enhanced the tensile modulus considerably whereas the extensibility remarkably decreased. The results obtained from thermogravimetric analysis suggested that an addition of LC3000 into both elastomer matrices improved the thermal resistance significantly in air, but not in nitrogen. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1610–1619, 2006