Morphology,mechanical and viscoelastic properties of nitrile rubber/epoxidized natural rubber blends

A new class of blend membranes from blends of nitrile rubber (NBR) and epoxidized natural rubber (ENR) has been prepared and their morphology, miscibility, mechanical, and viscoelastic properties have been studied. The ebonite method was used to study the blend morphology of the membranes. The morphology of the blends indicated a two‐phase structure in which the minor phase is dispersed as domains in the major continuous phase. The performance of NBR/ENR blend membranes has been studied from the mechanical measurements. The viscoelastic behavior of the blends has been analyzed from the dynamic mechanical data. An attempt was made to relate the viscoelastic behavior with the morphology of the blends. Various composite models have been used to predict the experimental viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by theoretical group contribution analysis. The homogeneity of the system was further evaluated by Cole–Cole analysis. Finally, a master curve for the modulus of the blend was generated by applying the time–temperature superposition principle. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1561–1573, 2005     

Effect of dynamic cross-linking on phase morphology and dynamic mechanical properties of polyamide 12/ethylene vinyl acetate copolymer blends

Dynamic cross-linking of polyamide 12 (PA12) and ethylene vinyl acetate copolymer (EVA) blends in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the PA12 phase through free radical reactions using dicumyl peroxide. The torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during the dynamic cross-linking process. The degree of cross-linking of EVA in the PA12/EVA materials was estimated based on the gel content (insoluble EVA fraction). The PA12/EVA phase morphology was investigated by scanning electron microscopy. The solid viscoelastic properties were investigated by dynamic mechanical thermal analysis (DMTA). The morphology, interfacial tension and viscoelastic results showed the immiscible nature of this system. The morphology of the blends was observed and the results revealed a two-phase system. The PA12/EVA 70/30 showed disperse-phase morphology, however a co-continuous phase was observed in blend ratios of 50/50 and 60/40. The dynamic cross-linking process resulted in a more stable EVA phase morphology with disperse and interconnected structures in the thermoplastic PA12 domains.     

In situ modulus enhancement of polypropylene monofilament through blending with a liquid‐crystalline copolyester

An immiscible blend of poly(propylene) (PP) with a thermotropic liquid‐crystalline polymer (TLCP, trade name Rodrun LC5000), a copolyester of 80/20 mol ratio of p‐hydroxy benzoic acid and polyethylene terephthalate was prepared in a twin‐screw extruder. The blend extrudate was fabricated as monofilament by using a single‐screw extruder equipped with a fiber line. The as‐spun filament was drawn at 120°C to enhance molecular orientation. Morphology, thermal, tensile, and dynamic mechanical properties of both as‐spun and drawn monofilaments were investigated. Almost continuously long TLCP fibers dispersed in PP matrix were obtained in the composite as‐spun monofilaments. The maximum modulus was found in 15 wt % TLCP/PP composite as‐spun filament, an increase of about 2.4 times that of the as‐spun neat PP. For the drawn filaments, the 10 wt % TLCP/PP composite showed a maximum modulus, an increase of about 1.5 times that of the drawn neat PP. The increase in the moduli was attributed not only to the reinforcement by TLCP fibrils with very high aspect ratio but also to the increases in PP crystallinity and molecular orientation through the drawing process. A remarkable improvement in the dynamic mechanical properties of the composite monofilaments was observed, especially in the high‐temperature region. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90:1337–1346, 2003     

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     

The linear viscoelastic behaviors of Nylon1212 blends toughened with elastomer

The linear viscoelastic behaviors of nylon1212 blends toughened with (styrene‐[ethylene‐(ethylene‐propylene)]‐styrene block copolymer) (SEEPS) elastomer were carried out. The results show that dynamic storage modulus (G′) curves of the blends are located between those of virgin nylon and SEEPS within the frequency (ω) tested, and the G′ of blends increases with increasing of the SEEPS content. Moreover, the predictive results of Palierne emulsion model show that it is unsuitable for describing the viscoelastic behaviors of the double phase systems toughened with elastomer, especially for the system with high content of elastomer. The positive deviation in the plots of G′ vs. blend composition demonstrates that the blends are immiscible. From the point of phase transition, the phase inversion region for these blends was predicted to be in the range of 30–50 wt % of SEEPS, which agrees with the morphology analysis of nylon1212/SEEPS blends. In addition, “Cole–Cole” plots of modulus at different temperatures show that the microstructures of blends are unstable in the phase transition region. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene/polyisoprene blend

The morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene (PB)/low vinyl content polyisoprene (LPI) blend have been investigated. Under steady shear flow where the applied shear rate is not too large, the steady sheared structures become increasingly anisotropic and interconnected with an “en route” to the formation of string phases as shear rate increases. After that, the further increase of shear rate leads to a blurred domain interface. These shear-induced complex structures in turn affect the rheological response greatly and both the shear thinning and shear thickening were observed in the steady shear behavior of the phase-separated PB/LPI blend. Under transient shear flow, the time (or strain) dependence of viscosity and morphology after a shear rate jump were extensively studied in order to obtain the insight into the steady state formation and found to be mainly determined by the final shear rates. Depending on whether the transient string phases which were formed by the transient shear flow can be stabilized and with clear domain interface, three kinds of transient shear viscosity changes have been observed. Some of the observations are quite different from the model immiscible blend and believed to be closely related to the significant shear-induced mixing effect happened in the PB/LPI blend.     

Mechanical and viscoelastic behavior of natural rubber and carboxylated styrene‐butadiene rubber latex blends

The morphology, mechanical and viscoelastic behavior of latex blends of unvulcanized natural rubber (NR) with carboxylated styrene‐butadiene rubber (XSBR) were investigated, with special reference to the effect of the blend ratio, temperature, and frequency. Mechanical properties like tensile strength, modulus, and elongation at break were also studied. As the XSBR content increased, the tensile strength increased up to a 50:50 NR/XSBR ratio and then decreased as a result of the self‐curing nature of XSBR. The dynamic mechanical properties of these latex blends were analyzed for loss tangent, storage modulus, and loss modulus. The entire blend yielded two glass‐transition temperatures, which corresponded to the transitions of individual components, indicating that the system was immiscible. To determine the change in modulus with time, a master curve of 50:50 NR/XSBR blends was plotted. Time–temperature superposition and Cole–Cole analysis were done to understand the phase behavior of the latex blends. The experimental and theoretical values of storage modulus of blends were compared using the Kerner and Halpin–Tsai models. With the help of optical micrographs, attempts were made to correlate the morphology and viscoelastic behavior of these blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2639–2648, 2003     

Dynamic mechanical, thermal, physico-mechanical and morphological properties of LLDPE/EMA blends

The effect of blend composition on the morphology, dynamic mechanical properties, thermal and physico-mechanical properties of linear low density polyethylene (LLDPE)/ ethylene-co-methyl acrylate (EMA) blends were studied. The blend showed both dispersed and continuous phase morphology that depends on the blend composition. A co-continuous structure is formed for blends containing 50 wt% of EMA. Dynamic mechanical studies showed that flexibility of the blend enhanced with the expansion of the amorphous region as EMA content increased. However, two separate melting temperature peak observed in differential scanning calorimetry (DSC) analysis indicate that the blends are immiscible in crystalline region of the two polymers. X-ray diffraction (XRD) studies showed that crystallinity of blends decreases with increase in EMA content and negative deviation of tensile strength from the mixing rule indicates the poor interfacial adhesion between the two components. FTIR spectroscopy established the lack of chemical interaction between LLDPE and EMA, which support the SEM, DSC, DMA and XRD observations. Parallel-Voids model has been applied to characterize phase morphology of these blends.     

聚对苯二甲酸乙二酯/聚丙烯不相容共混体系的结构流变学

通过熔融共混制备了不相容的聚对苯二甲酸乙二醇酯（PET）/聚丙烯（PP）复合体系,研究了复合体系的结构流变学。结果表明,PET/PP共混体系的不相容相形态显著影响其稳态和动态流变行为。当PP组分为分散相时,复合体系表现出动态形状松弛;当两组分呈多种相形态共存时,复合体系表现出强烈的低频区弹性响应;而当PET组分为分散相时,复合体系的剪切敏感性则相对较小。在较高剪切应力作用下,分散相液滴的凝聚是影响体系流变行为的控制因素,而在较低的剪切应力作用下,液滴的破碎则成为控制因素。     

Silicone Rubber Compatibilized Syndiotactic Polystyrene and Thermotropic Liquid Crystalline Polymer (Vectra A950) Blend

Blends of syndiotactic polystyrene (s-PS), thermotropic liquid crystalline polymer (Vectra A-950), and silicone rubber with two different loading levels, have been prepared through melt processing in internal mixer at 285°C. Silicone rubber was used as a compatibilizer for this blend system. The effect of silicon rubber on crystalline, dynamic mechanical, rhelogical, thermal properties, and phase morphology of the (s-PS/TLCP) blend has been investigated in details. With the addition of compatibilizer the viscosity of the blend system increased to an order of magnitude. Dynamic mechanical analysis (DMTA) and differential scanning calorimetry (DSC) results showed that the glass transition temperature (T_g) of the blend, in presence of silicone rubber, shifted towards lower temperature region. From FTIR analysis it is evident that the ‘C=O’ stretching frequency has shifted towards lower side. SEM analysis suggested that, the TLCP domain size is reduced in ternary blend in comparison to binary blend system.     

Morphology Development via Static Crosslinking of (Polylactic Acid/Acrylic Rubber) as an Immiscible Polymer Blend

The interrelation between crosslinking and morphology is investigated for an immiscible blend of polylactic acid (PLA) and acrylic rubber (ACM). The blends are prepared by solution mixing and static crosslinking is used to avoid the simultaneous effect of the flow field that occurs in dynamic vulcanization. It is carried out at different temperatures, times, and curing agent contents. Scanning force microscopy (SFM) and polarized optical microscopy are used to determine the morphology of the blends. The chemical interactions and viscoelastic properties of the blends after crosslinking are also studied using infrared spectroscopy and rheological tests, respectively. Before crosslinking, SFM shows matrix‐droplet morphology for the samples that it is retained after that for the blend with 30 wt% ACM; however, it is changed to cocontinuous one in the blend with 50 wt% ACM. Partially, grafting of PLA on the crosslinked ACM is confirmed by Fourier transform infrared spectroscopy. The rheological results show that the incorporation of ACM to the PLA slows down the chain relaxation and vulcanization intensifies this effect. A model is proposed to explain the morphology evolution during static crosslinking of an immiscible blend.     

PET/TLCP原位共混的研究

研究了PET／TLCP原位共混体系的热性能、流变性能、力学性能。结果表明,在PET中加入少量TLCP可起到结晶成核剂的作用,提高PET基体的结晶性能,并使共混物的熔体粘度降低;催化剂二月桂酸二丁基锡的加入,可增加共混物的熔体粘度,降低分散相的尺寸,增强经物两相间的界面粘接,从而提高PET／TLCP共混体系的力学性能。     

聚己内酯/聚乳酸共混体系的相形态及其流变行为

通过熔融共混制备了生物可降解的聚己内酯（PCL）/聚乳酸（PLA）共混体系,采用扫描电镜（SEM）和旋转流变仪分别研究了共混体系不相容的相形态及结构流变学。结果表明,共混体系的相形态强烈依赖于组分比。随PCL组分含量的增加,体系内部球形分散的形态逐渐向纤维状和部分双连续的相形态转变。两相界面的存在增加了体系动态弹性响应,并使体系出现了动态形状松弛。但从共混物模量对频率的依赖性仅能够判断体系是否存在不相容的相界面,相形态的差异则需通过松弛曲线来反映。     

An Insight into Phenomenology of Polytrimethylene Terephthalate Fibrillation

The objective of this work is to analyze the effect of the processing temperature on fibrillation of the dispersed phase and to correlate melt viscoelastic responses to formed morphologies. A blend system of polypropylene (PP)/polytrimethylene terephthalate (PTT) with varying ratios (PP/PTT: 99/1, 94/6, 90/10, and 80/20) is prepared on a co‐rotating twin screw extruder, and then pelletized blend samples are fed into a laboratory mixing extruder to spin monofilaments at three different orifice temperatures of 180, 195, and 240 °C. As revealed by scanning electron microscopy, a nano‐fibrillar morphology forms after employing spinning. Rheological approach performed in the linear region shows a transition from terminal trend into non‐terminal trend in the low‐frequency region when the fibrillar morphology forms, the magnitude and width of which are reflective of the fibril growth. Transient stress measurements prove its capability to enable the blend system to show potentials of morphology development during dynamic tests. Startup of steady shear flow shows that after reaching the percolation concentration of dispersed phase, fibril–fibril coalescence leads to the formation of long fibrils whose contribution to the blend system increases the elasticity of the blend fibers.     

PPS/TLCP共混体系结构与流变研究

采用热致液晶聚合物（TLCP）与聚苯硫醚（PPS）熔融共混的方式制备了PPS／TLCP复合材料,研究了PPS／TLCP共混体系的形貌、流变性能以及加工参数对微纤形成的影响。结果表明：TLCP可明显改善体系的加工特性,并能原位生成微纤化复合材料,TLCP对体系黏度有较大影响,在低剪切速率区黏度下降幅度较大,在高剪切速率区,黏度降低幅度小。PPS／TLCP复合材料存在皮芯结构,工艺参数对TLCP微纤的形成起着重要作用,通过提高注塑速度,对TLCP微纤的形成特别有利。     

热致液晶聚合物增强PP/mPE原位复合材料的研究

采用热致液晶聚合物（TLCP）对PP及PP/mPE共混物进行增强，制得PP／TLCP和PP／mPE／TLCP原位复合材料。探讨了TLCP对复合材料拉伸性能、低温冲击性能和加工流变行为的影响。结果表明，加入15％的TLCP可以显著提高PP和PP／mPE的刚性，改善加工流动性。但由于体系的相容性较差，基体的拉伸强度有所降低，低温冲击韧性也有显著的降低。     

Rheology and relaxation processes in a melting thermotropic liquid–crystalline polymer

The relaxation behavior of a thermotropic liquid–crystalline polymer (TLCP), LC‐5000 from Unichika, Japan, was investigated by rheology and optical microscopy. The solid‐nematic transition was shown by DSC and dynamic temperature ramp. The transitions of dynamic modulus with temperature correspond to the end of the melting process. The TLCP is composed of unmelted solid crystals and nematic liquid crystal during the melting process. Macroscopically, it changes from a viscoelastic solid to a viscoelastic liquid in this process, as verified by creep test and dynamic frequency sweep under different temperature. The relaxation spectra of the TLCP under different temperature were calculated from the dynamic modulus. The characteristic relaxation processes determined from the relaxation spectrum are consistent with the observation from polarized optical microscopy. During melting, in particular, the relaxation of deformed polydomains and chain orientation slows down due to the constraining effects of unmelted solid crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3780–3787, 2007     

Effect of viscosity variation with temperature on the compounding behavior of immiscible blends

Morphology development in the compounding of immiscible blends depends on a number of material properties and process conditions. In this work, different model blend systems are considered to outline the effects of the relative transition temperatures and viscosities of the blend components. We focus on the evolution of blend morphology, specifically phase continuity. A framework based on these factors is presented for analyzing the compounding behavior of immiscible blend systems. With the minor component at 10 wt%, it was found that phase inversion during compounding occurred in blends with a viscosity ratio of less than 0.2, independent of the relative transition temperatures. It was shown that in these constant mixer temperature runs, the torque trace was not a completely reliable indicator of phase inversion. When a temperature ramping program was used, the lower melting point component formed the continuous phase initially, independent of the viscosity ratio. Quantitative measures of the amount of minor component which was continuous at different mixing times were made using selective extraction in a Soxhlet apparatus. Results from compounding runs of polycarbonate/ polyethylene, an amorphous copolyester/polyethylene and polybutylene/polycaprolactone blends are presented.     

Characterization of thermotropic liquid crystalline polyester/polycarbonate blends: Miscibility,rheology, and free volume behavior

Miscibility, rheology, and free volume properties of blends of thermotropic liquid crystalline polymers (TLCPs) (Vectra A950) and polycarbonate (PC) are studied in this work. Despite the unusual increase in T_g of the PC phase, the blends are found to be generally immiscible. Transesterification may occur during blending and be the cause of the increase of T_g of the PC phase and the partial miscibility of the blends at high TLCP concentrations. With regard to the melt rheology of these materials, according to a three‐zone model, dynamic moduli of Vectra A950 show plateau‐ and transition‐zone behavior, while PC exhibits terminal‐zone behavior. The blends show only terminal‐zone behavior at low Vectra A950 contents (≤50%) and terminal‐ and plateau‐zone behavior at higher Vectra A950 contents. The relaxation time of Vectra A950 is much longer than PC and the blends have relaxation times greater than additivity. Both the complex and steady shear viscosities of the blends increase with the addition of Vectra A950. This is attributed to interfacial association, which retards the reorientation and alignment of the Vectra A950 phase in the molten state. The Cox–Merz rule holds true for PC but not for Vectra A950 and the blends. Free volume properties on an angstrom scale evaluated by positron annihilation lifetime spectroscopy (PALS) indicate that Vectra A950 has smaller, fewer free volume cavities than PC and the variation of free volume behavior in the blends can be explained in terms of blend miscibility. The measured densities of the blends agree well with the free volume fractions of the blends determined from PALS. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2319–2330, 2000