Nanostructured carbon black filled polypropylene/polystyrene blends containing styrene-butadiene-styrene copolymer: Influence of morphology on electrical resistivity

This paper is part of a comprehensive study on using selective localization of carbon black (CB) at the interface of immiscible polymer blends in order to reduce the percolation threshold concentration and enhance the conductivity of the blends. CB was successfully localized at the interface of polypropylene/polystyrene (PP/PS) blend by introducing styrene-butadiene-styrene (SBS) tri-block copolymer to the blend. In CB-PP/PS/SBS blends, CB has higher affinity for the polybutadiene (PBD) section of the SBS copolymer, whereas in CB-PP/PS blends, CB prefers the PS phase. PP/PS interface is one of the preferred locations for the SBS copolymer in the (PP/PS) blend; at which the PBD section of the SBS copolymer forms a few nanometers thick layer able to accommodate the CB nano-particles. The influence of SBS addition on the morphology and electrical properties of various PP/PS blends filled with 1 vol% CB were studied. SBS influence on the conductivity of PP/PS blends was found to be a function of the PP/PS volume ratio and SBS loading. The most dramatic increase in conductivity was found in the (60/40) and (70/30) PP/PS blends upon the addition of 5 vol% SBS. 5 vol% SBS was found to be the optimum loading for most blends. Using 10 vol% of SBS was reported to deteriorate electrical conductivity of the conductive co-continuous PP/PS blends. For all blends studied, SBS addition was found to compatibilize the blends. Finer morphologies were obtained by increasing SBS loading.     

静电纺丝法制备超细聚苯乙烯纳米纤维

采用静电纺丝方法制备了超细聚苯乙烯纤维, 通过向溶液中添加有机胺盐并降低溶液浓度将纤维的平均直径降至100 nm, 并研究了盐的添加量对纤维直径的影响.     

Polyaniline/poly(methyl methacrylate) coaxial fibers: The fabrication and effects of the solution properties on the morphology of electrospun core fibers

Electrically conductive polyaniline (PANi)/poly(methyl methacrylate) (PMMA) coaxial fibers were prepared through the chemical deposition of PANi onto preformed PMMA fibers via in situ polymerization. PMMA fibers were prepared as core materials via electrospinning. Spectral studies and scanning electron microscopy observations indicated the formation of PANi/PMMA coaxial fibers with a diameter of approximately 290 nm and a PANi layer thickness of approximately 30 nm. The conductivity of the PANi/PMMA coaxial fibers was significantly higher than that of electrospun fibers of PANi/poly(ethylene oxide) blends and blend cast films of the same PANi composition. To reproducibly generate uniform‐core polymer fibers, the organic solution properties that affected the morphology and diameter of the electrospun fibers were investigated. The polymer molecular weight, solution concentration, solvent dielectric constant, and addition of soluble organic salts were strongly correlated to the morphology of the electrospun fiber mat. In particular, the dielectric constants of the solvents substantially influenced both the fiber diameter and bead formation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3934–3942, 2004     

核-壳结构壳聚糖/聚乙烯醇-聚碳酸亚丙酯超细纤维的制备

利用同轴电纺丝技术制备出具有核-壳结构的壳聚糖/聚乙烯醇-聚碳酸亚丙酯电纺丝纤维,考察了溶剂复配对成纤的影响,采用扫描电镜和透射电镜对纤维的形貌、结构、直径分布等进行了探索,并在优化的工艺条件下,将羟基磷灰石负载在内层结构中.研究表明,采用氯仿/N,N-二甲基甲酰胺(1/1)复配溶剂可有效避免聚合物溶液在喷丝口处的凝结现象.同单纺纤维相比,核壳结构的纤维直径分布较宽,纤维壳层和核层界限清晰;红外谱图分析证明羟基磷灰石可负载在纤维的核结构中.     

Computer simulation of crystallization kinetics and morphology in fiber-reinforced thermoplastic composites. I. Two-dimensional case

A body of experimental evidence suggests that reinforcing fibers influence both the crystallization kinetics and morphology of those composite materials that are based on crystallizable thermoplastics. The absence of an analytical model to predict the effect of fibers on crystallization has hindered data analysis. A new approach, using computer simulation of polymer crystallization, makes it possible to study the influence that reinforcing fibers have on the crystallization kinetics and morphology of semicrystalline polymers. Fibers depress the crystallization rate relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism. On the other hand, reinforcing fibers can also enhance crystallization rate by providing added surface nucleation sites. This work describes a two-dimensional simplification of the crystallization process that occurs in bulk materials. It is demonstrated that the relative bulk and fiber nucleation densities, in addition to the fiber fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and also the spherulitic and transcrystalline morphologies that develop in reinforced thermoplastic composites. © 1993 John Wiley & Sons, Inc.     

Morphological changes in SBS block copolymers caused by oil extension as determined by absolute small angle x-ray scattering

A series of SBS block copolymers diluted with different amounts (0–60 wt%) of three different kinds of oil were investigated: 1) lithene PM (a low molecular weight polybutadiene); 2) a paraffinic mineral oil with its electron density close to that of the polybutadiene (PB) phase; 3) a highly aromatic mineral oil with an electron density close to the polystyrene (PS) phase. All the oils seem to go into the polybutadiene matrix. Paraffinic oil and lithene form a homogeneous phase with PB; the aromatic oil at low concentrations mixes with the PB phase with a high level of inhomogeneity, while at higher concentration partial phase separation occurs. In the undiluted polymer, styrene forms cylinders in hexagonal packing. The distance between cylinders (about 43 nm) is not significantly changed upon dilution up to 33 wt%. Previously proposed changes in the morphology of PS domains at larger oil contents can be related to observed changes in the long period, in the segment length distributions, and in the homogeneities of the phase (density fluctuations). The electron density difference obtained for pure SBS is lower than the theoretical one calculated from the densities of pure PS and pure PB. Dilution by paraffinic oil improves the phase separation.     

聚多巴胺在强负电型微球表面的形貌调控

多巴胺(DA)已被证实可在多种材料的表面进行氧化自聚而形成聚多巴胺(PDA),但其在带强负电荷的表面上的聚合机理和所形成的形貌却还不太明确。 为考察材料表面的电负性、氧化条件等对DA氧化自聚速度和聚多巴胺层形貌的影响,本文通过无皂乳液聚合制备了以聚苯乙烯(PS)为核、聚丙烯酸(PAA)为壳的纳米粒子(PS/PAA NPs),探究其表面的阴离子在不同pH缓冲液、反应时间下与DA的加入量对聚合过程及其形貌的影响。 通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)和Zeta电势对所得纳米粒子的结构、形貌与尺寸等进行分析。 结果发现,在pH值为8.5的三羟甲基氨基甲烷(Tris)缓冲溶液中,当DA与PS/PAA NPs的质量比为1∶1时,在反应24 h后,PDA以纳米颗粒的形式存在于PS/PAA NPs的表面,即所形成的PS/PAA/PDA NPs为明显的树莓状结构。 随着DA含量的增加和反应时间的延长,所形成的树莓状粒子粒径增大;当DA远远过量时,PDA最终在微球表面形成致密、均匀的壳层。 Zeta电势结果表明树莓状结构是由于DA在PAA表面聚合过程中受到静电相互作用和电荷排斥作用间的竞争而形成的,随着DA量的增大和反应时间的延长,形成的静电作用增大,使较多的PDA粘附至PAA表面而形成较致密的均匀壳层。 同时,DA在电负性较小的PS/SDS微球和非离子的PS微球表面聚合时,均形成致密的PDA壳层。 因而,材料表面的电负性大小可以调控DA在其表面的沉积,以制备不同形貌的PDA复合材料。     

Diameter control of electrospun chitosan‐collagen fibers

In this article, the effects of fundamental parameters including applied voltage, feed rate of solution, collecting distance of fibers, the ratio of chitosan to collagen in the fibers and polymer solution concentration on the diameter and morphology of electrospun collagen‐chitosan complex nanofibers were studied to produce ultrafine polymer fibers. Based on the systematic parametric study, it is possible to control the diameter and morphology of the electrospun polymer fibers. This will also be helpful for electrospinning of various polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1949–1955, 2009     

Vertical phase separation and liquid-liquid dewetting of thin PS/PCL blend films during spin coating

Thin films of an amorphous polymer, polystyrene (PS), and a crystalline polymer, poly(ε-caprolactone) (PCL), blend were prepared by spin coating a toluene solution. Surface chemical compositions of the blend films were measured by X-ray photoelectron spectroscopy (XPS), and the surface and interface topographical changes were followed by atomic force microscopy (AFM). By changing the PS concentration and keeping the PCL concentration of the solution at 1 wt %, a great variety of morphologies were constructed. The results show that the morphology of the blend films can be divided into three regions with increasing PS concentration. In region I, PS island domains are embedded in PCL crystals when the PS concentration is lower than 0.3 wt % and the size of the PS island increases with increasing PS concentration. In region II, holes with different sizes surrounded by a low rim are obtained when the concentration of PS is between 0.35 and 0.5 wt %. After selectively washing the PS domains, we studied the interface morphology of PS/PCL and found that the upper PS-rich layer extended into the bottom PCL layer, forming a trench surrounding the holes. In region III, an enriched two-layer structure with the PS-rich layer on top of the blend films and the PCL-rich crystal layer underneath is obtained when the concentration of PS is higher than 0.5 wt %. Last, the formation mechanism of the different surface and interface morphologies is further discussed in terms of the vertical phase separation to a layered structure, followed by liquid-liquid dewetting and crystallization processes during spin coating.     

Liquid crystal fibers produced by using electrospinning technique

This paper investigates the electrospinning process of liquid crystalline polysiloxane with cholesterol as side chain (LCPC) and the influence on the morphology of the formed fibers by mixing LCPC solution with small-molecule liquid crystal, triethylamine, and poly(ethylene oxide)(PEO). The mechanical properties of single fibers were characterized by a novel approach. The results indicate that, under appropriate conditions, fine liquid crystal fibers can be obtained and the preferable mechanical properties can be achieved, especially after annealing. WXRD was used to investigate the orientation of polymer molecules in the formed fibers, suggesting that strong interaction exists between LCPC and PEO molecule in the resulting composite fibers, and polymer molecular tends to arrange regularly during electrospinning processing. This research work provides a new and facile method of using electrospinning to prepare liquid crystal fibers, which would be useful for designing the related high-performance materials.     

Morphology, morphology development and mechanical properties of polystyrene/polybutadiene blends

Polystyrene/polybutadiene (PS/PB) blends with different plastic/rubber ratios were prepared by melt mixing. A detailed investigation on phase morphology development of 30/70 wt.% PS/PB blends as a function of processing conditions was quantitatively analyzed. Morphology is developed at the initial stages of mixing. Suitable blending conditions resulting in optimum phase morphology were obtained at 180 °C, 60 rpm and at 8 min mixing time. Phase morphologies of the blends were also studied as a function of composition. Mechanical properties of the blends were measured. Attempts were made to correlate the morphologies with the properties. Parallel-Voids model has been applied to characterize phase morphology of these blends.     

High-molar mass acrylamide-co-diacetoneacrylamide graft copolymers as viscosity enhancer for polymer flooding oil recovery

One of the most widely applied enhanced oil recovery processes is the polymer flooding, in which aqueous solution of polymer viscosifier is introduced in oil reservoirs to increase the recuperation of the remaining oil. From the current challenges of this process, it can be referred to a high cost of materials regarding their substantially required amount and the low impact on the mobility ratio during the process due to the reduction of solution viscosity at high temperatures and high salinity environments. The purpose of this study is to investigate the concept of acrylamide-based thermosassociating copolymer (TAP), with a specific morphology and chemistry (hydrophilic main backbone made of polyacrylamide with grafted amide functionalized pending chains) as viscosity enhancer at harsh conditions of high temperature and salinity. For that aim, a specific TAP microstructure was targeted (very high molar mass linear polymer chains with improved copolymer homogeneity). It is achieved in this study throughout applying the reaction engineering approach, such as synthesis in semi-batch mode or/and in heterogeneous dispersed media. As a result, the synthesized TAP presented excellent behavior as viscosity enhancer especially under high temperature and salinity conditions with improved performance in comparison to TAP synthesized by a conventional solution polymerization approach and to actual commercial high molar mass acrylamide-based polymer.     

Plateau–Rayleigh Instability Morphology Evolution (PRIME): From Electrospun Core–Shell Polymer Fibers to Polymer Microbowls

Electrospun core–shell fibers have great potentials in many areas, such as tissue engineering, drug delivery, and organic solar cells. Although many core–shell fibers have been prepared and studied, the morphology transformation of core–shell fibers have been rarely studied. In this work, the morphology evolution of electrospun core–shell polymer fibers driven by the Plateau–Rayleigh instability is investigated. Polystyrene/poly(methyl methacrylate) (PS/PMMA) core–shell fibers are first prepared by using blend solutions and a single axial electrospinning setup. After PS/PMMA core–shell fibers are annealed on a PS film, the fibers undulate and sink into the polymer film, forming core–shell hemispheres. The evolution process, which can be observed in situ by optical microscopy, is mainly driven by achieving lower surface and interfacial energies. The morphologies of the transformed structures can be confirmed by a selective removal technique, and polymer microbowls can be obtained.

     

Emulsion electrospinning: composite fibers from drop breakup during electrospinning

We evaluate the feasibility of electrospinning oil‐in‐water type emulsions. The emulsions had an aqueous solution of polyethylene oxide (PEO) as the continuous phase, and either mineral oil or a polystyrene (PS) in toluene solution as the drop phase. The Taylor cones and electrified liquid jets were stable even when the emulsion drops were as large as a few‐ten microns in diameter. The resulting electrospun PEO fibers incorporated the dispersed phase of the emulsion in the form of drops (in case of mineral oil), or in the form of solid particles (in case of PS). Mineral oil drops appear to be completely encapsulated in the PEO fibers, whereas the PS particles are either incompletely encapsulated, or covered by only a very thin layer of PEO. Calculations show that in both cases, the initially large emulsion drops are broken during the electrospinning process. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of composition and processing on the linear viscoelasticity of synthetic binders

The influence that composition and processing variables exert on the linear viscoelastic properties of model synthetic binders has been studied in a wide range of temperature and frequency. Model synthetic binders were prepared by blending a non-modified colophony resin (40-65%), a process aromatic oil and a styrene-butadiene-styrene (SBS) triblock copolymer (5-15%). At high SBS content (11% and 15%) and gentle processing conditions (i.e. 150 °C and 60 rpm), a plateau region in G′ is found in the mechanical spectrum. The microstructure of this binder is characterized by a continuous SBS-rich phase. On the contrary, a shoulder in G′ is found at low polymer content. The resulting microstructure consists of a continuous resin-rich phase and a dispersed polymer-rich phase. Under severe processing conditions (180 °C and 1200 rpm) and low polymer concentration, the polymer influence is dampened and the glassy region appears at higher temperatures or lower frequencies. At high polymer concentration, a phase inversion can be induced by processing (i.e. 180 °C and 1200 rpm.). Both resin oxidation and SBS degradation may explain such microstructural changes.     

Influence of Neem oil pretreatment on the dyeing and antimicrobial properties of wool and silk fibers with some natural dyes

Wool and silk fibers pretreated with neem oil and dyed with chlorophyll, saffron red and yellow natural dyes using economic methods such as microwave heating and ultrasonic energy. The effect of neem oil concentrations on color strength (K/S) was measured. The results indicated that, wool and silk fibers pretreated with neem oil recorded higher color strength values than the untreated fibers. Fastness properties and the color yield of the dyes under investigation on wool and silk fibers were evaluated. The results indicated that, color fastness to rubbing, washing and perspiration of all dyes are excellent to good and are approximately the same in microwave and ultrasonic method. The antimicrobial activity against bacteria and fungi were tested, and the results indicated that the samples pretreated exhibited higher inhibition percent than the untreated fibers. The morphologies structure of the untreated and treated wool fibers were examined by scanning electron microscopy (SEM). The untreated samples have a rough surface. The pretreated samples of wool fibers were swelling compared to the untreated fibers .The diameter of the fibers increased and have smooth and even surfaces. The changes in the surface morphology due to the effect of active ingredients of treatment with neem oil. This behavior as swelling and increase in diameter of the fibers leads to high penetration of the dyes in the fibers.     

Sol–gel synthesis of porous titania fibers by electro-spinning for water purification

In this study, porous ceramic fibers were prepared by the sol–gel-assisted electro-spinning process using colloidal dispersion of complex fluids for the application of phtotocatalysts. First, polystyrene nanospheres were synthesized by dispersion polymerization as sacrificial templates for porous fibers. Then, the mixture of polyvinylpyrrolidone and the ceramic precursor with the polymeric nanospheres was prepared as the spinning solution and self-organized by electro-spinning, followed by calcination of the electrospun composite fibers. The morphologies of the porous fibers could be controlled according to the size of the templates and the amount of the ceramic precursor. The nano-structure of the pores in the fibrous materials could also be adjusted as open or closed cavities with various potential applications. As a demonstrative application, the macroporous titania fibers could be utilized as photocatalysts for the removal of organic dyes dissolved in water. A better photocatalytic activity of the macroporous fibers with 700-nm pore diameter was observed compared to the result of nonporous titania fibers due to the increased porosity. Collectively, the macroporous ceramic fibers were found to be efficient functional materials to prepare the unique nano-structured materials other than simple nonporous fibers.     

三醋酸纤维素纳米纤维膜的制备及其油水分离应用

石油开采和油船运输泄露的油污污染日益突出,使得质轻、亲水疏油的油水分离材料得到广泛关注。本文在无任何添加剂条件下,以三醋酸纤维素(TCA)/N,N-二甲基乙酰胺(DMAc)溶液通过热致相分离(TIPS)制备TCA纳米纤维膜。研究了淬火时间、温度和聚合物浓度等条件对TCA纳米纤维膜形貌的影响。TCA纳米纤维膜的形貌、孔隙率和比表面积通过SEM、乙醇法和N2吸脱附表征。实验结果表明,最佳实验条件为:淬火时间180 min、淬火温度-20℃、聚合物质量分数5%,得到直径为(110±28)nm均匀纤维膜。与块状TCA流延膜相比,TCA纳米纤维膜的高孔隙率和大比表面积以及表面特殊的微/纳结构,使其水接触角由86.2°增加到137.5°。由于高疏水性和亲油性以及强烈的毛细作用,TCA纳米纤维膜的吸油容量达到21.5 g/g,分别是流延膜的20~42倍,且可快速吸收油水混合物中的油层。TCA纳米纤维膜是一种可生物降解的溢油污染清洁材料。     

Synthesis,Characterization and Properties of Novel Amphiphilic Phosphated Ionomers by Ring‐Opening Reaction of Epoxidized Styrene‐Butadiene‐Styrene Triblock Polymer

A method for synthesis of novel phosphated ionomer of (styrene‐butadiene‐styrene) triblock polymer (SBS) from epoxidized SBS was developed. The optimum conditions for the ring‐opening reaction of the epoxidized SBS with aqueous solution of disodium hydrogen phosphate were studied. It was found that during the ring‐opening reaction phase transfer catalyst, ring‐opening catalyst and pH regulator were necessary to enhance the conversion of epoxy groups to ionic groups. The products were characterized with Fourier Transform Infrared Spectrophotometry (FTIR) and transmission electron microscopy (TEM). Some properties of the phosphated ionomer were studied. With increasing ionic groups or the ionic potential of the cation of the ionomer, the water absorbency emulsifying volume and the intrinsic viscosity of the ionomer increase, whereas the oil absorbency decreases. The ionomer possesses excellent emulsifying property, as compared with the sulfonated ionomer. The disodium phosphated ionomers in the presence of 10% zinc stearate showed better mechanical properties than the original epoxy SBS. Optimum mechanical properties occurred at the ionic group content of 0.95 mmol/g ionomer. When the ionomer was blended with crystalline polypropylene, a synergistic effect occurs with respect to the tensile strength. The ionomer behaves as a compatibilizer for blending equal amount of SBS and oil‐resistant chlorohydrin rubber (CHR) to form an oil resistant thermoplastic elastomer. SEM microphotographs indicated enhanced compatibility between the two components of the blend in the presence of the ionomer.     

Structure and nanomechanical characterization of electrospun PS/clay nanocomposite fibers

Electrospinning has been emerging as one of the most efficient methods to fabricate polymer nanofibers. In this paper, PS/clay nanocomposite fibers with varying diameters were electrospun onto solid substrates. The fiber diameters were adjusted from 4 microm to 150 nm by changing the solution concentration. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to characterize the fiber morphology. Shear modulation force microscopy (SMFM) was utilized to investigate the surface nanomechanical properties of electrospun fibers as a function of the fiber diameter and temperature. In the absence of clay, no change in T(g) was observed, even though a large increase of shear modulus below the glass transition temperature was found. This effect was postulated to result from the molecular chain alignment during electrospinning. The addition of functionalized clays to the spinning solution produced fibers with a highly aligned montmorillonite layer structure at a clay concentration of 4 wt %. Clay agglomerates were observed at higher concentrations. The existence of clay further enhanced the shear modulus of fibers and increased the glass transition temperature by nearly 20 degrees C.