A method to characterize the biaxial orientation of the crystalline phase in polyethylene blown films

In accordance with an approach suggested by Kissin (J Polym Sci Polym Phys Ed 1992, 30, 1165), a general form of the Beer–Lambert law was employed to estimate the White–Spruiell biaxial orientation factors of the crystalline phase in various polyethylene blown films. Certain assumptions employed by Kissin are invalid for most polyethylene blown films. Alternate assumptions that are based on sound experimental evidence were employed, and the ensuing theory and equations are presented. This technique incorporates into the Beer–Lambert law all possible orthogonal configurations of the polyethylene orthorhombic unit cell with respect to the axes of a blown film along with IR absorption data at 719 cm⁻¹ and 730 cm⁻¹. Solving the various equations (the Beer–Lambert law at orthogonal polarizations for each band) provided estimates for the mass fractions of all orthogonal configurations of the crystal unit cell with respect to the axes of a blown film. The ultimate biaxial orientation features of the crystalline phase are described as a combination of these orthogonal configurations. The resulting White–Spruiell biaxial orientation factors are in good qualitative agreement with X‐ray diffraction patterns for various low‐ and high‐density polyethylene blown films. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 182–193, 2000     

静电纺羟基磷灰石/明胶微纳复合纤维

本文从仿生角度出发,模拟细胞外基质独特结构,采用静电纺丝法成功制备出HA均匀分布的HA/Gelatin复合纤维。根据影响静电纺丝的主要因素,分别考察了聚合物浓度、无机物含量、溶剂浓度、电纺电压等因素对纤维形貌和结构的影响。研究结果表明:聚合物浓度是制备复合纤维的首要影响因素,影响复合纤维的直径;无机物的添加使聚合物中的氢键减少,降低了电纺液的粘度,影响复合纤维中珠状物的形成;制备分布均匀的电纺纤维,溶剂起很大的作用,影响纤维的粘联;电纺电压增大使电场力过大,聚合物被强力拉伸,单根纤维出现卷曲。     

Influence of solid-state biaxial orientation on the adhesion between poly(ethylene terephthalate)/tie layer/isotactic polypropylene multilayer films

Current state-of-the-art packaging films typically consist of solid-state stretched multilayer polymer systems, in which each of the polymer layers provides a specific property. Often these polymer film layers are incompatible and need to be glued together by so-called “tie layers.” In this article, we apply a novel biaxial orientation technique to examine the effect of solid-state biaxial stretching on the adhesive behavior of a model multilayer system consisting of poly(ethylene terephthalate) and isotactic polypropylene, as an example of two typical incompatible base layers, glued together by a common tie layer. Two main factors affecting the adhesion, the temperature at which the biaxial stretching is performed and the thickness of the tie layer, are discussed in detail. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 446–454     

Thermally induced color change in electrospun fiber mats

Electrospinning is a process that employs a high static electrical potential to produce polymeric fibers of nanoscale diameter. The process has been utilized to achieve color change by electrospinning black polymer solutions to produce white fiber mats. When subsequently heated, the electrospun mats undergo a color change from white to black. This phenomenon is demonstrated with three polymer/solvent systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 752–757, 2004     

Surface orientation effect of asymmetric polyimide hollow fibers on their gas transport properties

In this study, we focused on the shear stress effects within a spinneret during hollow fiber spinning on the formation of the hollow fibers and their gas transport properties. We fabricated asymmetric polyimide hollow fibers with a completely defect-free thin skin layer using a dry/wet phase inversion process. The apparent calculated skin layer thickness of the hollow fiber was 280 nm and the O₂ permeance was 2.9×10⁻⁵ cm³ (STP)/(cm² s cmHg). Interestingly, the skin layer thickness was reduced at the high shear rate. In addition, the gas permeances and selectivities of the hollow fibers increased with the increasing shear rate. We concluded that the oriented skin layer of the hollow fiber induced by shear stress had a significant influence on the formation of the skin layer and its gas transport properties. From the ATR-IR spectra results, it was clear that the surface skin layer of the hollow fiber was parallel oriented.     

Characterization of macromolecular orientation in κ-carrageenan fibers using polarized Fourier-transform infrared spectroscopy

In the current study, polarized infrared (IR) microspectroscopy was employed to characterize the macromolecular orientation in wet-spun and stretched κ-carrageenan fibers. The fibers were shown to be well oriented by X-ray diffraction, suggesting that the κ-carrageenan molecules were generally aligned along the fiber axis direction. Longitudinal fiber pieces of about 10 μm thick were obtained by focused ion beam (FIB) micromilling. The fiber pieces were examined by polarized IR in transmission mode. Several bands, including those characteristic of κ-carrageenan at 845 and 930 cm⁻¹, were polarization-dependent, demonstrating polarized IR as a useful tool to evaluate macromolecular orientation in carrageenan fibers. Band assignments were discussed by considering the general alignment of molecules and the polarization dependence of vibration modes, and our results agreed well with band assignments from previous reports.     

Electrospun polystyrene fibers for HIV entrapment

The high versatility and ease of electrospinning of polymer solutions have recently resulted in electrospun fibers, which are of interest for a wide variety of chemical and biomedical applications. This is partially due to the high surface area of the fibers, which is attractive for the detection and capture of (bio)chemicals. In the present work, polystyrene (PS) fibers were electrospun and coated with cationic poly(allylamine hydrochloride) (PAH) or anionic dextran sulfate sodium (DSS). The fibers were physicochemically characterized. Upon incubation in a dispersion of inactivated HIV‐1, avid binding of HIV to all types of fibers occurred. By atomic force microscopy and spatial selective photobleaching, the binding of the inactivated HIV‐1 particles to the fibers could be confirmed. Interestingly, all fibers, especially the DSS‐coated and PAH‐coated ones, resulted in a significant reduction of infection of CD4⁺ TZMbl cells by replication‐competent HIV‐1. On top, DSS‐coated PS fibers were not toxic for vaginal epithelial cells, which may make these fibers of potential interest to inhibit HIV infection in the context of topical prevention. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of molecular orientation on the fracture behavior of carbon black-filled natural rubber compounds

The fracture behavior of carbon black-filled natural rubber compounds, differing in filler content, was studied performing tensile tests in biaxial loading conditions, using a central notched cross-shaped specimen. The test consisted of two steps: a drawing step was initially performed loading the specimen in the direction parallel to the notch plane, up to different draw ratios, and then the specimen was loaded in the direction normal to the notch plane up to fracture. Using a fracture mechanics approach, the fracture toughness was evaluated as a function of the draw ratio applied in the drawing step. A correlation between the fracture phenomenology observed and molecular orientability and orientation was attempted. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1509–1515, 2010     

Controlled release of dual drugs from emulsion electrospun nanofibrous mats

The purpose of this work is to develop a novel type of tissue engineering scaffold or drugs delivery carrier with the capability of encapsulation and controlled release drugs. In this study, Rhodamine B and Bovine Serum Albumin (BSA) were successfully incorporated into nanofibers by means of emulsion electrospinning. The morphology of composite nanofibers was studied by Scanning Electron Microscopy (SEM). The composite nanofibrous mats made from emulsion electrospinning were characterized by water contact angle measurement and X-ray diffraction. In vitro dual drugs release behaviors from composite nanofibrous mats were investigated. The results indicated that the incorporated drug and/or proteins in composite fibrous mats made from electrospinning could be control released by adjusting the processes of emulsions preparation.     

Mechanical investigation of bilayer vascular grafts electrospun from aliphatic polyesters

Electrospun biodegradable vascular grafts provide a wide range of design components from the selection of materials to the modification of fiber structure. In this study, both single layer and bilayer tubular scaffolds with inner diameter of 6 mm were electrospun from polycaprolactone with different molecular weights and poly(l ‐lactide) caprolactone polymers. Bilayer scaffolds were designed by using different combinations of the polymer types in each layer and obtaining fiber orientation in outer layers. Scaffolds were analyzed morphologically and mechanically. Obtained results of mechanical performance were discussed according to the used polymer‐type composition, fiber orientation, and composite effect of both layer in the final graft. Smooth muscle cells were seeded on the scaffolds to test biocompatibility of presented scaffolds. Results indicate that the use of different biodegradable polymers in different combinations in each layer causes notable differences in fiber morphology and mechanical performance of the scaffolds. Moreover, fiber orientation in outer layer improves tensile strength and burst pressures in radial directions while creating a suitable fibrous layer for smooth muscle cells by mimicking the extracellular matrix of tunica media in native vessels. Copyright © 2016 John Wiley & Sons, Ltd.     

Fiber motion and rheology of suspensions with uniform fiber orientation

One of the main goals in the studies of fiber suspensions is the prediction of fiber orientation in a short fiber composite part, using the processing variables, mold geometry, and material characteristics. The rheological properties of the fiber suspensions are strongly associated with the fiber orientation distribution. The understanding of the relations between the fiber structure in the suspension and its rheological properties is a key step in the design and implementation of processing operations. The fiber motion in shear flow is analyzed in this article. The study is focused on the relation between fiber orientation and rheological properties for a suspension with uniform (delta function) fiber orientation distribution in a Newtonian fluid. The study shows that the rheological properties of the suspension, measured during the start up of steady shear flow, can be used to determine the fiber orientation in the sample. The first normal stress coefficient is the property to measure in order to determine whether or not the suspension has a random fiber orientation. Any of the shear flow transient rheological properties can be used to determine the fiber initial orientation. It was found that the normal stress coefficients can show negative or positive values depending on the fiber orientation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1788–1799, 2000     

Evaluation of the orientation coefficient for the c axis in poly(ethylene terephthalate) fibers

The literature methods for the determination of the mean of the crystallite orientation distribution for the c axis, that is of the orientation coefficient f_c, for poly(ethylene terephthalate) (PET), based on the azimuthal scan of the (1 05) reflection, are reviewed. These methods appear unsuitable for samples presenting the “tilted orientation”; that is, the molecular chain axis inclined by some degrees with respect to the fiber axis, as frequently occurs for PET fibers. A new method for the determination of f_c for PET, also based on the azimuthal scan of the (1 05) reflection (which can be applied also to samples with “tilted orientation”), is proposed. This method implies as a first step the determination of the tilt angle, for which the complete fiber pattern is required. A possible simplifying assumption, which allows use of the sole azimuthal (1 05) profile and makes the method also applicable to poorly oriented samples (for which the determination of the tilt angle is not easy), is also discussed. © 1995 John Wiley & Sons, Inc.     

The effect of collector gap width on the extent of molecular orientation in polymer nanofibers

Electrospun poly(vinylidene fluoride) (PVDF) nanofibers were collected on aluminum foil across a gap with widths that varied in size from 2 to 10 mm. Scanning electron microscopy (SEM) images on fiber bundles showed that in all cases, fibers in the gap were macroscopically aligned across the gap. However, single fiber selected area electron diffraction (SAED) patterns and polarized Fourier Transform Infrared (FTIR) spectra demonstrated that fibers deposited across the gap were also highly aligned at the molecular level with the polymer backbones oriented along the fiber axis and that the extent of molecular orientation increased with the gap width. A possible explanation for this observation is based on the repulsion of similarly charged nanofibers and the simultaneous attraction of these fibers to the oppositely charged gap edges. This provides a plausible model for understanding the deposition kinetics and subsequent molecular orientation as a function of gap size when electrospinning using this method of fiber collection. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 617–623     

X-ray diffraction from the uniaxial and biaxial nematic phases of bent-core mesogens

X-ray diffraction patterns for the uniaxial and biaxial nematic phases exhibited by rigid bent-core mesogens were calculated using a simple model for the molecular form factor and a modified Lorentzian structure factor. The X-ray diffraction patterns depend strongly on the extent of the alignment of the molecular axes as well as the orientation of molecular planes. The X-ray diffraction can be unequivocally used to identify the biaxial nematic phase, study the uniaxial-biaxial phase transition, and estimate the order parameters of the nematic phase.     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

Processing and characterization of oriented electrospun poly(vinylidene fluoride) mats

Mats of highly oriented poly(vinylidene fluoride) nanofibers were electrospun by means of a conventional electrospinning equipment; the orientation, however, was obtained using a disk collector rotating at a speed of 4000 rpm and a device that reduced the influence of air displacement during nanofiber orientation. Thermal transitions of the mats were determined by differential scanning calorimetry, the predominant crystalline phase by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering and the nanofiber orientation and morphology by scanning electron microscopy. Relative permittivity, loss index, stable remnant polarization, and coercive field of the mats were also determined and compared with those obtained for a mat electrospun at 2000 rpm and an oriented commercial film. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2012     

Poly(methyl methacrylate)/silica nanocomposite fibers by electrospinning

Uniform poly(methyl methacrylate) (PMMA)/silica nanocomposite fibers containing up to 20 wt % silica were prepared by electrospinning. The electrospun solutions were prepared by mixing a solution of PMMA in dimethyl formamide (DMF) with colloidal silica in methyl ethyl ketone (MEK). The average fiber diameter decreases from 2.49 μm to 1.69 μm when 20 wt % silica is incorporated as a result of considerably increased solution conductivity, although the solution viscosity increases significantly, which should result in opposite effect. Thinner fibers (down to 350 nm) can be obtained by changing DMF/MEK proportion and by the addition of an ammonium salt. Nano‐sized silica particles (10–40 nm) distributes homogeneously in the fibers, as revealed by transmission electron microscopy. Furthermore, the incorporation of silica nanoparticles can change the thermal properties and surface wettability of the fiber mats. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1211–1218, 2009     

Preparation of porous ultrafine polyacrylonitrile (PAN) fibers by electrospinning

A facile method for the preparation of porous ultrafine nanofibers was demonstrated. The PAN/NaHCO₃ composite nanofibers were electrospun, and then NaHCO₃ was removed by a selective dissolution and reaction with the solution of hydrochloric acid (10 wt%). The obtained PAN fibers showed highly porous surfaces after the extraction of NaHCO₃. The structure and properties of ultrafine PAN nanofibers were characterized by Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), and thermogravimetry (TG). The results indicated that NaHCO₃ could be introduced into the PAN solution and successfully electrospun. CO₂ is released and pores are formed on the fibers. The morphology image of the fibers was detected by scanning electron microscope (SEM) and showed that many pores aligned the nanofibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and characterization of novel bone scaffolds based on electrospun polycaprolactone fibers filled with nanoparticles

Novel bone-scaffolding materials were successfully fabricated by electrospinning from polycaprolactone (PCL) solutions containing nanoparticles of calcium carbonate (CaCO(3)) or hydroxyapatite (HA). The diameters of the as-spun fibers were found to increase with the addition and increasing amounts of the nanoparticles. The observed increase in the diameters of the as-spun fibers with the addition and increasing amounts of the nanoparticulate fillers was responsible for the observed increase in the tensile strength of the obtained fiber mats. An increase in the concentration of the base PCL solution caused the average diameter of the as-spun PCL/HA composite fibers to increase. Increasing applied electrical potential also resulted in an increase in the diameters of the obtained PCL/HA composite fibers. Lastly, indirect cytotoxicity evaluation of the electrospun mats of PCL, PCL/CaCO(3), and PCL/HA fibers based on human osteoblasts (SaOS2) and mouse fibroblasts (L929) revealed that these as-spun mats posed no threat to the cells, a result that implied their potential for utilization as bone-scaffolding materials.