Simulation of Fibrillation of PC/LCP/Kevlar Blends and Its Characterizations

Kevlar fiber was fluorinated and oxy-fluorinated directly in presence of undiluted fluorine and fluorine gas mixture and processed with Polycarbonate and LCP at 320 °C under 20 rpm in a twin-screw extruder. The composites were then injection molded into dumbbell shaped specimens under different conditions like various mold temperatures, injection temperatures, injection speeds and mold filling rates. Various physico-chemical characterizations have been performed under definite processing parameter. Orientation of fibers under different injection parameters was evaluated using mold flow simulation technique. Most injection molded or extruded structures however, exhibit non-uniform fiber orientation across the final parts, with a diverging variety of different local fiber orientation states. Distinct skin and core regions were observed in the injection molded parts and it has also been found out that fiber orientation is different in skin and core region for both unmodified and modified derivative, which affects the flow behavior. Processing parameters significantly affect the fiber orientation pattern in the skin and core region for all blended materials. It is worth mentioning that the maximum fiber orientation occurred during the extrusion process at the wall but different extent of fiber orientation is observed during the injection molding depending on the shape of the dumbbell specimen. This fibrillation has been corroborated by the SEM study in both the skin and core region.     

Effect of surface preparation on the strength of vibration welded butt joint made from PBT composite

Vibration welding technique has been widely used to weld molded surfaces parts produced by injection or compression molding techniques. However, the majority of early studies used machined surfaces to eliminate the complication associated with molded surfaces. Different process parameters such as the welding pressure, frequency, and amplitude have been investigated to determine their optimal values that maximize the welding strength. However, some other parameters such as joint design and the welding interface preparation were leftover for real application test or for technology transfer studies. Most of molded parts from semi-crystalline materials and their composites usually have skin layer that was exposed to thermal history differs from that of the core. Moreover, the amount and the orientation of fibers in the skin layer differ from that of core and shell regions. Therefore, this work investigates and explores the effect of the molded surfaces with skin on tensile strength of vibration welded butt joints made from polybutylene terephthalate reinforced with 30% glass fiber (PBT GF30). The effect of fibers orientation on the welded joint strength has been also investigated.     

Swelling and dissolution mechanisms of regenerated Lyocell cellulose fibers

The swelling and dissolution mechanisms of dry, never-dried and re-wetted Lyocell fibers were investigated using mixtures of N-methylmorpholine N-oxide and water with various contents of water (from monohydrate to 24% w/w). A radial dissolution starting from the outer layers was observed. Dissolution kinetics was dependent on the water content, the drying state and the spinning conditions. A buckling of the core of dry fibers was observed during swelling. This phenomenon was attributed to the deformation of the unswollen core to accommodate the contraction of the swollen parts of the fiber. In purely swelling conditions with no dissolution, a huge swelling of a very thin skin layer was observed in the first stage, followed then by a progressive swelling of the inside of the fiber. We postulate that this mechanism arose from the fact that this skin is much less crystalline than the core.     

Thermal and light control of the chiral order of azopolymers

The control of the chiroptical properties of two azopolymers, which contain chiral terminal alkyl chains, by means of thermal and light irradiation processes has been studied. Both UV–vis and CD spectra of films and dichloromethane (DCM)/hexane solutions of the polymers have been registered and analyzed before and after different irradiation conditions: 488 nm circularly polarized light (CPL) and 365 nm unpolarized light. The chiroptical properties of the polymer containing chiral 1-methylheptyloxy terminal chains depended on the thermal history of the sample. As a result, the photocontrol of the chiral response in the bulk material by CPL irradiation has been evaluated on samples cooled from the isotropic state to room temperature at different rates. The chiroptical properties of these azopolymers show an intriguing combination of control from both the supramolecular and molecular chirality level as well as the thermal history of the sample and CPL irradiation.     

Micro- and nano-thermal analysis applied to multi-layered biaxially-oriented polypropylene films

In this paper we compare Wollaston and silicon probes for localized thermal analysis measurements (LTA) on biaxially oriented polypropylene (BOPP) films. Up till now, no real comparison was reported in literature between the different transition temperatures measured using Wollaston and silicon probes. Using different types of probes for studying the same material proves to be very interesting. Using the Wollaston probe, the thermal properties and thickness of a 1 μm thick skin layer can be determined by through-thickness local thermal analysis measurements. The improved resolution of the silicon probes, enables the measurement of thermal properties of individual layers in a cross-sectioned film, even for layers of only 1 μm thickness. Based on the results, the silicon probes seem to be more sensitive toward the start of the melting process, since the silicon probe already penetrates at lower temperature, as compared to the Wollaston probes. This sensitivity can be exploited for studying the effect of variations in thermal history between or within samples.     

Starch Gelatinization Kinetics in Bread Dough. DSC investigations on 'simulated' baking processes

Starch gelatinization in wheat flour dough of various moisture contents was quantitatively evaluated by means of DSC. The experimental records were worked out in the form of excess heat capacity vs. T traces which were deconvoluted to single out the contribution of starch gelatinization from that of the decomposition of amylose-lipid complexes. The quantitative procedure used put into evidence that a third endothermic process would take place in the dough with a poor moisture content. DSC runs carried out with sealed pans (i.e., at constant moisture level) and open pans (from which some water was free to evaporate) allow simulation of two extreme conditions of a real baking process, namely that relevant to the central core and to superficial layer of a dough loaf, respectively. The extent of starch gelatinization occurred in these conditions was quantitatively assessed. These data were collected at various heating rates and used to define temperature-time-transformation(TTT) diagrams which are useful tools to predict the progress of baking for any given thermal history of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure Evolution upon Uniaxial Drawing Skin‐ and Core‐Layers of Injection‐Molded Isotactic Polypropylene by In Situ Synchrotron X‐ray Scattering

The structure evolution of the oriented layer (skin) and unoriented layer (core) from injection‐molded isotactic polypropylene samples upon uniaxial drawing is probed by in situ synchrotron X‐ray scattering. The X‐ray data analysis approach, called “halo method”, is used to semiquantitatively identify the transformation process of crystal phase upon uniaxial drawing. The results verify the validation of the stress‐induced crystal fragmentation and recrystallization process in the deformation of the injection‐molded samples under different temperatures. Furthermore, the end of strain softening region in the engineering stress‐strain curves explicitly corresponds to the transition point from the stress‐induced crystal fragmentation to recrystallization process. Basically, the skin and core layers of the injection‐molded parts share the similar deformation mechanism as aforementioned. The stretching temperature which dramatically affects the relative strength between the entanglement‐induced tie chains and the adjacent crystalline lamellae determines the crystal structural evolution upon drawing. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1618–1631     

Effects of fabrication conditions on the structure and function of membranes formed from poly(acrylonitrile–vinylchloride)

Phase-inversion membranes formed from poly(acrylonitril–co-vinylchloride) (PAN–PVC) have been utilized for encapsulating living cells for transplantation; however, a detailed analysis of the structure and function of the integral skin layer has not been reported. PAN–PVC membranes fabricated under different precipitation conditions were analyzed using microscopic techniques and several functional tests. Structural analysis with scanning atomic force microscopy (AFM) revealed the presence of nodular elements in the skin layer which changed as a function of precipitation conditions. In addition, membrane hydraulic permeabilities, sieving coefficients, and diffusive permeabilities also varied with precipitation conditions. Furthermore, changes in the functional properties could be related to the size of the nodular elements and their accompanying interstitial space. The results provide insight into the fundamental interrelationships that exist between membrane fabrication, the fine surface morphology of the skin layer, and membrane performance.     

Effect of molding parameters on the properties of PP/PP sandwich injection moldings

The basic characteristics of a sandwich injection molded product depend on the properties of the respective resins that comprise the skin and core layers, and the skin/core resin volume ratio. The characteristics of the core layer resin and the skin/core ratio in particular may vary depending on the injection molding conditions. This report considers the influences that the molding conditions such as injection speed, cylinder temperature, and mold temperature confer on the mechanical properties of the sandwich moldings. The study employed, skin/core resin combinations involving similar and dissimilar materials i.e. homopolymer PP/homopolymer PP and homopolymer PP/copolymer PP, respectively. It was demonstrated that core cylinder temperature and mold temperature could be used to adjust the mechanical properties of sandwich injection moldings. In the case of single material sandwich moldings, injection speed seemed to play no significant role, even though it was clearly demonstrated that core volume increases with injection speed. However, core injection speed plays a significant role in the dual material system by lowering or increasing the mechanical strength of moldings as the case may be. Thus, the dormant or active role of injection speed depending on the material system has been highlighted.     

New π-conjugated electroluminescent polymers containing organoiridium quinolinolate complexes in the backbone and light diodes formed on their basis

New conjugated copolyfluorenes containing covalently bound quinolinolate complexes of iridium in the backbone are synthesized under conditions of the Yamamoto reaction. The structures and properties of the polymers are characterized via NMR spectroscopy, GPC, TMA, and TGA. All copolymers show solubility in common organic solvents and feature good thermal and thermo-oxidative properties. The absorption, luminescence, and electrochemical properties of the polymers are investigated. In thin films, the polymers emit blue light with wavelengths in the range 450–470 nm. The electroluminescence spectra of the copolymers show broad intense bands in the visible region with maxima at 500–525 nm corresponding to various emission colors with the chromaticity coordinates (0.361, 0.437) and (0.247, 0.411). The synthesized iridium-containing copolyfluorenes may be used as electron-hole transport materials in light-emitting diodes.     

On the multiple crystallization behavior of PTFE in PMMA/PTFE nanocomposites from core–shell nanoparticles

The peculiar thermal behavior of four PTFE/PMMA (Polymethylmethacrylate) core–shell nanoparticle samples, marked DV2M1, DV2M2, DV2M4, and DV2M6, was studied by combined differential scanning calorimetry and thermogravimetric analysis. The melting process of the PTFE in the various samples, subjected to annealing and thermal treatments, does not change. In contrast, a complex fractionated crystallization‐type behavior for the PTFE component was observed. The nanocomposite produced by the PMMA shell fluidification features a perfect dispersion of the nanometric PTFE cores. In these conditions, only one crystallization exotherm at very high undercooling is observed, possibly deriving from the homogeneous nucleation mechanism. In contrast, when high temperature thermal treatments cause the decomposition with partial loss of the PMMA shell and allows some cores to get in contact and merge, a crystallization process structured into several components is observed. This behavior indicates that different nucleation mechanisms are active, possibly involving the participation of distinct types of active nuclei with distinct crystallization efficiencies. Finally, when the PMMA shell amount is substantially reduced by the thermal degradation, only the expected crystallization process at moderate undercooling (310 °C) is observed, corresponding to the bulk crystallization induced by the most efficient heterogeneous nuclei. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 548–554, 2010     

Microencapsulation of capsaicin by solvent evaporation method and thermal stability study of microcapsules

With polylactic acid (PLA) as shell and capsaicin as core substances, microcapsules were prepared based on solvent evaporation method. The orthogonal test was used to analyze the effects of the process conditions such as polyvinyl alcohol and PLA concentrations, stirring rate, and oil/water ratio on the particle size of the microencapsulated capsaicin (MC) agents. The chemical composition, morphology and size distribution of the microcapsules prepared by the most satisfactory conditions were analyzed by Fourier transform infrared spectroscopy, laser light scattering, and scanning electron microscopy. The MC agents had a mean diameter of 3–5 μm. The thermal properties of the MC agents were measured by differential scanning calorimetry and thermogravimetric analysis, it was demonstrated that the thermal stability of the MC agents was changed or even improved by the encapsulated PLA over the surface, when compared with similar parameters of the uncovered capsaicin. The in vitro release profile suggested that the microcapsules could be a suitable material for controlled release of capsaicin.     

Crystallization and phase morphology of injection‐molded isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends

The crystallization and phase morphology of the injection‐molded isotactic polypropylene (iPP)/syndiotactic polypylenen (sPP) blends were studied, focusing on the difference between the skin layer and core layer. The distribution of crystallinity of PPs in the blends calculated based upon the DSC results shows an adverse situation when compared with that in the neat polymer samples. For 50/50 wt % iPP/sPP blend, the SEM results indicated that a dispersed structure in the skin layer and a cocontinuous structure in the core layer were observed. A migration phenomenon that the sPP component with lower crystallization temperature and viscosity move to the core layer, whereas the iPP component with higher crystallization temperature and viscosity move to the skin layer, occurred in the iPP/sPP blend during injection molding process. The phenomenon of low viscosity content migrate to the low shear zone may be due to the crystallization‐induced demixing based upon the significant difference of crystallization temperature in the sPP and iPP. This migration caused the composition inhomogeneity in the blend and influenced the accuracy of crystallinity calculated based upon the initial composition. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2948–2955, 2007     

Enhanced photocatalytic activity of ZnO nanoparticles by surface modification with KF using thermal shock method

ZnO nanoparticles were modified with KF using thermal shock method at various temperatures in order to improve the photocatalytic activity of ZnO under both UVA and visible light irradiation. The influences of KF-modification on the crystal structure, morphology, UV–visible absorption, specific surface area as well as surface structure of ZnO were respectively characterized by XRD, FE-SEM, UV–Visible diffuse reflectance, N₂ adsorption and XPS spectroscopy. The photocatalytic activity was evaluated via the degradation of methylene blue under UVA irradiation. According to the results, the thermal shock process with KF did not modify the structure, the particle size and the optical properties of ZnO nanoparticles but successfully increase their UVA and visible light induced photocatalytic activity. This enhancement of activity may be attributed to the increase of surface hydroxyl groups and zinc vacancies of modified ZnO samples.     

Partial carbonization of aramid fibers

Heat treatment of aramid fiber was conducted in the temperature range 300–710°C nominally for 10 and 30 s in both static air and flowing nitrogen atmosphere. Crystallinity, crystal orientation, and crystallite size were determined using x-ray diffraction. Fibers with a skin–core structure were produced at intermediate temperatures, as revealed by scanning electron microscopy of fibers after partial dissolution of the fiber in 95–98% sulfuric acid. The skin, which forms in both nitrogen and air, is amorphous and brittle. It is insoluble in sulfuric acid, suggesting it is a cross-linked polymer. Formation of the skin may be facilitated by the removal of an aggressive chemical species that forms during heat treatment. The species may diffuse out of the outer layer of the fiber, allowing it to cross-link. The molecular weight of the dissolved core, analyzed using intrinsic viscosity, decreases with increasing heat treatment temperature. The tenacity, modulus, elongation-to-break, and toughness of fibers with a skin–core structure decrease with heat treatment and the fiber loses its fibrillar character. Mechanical property reductions are greater in air than nitrogen. X-ray data are also consistent with the notion that oxygen assists attack of crystals at high temperatures. Scanning electron microscopy shows that fibers have become skin–core composites with quite different mechanical properties between the two regions. A fiber failure mechanism is proposed. © 1994 John Wiley & Sons, Inc.     

Morphological comparison of isotactic polypropylene parts prepared by micro‐injection molding and conventional injection molding

The morphological feature of microparts evolved during micro‐injection molding may differ from that of the macroparts prepared by conventional injection molding, resulting in specific physical properties. In this study, isotactic polypropylene (iPP) microparts with 200 µm thickness and macroparts with 2000 µm thickness were prepared, and their morphological comparison was investigated by means of polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and wide‐angle X‐ray diffraction (WAXD). The results presented some similarities and differences. PLM observations showed that the through‐the thickness‐morphology of micropart exhibited a similar “skin–core” structure as macropart, but presented a large fraction of shear layer in comparison to the macropart which presented a large fraction of core layer. The SEM observation of shear layer of micropart featured highly oriented shish‐kebab structure. The micropart had a more homogeneous distribution of lamellae thickness. The degree of crystallinity of the micropart was found to be higher than that of the macropart. High content of β‐crystal was found in micropart. The 2D WAXD pattern of the core layer of macropart showed full Debye rings indicating a random orientation, while the arcing of the shear layer indicates a pronounced orientation. The most pronounced arcing of the micropart indicates the most pronounced orientation of iPP chains within lamellae. Copyright © 2011 John Wiley & Sons, Ltd.     

Metallodielectric Hollow Shells: Optical and Catalytic Properties

Metallodielectric composites with tunable optical properties were prepared by layer‐by‐layer assembly of gold nanorods on polystyrene (PS) spheres and subsequent deposition of SiO₂ or TiO₂ encapsulating shells through a sol–gel process. The optical properties of the core‐shells were tailored in the visible and the near‐infrared region through the gold nanorod aspect ratio and the gold nanoparticle density. Removal of the PS core by dissolution in an appropriate solvent, such as THF, yielded metallodielectric hollow shells with optical properties identical to those of the original composites. The presence of gold and the porosity of the SiO₂ or TiO₂ shells, suitable to allow diffusion of reactants and products, make these materials of interest as catalysts, as demonstrated by the reduction of potassium hexacyanoferrate(III) with NaBH₄.     

Synthesis of Monodisperse Hollow Carbon Nanocapsules by Using Protective Silica Shells

Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high‐temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core–shell nanostructures. These core–shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer–Emmett–Teller (BET) method. The as‐synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m² g^?1) and formed stable dispersions in water after the pegylation process. The drug‐loading and drug‐release properties of these hollow carbon nanocapsules were also investigated.     

Investigation of the multiple melting behaviour of a PTT by DSC and polarized light optical microscopy

The multiple melting behaviour of isothermally crystallized bulk poly(trimethylene terephthalate) (PTT) observed using DSC has been correlated to the total depolarized light intensity (DLI) of thin films using hot-stage polarized light optical microscopy. The observation of partial melting, recrystallization and final melting in the DSC is correlated to the observation of the partial decrease, sudden increase and final decrease in DLI under the same heating conditions. Integration of real-time visible spectra of the transmitted light was used to separate the effects of retardation from pure birefringence of the colorful spherulitic thin-film PTT samples. The correlation of the results from these two methods has demonstrated clearly that the observed DSC multiple melting behaviour of this particular polymer is the illustrated effect of a process of continuous partial melting/recrystallization/final melting in the material during thermal analysis. The observed thermal behaviour of these metastable spherulitic materials is a complex function of their thermal history including crystallization temperature and anneal conditions, including scanning rate during thermal analysis.