Showing papers in "Polymers for Advanced Technologies in 2011"
TL;DR: In this paper, a mini-review is devoted to coaxial electrospinning (co-electrospinning), a group of novel methods for making core-shell nanofibers and hollow nanotubes.
Abstract: The mini-review is devoted to coaxial electrospinning (co-electrospinning, emulsion electrospinning), a group of novel methods for making core–shell nanofibers and hollow nanotubes. The physical aspects of the process are described in brief, in particular, its modeling and possible drawbacks of the process resulting in formation of fibers without a long intact core. After that the main applications of co-electrospinning are considered. They include drug release, encapsulation of different biologically active compounds, cell scaffolds, formation of nanotubes, and nanofluidics. Copyright © 2010 John Wiley & Sons, Ltd.
364 citations
TL;DR: A brief review of current research activities that focus on the fabrication of ceramic nanofibers by electrospinning, as well as their applications in various areas is provided in this paper.
Abstract: This paper provides a brief review of current research activities that focus on the fabrication of ceramic nanofibers by electrospinning, as well as their applications in various areas. We begin with a brief introduction to electrospinning in the context of ceramic nanofibers, and the methods for preparing aligned and/or hollow nanofibers. We then discuss approaches to the fabrication of nanofibers with a hierarchical structure. We continue with a highlight of some recent applications enabled by electrospun ceramic nanofibers, with a focus on three areas: catalysis, environmental science, and energy technology, which are expected to become the most important and exciting subjects of research in this century. In the end, we conclude this review with some perspectives on the future directions and implications for this new class of functional nanomaterials. Copyright © 2010 John Wiley & Sons, Ltd.
315 citations
TL;DR: This review explored two popular areas of biomedical nanofiber development: tissue regeneration and drug delivery, and included discussions on the basic principles for how nanofibers promote tissue Regeneration and drug Delivery, the parameters that affect nanof fiber performance and the recent progress in these areas.
Abstract: Nanofiber technology is an exciting area attracting the attention of many researchers as a potential solution to the current challenges in the biomedical field such as burn and wound care, organ repair, and treatment for osteoporosis and various diseases. Nanofibers are attractive in this field for several reasons. First, surface area on nanofibers is much higher compared to bulk materials, which allows for enhanced adhesion of cells, proteins, and drugs. Second, nanofibers can be fabricated into sophisticated macro-scale structures. The ability to fabricate nanofibers allows renewed efforts in developing hierarchical structures that mimic those in animals and human. On top of that, a wide range of polymers can be fabricated into nanofibers to suit different applications. Nanofibers are most commonly fabricated through electrospinning, which is a low cost method that allows control over fiber morphology and is capable of being scaled-up for mass production. This review explored two popular areas of biomedical nanofiber development: tissue regeneration and drug delivery, and included discussions on the basic principles for how nanofibers promote tissue regeneration and drug delivery, the parameters that affect nanofiber performance and the recent progress in these areas. The recent work on biomedical nanofibers showed that the large surface area on nanofibers could be translated into enhanced cell activities, drug encapsulation, and drug release rate control. Furthermore, by optimizing the electrospinning process via adjusting the material choices and fiber orientation, for example, further enhancement in cell differentiation and drug release control could be achieved. Copyright © 2010 John Wiley & Sons, Ltd.
200 citations
TL;DR: In this paper, the benefits of using electrospun nanofibers in enhancing the structural performance of engineered composite materials is discussed, where the authors demonstrate the use of the electrospinning process to produce nanofiber from a variety of materials including naturally occurring polymers.
Abstract: Over the past six decades, engineered composite materials found wide ranging applications in land, sea and air transport vehicles, space exploration, military equipment and defense, storage, buildings and construction, chemical processing, electrical engineering, healthcare, and general engineering industries. Performance of engineered composites is tailored for an intended application by judiciously selecting the matrix and reinforcement materials, by modifying the fiber–matrix interface, and by controlling the architecture of fibers in the matrix. Most widely used reinforcement fibers are micron size diameter fibers. There is growing need for engineered composites with enhanced structural performance in newer applications as well as existing applications, which are expected to meet higher functional requirements and enhanced safety requirements. Moreover the global movement toward sustainable development is seeking engineered materials which are environmentally benign. Recently the electrospinning process has emerged as a viable industrial process to produce nanofibers from a variety of materials including naturally occurring polymers. This paper illustrates the benefits of using electrospun nanofibers in enhancing the structural performance of engineered composite materials. Copyright 2010 John Wiley & Sons, Ltd.
186 citations
TL;DR: In this paper, a mini-review of the work in suspension electrospinning is presented, highlighting the efforts in this promising area of EMulsion and suspension electrics including their chances and limitations.
Abstract: For the process of electrospinning, either water or organic solvents are used as solvents depending upon the solubility of the materials to be spun. For many applications, such as tissue engineering, biomedical, agricultural, etc., the toxicity of the organic solvent used could be highly critical. Besides this, the high viscosities of such polymer solutions even for low weight per cent (wt%) polymer solutions (generally for conventional electrospinning a maximum of 10–15 wt% polymer solution can be used) prevent high polymer concentrations and thereby reduces the productivity of the electrospinning process. This justifies the need for an approach which would alleviate concerns regarding safety, toxicology, and environmental problems, in addition, would also overcome the restrictions of too high polymer concentrations of polymer solutions. The answer could be suspension electrospinning. The term suspension electrospinning is referred to the electrospinning of aqueous dispersions (lattices) of water insoluble polymers and is defined in this article as Green Electrospinning. The present mini review highlights the efforts in this promising area of Emulsion and Suspension Electrospinning including their chances and limitations. Copyright © 2011 John Wiley & Sons, Ltd.
159 citations
TL;DR: In this article, isosorbide epoxy resins were synthesized as a new class of thermosets with comparable dry mechanical property similar to bisphenol A (BPA) epoxide.
Abstract: Polymeric biomaterials, especially agricultural commodity-based polymers, have been moving forward quickly during the last few years because of the significant rise in oil and natural gas prices. From a life-cycle perspective, sugar is a renewable resource that has the potential to be used as an alternative to petroleum-based polymers. The objective of this work is to demonstrate the wide utility of a cereal-derived material, isosorbide, for high added value applications in polymers. As a bicyclic ether derivative of glucose, isosorbide is classified by the Food and Drug Administration as a “generally recognized as safe” (GRAS) material. Because of its rigidity, chirality, and nontoxicity, isosorbide can be incorporated into thermosets and thermoplastics. Such processes and products offer a more sustainable and “green” technology. By making the diglycidyl ether, isosorbide epoxy resins were synthesized in this work as a new class of thermosets with comparable dry mechanical property similar to bisphenol A (BPA) epoxide. These could be a potential replacement for BPA in coatings and adhesives. By controlling the stereochemistry, multiple isosorbide-derived AB monomers such as isosorbide methyl terephthalate were synthesized for future homopolymerization and copolymerizations with commercial available polymers like polyethylene terephthalate (PET) and PLLA. The increased glass transition temperature and semicrystalline morphology of these isosorbide copolyesters demonstrate a way to improve the performance of polyester thermoplastics in many applications such as hot-fill containers and engineering resins. All the intermediates generated during the syntheses were characterized by NMR. The thermal tests were conducted using the techniques of DSC and thermogravimetric analysis (TGA). Copyright © 2010 John Wiley & Sons, Ltd.
144 citations
TL;DR: In this article, β-cyclodextrin (CD) was used as an effective carbon source to replace pentaerythritol (PER) in an intumescent flame retardant (IFR).
Abstract: In this paper, β-cyclodextrin (CD) was used as effective “green” carbon source to replace pentaerythritol (PER) in an intumescent flame retardant (IFR). The combination of CD with traditional acid resource ammonium polyphosphate (APP) and/or blowing agent melamine (MA) at different weight ratios exhibited outstanding char-forming ability. It was demonstrated that strong interactions occurred in APP-CD and MA-CD systems through thermogravimetric analysis (TGA). Mechanisms of esterification between APP and CD or dehydration between MA and CD were discussed. The APP/MA/CD complexes showed doubled char residue of those calculated based on three single components in nitrogen atmosphere. For instance, the char residue of CD-APP (at the weight ratio of 1:1) complex was 38 wt% at 700°C, while the calculated char formation was only 19 wt% in N2. After addition of these complexes into polylactic acid (PLA), the flammability of these PLA resins was evaluated by limited oxygen index (LOI) and vertical combustion (UL-94). The TGA results indicated that the cyclodextrin mixed with APP and MA as a “green” char agent demonstrated outstanding char formation ability for PLA. When the complex contained CD/APP/MA at weight ratio of 1/2/1 and the addition amount of complex in PLA was 20 wt%, the PLA composites showed LOI values of 34.2 and passed UL 94 V0 rating, and the char residue of the PLA composite was 17.4 wt% at 700°C while only 7.4 wt% was achieved for the calculated composition. Copyright © 2011 John Wiley & Sons, Ltd.
131 citations
TL;DR: An overview of the recent developments in producing ultra-sensitive metal oxide gas sensors by electrospinning of polymer solutions containing inorganic precursors that subsequently oxidize and crystallize into metal oxide nanoparticles is presented in this paper.
Abstract: Electrospinning provides a simple and versatile route to produce nanocrystalline metal oxide layers with a highly porous fibrous morphology. The combination of small grain size, high surface area, and high porosity that includes both small and large pores is ideally suited for gas sensing. This work presents an overview of the recent developments in producing ultra-sensitive metal oxide gas sensors by electrospinning of polymer solutions containing inorganic precursors that subsequently oxidize and crystallize into metal oxide nanoparticles. The key process parameters and their effect on microstructure evolution and gas sensing properties of TiO2 and SnO2 sensors produced by electrospinning are described. Copyright © 2010 John Wiley & Sons, Ltd.
120 citations
TL;DR: In this paper, a series of flame retardant toughened PLA composites were prepared using poly(ethylene glycol) 6000 (PEG6000) as a toughening and charring agent together with ammonium polyphosphate (APP) as an acid source and blowing agent.
Abstract: In order to modify the brittleness and flame retardant properties of poly(lactic acid) (PLA), a series of flame retardant toughened PLA composites were prepared using poly(ethylene glycol) 6000 (PEG6000) as a toughening and charring agent together with ammonium polyphosphate (APP) as an acid source and blowing agent. The fire and thermal behavior of PLA/PEG/APP composites was evaluated by limiting oxygen index (LOI), UL-94, cone calorimeter, and thermogravimetric analysis (TGA). The results showed that the PLA/PEG/APP system had good charring ability and could improve the flame retardancy of PLA. When the content of APP in the composites was more than 5 wt%, all samples could reach UL-94 V-0 rating. The results of mechanical property tests demonstrated that the brittleness of PLA was also improved after blended with PEG6000. All the PLA/PEG/APP composites with an APP content of less than 10 wt% showed an obvious neck and fracture behavior, that is, the tensile behavior of PLA was changed from brittle to ductile. Copyright © 2010 John Wiley & Sons, Ltd.
114 citations
TL;DR: In this paper, the synthesis and use of novel derivatives of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10oxide (DOPO, 1) and 5,5-dimethyl-1,3,2-dioxaphosphorinan-2-one (DDPO, 2) as flame retardant additives for epoxy resins were presented.
Abstract: This report presents the synthesis and use of novel derivatives of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO, 1) and 5,5-dimethyl-1,3,2-dioxaphosphorinan-2-one (DDPO, 2) as flame retardant additives for epoxy resins. DOPO-based and DDPO-based compounds were synthesized via nucleophilic substitution with 1,3,5-tris-(2-hydroxyethyl) isocyanurate (THIC, 3) and subsequent oxidation (Schemes 1 and 2). Another trivalent DOPO derivative recently reported by our group was obtained by transamination followed by a Michaelis–Arbuzov rearrangement (Scheme 1). These products were blended into two epoxy resin systems [DEN 438 and diglycidyl ether of bisphenol A (DGEBA), both cured with dicyandiamide (DICY) and Fenuron] to obtain flame retardant thermosets. The flame retardancy and thermal properties of these epoxy resin systems were examined by UL 94-V, Thermogravimetric analysis, and differential scanning calorimeter analysis. Furthermore, all reactions with phosphorus-containing compounds were iterated employing the THIC oligomer, which was prepared via polycondensation of THIC (Scheme 3) using catalytic amounts of p-toluenesulfonic acid. In addition, Atherton–Todd reaction with the THIC oligomer was studied as a novel synthetic method for phosphorus-containing flame retardants (Scheme 4). The resulting products were utilized as flame retardants in epoxy resins and compared with the analogous monomeric compounds. Copyright © 2011 John Wiley & Sons, Ltd.
108 citations
TL;DR: In this paper, the formation of the inorganic carbonaceous residue is influenced by bubbling, migration, reorientation, agglomeration, ablation, and perhaps also delamination induced thermally and by decomposition.
Abstract: The layered silicate (LS) modification and processing parameters applied control the morphology of the LS/polymer composites. Here, increasing the surface area of the LS particles by using alternative drying processes increases dispersion towards a more typical nanocomposite morphology, which is a basic requirement for promising flame retardancy. Nevertheless, the morphology at room temperature does not act itself with respect to flame retardancy, but serves as a prerequisite for the formation of an efficient surface protection layer during pyrolysis. The formation of this residue layer was addressed experimentally for the actual pyrolysis region of a burning nanocomposite and thus our results are valid without any assumptions or compromises on the time period, dimension, surrounding atmosphere or temperature. The formation of the inorganic-carbonaceous residue is influenced by bubbling, migration, reorientation, agglomeration, ablation, and perhaps also delamination induced thermally and by decomposition, whereas true sintering of the inorganic particles was ruled out as an important mechanism. Multiple, quite different mechanisms are relevant during the formation of the residue, and the importance of each mechanism probably differs from one nanocomposite system to another. The main fire protection effect of the surface layer in polymer nanocomposites based on non-charring or nearly non-charring polymers is the increase in surface temperature, resulting in a substantial increase in reradiated heat flux (heat shielding). Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the synthesis of polylactide (PLA) is done by reactive extrusion via ring opening polymerization of L,L-lactides using a continuous single-stage process which is a fast and an easy method.
Abstract: Aliphatic polyesters such as polylactide (PLA) currently deserve particular attention in the area of environmentally degradable polymer materials. PLA is produced via polymerization of renewable products, namely lactic acid or lactide. In this work, the synthesis of PLA is done by reactive extrusion via ring opening polymerization of L,L-lactide using a continuous single-stage process which is a fast and an easy method. The resulting PLA is fully characterized by solid state NMR. It is shown that it exhibits properties similar to those of PLA synthesized by the traditional methods. A kinetic model based on a phenomenological approach permits one to describe the polymerization of L,L-lactide. PLA nanocomposites containing multi-wall carbon nanotube (MWNT) are also prepared by reactive extrusion. Reaction to fire of PLA nanocomposite shows a slight improvement of the flame retardancy. The nanodispersion characterized by transmission electronic microscopy (TEM) is acceptable but should be improved to obtain the best flame retardancy. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, an intumescent gel-silica/ammonium polyphosphate core-shell flame retardant (MCAPP), which contains silicon, phosphorus, and nitrogen, has been prepared by in situ polymerization.
Abstract: A novel intumescent gel-silica/ammonium polyphosphate core-shell flame retardant (MCAPP), which contains silicon, phosphorus, and nitrogen, has been prepared by in situ polymerization. The structure of MCAPP was characterized by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The properties of MCAPP were investigated by water solubility, hydrophilicity, and morphological determination. The flame retardancy and thermal stability of polyurethane (PU) composite with MCAPP were evaluated by limiting oxygen index (LOI), UL-94 test, cone calorimetry, and thermogravimetric analysis (TGA). The results showed that MCAPP could decrease the heat release rate (HRR) and increase the thermal stability of PU materials greatly. Finally, water-resistant properties of PU/FR composites were also studied. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a new phosphorus flame retardant (FR) methyl-DOPO 9,10-dihydro-9-oxa-methylphosphaphenthrene-10-oxide in flexible polyurethane foam with low density is investigated.
Abstract: Flexible polyurethane foams are widely used in many industrial applications, such as upholstered furniture and mattresses, automotive applications, etc. The chemical nature of the polyurethane, the low density, the high air permeability, and the open cell structure cause this material to be highly flammable. In this study, the influencing variables on the burning behavior of flexible polyurethane foams are investigated. Additionally the synthesis, formulation, characterization, and testing of a new phosphorus flame retardant (FR) methyl-DOPO 9,10-dihydro-9-oxa-methylphosphaphenthrene-10-oxide in flexible polyurethane foam with low density is performed. The new FR shows an excellent flame retarding behavior by acting mainly in the gas phase. Here the vaporization of methyl-DOPO occurs in the same temperature region as the depolymerization of the urethane and the bisubstituted urea groups during pyrolysis of the foam. Furthermore TG-MS measurements revealed the release of high concentrations of low molecular weight species like HPO, CH3PO, or PO2 in the mentioned temperature region. These species are able to scavenge the H- and OH-radicals in the radical chain reactions of the flame leading to a significant increase of the CO/CO2 ratio during cone calorimeter experiments. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, the pyrolysis and flame retardancy of poly(butylene terephthalate) (PBT) containing aluminum diethylphosphinate (AlPi) and nanometric Fe2O3 were investigated using thermal analysis, evolved gas analysis (Thermogravimetry-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analysis of residue (FTIR).
Abstract: The pyrolysis and the flame retardancy of poly(butylene terephthalate) (PBT) containing aluminum diethylphosphinate (AlPi) and nanometric Fe2O3 were investigated using thermal analysis, evolved gas analysis (Thermogravimetry-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analysis of residue (FTIR). AlPi mainly acts as a flame inhibitor in the gas phase, through the release of diethylphosphinic acid. A small amount of Fe2O3 in PBT promotes the formation of a carbonaceous char in the condensed phase. The combination of 5 and 8 wt% AlPi, respectively, with 2 wt% metal oxides achieves V-0 classification in the UL 94 test thanks to complementary action mechanisms. Using PBT/metal oxide nanocomposites shows a significant increase in the flame retardancy efficiency of AlPi in PBT and thus opens the route to surprisingly sufficient additive contents as low as 7 wt%. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors reviewed the recent developments in the synthetic strategies to chemically modify several chain-growth polymers that were primarily developed in our laboratories, with a view to improve their flame retardance.
Abstract: This article reviews the recent developments in the synthetic strategies to chemically modify several chain-growth polymers that were primarily developed in our laboratories, with a view to improve their flame retardance. In addition, it also incorporates the corresponding methodologies for the step-growth thermoplastics and thermoset materials. For chain-growth polymers, this involves primarily copolymerization reactions, under radical initiation, of acrylic or styrenic monomers with phosphorus-containing comonomers, or optionally, by post-modification reactions on preformed olefinic polymeric substrates with appropriate phosphorus-containing reagents. In the case of step-growth polymers, generally, an appropriate phosphorus-bearing moiety is employed, as one of the reactive components, during the step-growth synthetic process. The relative predominance of vapor- and condensed-phase mechanisms of flame retardance in the modified systems was evaluated through a combination of various analytical techniques. It was found that incorporation of phosphorus, through chemical modification reactions, on to the various thermoplastics resulted in substantial increases in the flame retardation. Furthermore, mechanistic aspects of flame retardation revealed both vapor-phase and condensed-phase elements depending on the chemical nature of the parent polymer in question and to a lesser extent on the chemical environment of the phosphorus-bearing moiety. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: In this paper, variable amounts of transition metal oxides (MO), such as MnO2, ZnO, Ni2O3, etc., were incorporated into blends of polypropylene (PP)/ammonium polyphosphate (APP)/dipentaerythritol (DPER) with the aim of studying and comparing their effects with main-group MO on intumescent flame retardance.
Abstract: Variable amounts of transition metal oxides (MO), such as MnO2, ZnO, Ni2O3, etc., were incorporated into blends of polypropylene (PP)/ammonium polyphosphate (APP)/dipentaerythritol (DPER) with the aim of studying and comparing their effects with main-group MO on intumescent flame retardance (IFR). The PP/IFR/MO composites were prepared using a twin-screw extruder, and the IFR behavior was evaluated through oxygen index and vertical burning tests. The progressive enhancement of flame retardancy has proved to be strongly associated with the interaction between APP and MO. With the aid of thermogravimetry (TG) analysis, Fourier transform infrared (FTIR) spectra and scanning electron microscopy, Ni2O3 has been shown to be the most effective among the aforementioned three MO. The flame-retardant mechanism of the IFR system is also discussed in terms of catalytic charring, which relates to complex formation through the d-orbitals of the transition metal elements. It is considered that the melt viscosity of a PP/APP/DPER blend containing Ni2O3 corresponds well to the gas release with increasing temperature. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, a novel heterostructure made of polyaniline (PANI) nanoparticles coated by nanolayer of bismuth oxide Bi2O3 was synthesized.
Abstract: A novel heterostructure made of polyaniline (PANI) nanoparticles coated by nanolayer of bismuth oxide Bi2O3 was synthesized. The structure was characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. These characterizations showed that the bismuth oxide nanoshell was pure and crystalline, and has thickness in the range of 10 nm. The experiment on photoluminescence (PL) of Bi2O3 nanoshell coated polyaniline nanoparticle, at room temperature, shows an emission band peaked at around 385 nm. When compared with the PL spectrum of Bi2O3 nanoparticles, about 100 times PL enhancement was found in the PL spectrum of Bi2O3 nanoshell coated polyaniline nanoparticle. The current density versus voltage (J–V) measurements in dark and illumination showed that this heterojunction has 4 orders of magnitude rectification in the dark and 3 orders of magnitude rectification under illumination. The obtained power conversion efficiency of polyaniline nanoparticles coated by nanoshell of bismuth oxide (h ¼ 7.453%) was much enhanced compared with polyaniline alone (h ¼ 8.33 T 10 S4 %) this indicates that the prepared heterostructure represents a promising photovoltaic solar cell. Copyright 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, three kinds of self-catalyzed phthalonitrile compounds with low melting point were synthesized, whose structures were characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance.
Abstract: Phthalonitrile resins with many striking properties have drawn much attention as potential candidates for use in composite matrices, adhesives, films, and electrical conductors for the last 30 years. However, it is common shortcomings for phthalonitrile monomers to have high-temperature melting point and need extreme conditions to develop binary phthalonitrile/additives composition. Here, three kinds of self-catalyzed phthalonitrile compounds with low melting point were synthesized, whose structures were characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance. The different cure behaviors, owing to the different positions of catalyzed group on benzene ring, were investigated by differential scanning calorimetry, and cure kinetics parameters were also calculated. The results showed that the meta and para position monomers possessed better reactivity. Melt-processability study by a rheometer indicated that the ortho one owned the largest processing window. Furthermore, the FTIR spectra demonstrated that the cured monomers contained the same structure with a conventional binary phthalonitrile system. All the cured monomers had excellent thermal stability according to thermogravimetric analysis. Mechanical property was determined by dynamic mechanical analysis, and the results showed that the glass transition temperature (represented by the peak temperature of tanδ) was high up to 550°C for all the three cured monomers. Consequently, these autocatalytic phthalonitrile monomers may be good candidates as matrix for high-performance polymeric materials. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: A triazine ring-containing charring agent (PEPATA) was synthesized via the reaction between 2,6,7-trioxa-l-phosphabicyclo-[2.2]octane-4methanol (PEPA) and cyanuric chloride as discussed by the authors.
Abstract: A triazine ring-containing charring agent (PEPATA) was synthesized via the reaction between 2,6,7-trioxa-l-phosphabicyclo-[2.2.2]octane-4-methanol (PEPA) and cyanuric chloride. It was applied into intumescent flame retardant epoxy resins (IFR-EP) as a charring agent. The effect of PEPATA on fire retardancy and thermal degradation behavior of IFR-EP system was investigated by limited oxygen index (LOI), UL-94 test, microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA) and thermogravimetric analysis/infrared spectrometry (TG-IR). The glass transition temperatures (Tg) of IFR-EP systems were studied by dynamic mechanical analysis (DMA). The LOI values increased from 21.5 for neat epoxy resins (EPs) to 34.0 for IFR-EP, demonstrating improved flame retardancy. The TGA curves showed that the amount of residue of IFR-EP system was largely increased compared to that of neat EP at 700 °C. The new IFR-EP system could apparently reduce the amount of decomposing products at higher temperatures and promotes the formation of carbonaceous charred layers that slowed down the degradation. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize PVA/PbSe nanocomposite films under illumination.
Abstract: Polyvinyl alcohol (PVA) with different molecular weights (8000, 14,000, and 132,000 g/mol) capped lead selenide (PbSe) quantum dots (QDs) are prepared. The nanocomposites are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM studies show that the particle size of PbSe QDs decrease with the increase in PVA molecular weight and/or PVA amount. This may be due to the increase in molecular weight inhibiting further growth of PbSe into the polymer matrix. Thermogravimetric analysis showed that the introduction of PbSe QDs into PVA decreases the crystallinity of the polymer. The optical absorption spectroscopy of prepared nanocomposites showed that the absorption peaks are strongly shifted to the lower wavelength (blue shift) from near infrared region to visible region by increasing the PVA molecular weight. The (I–V) characteristic curves of the PVA/PbSe nanocomposite films under illumination showed a photovoltaic cell-like behavior. The results indicated that as the molecular weight of polymer increases, the conversion efficiency increases. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the behavior of thermoplastic polymers and polymer nanocomposites prior to ignition, under irradiation in a cone calorimeter, was investigated and an explanation for the reduction of ignition time by the presence of nanoclays, based on nanoparticle-catalyzed oxidation, was proposed and discussed.
Abstract: This paper addresses the behavior of thermoplastic polymers and polymer nanocomposites prior to ignition, under irradiation in a cone calorimeter. Insights into the physical evolution of material controlling ignition are obtained from the measurement of the condensed phase surface temperature and by the observation of specimen residues obtained from interrupted tests. Significant differences are evidenced between evolution of montmorillonite nanocomposites and reference polymers, in terms of both reduced ignition time and reduced thickness of material contributing to fuel production at ignition, whereas limited differences in the temperature of the surface layer at ignition were measured. An explanation for the reduction of ignition time by the presence of nanoclays, based on nanoparticle-catalyzed oxidation, is proposed and discussed. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: In this paper, the β-form crystalline and morphological change induced by rare earth nucleator (WBG) were adopted to prepare β-nucleated isotactic polypropylene (iPP) at a fixed final molten temperature (240°C).
Abstract: As part of a continuous effort to develop high performance isotactic polypropylene (iPP) based on β-form crystalline and morphological change induced by rare earth nucleator (WBG), various WBG contents (from 0.025 to 1.0 wt%) were adopted to prepare β-nucleated iPP at a fixed final molten temperature (240°C) in this study. The crystallinity, polymorphic composition, and crystalline morphology were inspected in detail by a series of crystallographic characterizations, including calorimeter, X-ray diffraction, polarized light microscopy (PLM), and electron microscopy. Furthermore, the self-organization and re-crystallization behavior of β-nucleating agent occurred during cooling was characterized by rheometry. Finally, the dependence of mechanical properties, including tensile strength, elongation at break, and impact strength, on WBG content was discussed based on the variations in β-form content and crystalline morphology. Interestingly, it is found that while the WBG content is below 0.1 wt%, the toughness of β-nucleated iPP increases with increase in WBG content due to additional β-form content; as the WBG content is in range of 0.1–0.5 wt%, the toughness increases at a lower rate with increase in WBG content due to β-crystalline morphological change. However, a decrease in toughness is observed while nucleator content is above 0.5 wt% as WBG remains undissolved in iPP upon the adopted processing conditions. The result of this study provides valuable information for potential industrial applications. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, PEDOT-coated viscose fibers, prepared under specific conditions, exhibited high conductivity 142 s/cm and the effects of polymerization conditions, such as polymerization time, oxidant concentration, dipping time of viscose fiber in oxidant solution, and drying time of oxidant treated viscose fibre, were carefully investigated Scanning electron microscopy (SEM) and FT-IR analysis revealed that polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) has been taken place and structural analysis showed strong
Abstract: An oxidative chemical vapor deposition (OCVD) process was used to coat flexible textile fiber (viscose) with highly conductive polymer, poly (3,4-ethylenedioxythiophene) (PEDOT) in presence of ferric (III) chloride (FeCl3) oxidant OCVD is a solvent free process used to get uniform, thin, and highly conductive polymer layer on different substrates In this paper, PEDOT coated viscose fibers, prepared under specific conditions, exhibited high conductivity 142 S/cm The effects of polymerization conditions, such as polymerization time, oxidant concentration, dipping time of viscose fiber in oxidant solution, and drying time of oxidant treated viscose fiber, were carefully investigated Scanning electron microscopy (SEM) and FT-IR analysis revealed that polymerization of PEDOT on surface of viscose fiber has been taken place and structural analysis showed strong interactions between PEDOT and viscose fiber Thermogravimetric analysis (TGA) was employed to investigate the amount of PEDOT in PEDOT coated viscose fiber and interaction of PEDOT with viscose fiber The effect of PEDOT coating on the mechanical properties of the viscose fiber was evaluated by tensile strength testing of the coated fibers
The obtained PEDOT coated viscose fiber having high conductivity, could be used in smart clothing for medical and military applications, heat generation, and solar cell demonstrators Copyright © 2010 John Wiley & Sons, Ltd
TL;DR: In this paper, the optical properties of the nanocomposite films were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300-800 nm.
Abstract: Poly (vinyl acetate) (PVAc) loaded bismuth oxide (Bi2O3) nanorods were successfully prepared at ambient pressure. X-ray diffraction (XRD) and transmission electron microscopy were used to characterize the final product. It was found that Bi2O3 nanorods were formed and the diameter of the rods was confined to about 8 nm. The diameter and length of formed rods were found to increase by increasing the bismuth oxide concentration in the PVAc matrix. The optical properties of the nanocomposite films were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300–800 nm. The values of some important parameters of the studied films are determined such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α), and band energy gap (Eg). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple–DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (e∞) and the third-order optical nonlinear susceptibility χ(3) were determined. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, a series of poly(ethylene oxide) (PEO) blends with cellulose (CEL) or cellulose derivatives (carboxymethyl cellulose), cellulose acetate (CAC), and cellulose ether (CET) has been investigated as phase change materials for thermal energy storage.
Abstract: A series of poly(ethylene oxide) (PEO) blends with cellulose (CEL) or cellulose derivatives—carboxymethyl cellulose (CMC), cellulose acetate (CAC), and cellulose ether (CET)—has been investigated as phase change materials for thermal energy storage. For PEO/CEL blends solid–solid phase transition has been observed in the whole concentration's range; for PEO/CMC and PEO/CET blends solid–solid phase transition has been found for PEO content 25 or 50 and 25 wt%, respectively. Otherwise, solid–liquid phase transition takes place. MTDSC investigations revealed that for PEO/CEL and PEO/CMC blends transition the strongest recrystallization effect (as evidenced by exothermic effect in reversing heat flow) as melting process occurred. FTIR analysis shows a shift of the stretching vibration bands of both the proton-donor OH groups from CEL and PEO due to intermolecular hydrogen interactions between the blends' components. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, radio-opaque shape-memory polymer composites were obtained by incorporation of barium sulfate (BaSO4) microparticles into an amorphous polyether urethane (PEU) via co-extrusion technique.
Abstract: The formation of functional tissue is strongly dependent on biochemical as well as physical signals. A common approach in tissue engineering is the application of passive scaffold systems with fixed morphology and stiffness. In this paper, we explored whether mechanically active scaffolds, exhibiting self-sufficient shape changes under physiological conditions, can be prepared from radio-opaque shape-memory polymer composites (SMPCs). The influence of different thermomechanical treatments on the kinetics of the shape change was studied. Radio-opaque SMPCs were obtained by incorporation of barium sulfate (BaSO4) microparticles (up to 40 wt%) into an amorphous polyether urethane (PEU) via co-extrusion technique. The shape-memory properties of the composites were investigated by cyclic, thermomechanical tensile tests consisting of a specific shape-memory creation procedure (SMCP), in which the programming temperature (Tprog) was varied, followed by recovery under stress-free condition, enabling the determination of the switching temperature (Tsw). An almost complete recovery with shape recovery rate (Rr) values ranging from 88% to 98% was realized within a small temperature interval of ΔTrec ≈ 30°C for all composites, while Tsw was found to be close to the applied Tprog. The feasibility of actively moving scaffolds was demonstrated using model scaffolds, where originally square-shaped pores were temporarily fixed in an expanded circular shape at different Tprog. We found that the kinetics of the shape change obtained under physiological conditions could be adjusted by variation of Tprog between 1 and 6 hr. Such radio-opaque scaffolds could serve as model scaffolds for investigating the active mechanical stimulation of cells in vitro or in vivo. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this article, a review of biohybrid materials comprised of encapsulated cells in electrospun polymer fibers is presented, which allows for the protection of cells from harsh environments as well as the control of the physico-mechanical properties in the cell's immediate surroundings.
Abstract: Successful encapsulation of cells is of interest for a wide variety of biotechnological applications such as microbial fuel cells (MFCs), food systems, environmental remediation, fermentation reactors, and regenerative medicine. In this review paper, biohybrid materials comprised of encapsulated cells in electrospun polymer fibers are presented. Such bio-encapsulation allows for the protection of cells from harsh environments as well as the control of the physico-mechanical properties in the cell's immediate surroundings, i.e. the chemical structure and permeability of the matrix as well as its density. This review paper discusses the preparation methods of these “living materials” and their potential applications using examples of the encapsulation of bacterial cells in various electrospun fibers which can be monolithic, core–shell, or hollow. Copyright © 2010 John Wiley & Sons, Ltd.