Showing papers in "Macromolecular Research in 2013"

Diketopyrrolopyrrole: A versatile building block for organic photovoltaic materials

Abstract: In recent years, diketopyrrolopyrroles (DPPs) have become one of the extensively studied organic building blocks of oligomers and polymers having promising optoelectronic properties, especially in organic solar cells. There are a large number of reports on structural modification of DPP cores to improve their properties in devices. There is plenty of room left for research in the field of structural modification and bandgap engineering to maintain energy level alignment and to achieve optimum morphology/crystallinity leading to high performance in organic photovoltaic (OPV) devices. This article reviews the DPP containing materials and their variants as potential active layer materials for OPV devices. An attempt has been made to go through their synthesis, structure and optoelectronic properties in such a way that any future efforts to modify this versatile structure have benefited.

Emulsion grafting vinyl monomers onto starch for reinforcement of styrene-butadiene rubber

Abstract: Three types of modified starches (MST): Starch-g-poly(butyl acrylate) (ST-g-PBA), starch-g-poly (methyl methacrylate) (ST-g-PMMA) and starch-g-polystyrene (ST-g-PS) latexes were successfully synthesized by emulsion polymerization. These synthesized MST latexes were then directly compounded with styrene-butadiene rubber (SBR) latex in order to prepare MST/SBR compounds. The vulcanization characteristics, morphology, swelling ratio, mechanical and dynamic mechanical properties were investigated. Results indicated that the incorporation of starch or MST led to both an increase in the torque values and the cure rate of SBR compounds. MST with a particle size of approximately 200–400 nm uniformly dispersed in the SBR matrix, indicating the significantly improved dispersion. MST/SBR compounds exhibited better mechanical properties compared with starch/SBR (ST/SBR) compounds. Among the MST/SBR compounds, ST-g-PMMA/SBR compounds showed optimum tensile strength, which was even higher than that of carbon black/SBR (CB/SBR) compounds with the same loading of fillers. Finally, the reinforcing mechanism of MST in the SBR matrix was discussed.

Effects of hybrid fillers on the electrical conductivity and EMI shielding efficiency of polypropylene/conductive filler composites

Abstract: In this study, the effects of hybrid fillers on the electrical conductivity and electromagnetic interference shielding efficiency (EMI SE) of the polypropylene (PP)/Ni-coated carbon fiber (NCCF) composites with the second fillers, such as multi-walled carbon nanotube (MWCNT), carbon black and TiO2, were investigated. The morphological behavior showed that the NCCF and the second fillers, such as MWCNT, carbon black and TiO2, seemed to disperse evenly in the PP phase. Among the PP/NCCF composites with MWCNT, carbon black and TiO2, the PP/NCCF/TiO2 composites showed the higher electrical conductivity and EMI SE compared with those of the PP/NCCF/MWCNT and PP/NCCF/carbon black composites. This was the case because TiO2 has high dielectric constant with dominant dipolar polarization. The estimated EMI SE values of the PP/NCCF composites with MWCNT, carbon black and TiO2 are in good agreement with the experimentally obtained values of the composites. Based on the electrical properties of the composites, it was suggested that TiO2 was the most effective second filler when it was hybridized with the NCCF of the PP/NCCF/TiO2 composite. Based on the analysis of the flexural modulus, the PP/NCCF/MWCNT composite had a higher flexural modulus than the PP/NCCF/TiO2 and PP/NCCF/carbon black composites because of the higher aspect ratio of the MWCNT. Open image in new window

Mechanical Performance, Water Absorption Behavior and Biodegradability of Poly(methyl methacrylate)-Modified Starch/SBR Biocomposites

Abstract: Natural corn starch was modified by surface grafting with poly(methyl methacrylate) (PMMA) through emulsion copolymerization and then compounded with styrene-butadiene rubber (SBR) latex in order to prepare PMMA-modified starch/SBR biocomposites. The effect of methyl methacrylate (MMA) and starch concentration on the mechanical properties, morphology, toluene swelling behavior, water absorption behavior and biodegradabil- ity of PMMA-modified starch/SBR biocomposites was investigated. Results showed that the optimum mechanical properties were achieved when the concentrations of MMA and starch were 10 and 30 phr, respectively, which could be also confirmed through the observations from FE-SEM micrographs and equilibrium welling test. Guth-Gold and Halpin-Tsai models were employed to predict the modulus of PMMA-modified starch/SBR biocomposites. Halpin- Tsai model was better fitted with the experimentally measured data than Guth-Gold model. The water absorption ratio of PMMA-modified starch/SBR biocomposites was strongly influenced by the immersion time and the starch concentration, which further caused a significant effect on the biodegradability of biocomposites.

Fabrication and characterization of electrospun gelatin-heparin nanofibers as vascular tissue engineering

Abstract: In this paper, heparin was introduced into electrospun gelatin nanofibrous scaffold for assessment as a controlled delivery device in vascular tissue engineering application. Hybrid gelatin-heparin fibers with smooth surfaces and no bead defects were produced from gelatin solutions with 18% w/v in acetic acid aqueous solution. A significant decrease in fiber diameter was observed when the heparin content was increased from 1 to 5 wt%. The properties of composite gelatin-heparin scaffolds were confirmed by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurement. The gelatin-heparin fibrous scaffolds were also cross-linked using 1 wt% glutaraldehyde vapor-phase for 7 days. A sustained release of heparin could be achieved from gelatinheparin scaffolds over 14 days. The results of the biocompatibility in vitro tests carried out using human umbilical vein endothelial cells indicated good cell viability and proliferation on the gelatin-heparin scaffolds. The results demonstrated that the use of electrospun gelatin fibers as heparin carriers could be promising for vascular tissue applications. Open image in new window

Photoreduction processes of graphene oxide and related applications

Abstract: Graphene based electronic materials and devices need efficient production methods, in which graphene oxide (GO) is most frequently used as starting material and is combined with a suitable reduction process. This review discusses recent progress in the photoreduction of GO, which is usually realized by means of photochemical or photothermal reducing procedures. Thin films of photoreduced GO possess good electrical conductivity and can be fabricated with various additives such as polymers, clusters, and nanoparticles. This way, nanocomposites become available with synergistic functionalities for a wide range of applications in electronics such as thin film transistors, microelectrodes and photoelectric devices. Furthermore, sensors and superhydrophobic surfaces can be also fabricated. Open image in new window

Cell-penetrating peptide-modified PLGA nanoparticles for enhanced nose-to-brain macromolecular delivery

Abstract: Macromolecular drugs become an essential part in neuroprotective treatment. However, the nature of ineffective delivery crossing the blood brain barrier (BBB) renders those macromolecules undruggable for clinical practice. Recently, brain target via intranasal delivery have provided a promising solution to circumventing the BBB. Despite the direct route from nose to brain (i.e. olfactory pathway), there still are big challenges for large compounds like proteins to overcome the multiple delivery barriers such as nasal mucosa penetration, intracellular transport along the olfactory neuron, and diffusion across the heterogeneous brain compartments. Herein presented is an intranasal strategy mediated by cell-penetrating peptide modified poly(lactic-co-glycolic acid) (PLGA) nanoparticles for the delivery of insulin to the brain, a potent therapeutic against Alzheimer’s disease. The results revealed that the cell-penetrating peptide can potentially deliver insulin into brain via the nasal route, showing a total brain delivery efficiency of 6%. It could serve as a potential treatment for neurodegenerative diseases. Open image in new window

Immobilized bioactive agents onto polyurethane surface with heparin and phosphorylcholine group

Abstract: Heparin (HEP) and phosphorylcholine groups (PC) were grafted onto the polyurethane (PU) surface in order to improve biocompatibility and anticoagulant activity. After the surface grafting sites of PU were amplified with the primary amine groups of polyethylenimine (PEI), heparin was covalently linked onto the surface by the reaction between the amino group and the carboxyl group. PC groups were covalently immobilized on the PU-PEI surface through the reaction between the amino group and the aldehyde group of phosphorylcholine glyceraldehyde (PCGA). The surface density of primary amine groups was determined by a ninhydrin assay. The amino group den- sity reached a maximum of 0.88 µmol/cm 2 upon incorporation of 10 wt% PEI. The amount of heparin covalently immobilized on the PU-PEI surface was determined by the toluidine blue method. The grafting chemistry resulted in the comparatively dense immobilization of HEP (2.6 µg/cm 2 ) and PC to the PU-PEI surfaces. The HEP and PC modified surfaces were characterized by water uptake (PU 0.15 mg/cm 2 , PU-PEI 3.54 mg/cm 2 , PU-HEP 2.04 mg/ cm 2 , PU-PC 2.38 mg/cm 2 ), water contact angle (PU 95.3o, PU-PEI 34.0o, PU-HEP 39.5o, PU-PC 37.2o), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscope (SEM). The results demonstrated that the PU- PEI surface was successfully grafted with HEP and PC. The hydrophilicity and hemocompatibility of these grafted surfaces were significantly improved. These results suggested that the PU-HEP and PU-PC composite films are promising candidates for blood contacting tissue engineering.

Influence of cellulose nanofibers on the morphology and physical properties of poly(lactic acid) foaming by supercritical carbon dioxide

Abstract: The foaming process of poly(lactic acid) (PLA)/cellulose nanofiber (CNF) nanocomposites using supercritical CO2 as a foaming agent was studied with various CNF contents. CNFs were obtained by sonication, and their morphology was examined by transmission electron microscopy. According to the CNF content, the changes in the rheological and the thermal properties of the nanocomposites were studied through viscometry and differential scanning calorimetry. The viscosity of the composites increased with increasing CNF content. The effects of the CNF content on the foam properties and morphologies were evaluated. Compared to neat PLA foam, the PLA/CNF nanocomposite foams exhibited decreased cell size as well as increased cell density and foam density due to the improved viscous properties.

Polylactide nanofibers loaded with vitamin B6 and polyphenols as bioactive platform for tissue engineering

Abstract: Electrospun polylactide nanofibers loaded with different antioxidants (i.e. vitamin B6 in pyridoxine and pyridoxal form, p-coumaric acid and caffeic acid) are prepared from N,N-dimethylformamide/dimethylsulfoxide solutions. Morphology, structure and crystallinity of the nanofibers are evaluated by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction and differential scanning calorimetry (DSC) techniques. Fibers are highly amorphous but able to crystallize easily due to the high molecular orientation induced by the electrospinning process. The drug molecules are incorporated into the polymeric matrix or formed isolated crystals. A fast release of loaded drug occurs within the first 8 h in hydrophobic medium; but, a slow and sustained release during several days occurs in a hydrophilic medium. Cell attachment on the loaded scaffolds was unaffected by the incorporation of the antioxidants. In contrast, cell proliferation increases with high antioxidative activity against free radicals responsible for cell damage. These new electrospun scaffolds provide high protection of cells against oxidative stress and resulting in innovative 3D fibrous platforms for tissue growth and proliferation.

Effect of total acrylic/fluorinated acrylic monomer contents on the properties of waterborne polyurethane/acrylic hybrid emulsions

Abstract: Stable emulsions of waterborne poly(urethane-urea) (WBPU, soft segment content: 57 wt%, dimethylol propionic acid: 19 mol%/5.8 wt%)/n-butyl acrylate (BA)/glycidyl methacrylate (GMA)/perfluorodecyl acrylate (PFA) (weight ratio of BA/GMA/PFA: 5/3/2) hybrid materials containing 0-30 wt% of acrylate content (fluorinated acrylate content: 0–6 wt%) were successfully prepared by an emulsifier-free/solvent-free prepolymer mixing process. However, the as-polymerized hybrid emulsion containing 40 wt% of acrylic monomer content was found to be unstable, indicating that near 40 wt% in acrylic monomer content was beyond the limit of the self-emulsifying ability. By the curve fitting analysis of IR-peaks and X-ray photoelectron spectroscopy (XPS) analysis, the C-F content was found to increase with the increase in acrylate content. The average particle size of emulsion, young modulus/ yield point in stress-strain curve, hardness, thermostability, and water/methylene iodide-contact angles of the film sample increased with increasing acrylate content. However, the viscosity of emulsion, the elongation at break, water swelling and surface energy of film samples were significantly decreased with increasing acrylate content. The tensile strength of film sample decreased a little with increasing acrylate content. These results point to the strong potential of WBPU (70 wt%)/acrylate copolymer (30 wt%) hybrid as a coating material with the lowest surface energy (18.18 mN/m) and the highest contact angles (water: 111.76o, and methylene iodide: 79.95°). Open image in new window

Preparation of Cellulose Nanowhiskers and Their Reinforcing Effect in Polylactide

Abstract: Cellulose nanowhiskers (CNW) were isolated from microcrystalline cellulose (MCC) using acid hydrolysis and ultrasonication. Polylactide (PLA) composites were prepared by incorporating CNW (0.1 and 0.5 wt%) into a PLA matrix and casting the composite films. To investigate the effects of the CNW as reinforcement in the PLA composites, analyses of rheological properties, thermal stability, thermal behavior, and mechanical properties were performed. In rheological analysis, complex viscosity of the PLA/CNW solutions in CHCl3 was decreased with an increase in frequency and the storage modulus and loss tangent were increased with filler loading. Despite filler loading on the PLA matrix, transmittance was decreased slightly. Thermal stability was decreased with CNW loading. The nanocellulose filler did not affect glass transition or melting temperature; however, it promoted crystallization, resulting in an increase in crystallinity for the PLA composites. The tensile strength and tensile modulus of the PLA composite films increased with a rise of CNW contents. These results suggest that high performance PLA bionanocomposites with high transparency can be obtained by adding uniformly dispersed small amount of the CNW.

Highly transparent, hydrophobic fluorinated polymethylsiloxane/silica organic-inorganic hybrids for anti-stain coating

Abstract: Organic-inorganic hybrids were synthesized using polymethylhydrosiloxane, 2,2,3,4,4,4 hexafluorobutylmethacrylate and tetraethyl orthosilicate with a platinum catalyst. The resulting hybrids formed transparent thin films on glass substrate by spin coating. The functional groups, molecular structure, surface morphology and chemical composition of the hybrids were analyzed by 1H nuclear magnetic resonance spectroscopy (NMR), 29Si MASNMR spectroscopy, high resolution scanning electron microscopy with energy-dispersive X-ray spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The thermal stability, mechanical scratch resistance, static and advancing/receding dynamic contact angles were measured by thermogravimetry, the pencil hardness test and a drop shape analysis system. The prepared hybrid thin films exhibited good transparency, hydrophobicity, as well as good mechanical and anti-stain properties. Open image in new window

Tumor Targeting and pH-Responsive Polyelectrolyte Complex Nanoparticles Based on Hyaluronic Acid-Paclitaxel Conjugates and Chitosan for Oral Delivery of Paclitaxel

Abstract: A new platform of paclitaxel (PTX) for application as an oral delivery system was developed, by combining the pH sensitivity of polyelectrolyte complex nanoparticles (CNPs) and the active targeting of hyaluronic acid (HA). Chitosan/hyaluronic acid-paclitaxel (CS/HA-PTX) CNPs were prepared by coating the CS onto the HA-PTX nanoparticles (NPs), and characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM) and high-performance liquid chromatography (HPLC). HA-PTX conjugates could self-assemble into NPs in aqueous solution with an average size of 100±5 nm, and the PTX content of HA-PTX conjugates was 10.6 wt%. The CS/HA-PTX CNPs had a smaller size and higher PTX content when the ratio of positive charge to negative charge was 2:1. The in vitro release of PTX from CNPs was pH-responsive, suggesting that the CS shell could prevent the breakage of the ester bond in HA-PTX NPs in acidic pH conditions. HA-PTX NPs exhibited higher cellular uptake than free PTX against HepG2 cells via receptor-mediated endocytosis. PTX could accumulate remarkably into tumor sites after oral administration of CNPs. These results indicate that the CNP drug delivery system has great potential for applications in the oral administration of hydrophobic drugs.

Immobilization of laccase onto polyethyleneimine grafted chitosan films: Effect of system parameters

Abstract: Chitosan films were prepared via phase-inversion technique The polyethyleneimine (PEI) was grafted onto chitosan films after activation with various agents, such as epichlorohydrin, genipin and glutaraldehyde The PEI grafted activated chitosan films (Ch-g-PEI) were used for immobilization of laccase by adsorption The effects of adsorption parameters on immobilization efficiency were researched Activity and stability of immobilized laccase on Ch-g-PEI films were investigated under desired optimum conditions Characterization studies of the supports were also performed The effect of pH on the activity of free and immobilized laccase was carried out in the pH range 40–80, and the optimum pH was determined as 55 Kinetic constants of the free and immobilized laccase were calculated The maximum activity (V max ) and Michealis constant (K m ) of immobilized laccase on the films were found to be 712 U/mg and 051 mM, respectively Thermal stability of the enzyme increased together with immobilization on the support Free laccase retained 39% of its original activity at 55 °C for a 120 min incubation period Immobilized laccase retained 72% of its original activity for the same period at 55 °C The free enzyme lost all of its activity during the 7 weeks storage period Conversely, immobilized laccase lost 36% of its activity during the 7 weeks storage period

Preparation of macroporous carbon foams using a polyurethane foam template replica method without curing step

Abstract: Macroporous carbon foams were synthesized without a curing step using polyurethane (PU) foam as the sacrificial template and resorcinol-formaldehyde (RF), phenol-formaldehyde (PF), and phenol-resorcinol-formaldehyde (PRF) resins as the carbon precursors. PU foam was impregnated with these three aqueous resin solutions and carbonized directly at 830 °C in an inert atmosphere for 3 h without a pre-curing step. During heating to carbonization temperature, the impregnated resins were cured and subsequently carbonized. The curing, degradation of PU foam and carbonization mechanism were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The pore structure, electrical conductivity, and compressive strength of the prepared carbon foams using the RF, PF, and PRF resin carbon precursors were measured. Among them, the carbon foam fabricated from PF resin had a surface area, electric conductivity and compressive strength of 63 m2/g, 3.409 S/m and 0.25 MPa, respectively.

Adsorption kinetics and thermodynamics of water-insoluble crosslinked β-cyclodextrin polymer for phenol in aqueous solution

Abstract: A water-insoluble β-cyclodextrin (β-CD) polymer was synthesized by reacting β-CD with hexamethyl- ene diisocyanate, and its adsorption kinetics and thermodynamics for phenol from aqueous solution was investi- gated. The kinetics of adsorption followed the pseudo-second-order model and the adsorption isotherms could be well fitted by the Freundlich adsorption equation. The values of thermodynamic parameters demonstrated that the adsorption was a physisorption in a spontaneous and exothermic process.

Preparation and release properties of electrospun poly(vinyl alcohol)/poly( ɛ -caprolactone) hybrid nanofibers: Optimization of process parameters via D-optimal design method

Abstract: The main purpose of this work was to develop biomedical electrospun nanofibrous mats based on a poly(vinyl alcohol)/poly(ɛ-caprolactone) (80/20) hybrid with a defined drug release rate using tetracycline hydrochloride as a model drug. The electrospinning process parameters, such as polymer solution concentration, distance between injecting syringe tip/collector, voltage, injected flow rate and the polyvinyl alcohol cross-linking time were optimized via a D-optimal design method for a suitable nanofiber diameter with an optimal drug release rate. The morphology of nanofibers and their mean diameters were studied by a scanning electron microscopy technique. The results showed that the mean diameters of nanofibers were significantly reduced after drug loading. The swelling, weight loss and biodegradability of nanofibers samples investigated by FTIR were also determined. Two main mechanisms via penetration and erosion were evaluated. In vitro drug release in a phosphate buffer environment at pH=7.2 for the samples demonstrated that the polymer type and hydrophilic nature of the polymer/drug system is very effective in the kinetics and mechanism of drug release. Hybridization of poly(vinyl alcohol)/poly(ɛ-caprolactone) with a known ratio showed to be a suitable and useful method in the electrospinning of nanofibers samples for superior control of the drug release rate. Finally, nanofibrous mats of polyvinyl alcohol and polyvinyl alcohol/poly(ɛ-caprolactone) hybrid (80/20) had much better drug release rate characteristics for tetracycline hydrochloride as a model drug compared with cast film samples loaded with the same drug. Open image in new window

Precision synthesis of tailor-made polythiophene-based materials and their application to organic solar cells

Abstract: Polymer-based solar cells (PSCs) have been promising candidates as renewable energy resources, having multiple advantages of flexible, low-cost and large-area processing for their mass production. Among them, much attention has been paid to fundamental bulk-heterojunction (BHJ) devices using a blend of regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer. However, there are still significant limitations not only in the low power conversion efficiency (PCE), but also in the device stability. The morphological control of BHJ PSCs is one of the most important issues to improve the device performances. On the other hand, P3HT itself has received much attention in many fields, because it is the best class of balanced high-performance materials as a p-type semiconductor in terms of solubility, chemical stability, charge mobility, and commercial availability. The discovery of the quasi-living Grignard metathesis polymerization (or called catalysttransfer polycondensation) system has made it possible to synthesize a wide variety of chain-end-functional P3HT derivatives, their block copolymers and star-branched polymers. Since the competitive research areas including PSC applications have strongly demanded the accelerated developments of new materials and well-defined morphologies related to polythiophenes, the fundamental studies of P3HT have still been targeted by many research groups. In this review, the controlled synthesis of P3HT, the synthesis of P3HT-based block copolymers, their applications to PSCs, as well as the scope and potential of new thiophene-based materials are described.

Synthesis and physicochemical characterization of reduction-sensitive block copolymer for intracellular delivery of doxorubicin

Abstract: An amphiphilic diblock copolymer bearing the reduction-sensitive linker, composed of poly(ethylene glycol) (PEG) and hydrophobic poly(γ-benzyl L-glutamate) (PBLG), was prepared as the potential carrier of doxo- rubicin (DOX) via a facile synthetic method in the presence of a shell-sheddable PEG macroinitiator (PEG-SS-NH2). Owing to its amphiphilic nature, the copolymer (PEG-SS-PBLG) formed spherical micelles (137 nm in diameter) in aqueous conditions. The micelles were stable under the physiologic condition (pH 7.4) and were readily cleaved in the presence of glutathione (GSH), a tripeptide reducing the disulfide bond in the cytoplasm of the cell. DOX, chosen as a model anticancer drug, was effectively encapsulated into the hydrophobic core of the micelle with high loading efficiency (>75%). The micelle released DOX completely within 18 h at 10 mM GSH mimicking the intracellular condition, whereas only 34% of the drug was released from the micelle at 2 µM GSH. In vitro cytotoxicity tests revealed that DOX-loaded reduction-sensitive micelles are more toxic to SCC7 cells than reduction-insensitive con- trol micelles. These results suggest that PEG-SS-PBLG is the promising carrier for the intracellular delivery of DOX.

Comparison of the effectiveness of polyethylenimine, polyamidoamine and chitosan in transferring plasmid encoding interleukin-12 gene into hepatocytes

Abstract: Interleukin-12 (IL-12) has been proposed for cancer immunotherapy due to its versatile antitumor and antiangiogenesis effects. Although cancer immunotherapy through systemic administration of IL-12 has shown antitumor effects in tumor-bearing mice, broad application of recombinant IL-12 protein has been limited by its cytotoxicity. Therefore, the use of various polycationic polymers such as polyethylenimine (PEI), polyamidoamine (PAMAM) and chitosan has been considered as an effective strategy to transfer plasmid encoding IL-12 gene into cells. In this investigation, polyplexes (polymer/pDNA complexes) were prepared using PEI, PAMAM and chitosan at different N/P ratios and their ability in transferring plasmid encoding IL-12 gene was evaluated. Furthermore, these polyplexes were characterized and compared with regarding their cytotoxicity, DNA condensation ability, particle size, zeta potential, buffering capacity and pDNA protection against enzyme degradation. The results revealed that the polyplexes formulated with 25 kDa PEI and chitosan had the highest transfection efficiencies. The highest level of IL-12 gene expression was achieved by the nanoparticles prepared by 25 kDa PEI where they could increase the level of gene expression up to 12 times compared to that of naked plasmid encoding IL-12 gene. These results suggest that 25 kDa PEI and chitosan are the best candidates for adding targeting ligands into their structures in order to create a liver targeting gene delivery system. Open image in new window

Rheological, Thermal and Mechanical Properties of Nano-Calcium Carbonate (CaCO3)/ Poly(methyl methacrylate) (PMMA) Core-Shell Nanoparticles Reinforced Polypropylene (PP) Composites

Abstract: Nano-calcium carbonate (nano-CaCO3)/poly(methyl methacrylate) (PMMA) core-shell nanoparticles in the range of 10–100 nm were successfully synthesized by the atomized microemulsion method. The polymer chains were grafted onto the surface of nano-CaCO3 through triethoxyvinyl silane (TEVS) as a coupling agent. Encapsulation of nano-CaCO3 by PMMA was confirmed through the use of a transmission electron microscope (TEM). Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques, revealed the existence of favorable interaction between the surface of nano-CaCO3 particles and PMMA, which implies that the polymer chains were successfully grafted onto the surface of nano-CaCO3 particles through the link of the coupling agent. Nano-CaCO3/PMMA particles were blended with the polypropylene (PP) matrix on Brabender Plastograph by the melt process with different wt% (i.e. 0.1–1.0 wt%) loading. The dispersion of nano-CaCO3 particles into the PP matrix significantly improved when the nano-CaCO3 nanoparticles were grafted with PMMA, which enhanced the thermal, rheological, and mechanical properties of (nano-CaCO3/PMMA)/PP composites. Scanning electron microscopic (SEM) and atomic force microscopic (AFM) images showed a perfect dispersion of the nano-CaCO3 particles via the PMMA shell in the PP matrix. Open image in new window

Colorless and transparent polyimide nanocomposites: Thermo-optical properties, morphology, and gas permeation

Abstract: A series of colorless and transparent polyimide (PI) hybrid films was synthesized from bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTDA) and bis[4-(3-aminophenoxy)phenyl] sulfone (m-BAPS) with various clay contents, by solution intercalation polymerization to poly(amic acid)s, followed by thermal imidization. The thermal properties, morphologies, optical transparencies, and gas permeations of the PI hybrid films were examined for organoclay loadings ranging from 0 to 40 wt%. Up to a clay loading of 20 wt%, the clay particles were found to be highly dispersed in the PI matrix without any agglomeration of particles. However, for a clay content above 20 wt% some agglomerated structures form in the polymer matrix. The thermal and oxygen barrier properties of the PI hybrid films were gradually improved by increasing the organoclay content from 0 to 40 wt%. However, the optical transparency of the PI hybrid films deteriorated with increasing organoclay content. Open image in new window

Effects of isocyanate index and environmentally-friendly blowing agents on the morphological, mechanical, and thermal insulating properties of polyisocyanurate-polyurethane foams

Abstract: The effects of the isocyanate (NCO) index and blowing agent on the morphology, mechanical strength, thermal conductivity and thermal stability of the polyisocyanurate-polyurethane (PIR-PUR) foams were investigated. When the NCO index was increased, the isocyanurate ring content in the PIR-PUR foams was found to be increased regardless the type of blowing agents. As a results, the thermal stability of the PIR-PUR foams was improved. When the isocyanurate ring content in the PIR-PUR foams was increased, the cell size was slightly decreased. The decreased cell size of the foams affected the decrease in the thermal conductivity of the PIR-PUR foams regardless the type of the blowing agents. From the results of thermogravimetric analysis (TGA), the thermal stability of the PIR-PUR foams was found to increase with an increase in the NCO index. When the NCO index was 200, the compressive strength was maximal for the PIR-PUR foams regardless the type of the blowing agents. The compressive strength of the foams blown by cyclopentane was higher than that of the water blown foams. From the above results, it is suggested that the thermal insulation property and thermal stability of the PIR-PUR foams increased with an increase in the NCO index. However, the compressive strength of the PIR-PUR foams showed maximum value at a specific NCO index. Open image in new window

Electrofluorescence switching of fluorescent polymer film

Abstract: Electrofluorescence switching has attracted much research attention recently due to its potential applications in the areas of ion sensing, bio analysis, fluorescence imaging, and signaling recognition events. This review describes the chemical structure of electrofluorescent polymers their synthetic strategies, and their patterning characteristics. The designs of these polymers are based on fluorescence quenching through an energy transfer between a fluorophore and an acceptor, which is similar to various types of fluorescence-based sensors. Electrofluorescence devices were designed to demonstrate stable switching processes with different durations while measuring the photophysical properties. The patterning process has shown promise if used to create fluorescent displays, sensors, or for security document applications, but an investigation of patternable polymers and related mechanisms remains for future work. Open image in new window

Ionic Liquid Crystals: Synthesis, Structure and Applications to I2-Free Solid-State Dye-Sensitized Solar Cells

Abstract: A novel type of ionic liquid crystal (ILC) was synthesized and used as a solid electrolyte in I2-free solidstate dye-sensitized solar cells (ssDSSCs). In particular, the properties of two ILCs, 1-[(4-ethenylphenyl)methyl]-3-butyl-imidazolium iodide (EBII) with a single aliphatic C=C bond and 1-[(4-ethenylphenyl)methyl]-3-vinyl-imidazolium iodide (EVII) with two aliphatic C=C bonds, were evaluated. The structures and morphologies of the ILCs were characterized using Fourier transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM). Ultraviolet (UV)-visible spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses revealed that EBII exhibited weaker π-π stacking interactions, longer d-spacing, and a lower melting temperature. The energy conversion efficiency of I2-free ssDSSC with EBII (4.7% at 100 mW/cm2) was higher than with EVII (3.8%) due to facile charge transport and lower electron recombination in the former, as supported by electrochemical impedance spectroscopy (EIS). Open image in new window

Effect of TiO2 on PVDF/PMMA composite films prepared by thermal casting

Abstract: Melt-extruded poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend films were prepared at different rutile (titanium dioxide, TiO2) concentrations for use as a protective sheet on a photovoltaic cell and module. The rheology, structure, morphology, crystalline behavior, thermal, and mechanical properties of PVDF/PMMA/TiO2 composite films were investigated through reflectance difference spectrometer (RDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and color spectrometry. The results showed that the blended material and its film have favorable thermal and mechanical properties. The TiO2 is finely dispersed in the composite, as shown by the crystalline regions of the PVDF and the homogeneous amorphous regions consisting of PVDF and PMMA, resulting in advantageous and optical properties of PVDF/PMMA/TiO2 composite films. However, the TiO2 can also greatly narrow the thermally stable region of the PVDF in PVDF/PMMA/TiO2 composite film because of the catalytic decomposition effect. The tensile strength and elongation at break are higher than those of a PVDF/PMMA blend as TiO2 content increases. Increases in the crystalline behavior and rheological properties appeared below 20 wt% TiO2 content. Open image in new window

A new polymeric binder for silicon-carbon nanotube composites in lithium ion battery

Abstract: We introduced polyethyleneimine (PEI) as a new binder for silicon (Si)-carbon nanotube (CNT) anode materials in lithium ion batteries (LIBs). The PEI binder was chosen to enhance the binding of electrode material containing Si-CNT nanocomposites through the formation of a PEI thin layer on the surfaces of CNTs. It was expected that the spontaneous electrostatic interactions between weakly charged PEI molecules with CNT surfaces could promote the binding performance. In other words, the formation of solid-electrolyte interface (SEI) could be suppressed owing to the effect of dominant electrostatic interactions between PEIs and CNTs. Zeta potential analyses demonstrated the real presence of electrostatic interactions between PEIs and CNTs. Accordingly, lithium battery half-cell tests showed that improved capacity retention behavior was observed in the sample with PEI than that with polyvinyldifluoride (PVDF) binder. Remarkably, for the case of Si-CNT anode materials prepared without or with relatively less amount of CNT, a higher reduction in capacity was observed with PEI binder than with PVDF. An additional advantage of the incorporation of PEI binder is an increase of initial coulombic efficiency approximately 5%∼10%. Consequently, all these findings support that PEI is highly desirable as an alternative binder for electrode materials containing CNT.

Enhanced Moisture Barrier Films Based on EVOH/Exfoliated Graphite (EGn) Nanocomposite Films by Solution Blending

Abstract: A series of ethyl-vinyl alcohol (EVOH) nanocomposite films with exfoliated graphite nanosheets (EGn) were prepared via a solution blending method and their physical and moisture barrier properties were investigated as a function of the EGn content. The physical properties were strongly dependent upon the chemical and morphological structures originating from the differences in EGn composition. The nanocomposite films showed no strong interactions between the polymer and EGn filler, and this resulted in poor dispersion in relatively high content EVOH/EGn nanocomposites. With increasing content of EGn particles, the water vapor transmission rate varied in the range of 1.29 to 3.14 cc/m2/day and the water uptake greatly decreased from 9.1 to 3.4 wt%. The water resistance capacity of EVOH was greatly enhanced and moisture diffusion in the pure EVOH film was retarded by introducing the EGn. However, thermal stabilities were not improved by incorporating EGn due to the poor interaction between EVOH polymer chains and the EGn surface. Open image in new window

Barrier properties of PLA to water vapour: Effect of temperature and morphology

Abstract: In this paper the barrier properties to water vapour of polylactic acid (PLA) films prepared with different thermal treatments were analyzed with the aim of correlating them to the morphology of the samples. The crystallization kinetics of the material was assessed during isothermal steps reached after cooling from the melt or heating from the solid. The temperature at which the maximum crystallization rate was attained was selected as the crystallization temperature for the samples analyzed for barrier properties. The structural and morphological organization was analyzed by means of X-ray diffraction analysis, differential thermal analysis (DSC) and optical analysis. Sorption and diffusion experiments were conducted either varying the temperature or the morphology of the samples. It was found that sorption was mainly dependent on the amount of the permeable non crystalline phase, while diffusion was also dependent on the morphological organization of the crystalline domains. Open image in new window