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Showing papers on "Differential scanning calorimetry published in 2002"


Journal ArticleDOI
01 Jul 2002-Polymer
TL;DR: In this paper, an electrospinning method was used to fabricate bioabsorbable amorphous poly( d, l -lactic acid) (PDLA) and semi-crystalline poly( l-lactic acids) (PLLA) nanofiber non-woven membranes for biomedical applications.

1,779 citations


Journal ArticleDOI
TL;DR: Chitin, chitosan and their O, N -carboxymethyl derivatives were characterized by differential scanning calorimetry (DSC) mainly focusing on changes in physical and chemical structures at different levels of acetyl and carboxy-methyl contents as discussed by the authors.

544 citations


Journal ArticleDOI
01 Jun 2002-Polymer
TL;DR: In this article, a First Law procedure is suggested which involves heating the sample between two set temperatures, T1 and T2, by the requirement that the degree of crystallinity of the sample should not change either with temperature or time.

460 citations



Journal ArticleDOI
TL;DR: In this paper, the effect of cell temperature on the electrochemical reaction behavior of LiFePO4 was investigated by using cyclic voltammetry and electrochemical impedance spectroscopy (EIS).

416 citations


Journal ArticleDOI
TL;DR: The thermal decomposition of borazane BH 3 NH 3 has been studied by differential scanning calorimetry (DSC) and thermogravimetry combined with the FTIR spectroscopic and mass spectrometric analysis of the gas phase as discussed by the authors.

411 citations


Journal ArticleDOI
01 Jun 2002-Polymer
TL;DR: In this paper, nanocomposites of poly(e-caprolactone) (PCL) were prepared by melt blending the polymer with natural Na + montmorillonite and montminillonite modified by hydrogenated tallowalkyl (HTA)-based quaternary ammonium cations, such as dimethyl 2-ethylhexyl HTA ammonium and methyl bis bis(2-hydroxyethyl) ammonium.

407 citations


Journal ArticleDOI
TL;DR: A series of long-chain 1-alkyl-3-methylimidazolium (LSM) and tetrafluoroborate (TFL) anions, including trifluoromethanesulfonate (OTf) and bis(trifluorsulfonyl)imide (TFI), have been synthesized and characterized as mentioned in this paper.
Abstract: A series of long-chain 1-alkyl-3-methylimidazolium salts ([Cn−mim]X, n = 12−18) containing the anions, chloride, bromide, trifluoromethanesulfonate (OTf), and bis(trifluoromethanesulfonyl)imide (TFI), have been synthesized and characterized. The salts have amphiphilic characteristics, and the thermotropic phase behavior of these salts and the analogous tetrafluoroborate salt has been investigated by variable temperature small-angle X-ray scattering, polarizing optical microscopy, and differential scanning calorimetry. The salts form lamellar, sheetlike arrays in the crystalline phase and an enantiomeric smectic liquid crystalline phase at higher temperatures, except for the salts containing the bis(trifluoromethanesulfonyl)imide anion which melt directly to form isotropic liquids. The nature of the anion influences the size of the interlayer spacing in both the crystal and in the mesophase. The interlayer spacing in the mesophase is largest for the anions with the greatest ability to form a three-dimensio...

394 citations


Journal ArticleDOI
TL;DR: It was found that the glass-rubber transition temperature of the plasticized amylopectin matrix first increases up a whiskers content around 10-15 wt % and then decreases, and a significant increase in crystallinity was observed in the composites by increasing either moisture content or whisker content.

381 citations


Journal ArticleDOI
TL;DR: Differential scanning calorimetry (DSC) was used to compare the thermal stability of charged cathodes in 1-M LiPF 6 EC/DEC electrolyte as discussed by the authors.

371 citations


Journal ArticleDOI
TL;DR: In this paper, a batchwise mixture of poly(lactic acid) and five plasticizers was mixed in a batch-wise mixer and then pressed into films, which were analyzed by means of dynamic mechanical analysis and differential scanning calorimetry.
Abstract: Poly(lactic acid) (PLA) was blended with five plasticizers in a batchwise mixer and pressed into films. The films were analyzed by means of dynamic mechanical analysis and differential scanning calorimetry to investigate the properties of the blends. Triacetine and tributyl citrate proved to be effective as plasticizers when blended with PLA. The glass transition temperature of PLA decreased linearly as the plasticizer content was increased. Both plasticizers were miscible with PLA to an extent of similar to 25 wt %. At this point, the PLA seemed to be saturated with plasticizer and the blends tended to phase separate when more plasticizer was added. There were also signs of phase separation occurring in samples heated at 35, 50, and 80degreesC, most likely because of the material undergoing crystallization. The presence of the plasticizers induced an increased crystallinity by enhancing the molecular mobility. (Less)

Journal ArticleDOI
TL;DR: In this article, the morphology and thermal properties of polylactide (PLA)/clay nanocomposites and microcomposites were compared with unfilled PLA, keeping the same thermomechanical history.
Abstract: Polylactide (PLA)/clay nanocomposites loaded with 3 wt % organomodified montmorillonite and PLA/clay microcomposites containing 3 wt % sodium montmorillonite were prepared by melt blending. We investigated the morphology and thermal properties of the nanocomposites and microcomposites and compared them with unfilled PLA, keeping the same thermomechanical history. The influence of the processing temperature on the structural characteristics of the investigated systems was determined. The investigations were performed with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), size exclusion chromatography (SEC), and polarized light microscopy (LM). XRD showed that the good affinity between the organomodified clay and the PLA was sufficient to form intercalated structure in the nanocomposite. The microcomposite featured a phase-separated constitution. DSC and LM studies showed that the nature of the filler affected the ordering of the PLA matrix at the molecular and supermolecular levels. According to TGA, the PLA-based nanocomposites exhibited improvement in their thermal stability in air. Reduced flammability, together with char formation, was also observed for nanocomposites, compared to the microcomposites and pure PLA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1497–1506, 2002

Journal ArticleDOI
TL;DR: Yam starch films were produced by thermal gelatinization of starch suspensions using different starch and glycerol concentrations and were compared to control samples without glyceroline as discussed by the authors. But, they did not show that starch gelatinization was complete.

Journal ArticleDOI
TL;DR: In this paper, the preparation and properties of polyvinylidene fluoride (PVDF)/clay nanocomposites were reported for the first time, and the composites were characterized with X-ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis.
Abstract: The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X-ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X-ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of −100 to 150 °C. The tan δ peak signifying the glass-transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002

Journal ArticleDOI
TL;DR: In this paper, a novel polymeric shape memory system of chemically cross-linked polycyclooctene (PCO) was developed and characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide-angle X-ray scattering (WAXS).
Abstract: A novel polymeric shape memory system of chemically cross-linked polycyclooctene (PCO) was developed and characterized. PCO was synthesized via ring-opening metathesis polymerization of cyclooctene using the dihydroimidazolylidene-modified Grubb's catalyst. After dicumyl peroxide was added to PCO, the mixture was compression-molded into a film and further cured through chemical cross-linking upon heating. The chemically cross-linked PCO samples were fully characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide-angle X-ray scattering (WAXS) in order to gain insight into the rapid shape memory behavior. We observe that the transition temperature of PCO is tunable through the change of the trans/cis ratio of vinylene groups. A fast shape memory behavior was observed, where the primary stress-free shape was recovered within 1 s on immersion in hot water above the melting point of the crystalline PCO phase. In contrast with glassy shape memory polymers, chemical...

Journal ArticleDOI
TL;DR: In this article, a calorimetric method of obtaining directly the fragility of liquids from the fictive temperatures of variably quenched glasses, is outlined, and the authors find that the most fragile liquids known are: glycerol, dibutylphthallate, 9-bromophenanthrene, salol, orthoterphenyl, propylene carbonate, decalin and its nitrogen derivative decahydroisoquinoline.
Abstract: A calorimetric method of obtaining directly the fragility of liquids from the fictive temperatures of variably quenched glasses, is outlined. “Steepness indexes” m, have been determined for a group of molecular liquids of diverse character, and vary in the range 50–150. The values obtained mostly agree well with those from earlier studies using dielectric relaxation, heat capacity spectroscopy, and viscosity data. In our method there is the advantage that the fragility is determined from the relaxation process that is basic to the calorimetric glass transition temperature measurement, namely, that of the enthalpy. The calorimetric measurements also yield the liquid and glass heat capacities, and entropies of fusion, permitting relationships between thermodynamic and kinetic responses to be examined simultaneously. We study glycerol, dibutylphthallate, 9-bromophenanthrene, salol, orthoterphenyl, propylene carbonate, decalin and its nitrogen derivative decahydroisoquinoline, and find the latter two to be the most fragile liquids known, m =145 and 128 respectively. Surprisingly, of the liquids studied, decalin has the smallest increase in heat capacity at the glass transition. By contrast, the strongest liquid, glycerol, has the largest increase. However, the thermodynamic fragility of decalin, assessed from the scaled rate of increase of the excess entropy above Tg, is found to be high, due to the unusually small value of the excess entropy at Tg. Conversely, the entropy-based fragility for glycerol is the lowest. Thus the correlation of kinetic and entropy-based thermodynamic fragilities reported in recent work is upheld by data from the present study, while the basis for any correlation with the jump in heat capacity itself is removed.

Journal ArticleDOI
TL;DR: In this article, the curing kinetics of diglycidyl ether of bisphenol A (DGEBA) and DGEHQ epoxy resins in the presence of TETA as a reactive diluent and triethylenetetetramine (TETA) as the curing agent were studied by non-isothermal differential scanning calorimetry (DSC) technique at different heating rates.

Journal ArticleDOI
TL;DR: It is argued that physical factors, namely residual crystal phase and specific surface area, determine the isothermal and nonisothermal crystallization behavior of ground amorphous samples as opposed to intrinsic differences in the structure of theAmorphous phase.

Journal ArticleDOI
TL;DR: In this article, the melting and crystallization behavior of poly(ethylene glycol) (PEG) with different molecular weights and chosen blends of PEG is investigated by means of differential scanning calorimetry (DSC) operating in dynamic mode at different heating rates.
Abstract: Melting and crystallization behaviour of poly(ethylene glycol) (PEG) with different molecular weights (from 1000 to 35 000) and chosen blends of PEG is investigated by means of differential scanning calorimetry (DSC) operating in dynamic mode at different heating rates. The influence of the molecular weight of PEG on its melting point and enthalpy of fusion is evaluated; from the DSC data the degree of crystallinity is calculated–it is found that there is an increased tendency of higher-molecular-weight PEGs towards the formation of crystalline phase owing to their lower segmental mobility and more convenient geometrical alignment. During the freezing cycle, an increase in the molecular weight of PEG causes an increase in the solidification temperature and heat of crystallization. Thermal transition data are supplemented by optical microscopy–numerous small sphere-shaped crystalline structures are observed to join together and impinge on their neighbours, forming eventually a multilayered lamellar texture. By implementing second polymeric component the polydispersity of the system increases, thus lowering the crystallization degree during preparation phase. It influences also the course of solidification by lowering the crystallization temperature, Tc. An additional effect observed in the case of the blend's freezing is associated with larger supercooling, probably due to morphological constraints and entanglements in interlamellar regions. The possible advantage of using PEG blends to replace pure components is connected with the possibility of changing the temperature range and heat associated with melting/freezing. Copyright © 2003 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this paper, the properties of three regioregular poly(3-alkyl thiophene)s (P3ATs) are studied: poly (3-hexylthiophene), poly( 3-octyl THiophene, P3OT), and poly ( 3-dodecyl thyphene) (P 3DDT).
Abstract: The crystallization properties of three regioregular poly(3-alkyl thiophene)s (P3ATs) are studied: poly(3-hexyl thiophene) (P3HT), poly(3-octyl thiophene) (P3OT), and poly(3-dodecyl thiophene) (P3DDT). The morphology of the isothermally crystallized samples is a whisker type. The values of the enthalpy of fusion of ideal crystals (ΔH), determined from the melting point depression in the polymer–diluent system, are 99, 73.6, and 52 J/g for P3HT, P3OT, and P3DDT, respectively. The values of the equilibrium melting point (T), determined from the Hoffman–Weeks extrapolation procedure, are 300, 230, and 180 °C for P3HT, P3OT, and P3DDT, respectively. From the linear extrapolation of the P3AT data, the T and ΔH values of unsubstituted polythiophene are predicted to be 400 °C and 139 J/g, respectively. The crystallization kinetics of these polymers are studied with differential scanning calorimetry, and the Avrami exponents vary between 0.6 and 1.4, indicating one-dimensional heterogeneous nucleation with linear growth. As the P3AT whiskers are produced from the chain-folding process, the Lauritzen–Hoffman growth rate theory is applied to analyze the temperature coefficient of the crystallization rate data. Graphical plots indicate a transition from regime I to regime II during isothermal crystallization for all the P3ATs studied. The fold surface energy and the work of chain folding calculated from the slopes of the graphical plots decrease with an increase in the number of carbon atoms of the side chain. The primary crystallization process of the side-chain crystallization is very fast and is attributed to the zipping effect of the main-chain crystals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2073–2085, 2002

Journal ArticleDOI
TL;DR: In this paper, phase equilibria among the A2, B2, D03, L12 and D019 phases were determined by transmission and scanning electron microscopies (TEM and SEM) and energy dispersion spectroscopy (EDS), mainly using a conventional diffusion couple (DC) technique.

Journal ArticleDOI
TL;DR: Both the preparation and nature of carrier played an important role in the dissolution performance of the system, and all the combinations with HPbetaCD were more effective in achieving the enhancement of the NC dissolution rate, yielding better performances than the corresponding ones with betaCD.

Journal ArticleDOI
TL;DR: In this article, the effect of molecular weight of polypropylene (PP)-MA on clay dispersion and mechanical properties of nanocomposites was investigated, and the best overall mechanical properties were found for composites containing PP-MA having the highest molecular weight.
Abstract: Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin-screw extruder. The effect of molecular weight of PP-MA (maleic anhydride- modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP-MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP- MA330k/clay, a well-dispersed two-component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP-MA330k/clay, an intercalated three-component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002

Journal ArticleDOI
TL;DR: In this article, the tensile properties of martensitic alloys were investigated to provide superelasticity for biomedical applications as a function of heat treatment and Sn content.
Abstract: Martensitic transformation and tensile properties of 4 to 5 mol%Sn-doped Ti–16 mol%Nb alloys consisting of biocompatible elements were investigated to provide superelasticity for biomedical applications as a function of heat treatment and Sn content. Martensitic transformation (bcc to orthorhombic structure) is accelerated at such quenching conditions that the bcc parent phase is slightly decomposed. Martensitic transformation temperature decreases rapidly with increasing Sn content. In-situ optical microscopic observation on cooling and heating indicates that the martensite is thermoelastic, corresponding to small temperature hysteresis between the martensitic and the reverse transformations, which is determined by differential scanning calorimetry. By controlling the heat treatment condition and Sn content, large superelastic strain is obtained at room temperature.

Journal ArticleDOI
TL;DR: In this article, the results were interpreted assuming progressive evolution of the random coil regions forward the more stable β-sheet conformation, as induced by the different applied preparation conditions or treatment.
Abstract: Films of silk fibroin cast from fibroin-water solutions at different casting temperatures and untreated or treated after casting with methanol, were characterized by differential scanning calorimetry (DSC), under static and dynamic mode, thermogravimetric analysis and dynamic mechanical thermal analysis. DSC revealed the presence of a lower temperature endothermic phenomenon centered at about 70 °C for the as-prepared room temperature cast film, and other typical material thermal parameters - glass transition, crystallization, and thermal degradation - more or less pronounced depending on the specific preparation procedure and thermal or solvent treatment. These results were interpreted assuming progressive evolution of the random coil regions forward the more stable β-sheet conformation, as induced by the different applied preparation conditions or treatment. The low temperature endothermic transition observed in DSC (30-120 °C) corresponded in the dynamic mechanical analysis to a quite anomalous behavior, with a sharp decrease and immediate increase of E'. Conditions producing modifications of the thermal and dynamic mechanical curves, as well as analogies with the thermogravimetric analysis findings, were analyzed and discussed.

Journal ArticleDOI
TL;DR: In this article, a comparative study was conducted to determine the oxidative stability of twelve different edible oils with two different instruments: a differential scanning calorimeter and an oxidative stability index (OSI) instrument.

Journal ArticleDOI
TL;DR: In this article, a support for the grafting of thin films of molecularly imprinted polymers (MIPs) was used as a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity.
Abstract: Silica particles containing surface-bound free radical initiators have been used as supports for the grafting of thin films of molecularly imprinted polymers (MIPs). This technique offers a means of fine-tuning the layer thickness for improved kinetic properties or enhanced capacity in chromatographic or sensor applications. Thus prepared MIPs imprinted with l-phenylalanine anilide, have been characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), elemental analysis, fluorescence microscopy, and scanning electron microscopy (SEM), providing evidence concerning the reproducibility in each step and the quantity and quality of the grafted films. The chromatographic properties of the materials have been investigated with respect to the average layer thickness of the polymer on the surface, the solvent, the support pore diameter, the cross-linker concentration, and the composition of the mobile phase. For the porous particles, the column efficiency depend...

Journal ArticleDOI
TL;DR: In this article, the phase behavior, miscibility, and morphology of poly(L-lactic acid) and poly(butylene succinate) blends were investigated using differential scanning calorimetry, wide-angle X-ray diffraction, small-angle x-ray scattering techniques, and polarized optical microscopy.
Abstract: Blends of poly(L-lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared with various compositions by a melt-mixing method and the phase behavior, miscibility, and morphology were investigated using differential scanning calorimetry, wide-angle X-ray diffraction, small-angle X-ray scattering techniques, and polarized optical microscopy. The blend system exhibited a single glass transition over the entire composition range and its temperature decreased with an increasing weight fraction of the PBS component, but this depression was not significantly large. The DSC thermograms showed two distinct melting peaks over the entire composition range, indicating that these materials was classified as semicrystalline/semicrystalline blends. A depression of the equilibrium melting point of the PLA component was observed and the interaction parameter between PLA and PBS showed a negative value of −0.15, which was derived using the Flory–Huggins equation. Small-angle X-ray scattering revealed that, in the blend system, the PBS component was expelled out of the interlamellar regions of PLA, which led to a significant decrease of a long-period, amorphous layer thickness of PLA. For more than a 40% PBS content, significant crystallization-induced phase separation was observed by polarized optical microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 647–655, 2002

Journal ArticleDOI
TL;DR: High Performance DSC (HPer DSC) as discussed by the authors is a state-of-the-art mode of measurement for high-speed calorimetry, which facilitates the study of the kinetics and metastability of macromolecular systems.
Abstract: This paper reports on the characteristics and use of a new mode of measurement: High Performance DSC (HPer DSC), which represents a major step forward in high-speed calorimetry, as compared to standard DSC. It facilitates the study of the kinetics and metastability of macromolecular systems, especially the analysis of rate-dependent phenomena in real time. Controlled and constant scan rates at hundreds of degrees per minute and combinations thereof both in cooling and in heating are possible. Heats of transition, heat capacities, temperature-dependent crystallinities, etc. can be established at the extreme rates applied. Examples of the utilization of HPer DSC are given for polymers with respect to the effective hindrance of crystallization and cold crystallization, avoidance of recrystallization and the rate dependency of vitrification and devitrification. Low, milligram-scale sample masses, even down to the microgram level, are utilized. The short measuring times also provide the high throughput needed...

Journal ArticleDOI
TL;DR: In this paper, Li0.49CoO2 was investigated by means of differential scanning calorimetry (DSC) with/without an electrolyte (1 M LiPF6/ethylene carbonate/EC)+dimethyl carbonate (DMC).