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Showing papers on "Differential scanning calorimetry published in 1992"


Journal ArticleDOI
TL;DR: It is shown that ligand and protein concentration effects on transitions corresponding to situation C (strongly rate-limited transitions) are similar to those predicted by equilibrium thermodynamics for simple reversible unfolding models.

473 citations


Journal ArticleDOI
TL;DR: In this paper, the physicochemical properties of 7S globulin were studied by differential scanning calorimetry (DSC) and by dynamic viscoelastic measurements, and it was shown that at slow heating rates in DSC curves to 0 o C/min, T i0 =64 o C and T p0 =70 o C.
Abstract: 7S globulin was isolated according to a new method from soybeans. Its physicochemical properties were studied by differential scanning calorimetry (DSC) and by dynamic viscoelastic measurements. Heating DSC curves for 7S globulin showed only one endothermic peak. Extrapolation of the incipient temperature (T i ) and the endothermic peak temperature (T p ) observed at slow heating rates in DSC curves to 0 o C/min led to the result T i0 =64 o C and T p0 =70 o C

408 citations


Journal ArticleDOI
TL;DR: In this paper, the glass transition in amorphous amylopectin derived from waxy maize starch, and containing between 10 and 22% water, has been studied using differential scanning calorimetry, dynamic mechanical thermal analysis, the Instron texturometer and nuclear magnetic resonance (both pulsed and solid state NMR).

369 citations


Journal ArticleDOI
TL;DR: In this paper, the effect on browning of dehydrated vegetables and of model systems (composed of amino acids and sugars reacting in matrices with different physical characteristics) was studied, and the rates of nonenzymatic browning were then derived for vegetables and for model systems by measuring absorbance at 280 and 420 nm.
Abstract: The effect on browning of dehydrated vegetables and of model systems (composed of amino acids and sugars reacting in matrices with different physical characteristics) was studied. Glass transition temperature (T g ) was determined by differential scanning calorimetry. The rates of nonenzymatic browning were then from the literature for vegetables and were determined for model systems by measuring absorbance at 280 and 420 nm. Rate constants were analyzed as a function of temperature (T) and of (T-T g )

302 citations


Journal ArticleDOI
TL;DR: Differential scanning calorimetry and dynamic mechanical analysis were used to study low moisture (10−50%) gelatinized cornstarch in order to understand the severe embrittlement on aging often seen in these systems.

291 citations


Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: In this paper, the crystallization conditions for the preparation of different modifications of the orthorhombic form (β form) of syndiotactic polystyrene (s-PS) are described.

243 citations


Journal ArticleDOI
TL;DR: In this paper, at constant water content and at constant relative humidity above glass transition temperature (Tg), the rate of crystallization was followed using differential scanning calorimetry, which can be used to evaluate diffusion and crystallization kinetics of amorphous carbohydrates.
Abstract: Crystallization of amorphous lactose was studied at constant water content and at constant relative humidity above glass transition temperature (Tg). The rate of crystallization was followed using differential scanning calorimetry. Crystallization at constant water content increased the amount of water in the remaining amorphous matrix, which decreased Tg and accelerated crystallization. At constant relative humidity crystallization proceeded at a rate determined by T -Tg which increased with crystallinity. Temperature dependence of time to complete crystallization was confirmed to follow Williams-Landel-Ferry (WLF) equation. The results can be used to evaluate diffusion and crystallization kinetics of amorphous carbohydrates.

229 citations


Journal ArticleDOI
TL;DR: In this article, the authors used subambient thermal analysis with differential scanning calorimetry and thermomechanical analysis to optimize the lyophilization of proteins based on the thermal behavior of solution components.

209 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the second-order transition in the differential scanning calorimetry (DSC) thermogram for sucrose and glycerol solutions as a function of moisture content.
Abstract: Differential scanning calorimetry (DSC) thermograms have been recorded for sucrose and glycerol solutions as a function of moisture content. Simple second-order transitions were observed at the glass transition for the higher concentration samples which did not form ice. More complicated thermograms were observed from the lower solution concentrations which formed ice. The origin of these transitions in the DSC thermograms from frozen solutions is discussed, together with the methods used to calculate the amount of ice in the freeze-concentrated solutions. The glass-transition temperatures (Tg) and the ice-melting temperatures (Tm) were used to construct the supplemented phase diagrams for both of these solutes. The maximum freeze concentration (C′g) for sucrose is determined to be 81.2% sucrose, and is shown by a novel experimental approach to occur at a temperature (T′g) of –40 °C.

209 citations


Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: In this article, the glass transition temperature (Tg) of polyaniline films in emeraldine base form was determined and characterized for the first time to be in the range of ∼ 105-220°C for the films containing ∼ 16-0% of 1-methyl-2-pyrrolidinone (NMP) residual solvent, respectively.

207 citations


Journal ArticleDOI
TL;DR: In this paper, a sample of triblock copolym Synperonic F127 was purified and the micellisation and gelation properties of aqueous solutions of purified and unpurified copolymers were investigated by surface tension measurement, static and dynamic light scattering, differential scanning calorimetry and NMR spectroscopy.
Abstract: A sample of triblock copoly(oxyethylene/oxypropylene/oxyethylene) Synperonic F127 was purified. The micellisation and gelation properties of aqueous solutions of purified and unpurified copolymers were investigated by surface tension measurement, static and dynamic light scattering, differential scanning calorimetry and NMR spectroscopy. Generally, the results obtained for the two samples were similar: an exception was the surface tension. Endothermic standard enthalpies of micellisation were obtained over a wide concentration range, with corresponding endothermic standard enthalpies of gelation in the high concentration range. Considered on an equivalent basis, i.e. kJ mol–1(chains), gelation was found to be an almost athermal process compared to micellisation. Based on the presented evidence, particularly that from DSC, and considering other recent studies, it was concluded that the thermal gelation of F127 (i.e. gelation on raising the temperature) resulted essentially from the packing of spherical micelles. A small thermal event at the gelation point was ascribed to a disorder–order discontinuity.

Journal ArticleDOI
TL;DR: In this paper, values of global kinetic constants for pyrolysis, thermal oxidative degradation, and char oxidation of a cellulosic paper were determined by a derivative thermal gravimetric study.

Journal ArticleDOI
TL;DR: In this article, hot-stage microscopy and differential scanning calorimetry were used to investigate the isothermal crystallization of polypropylene in the presence of a large variety of fibres, and the occurrence of transcrystallization was found to depend on the type of fibre used and the crystallization temperature.
Abstract: Hot-stage microscopy and differential scanning calorimetry were used to investigate the isothermal crystallization of polypropylene in the presence of a large variety of fibres. The occurrence of transcrystallization was found to depend on the type of fibre used and the crystallization temperature. The list of fibres which transcrystallize polypropylene is similar to that for other semicrystalline thermoplastics. In particular we found that aramid fibres and high-modulus carbon fibres do induce transcrystallization, whereas high-strength carbon fibres and glass fibres do not transcrystallize polypropylene

Book ChapterDOI
01 Jan 1992
TL;DR: In contrast to the slow heating rates employed for other thermal characterization techniques, such as differential scanning calorimetry (DSC), analytical pyrolysis has a high rate of heating to the final temperature in the millisecond range as discussed by the authors.
Abstract: Pyrolysis is the transformation of a nonvolatile compound into a volatile degradation mixture by heat in the absence of oxygen. A rate of heating to the final temperature in the millisecond range is typical for analytical pyrolysis, in contrast to the slow heating rates employed for other thermal characterization techniques, e.g., thermogravimetry (TG) and differential scanning calorimetry (DSC), that are in the range of minutes or hours. Simple sample preparation (drying and milling), rapid analysis times (from minutes up to 1.5 h) and small sample size (1 to 100µg) are the key features of analytical pyrolysis. Comprehensive books on special applications of pyrolysis are available (Irwin 1982, Meuzelaar et al. 1982, Voorhees 1984, Liebman and Levy 1985, Linskens and Jackson 1986).

Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: In this paper, the authors investigated the physical properties of poly(l-lactic acid (PLLA) and showed that a decrease in molecular weight increases the magnitude of the enthalpy relaxation at the glass-to-rubber transition.

Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: In this paper, the photopolymerization kinetics of four bisphenol-A based dimethacrylate resins were studied from −40 to 160°C by isothermal differential scanning calorimetry.

Journal ArticleDOI
TL;DR: The HII-L alpha-HII double-phase transition at temperatures below 22 degrees C can be shown to be a consequence of the greater degree of hydration of the HII phase in excess water and the relative sensitivities with which the lamellar and hexagonal phases dehydrate with increasing osmotic pressure.
Abstract: The phase diagram of DOPE/water dispersions was investigated by NMR and X-ray diffraction in the water concentration range from 2 to 20 water molecules per lipid and in the temperature range from -5 to +50 degrees C. At temperatures above 22 degrees C, the dispersions form an inverse (HII) phase at all water concentrations. Below 25 degrees C, an HII phase occurs at high water concentrations, an L alpha phase is formed at intermediate water concentrations, and finally the system switches back to an HII phase at low water concentrations. The enthalpy of the L alpha-HII-phase transition is +0.3 kcal/mol as measured by differential scanning calorimetry. Using 31P and 2H NMR and X-ray diffraction, we measured the trapped water volumes in HII and L alpha phases as a function of osmotic pressure. The change of the HII-phase free energy as a function of hydration was calculated by integrating the osmotic pressure vs trapped water volume curve. The phase diagram calculated on the basis of the known enthalpy of transition and the osmotic pressure vs water volume curves is in good agreement with the measured one. The HII-L alpha-HII double-phase transition at temperatures below 22 degrees C can be shown to be a consequence of (i) the greater degree of hydration of the HII phase in excess water and (ii) the relative sensitivities with which the lamellar and hexagonal phases dehydrate with increasing osmotic pressure. These results demonstrate the usefulness of osmotic stress measurements to understand lipid-phase diagrams.

Journal ArticleDOI
TL;DR: Five molecular weight grades of poly(DL-lactic acid) were characterized using gel permeation chro-matography, differential scanning calorimetry, and viscometry to determine the effect of molecular weight on the glass transition temperature and the intrinsic viscosity and correlated very well with both the physical-mechanical properties of the polymer and drug release profiles.
Abstract: Five molecular weight grades of poly(DL-lactic acid) were characterized using gel permeation chromatography, differential scanning calorimetry, and viscometry to determine the effect of molecular weight on the glass transition temperature and the intrinsic viscosity. In addition, dynamic mechanical thermal analysis was used to assess the dynamic storage modulus and the damping factor of the polymer samples by detecting motional and structural transitions over a wide temperature range. Significant relationships were found between the molecular weight and these polymer properties. The five grades of poly(DL-lactic acid) were also incorporated as binders into matrix tablet formulations containing the model drug theophylline and microcrystalline cellulose. Dissolution studies showed significant correlations between the properties of the polymer and the matrix release profiles of the tablets. The release of theophylline slowed down progressively as the polymer molecular weight increased. The differences in release became less significant and reached a limiting asymptotic value as the molecular weight increased to 138,000. Further, tablet index testing was utilized to determine the compaction properties of the polymer granulations. Although there was no correlation with the molecular weight of PLA, brittle fracture index testing indicated very low brittleness for all granulations tested. However, bonding index determinations correlated very well with both the physical-mechanical properties of the polymer and drug release profiles.

Journal ArticleDOI
TL;DR: In this paper, the effects of confinement on the glass transition of several molecular liquids in porous silica glasses were investigated by differential scanning calorimetry, and the authors used the Kelvin equation and the Ehrenfest relation in a phenomenological way to describe the observed trends of glass transition with the pore size.
Abstract: Effects of confinement on the glass transition of several molecular liquids in porous silica glasses were investigated by differential scanning calorimetry. The glass transition temperature, T g , of liquid isopropylbenzene, glycerol, di-n-butyl phthalate, tret-butylbenzene, and n-butyl acetate confined to sol-gel silica glasses with pore radii in the range 18-152 A was determined. For all liquids the confinement lowers the T g observed, and the Kelvin equation and the Ehrenfest relation were used in a phenomenological way to describe the observed trends of the glass transition with the pore size

Journal ArticleDOI
TL;DR: Study of the interaction of a synthetic model hydrophobic peptide and members of the homologous series of n-saturated diacylphosphatidylcholines indicates that the peptide alters the conformational disposition of the acyl chains in contact with it and that the resultant conformations in the lipid hydrocarbon chains tend to minimize the extent of mismatch.
Abstract: High-sensitivity differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the interaction of a synthetic model hydrophobic peptide, Lys2-Gly-Leu24-Lys2-Ala-amide, and members of the homologous series of n-saturated diacylphosphatidylcholines. In the low range of peptide mole fractions, the DSC thermograms exhibited by the lipid/peptide mixtures are resolvable into two components. One of these components is fairly narrow, highly cooperative, and exhibits properties which are similar to but not identical with those of the pure lipid. In addition, the fractional contribution of this component to the total enthalpy change, the peak transition temperature, and cooperativity decrease with an increase in peptide concentration, more or less independently of acyl chain length. The other component is very broad and predominates in the high range of peptide concentration. These two components have been assigned to the chain-melting phase transitions of populations of bulk lipid and peptide-associated lipid, respectively. Moreover, when the mean hydrophobic thickness of the PC bilayer is less than the peptide hydrophobic length, the peptide-associated lipid melts at higher temperatures than does the bulk lipid and vice versa. In addition, the chain-melting enthalpy of the broad endotherm does not decrease to zero even at high peptide concentrations, suggesting that this peptide reduces but do not abolish the cooperative gel/liquid-crystalline phase transition of the lipids with which it is in contact. Our DSC results indicate that the width of the phase transition observed at high peptide concentration is inversely but discontinuously related to hydrocarbon chain length and that gel phase immiscibility occurs when the hydrophobic thickness of the bilayer greatly exceeds the hydrophobic length of the peptide. The FTIR spectroscopic data indicate that the peptide forms a very stable alpha-helix under all of our experimental conditions but that small distortions of its alpha-helical conformation are induced in response to any mismatch between peptide hydrophobic length and bilayer hydrophobic thickness. These results also indicate that the peptide alters the conformational disposition of the acyl chains in contact with it and that the resultant conformational changes in the lipid hydrocarbon chains tend to minimize the extent of mismatch of peptide hydrophobic length and bilayer hydrophobic thickness.

Journal ArticleDOI
TL;DR: In this paper, it was shown that crystalline Si (c-Si) nucleates within the Al layers and penetrates the Al as the c-Si grows, and the overall activation energy of the reaction, determined by calorimetry, is 1·2 ± 1 eV.
Abstract: The crystallization of amorphous Si (a-Si) in Al/a-Si multilayer thin films has been investigated by ex situ and in situ transmission electron microscopy (TEM), X-ray diffraction and calorimetry. The a-Si crystallizes at about 200°C, a significantly lower temperature than for the pure elemental state, with a heat of crystallization of about 12 kJ (mol Si)−1. We show that crystalline Si (c-Si) nucleates within the Al layers and penetrates the Al as the c-Si grows. The speed of the growth of c-Si observed by in situ TEM was a few angstroms per second at 220°C. Al grains are separated and the layered structure is destroyed, while the Al(111) film texture is enhanced. The overall activation energy of the reaction, determined by calorimetry, is 1·2 ± 01 eV. We propose a model in which diffusion of Si through the Al grains and rearrangement of the Al grains occur simultaneously.

Journal ArticleDOI
TL;DR: The results show that the formation of the ripple (P(beta')) phase is inhibited in single bilayers on a solid support, which confirms a conclusion which was reached previously on the basis of neutron scattering data obtained on planar supported bilayers.


Journal ArticleDOI
TL;DR: In this article, the multiphase structure and related relaxations of a segmented polyurethane were characterized by using a combination of differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), stress-strain test, thermally stimulated discharge current (TSDC), and synchrotron small-angle X-ray scattering (SAXS).
Abstract: : The multiphase structure and related relaxations of a segmented polyurethane were characterized by using a combination of differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), stress-strain test, thermally stimulated discharge current (TSDC), and synchrotron small-angle X-ray scattering (SAXS) The polymers studied consisted of 4,4'-diphenylmethane diisocyanate (MDI), 1,4'-butanediol (BD) hard segments with soft segments comprised of PTMO end-capped with PPO at a 70/30 PTMO/PPO weight ratio The results showed a soft segment glass transition temperature (Tg,s) which is significantly higher than the Tg,s (-84 deg C) of the corresponding pure soft segment, suggesting an incomplete phase separation behavior for the soft segments The specimen lost its mechanical strength at above 200 deg C while DSC indicated an endotherm ca 195 deg C due to the hard segment domain consisting of dissolution into the soft segment matrix TSDC showed interfacial polarization due to the multiphase characteristics Synchrotron SAXS scanning from 26 deg C to 250 deg C indicated that the sample structure remained stable with increasing temperature A small change around 75 deg C was attributed to the glass transition of the amorphous hard segment domain Phase mixing took place when the temperature was above 190 deg c, in agreement with the DSC and DMA results Polyurethanes, Elastomers, X-ray scattering, Multiphase structure, Thermal analysis, Morphology, Annealing effects, Microphase, Glass transition

Journal ArticleDOI
TL;DR: Amorphous poly(vinylpyrrolidone) (PVP) varying in molecular weight (MW) (10 000, 24 000, and 40 000) was used to study the effect of molecular weight on the glass transition temperature (Tg) as mentioned in this paper.
Abstract: Amorphous poly(vinylpyrrolidone) (PVP) varying in molecular weight (MW) (10 000, 24 000, and 40 000) was used to study the effect of molecular weight on the glass transition temperature (Tg). Tg was measured by differential scanning calorimetry (DSC). Blends with several diluents (water, butylamine, glycine, hexanal, xylose, glucose, and lysine) were also analyzed and the effect of blend composition on Tg was evaluated. The effect of average molecular weight and of composition in the blends of PVP-plasticizer on Tg was well described by previously reported relationships developed for synthetic polymers. The quantitative results obtained can be used for formulation of mixtures with known Tg and for prediction of their behavior in storage.

Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: A set of polypropylene (PP) fractions with similar molecular masses and molecular mass distributions but different isotacticities have been investigated and their overall crystallization and crystal melting behaviors determined by differential scanning calorimetry and time resolved small-angle X-ray scattering experiments.

Journal ArticleDOI
TL;DR: In this article, a series of different modified chitosan membranes were prepared by blending with polyvinylpyrrolidone (PVP), and the physical, thermal, and mechanical properties were evaluated in terms of the amorphous and hydrophilic nature of PVP.
Abstract: Chitin was isolated from prawn shells, and chitosan was prepared from it. The degree of N-deacetylation and the molecular weight were determined using IR spectroscopy and viscometry, respectively. A series of different modified chitosan membranes were prepared by blending with polyvinylpyrrolidone (PVP). These membranes were characterized by various techniques, including differential scanning calorimetry (DSC), wide-angle X-ray diffractometry (WAXD), and tensile testing. The physical, thermal, and mechanical properties were evaluated, and the change in these properties upon the addition of PVP into the blends has been discussed in terms of the amorphous and hydrophilic nature of PVP. Hydrophilicity of the blends increases due to the presence of PVP in the chitosan substrate. This helps in breaking the hydrogen bonds in between chitosan molecules and causes the blends to swell in three dimensions.

Journal ArticleDOI
01 Jan 1992-Polymer
TL;DR: In this paper, a new procedure for analysing the structure of linear low-density polyethylene (LLDPE) based on differential scanning calorimetry (d.s.c.) has been developed.

Journal ArticleDOI
TL;DR: In this paper, a-CD molecules were found to be more effective in reducing protein stability than either urea or guanidine hydrochloride under similar conditions, although it is much less soluble.
Abstract: Since unfolding of globular proteins normally involves exposure of buried hydrophobic side chains,' the binding of cyclodextrins2 to these exposed residues should destabilize native conformations by shifting the equilibrium in favor of the unfolded polypeptide chain. This indeed appears to be the case. Differential scanning calorimetry (DSC)3 of a range of proteins shows that a-CD reduces the mean unfolding temperature (T,,,) for all proteins examined (Figure l ) , and increasing cyclodextrin concentration progressively reduces the thermal stability of the proteins in a manner consistent with weak non-covalent attachment of a-CD molecules onto the unfolded chain (Figure 2). On a molar basis, a-CD is more effective in reducing protein stability than either urea or guanidine hydrochloride under similar condition^,^ although it is much less soluble. Alongside this reduction in T,,, there is a consistent decrease in the transition enthalpy (AH,,,). Part of this arises from the normal temperature dependence of AH,,, for globular proteins arising from heat capacity effects (ACP).l However, even after correction for this effect, the observed enthalpies are consistently lower than expected by up to 10 kcal mol-' at the highest a-CD concentrations available. The ACp values themselves are also generally lower in the presence of a-CD, as indicated by the post-transition heat capacity base lines (Figure 1, except for PGK where this is obscured by exothermic aggregation). Both these effects are consistent with the binding of a-CD molecules to hydrophobic sites exposed on the unfolded polypeptide. Heats of complex formation between a-CD and aromatic groups are small but exothermic (-1 to -4 kcal mol-'),6 and complex formation with such groups on the unfolded polypeptide would both reduce the overall transition enthalpy and, by burying these groups within the CD cavity, also reduce AC,. A simple equilibrium model assuming n identical and independent a-CD binding sites on the unfolded protein shows that the shift in transition temperature (AT,,, = T,,, Tm0) should depend on ligand concentration [a-CD] thus:

Journal ArticleDOI
TL;DR: In this article, a simulation was performed to determine whether the multiple melting endotherms observed during the thermal analysis of PBT can be explained by the simultaneous melting and recrystallization of an initial distribution of crystal melting temperatures that contains only one maximum and two inflection points.
Abstract: The melting behavior of poly(butylene terephthalate) (PBT) has been investigated, and a simulation has been performed to determine whether the multiple melting endotherms observed during the thermal analysis of PBT can be explained by the simultaneous melting and recrystallization of an initial distribution of crystal melting temperatures that contains only one maximum and two inflection points. Specimens that were cooled at constant rates from the melt showed between one and three melting endotherms upon heating in a differential scanning calorimeter (DSC). The position and breadth of the crystallization exotherms upon cooling from the melt and small-angle x-ray scattering showed that as the cooling rate is increased, the distribution of melting temperatures broadens and shifts to lower temperatures. By combining temperature-dependent recrystallization with an initial distribution of melting temperatures, simulated DSC curves were produced that agreed well with experimental DSC curves. In instances of triple peaked curves, the high temperature peak was due to crystals formed during the scanning process, and the middle and low temperature peaks were due to crystals originally present in the material. Satisfactory agreement between the experimental and simulated curves was found without considering additional crystallization from the amorphous regions during the scanning process.