scispace - formally typeset
Search or ask a question

Showing papers on "Differential scanning calorimetry published in 1991"


Journal ArticleDOI
TL;DR: The physico-mechanical properties of degradable polymers used for medical applications have been characterized and flexural storage modulus as a function of temperature was determined by dynamic mechanical analysis.

736 citations


Journal ArticleDOI
TL;DR: In this article, the glass transition temperatures of organic liquids confined to small pore sizes were measured as a function of pore size in controlled pore glasses (CPG) having pore diameters in the range of 40-730 A. The surface of the glass was treated with hexamethyldisilazane to promote wetting by the organic liquids studied.
Abstract: The glass-transition temperatures, Tg, of organic liquids confined to small pores were studied by differential scanning calorimetry (DSC). The Tg was measured as a function of pore size in controlled pore glasses (CPG) having pore diameters in the range of 40–730 A. The surface of the glass was treated with hexamethyldisilazane to promote wetting by the organic liquids studied (o-terphenyl and benzyl alcohol). Glasses formed in the pores had a lower Tg than in the bulk and the reduction in Tg increased as the pore size decreased. For example, the depression of the glass transition temperature, ΔTg, of benzyl alcohol in 40 A and 85 A pores was 7.2 K and 3.1 K, respectively. The magnitude of ΔTg also depends on the material; e.g. for o-terphenyl in the 85 A pores, ΔTg was 8.8 K versus 3.1 K for benzyl alcohol. In general, it was noted that ΔTg was considerably less than for the depression of the crystalline melting point, ΔTm, studied in related work. For example, for benzyl alcohol in the 85 A pores, ΔTm was ∼ 25 K and ΔTg was ∼ 3 K.

399 citations



Journal ArticleDOI
TL;DR: In this article, conditions for the synthesis of polymers with respect to reaction time and yield were studied with a number of monomers at different concentrations and in solvents with different buffers with pH range of 5.0-7.5.
Abstract: Polymers were synthesized from substituted phenolic and aromatic amine compounds with hydrogen peroxide as the source of an oxidizing agent and horseradish peroxidase enzyme as the catalyst. The polymerization reaction was carried out in a monophasic organic solvent with small amounts of water at room temperature. Conditions for the synthesis of polymers with respect to reaction time and yield were studied with a number of monomers at different concentrations and in solvents with different buffers with pH range of 5.0–7.5. Physical and chemical properties of these homo-and copolymers were determined with respect to melting point, solubility, elemental analysis, molecular weight distribution, infrared absorption (including FTIR), solid-state 13C nuclear magnetic resonance, thermal gravimetric analysis, and differential scanning calorimetry. The enzyme catalyzed reactions produced polymers of molecular weight greater than 400,000 which were further fractionated by differential solubility in solvent mixtures and the molecular weight distribution of the polymer fractions were determined. In general, the polymers synthesized have low solubilities, high melting points, and some degree of branching.

247 citations


Journal ArticleDOI
TL;DR: In this paper, the thermal decomposition of hexabromoplatinie acid was studied by derivatograph and differential scanning calorimetry, and the natures of pyrolysis processes were discussed and compared with those obtained for the analogous ehlorocomplexes.
Abstract: The potassium, ammonium and thirteen amine salts of hexabromoplatinie acid were obtained and characterized by chemical analysis. The thermal decompositions of these complex salts were studied by derivatograph and differential scanning calorimetry. The natures of the pyrolysis processes are discussed and compared with those obtained for the analogous ehlorocomplexes. From the TG curves, kinetic parameters were derived for different stages of the thermal decomposition.

216 citations


Journal ArticleDOI
TL;DR: In this paper, X-ray, differential scanning calorimetry (DSC), and cross-polarization/magic angle spinning 13 C nuclear magnetic resonance (MAGS) were used to evaluate α-amylolysis in the solid state using Bacillus subtilis and porcine pancreatic α-AMylases.

193 citations


Journal ArticleDOI
TL;DR: In this paper, a food model was used to study the effect of physical changes in the amorphous matrtix on the rate of lipid oxidation and the glass transition temperature (T g ) and crystallisation behavior of the material were determined by using differential scanning calorimetry.
Abstract: A food model was used to study the effect of physical changes in the amorphous matrtix on the rate of lipid oxidation. The glass transition temperature (T g ) and crystallisation behaviour of the material were determined by using differential scanning calorimetry. The rate of oxidation was measured spectrophotometrically in samples incubated at various temperatures above T g .

185 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used an equation of the form Cp = k0 + kln ln T + k1/T + k2/T2 + k3/T3.
Abstract: Relative enthalpy measurements have been made from 800 to 1700 or 1800 K for periclase, lime, spinel, diopside, pseudowollastonite, and anorthite. Significant premelting effects have been observed for diopside. pseudowollastonite, and anorthite, showing that only part of the structural changes that take place near the melting point can be quenched to room temperature. With the heat capacities derived from these measurements and other data for SiO2 polymorphs, corundum, forsterite and pyrope, the validity of proposed Cp equations has been tested, particularly with respect to extrapolations at higher and lower temperatures. For high-temperature extrapolations, the best results have been obtained with an equation of the form Cp = k0 + kln ln T + k1/T + k2/T2 + k3/T3. Comparisons of experimental heat capacities with values calculated from polyhedral modeling show that significant deviations from additivity can be found above 1000 K, likely as a result of anharmonic factors. This raises the possibility that enthalpies and entropies of formation are temperature dependent under mantle conditions. Finally, the difficulties of extrapolating differential scanning calorimetry data for mantle minerals are emphasized.

167 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, a set of polypropylene (PP) fractions with similar molecular masses and distributions but different isotacticities have been studied through wide-angle X-ray diffraction, small-angle x-ray scattering and differential scanning calorimetry measurements.

156 citations


Journal ArticleDOI
TL;DR: Two polymorphs of carbamazepine that melt at 176 and 189 degrees C and are known to be enantiotropic have been characterized more fully than in previous reports and a value for the heat of fusion is estimated.

150 citations


Journal ArticleDOI
TL;DR: Differential scanning calorimetry was used to study was precipitation from a series of North Sea crude oils by measuring glass transition temperatures, wax precipitation and dissolution temperatures (wax appearance and disappearance, respectively), and was precipitation enthalpies in the temperature range from +70 to −140 o C as mentioned in this paper.
Abstract: Differential scanning calorimetry was used to study was precipitation from a series of North Sea crude oils by measuring glass transition temperatures, wax precipitation and dissolution temperatures (wax appearance and disappearance, respectively), and was precipitation and dissolution enthalpies in the temperature range from +70 to −140 o C. With respect to physical characteristics, the oils ranged from very light paraffinic condensates to heavy waxy crudes including biodegraded and asphaltenic oils. On the basis of glass transition temperatures, the oils could be sorted into groups that corresponded to their physical descriptions, whereas a similar grouping according to the precipitation or dissolution temperatures did not correspond to the physical characteristics

Journal ArticleDOI
TL;DR: The order-disorder transition that occurs on heating an aqueous suspension of starch granules has been investigated using differential scanning calorimetry (d.s.c.), X-ray crystallinity, and birefringence methods.

Journal ArticleDOI
TL;DR: In this article, the effect of thermal treatment on compression-molded poly(L-lactic acid) (PLLA) has been investigated by means of viscosimetric molecular weight determination, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA).
Abstract: The effect of thermal treatment on compression-molded poly(L-lactic acid) (PLLA) has been investigated by means of viscosimetric molecular weight () determination, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). Starting from two initial molecular weight PLLAs, amorphous samples with different have been obtained due to degradation occurring during the molding. The crystallization capability of the materials after different thermal treatments has been determined as a function of the molecular weight, and their dynamic mechanical properties have been measured. Initially fully amorphous PLLA matrices attained very high degrees of crystallinity (up to 90%) following different annealing processes. Concomitantly, PLLA degrades due to thermal cleavage of the chains. This is an unavoidable effect that must be taken into consideration when defining the material processing and annealing conditions. Crystallization phenomena occurring in the material during the treatment are clearly documented by DMTA.

Journal ArticleDOI
TL;DR: In this paper, the crystal to non-equilibrium phase transition induced by ball-milling has been evidenced in the CuW system, which exhibits a total immiscibility in both solid and liquid states.
Abstract: For the first time, based on X-ray diffraction, scanning electron microscopy/energy dispersion X-ray analyses, differential thermal analysis and differential scanning calorimetry experiments, the crystal to non-equilibrium phase transition induced by ball-milling has been evidenced in the CuW system. This system exhibits a total immiscibility in both solid and liquid states. Starting from elemental copper and tungsten powders, a partial solubility of copper into the cubic tungsten lattice as well as of tungsten into the f.c.c. copper lattice is induced by ball-milling. Such an enhancement of the solubility is revealed by an effect on the lattice parameter of both Cu(W) and W(Cu) crystalline solid solutions over the whole investigated composition range, i.e. Cu 5 W 95 to Cu 95 W 5 (wt.%). Such an experimental investigation of the crystal to amorphous phase transition induced by ball-milling in a system which exhibits a positive heat of mixing either in the solid or in the liquid states supports our previous results leading to the conclusion that the mechanisms of the phase transitions induced by ball-milling are different from those of the so-called classical solid-state amorphization.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, the influence of composition and thermal history on the phase structure and crystallization processes of poly( d (−)-3-hydroxybutyrate) (PHB) and poly(ethylene oxide) (PEO) blends at temperatures below the melting temperature of PHB has been investigated by differential scanning calorimetry and scanning electron microscopy.

Journal ArticleDOI
TL;DR: In this paper, the glass transition temperature of dry amorphous sucrose at 57°C was decreased to -46°C as the sucrose was plasticized with excess water.
Abstract: Amorphous sucrose showed typical thermal transitions of amorphous materials. The temperatures of those transitions, glass transition, crystallization and melting, decreased with increasing moisture content. The glass transition temperature of dry amorphous sucrose at 57°C was decreased to -46°C as the sucrose was plasticized with excess water. That value remained constant due to maximal freeze-concentration with 72-73% sucrose in the unfrozen matrix which showed ice melting at -34°C. Concentrated solutions may become supercooled resulting in partial freeze-concentration with resultant lowering of glass transition temperature.

Journal ArticleDOI
TL;DR: The physicochemical properties of progesterone-loaded poly(l-lactide) microspheres prepared by the solvent evaporation method were studied, focusing on the crystallinity of the polymer matrices as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, the Gibbs-DiMarzio equation for glass transition of a cross-linked polymer as a function of cross-link density was modified to obtain the average coordination number.
Abstract: High purity chalcogenide glasses incorporating Ge, Sb, Se, As and Te were prepared by vacuum melting of previously distilled 5 N to 6 N pure raw materials from which the surface oxide was also removed in some instances. Glass transition temperatures, Tg, of several chalcogenide glasses prepared by similar processing techniques were determined using differential scanning calorimetry (DSC). An emperical relationship between the glass transition temperature and average coordination number is proposed by modifying the Gibbs-DiMarzio equation for glass transition of a cross-linked polymer as a function of cross-link density. The results for the Tg of three ‘iso-structural’ systems are reported and discussed in light of presumed structural arrangements in these glasses.

Journal ArticleDOI
TL;DR: In this article, the glass transition temperature of hydrated glutenin was studied using mechanical spectrometry and differential scanning calorimetry (DSC) and small amplitude oscillatory measurements showed that hydrated wheat glutenin between 4% and 14% moisture content showed glass transition temperatures between 132 and 22°C.
Abstract: Hydrated glutenin was studied using mechanical spectrometry and differential scanning calorimetry (DSC). Small amplitude oscillatory measurements showed, as a function of temperature, that hydrated glutenin between 4% and 14% moisture content showed glass transition temperatures between 132 and 22 °C. Over the same moisture range, glutenin samples had glass transitions temperatures between 110 and 21 °C as measured by DSC. Both techniques showed that the glass transition temperature of glutenin shifted to lower temperatures with increasing moisture content. Linear approximations of the glass transition temperatures obtained by DSC vs moisture content showed a depression of about 9 °C/wt. %. Both methods showed that glutenin was very sensitive to the plasticizing effect of water in the moisture range studied and appears to be an amorphous, water plasticizable polymer.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, the phase separation of pure hard-block polyurethanes and amorphous segmented hydrogenated polybutadiene (H.PBD) was analyzed using dielectric measurements.

Journal ArticleDOI
TL;DR: The results show that the differential scanning calorimetry transitions for the denaturation of phosphoglycerate kinase are highly distorted by the rate-limited irreversible process, and the use of equilibrium thermodynamics in the analysis of irreversible protein denaturation is questioned.
Abstract: Differential scanning calorimetry transitions for the irreversible thermal denaturation of yeast phosphoglycerate kinase at pH 7.0 are strongly scanning-rate dependent, suggesting that the denaturation is, at least in part, under kinetic control. To test this possibility, we have carried out a kinetic study on the thermal inactivation of the enzyme. The inactivation kinetics are comparatively fast within the temperature range of the calorimetric transitions and can be described phenomenologically by the equation dC/dt = -alpha C2/(beta + C), where C is the concentration of active enzyme at a given time, t, and alpha and beta are rate coefficients that depend on temperature. This equation, together with the values of alpha and beta (within the temperature range 50-59 degrees C) have allowed us to calculate the fraction of irreversibly denatured protein versus temperature profiles corresponding to the calorimetric experiments. We have found that (a) irreversible denaturation takes place during the time the protein spends in the transition region and (b) there is an excellent correlation between the temperatures of the maximum of the calorimetric transitions (Tm) and the temperatures (Th) at which half of the protein is irreversibly denatured. These results show that the differential scanning calorimetry transitions for the denaturation of phosphoglycerate kinase are highly distorted by the rate-limited irreversible process. Finally, some comments are made as to the use of equilibrium thermodynamics in the analysis of irreversible protein denaturation.


Journal ArticleDOI
TL;DR: In this article, the thermal behavior of chitosans with various degrees of deacetylation has been studied and the differential scanning calorimetry curves of the samples exhibit two peaks.

Book ChapterDOI
TL;DR: Differential scanning calorimetry (DSC) or differential thermal analysis (DTA) is a group of techniques in which a physical property of a substance is measured as function of temperature while the substance is subjected to a controlled temperature program.
Abstract: Publisher Summary Thermal analysis (TA) is a group of techniques in which a physical property of a substance is measured as function of temperature while the substance is subjected to a controlled temperature program. Most foods have been subjected to some form of heat transfer treatments during harvesting, processing, distribution, and preparation. These treatments can cause significant changes in the physicochemical and functional properties of the major food constituents, thus affecting the quality and acceptability of the products. Thermal analysis encompasses a wide variety of techniques, and only a few are useful for food study. These include differential scanning calorimetry (DSC) or differential thermal analysis (DTA), thermogravimetry (TG), thermal mechanical analysis (TMA), and dynamic mechanical analysis (DMA). Protein is a major component in many foods and, apart from its nutritional values, contributes to the functional properties of various foods. The use of DSC to study protein conformation and the influence of processing helps to elucidate the mechanisms of protein denaturation, aggregation, and gelation and provides practical guidelines for maximizing protein functionality for specific applications.

Journal ArticleDOI
TL;DR: The role of metal catalysts on the curing characteristics of bisphenol A-based cyanate ester resin systems was investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, and rheological measurements.
Abstract: The role of metal catalysts on the curing characteristics of bisphenol A-based cyanate ester resin systems was investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, and rheological measurements. Bisphenol A dicyanate was cured with the octoates and naphthenates of zinc and manganese and with cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. Nonylphenol at concentrations between 0 and 8 phr was used as the cocatalyst. The results show that at metal catalyst concentrations less than 100 ppm and nonylphenol concentrations less than 4 phr, a maximum glass transition temperature of 250 to 260°C is obtained, irrespective of the type of catalyst used. For samples cured without nonylphenol, the maximum Tg was 298 to 302°C. At high catalyst concentrations, the Tg decreases with increasing catalyst concentration for the zinc catalysts, whereas no concentration effect was observed for samples cured with either manganese or cobalt. Nonylphenol was effective as a cocatalyst in achieving high conversions; however, the Tg at full conversion was found to decrease with increasing nonylphenol levels.

Journal ArticleDOI
TL;DR: In this article, a method of determination of the crystallized fractions is described, and a comparison with the L.S.P.C. method was found to underestimate the real percentage of the crystalized fractions.
Abstract: Differential Scanning Calorimetry (D.S.C.) has been used to characterize the thermal behavior of various paving asphalts and their chromatographic fractions. In a single determination, several parameters, such as the glass transition temperature of the hydrocarbon matrix and the crystallized fractions, may be determined with good reproducibility. The glass transition is attributed to the aromatic and one part of the saturated fractions. The rest of the satured fraction has been found responsible for the endoihermal effect observed on warming which corresponds to the dissolution into the matrix. A method of determination of the crystallized fractions is described, and a comparison with the L.C.P.C. (Laboratoire Central des Ponts et Chaussdes - French Highway Administration Laboratory) method is made. The L.C.P.C. method was found to underestimate the real percentage of the crystallized fractions.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: The results of an investigation into the isothermal crystallization and thermal behaviour of syndiotactic polystyrene (sPS) are reported in this paper, using differential scanning calorimetry, optical microscopy and dilatometry.

Journal ArticleDOI
TL;DR: In this paper, the melting behavior of a range of different molecular weight polyethylene glycol (PEG) samples has been studied using differential scanning calorimetry (DSC).

Journal ArticleDOI
TL;DR: In this paper, the aging process of 6061 AA and SiC particle composite was studied by hardness measurements and differential scanning calorimetry (DSC) and the results showed that the two materials showed the same aging rate when solution treatment was complete.
Abstract: Kinetics of natural aging and precipitation hardening (T4 and T6 tempers) were compared in 6061 aluminium alloy (AA) and 6061 AA−14vol.%SiC particle composite. Aging processes have been studied by hardness measurements and differential scanning calorimetry (DSC). The latter technique is used as a screening tool to follow the aging sequence; in fact, the DSC thermogram depicts characteristic features of different heat treatments undergone by samples. DSC curves for both 6061 AA and 6061AA-SiCp, after solution treatment, display the same aging path; on the contrary, the two materials differ in solution temperature, which is about 30 °C higher in the case of the composite. The precipitation hardening (at 180°C) occurs faster in the composite than in 6061 alloy. The latter presents a broad hardness peak ranging between 4 and 10 h of aging while the composite shows a sharp peak after about 4 h. Probably this behaviour is due to the high dislocation density close to the metal matrix-SiC particle interface. In these strongly deformed zones nucleation processes are accelerated. The aging kinetics at room temperature for the composite is slower than for the 6061 AA. In fact the two materials show the same aging rate when solution treatment in the case of the composite is complete. On the contrary, the composite ages more slowly than 6061 AA. Hence the high dislocation density at the interface, between composite constituents, does not affect T4 treatment.

Journal ArticleDOI
TL;DR: In this article, the viscosimetric molecular weights of four l-lactic acid polymers (PLLA) having different initial molecular weight, i.e. 18 000, 31000, 156000 and 425000, have been determined as functions of the polymer thermal history.