Differential Calorimetry Research Articles

In situ polymer nanocomposites: Effect of nanoparticles on the interfacial region

Composites based on the blends of polyurethane and poly(methyl methacrylate) of various composition were synthesized in situ in the presence of various amounts of nanoparticles (fumed silica). From thermophysical measurements it was found that, during reaction, phase separation and evolution of two phases occur. The temperature transitions in the systems and their positions depend on the blend composition and on various amounts of nanoparticles. Using scanning differential calorimetry from the changing of heat capacity increments the fraction of an intermediate region between two main phases has been estimated. For the first time it was observed that in nanocomposites in the temperature region between two main relaxation transitions, there appears a third transition, which was related to the adsorption layers formed by both components at the interface of the nanoparticles. The appearance of such intermediate regions increases essentially the fraction of an interfacial region in the system.

Thermal stabilization of collagen molecules in bone tissue

Differential thermal calorimetry (DSC) analysis of partially dehydrated bovine bone, demineralized bone and bovine tendon collagen was performed up to 300 °C to determine factors influencing stability of mineralized collagen in bone tissue. Two endothermal regions were recognized. The first, attributed to denaturation of collagen triple helix, was hydration dependent and had a peak at 155–165 °C in bone, 118–137 °C in tendon and 131–136 °C in demineralized bone. The second region extended from 245 to 290 °C in bone and from 200 to 280 °C in tendon and was connected with melting and decomposition of collagen. Differences in thermodynamic parameters between cortical and trabecular bone tissue were stated. Activation energy of collagen unfolding in native bone tissue increased with dehydration of the bone. From the results of the present study we conclude that dehydrated bone collagen is thermally very stable both in native and in demineralized bone. Presence of mineral additionally stabilizes bone tissue.

Thermoelastic Behavior of Polyurethanes Reinforced with the In situ‐Generated Sodium Silica‐Polyphosphate Nanophase

Segmented polyurethane‐based nanocomposites prepared by reaction between the organic precursor (macrodiisocyanate, MDIC) and the inorganic precursor (sodium silica‐polyphosphate, SSP) were characterized by differential calorimetry, wide‐angle and small‐angle X‐ray diffraction, and stretching calorimetry techniques. Steric restrictions on the mobility of soft MDIC chain segments by a spatial network of self‐associated stiff segments were assumed responsible for the overshoot of experimental values of the glass transition temperature above that expected for completely miscible components. The initial spatial network of self‐associated stiff segments of the MDIC was destroyed by the randomly distributed SSP particles, giving rise to their own fractal‐like structure. Low reinforcement efficiency of the SSP nanophase was tentatively attributed to the relatively large size of its spatial aggregates. The scale of particle displacements within an infinite cluster during stretching is likely to be negligibly small.

Effect of Preadsorbed Water on the Adsorption of p-xylene and m-xylene Mixtures on BaX and BaY Zeolites

Adsorption of an equimolar p-xylene/m-xylene mixture on partially hydrated barium-exchanged X and Y zeolites is studied at 423 K in the pressure range 10(-2)-8 hPa by differential calorimetry coupled with manometry and chromatography. Results are consistent with structural studies and Monte Carlo simulations of the literature. The presence of preadsorbed water in supercages increases the adsorption selectivity toward p-xylene to the detriment of the adsorption capacity and the adsorption affinity, as indicated by a sharp decrease of the Henry constants. However, the coadsorption heats at zero filling are not influenced by the presence of water. Therefore, entropic effects seem to play an important role in the coadsorption process. Two adsorption sites whose energy differs are identified by calorimetry. The more energetic site could correspond to the p-xylene or m-xylene molecule in interaction with the compensation cation located in sites II in the supercage, the less energetic to the adsorption of p-xylene molecule in the 12-ring window joining two supercages. The presence of this second site for p-xylene could be at the origin of the selectivity.

The Curing Behavior and Adhesion Strength of the Epoxidized Natural Rubber Modified Epoxy/Dicyandiamide System

The curing properties and adhesive strengths of the epoxidized natural rubber (ENR, 25 mole percent epoxidation) modified epoxy systems are studied with differential thermal calorimetry (DSC), scanning electron microscopy (SEM), and lap shear strength (LSS) measurement. The results of DSC analyses indicate that the curing exotherm, the curing rate, the reaction order, and the glass transition temperature of the epoxy system are affected by the presence of reactive ENR. From SEM micrographs, it is obtained that a second spherical rubber phase is formed during cure and the particle size of the rubber phase is increased by increasing the curing temperature and the ENR content. The changes of the volume fraction of the rubber phase and the Tg of the cured systems indicate that the mutual dissolution between epoxy resin and ENR happens and which changes with the curing temperature and the ENR content. The LSS of adhesive joints prepared with the ENR modified adhesives are all lower than those of the unmodified epoxy system, and decrease with increasing the amount of ENR added because of the limited compatibility of the ENR with the epoxy matrix.

Solid-liquid phase equilibria of binary salt hydrate mixtures involving ammonium alum

The solid-liquid phase diagrams of binary mixtures of ammonium alum with ammonium iron(III) alum, with aluminum nitrate nonahydrate and with ammonium nitrate and of aluminum sulfate hexadecahydrate with aluminum nitrate nonahydrate are presented. The alum rich branches of the former three-phase diagrams were fitted by the Ott equation. The specific enthalpy of fusion/freezing of some compositions of the former three mixtures was determined by differential drop calorimetry.

Oxidative stability of lubricants measured by PDSC CEC L-85-T-99 test procedure

The CEC L-85-T-99 pressure differential calorimetry (PDSC) test was developed in Europe for ACEA E5 specification for heavy duty diesel oils. This test differentiate between base oils, additives, indicates synergies between antioxidants and correlates with other oxidation tests. Occasionally, the PDSC test can have difficulties to provide a true value for the OIT, which can vary between samplings. This work gives evidence of such case and concludes that variability in results is caused by variability in the oil rather than in the test itself. It appeared possible that certain oils might not be fully homogenous and this could produce a problem for representative PDSC sampling.

Glass Transition Phenomena in Dehydrated Model Systems and Foods: A Review

It is interesting to observe the evolution of the science of the glassy phenomena by following its development to a highly specialized subject, especially one that cuts across several conventional fields, such as the subject of this review. The manuscript is written with several objectives in view. First, I have compiled some basic information on the nature of vitrification for investigators who aspire to develop such an understanding of the subject. Second, a straightforward enough, I hope, exposition of food scientists to the synthetic polymer approach is provided, which constitutes the cornerstone of advances in the molecular understanding of biological rubbers and glasses. Third, a critical discussion of conceptual schemes applied to the vitrification of foodstuffs via rheology and differential calorimetry is developed in order to highlight the current state-of-the-art in the field. Finally, certain needs for further theoretical and experimental advances are pointed out in the hope that these will stimulate a much wider use of this framework of thought to a wide variety of conditions.

Crystallization behavior of the Zr 63Al 7.5Cu 17.5Ni 10B 2 amorphous alloy during isothermal annealing

The crystallization behavior of Zr 63Al 7.5Cu 17.5Ni 10B 2 amorphous Alloy was studied by means of scanning differential calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). A single stage transformation of the amorphous phase forming a Zr 2Cu-type crystalline phase was observed. Kinetics for such single stage crystallization was analyzed by means of Johnson–Mehl–Avrami equation and discussed regarding to the value of Avrami exponent. In addition, the cube of crystal size presents a linear relationship with isothermal annealing time. This indicates that the crystallization process of Zr 63Al 7.5Cu 17.5Ni 10B 2 amorphous alloy belongs to thermally activated process of Arrhenius type. From the HRTEM analysis, small amount of Zr 2Cu-type crystals in the nano-scale dimension (10–20 nm) were observed to precipitate from the amorphous matrix upon the early stage of isothermal annealing the amorphous alloy at the temperature between the glass transition ( T g) and the onset crystallization temperature ( T x).

Controlled/Living Free Radical Copolymerization of Styrene and Butyl Acrylate in Bulk and Emulsion with Industrial Monomers. Influence of Monomer Addition on Polymer Properties

Controlled/living free radical polymerization of styrene and butyl acrylate was performed in bulk and emulsion using a reversible addition−fragmentation transfer (RAFT) process. The effect of the transfer agent to initiator ratio was explored in bulk and emulsion polymerizations. The effect of monomer addition was investigated in emulsion, and two different processes were used: batch and semicontinuous. Better control was obtained with the continuous addition of the monomers, resulting in clear films of the styrene−butyl acrylate copolymers. These copolymers were characterized and studied by size exclusion chromatography, scanning differential calorimetry, dynamic mechanical analysis, transmission electron microscopy, and simulation, indicating that the semicontinuous process produces copolymers with a block of styrene and a block of tapered random copolymer.

Relation between time–temperature transformation and continuous heating transformation diagrams of metallic glassy alloys

The time–temperature transformation (TTT) diagrams for the onset of devitrification of the Ge–Ni–La and Cu–Hf–Ti glassy alloys were calculated from the isothermal differential calorimetry data using an Arrhenius equation. The continuous heating transformation (CHT) diagrams for the onset of devitrification of the glassy alloys were subsequently recalculated from TTT diagrams. The recalculation method used for conversion of the TTT into CHT diagrams produces reasonable results and is not sensitive to the type of the devitrification reaction (polymorphous or primary transformation). The diagrams allow to perform a comparison of the stabilities of glassy alloys on a long-term scale. The relationship between these diagrams is discussed.

Model To Obtain the True Parameters of Decomposition of Volatile Liquids Such as Acrylonitrile and Nitromethane

The heat flow data of a decomposable volatile liquid obtained by a microcalorimetric technique denote the combined effect of two competing processes, viz., vaporization and decomposition. A model, therefore, is needed to evaluate the true decomposition parameters such as onset temperature, peak temperature, and enthalpy of decomposition. Such an exercise was carried out for the highly volatile and decomposable liquids such as nitromethane and acrylonitrile, using high-pressure differential calorimetry (HPDSC). A model has been proposed further under conditions where vaporization was suppressed as in HPDSC. On the basis of the experimental data, a mass-transfer coefficient was derived at low pressures (where only vaporization took place). This was employed for the prediction of the decomposition parameters at higher pressures. The predicted data agreed well with the experimental results carried out at higher pressures. It is believed that the results are useful in reaction systems in plants where chemicals such as the ones considered here are subjected to higher pressures.

Recycling of PET and Polyolefin Based Packaging Materials by Reactive Blending

Results concerning the compatibilization and the chemical-physical characterisation of blends of PET and polyolefins (HDPE, PP) obtained from postconsumer packaging materials are presented. The blend compatibilization was carried out by melt mixing and extrusion processes in the presence of a variety of polyolefins functionalized with reactive groups, such as maleic anhydride, acrylic acid, and glycidyl methacrylate. The effect of the type and concentration of compatibilizer, as well as the mixing conditions on the morphology, crystallization behavior, thermal stability, rheological, and dynamic-mechanical properties of the blends was investigated by various techniques, such as scanning electron microscopy, rheometry, differential calorimetry, thermogravimetry, FTIR, NMR, and mechanical analysis.

Structural and Thermal Characterization of Mono- and Diacyl Polyoxyethylene Glycol by Infrared Spectroscopy and X-ray Diffraction Coupled to Differential Calorimetry

Physical and thermal properties of polyoxyethylene glycol glycerides (Gelucire 50/13) used as sustained-release matrix forming agent in pharmaceutical applications are studied by coupled time-resolved synchrotron X-ray diffraction and differential scanning calorimetry combined with infrared spectroscopy. With these techniques, all polymorphs formed after various thermal treatments from quenching to slow crystallization are characterized. In particular, the fatty esters of polyoxyethylene glycol (PEG) polymorph conformations are all provided by the same lamellar phase with the PEG chains under a helical conformation but with a more or less important tilt of the PEG chains. The rate of crystallization was crucial for the formation of these polymorphs. A slow crystallization rate (0.1 °C/min) will induce the formation of a 120 Å lamellar phase presenting a higher melting point and consequently a better stability in time and in temperature. Inversely, a rapid crystallization rate will induce the formation of a 90 Å lamellar phase. We show, however, the possibility of a rapid transition toward the most stable form. Possible interdigitation of fatty acid chains is also discussed.

Preparation, characterization and dielectric property of Sr5LaTi3Nb7O30 ceramic

Sr5LaTi3Nb1O30 ceramic was prepared by the conventional high temperature solid-state reaction route. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), differential thermal calorimetry (DSC) and dielectric measurements. The results show Sr5LaTi3Nb7O30 belongs to paraelectric phase of filled tetragonal TB structure at room temperature, and undergoes a diffuse phase transition in the temperature range of−54-34°C. And Sr5LaTi3Nb7O30 ceramic shows a high dielectric constant of 479 with a low dielectric loss of 0.005 at 1 MHz. In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant (τe) is significantly reduced.

Tacticity distribution of isotactic polypropylene prepared with heterogeneous Ziegler–Natta catalyst. 1. Fractionation of polypropylene

Two polypropylene samples, one with relatively low isotacticity and the other with high isotacticity were fractionated using a series of solvents and temperatures. For both samples 4–9 fractions were collected and characterised with differential calorimetry, size exclusion chromatography and 13C NMR spectroscopy. The collected fractions showed typical characteristics of a fractionation based on isotacticity, but also similarities to results from temperature rising elution fractionation (TREF), even though a separate controlled crystallisation step was not used. The melting temperatures of the fractions were found to increase linearly as a function of the meso diad fraction. A calibration, which can be used to convert DSC melting curves to wt% curves of isotacticity, was constructed for the temperature range 108–165 °C. The calibration enables quick analysis of samples in polypropylene manufacturing processes.

Diesel soot combustion on Mo/Al2O3 and V/Al2O3 catalysts: investigation of the active catalytic species

Abstract We studied the reactivity of Mo/Al2O3 and V/Al2O3 catalysts for soot combustion, and the influence of their volatile (MoO3 and V2O5) and superficial dispersed species. Differential exploratory calorimetry and temperature-programmed oxidation (TPO) experiments with catalyst and soot mixtures showed that lower combustion temperatures were obtained with increasing loading of Mo or V. TPO experiments performed on separate layers of soot and catalyst showed that both species were able to oxidize CO to CO2, but the combustion temperature was lowered only when soot was in contact with the dispersed species. Infrared absorption spectroscopy analyses of CO adsorbed at several temperatures showed that all catalysts formed superficial carbonated species; however, on molybdenum catalysts, they were easily decomposed. Therefore, it is suggested that the reaction occurs by formation of carbonate species at the catalyst/soot interface yielding CO2, and the better performance of molybdenum catalysts is due to the higher instability of carbonated species.

The curing behaviors of the epoxy/dicyanamide system modified with epoxidized natural rubber

The effects of epoxidized natural rubber (ENR) on the curing behaviors and adhesive strengths of an epoxy (diglycidyl ether of bisphenol-A) and dicyandiamide/2-methyl imidazole system are studied with differential thermal calorimetry (DSC), scanning electron microscopy (SEM), and Instron tensile testing instrument. From DSC analyses of specimens prepared with unsealed aluminum pans, it is obtained that the reaction exotherm, the time to maximal curing rate, the glass transition temperature, the rate constant, and the reaction order of the epoxy system change with respect to the content of ENR added because of the reaction of ENR with the epoxy system. The results obtained from SEM micrographs indicate that the particle size of the rubber phase increases with increasing the curing temperature and the ENR content. The volume fraction of the separated rubber phase also follows the similar trend except at the high curing temperature which implying that the dissolution of epoxy resin in the ENR phase also depends on the curing temperature and the amount of ENR present. The lap shear strengths of specimens prepared with etched aluminum substrates increase with increasing the curing temperature because of a better cure at a higher temperature, but decrease with increasing the ENR content resulting from an adverse effect of ENR on the mechanical properties of the cured resins.

Simultaneous heat-flow differential calorimetry and thermogravimetry for fast determination of sorption isotherms and heat of sorption in environmental or food engineering

A new experimental technique is described for the determination of desorption characteristics for engineering purposes. A TGA-DSC set-up is used in isothermal mode to achieve the thermal desorption of deformable standard materials like microcrystalline cellulose and kaolin in dry air. Assumptions on heat and mass transfer are made and discussed in order to derive desorption isotherms and heat of sorptions from the calorimetric and gravimetric signals. The method is rapid and accurate for high-temperature desorption processes T⩾40 ∘C. It is particularly reliable for small water activity values 0⩽ a w ⩽0.4 where a good agreement with standard methods is observed in spite of small apparent diffusion coefficients D≅10 −10 m 2 s −1 for the two products tested. The method is suitable for heat sensitive biological products because of the small residence time in the furnace (1 or 2 h ).

Kinetics of short-range-ordering in αCu–10at.% Al conducted through differential isothermal calorimetry as influenced by solute–vacancy complexes

A modified first-order kinetic law which takes into account defect decay during an ordering process was employed to predict the short-range-order kinetics of a quenched αCu–10at.% Al alloy, in conjunction with experiments performed by differential isothermal calorimetry (DIC). The effective activation energy of point defect migration and its temperature dependence strongly suggests the contribution of bound vacancies to the ordering process. An estimate of 87.6 kJ mol −1 was made for the activation energy of solute–vacancy migration by applying an effective rate constant, a value which is quite reasonable, since it lies between the activation energy of migration of unbound vacancies and the activation energy for complex dissolution. The isothermal curves were utilized to determine the ordering energy: w=−3.66 kJ mol −1 .