Differential Scanning Calorimetry Scans Research Articles

Synthesis and thermal behaviour of new benzo-1,2-thiazine long-chain aryl-piperazine derivatives

A series of potential biologically active 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides was synthesized in a straightforward manner by condensation of respective 3-substituted-4-hydroxy-1,2-benzothiazine 1,1-dioxides with 1-(1-chloropropyl)-4-phenylpiperazine. The structures of all of the newly formed compounds were identified by elemental analysis, FTIR and 1H NMR. The synthesized compounds were subjected to preliminary evaluation using differential scanning calorimetry (DSC) to determine the existence of multiple crystal forms. The DSC scans for all compounds show more than one endothermic effect, which might suggest dynamic proton transfer between two or three possible tautomeric forms: O-keto/O-enol, O-enol/O-keto and O-keto/O-keto/CH2 in crystals 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides.

An Understanding of the Non-isothermal Grain Growth Behavior of Sono-Electroplated Cu Thin Film

The kinetics and microstructural evolution during the non-isothermal growth of 763 nm thick sono-electroplated Cu thin film has been investigated by differential scanning calorimetry (DSC), scanning electron microscopy and atomic force microscopy. The DSC scan from 25 °C to 400 °C at a ramp rate of 2 °C min−1 was found to consist of one main exothermic peak with post-shoulder peaks. The grain growth mechanism and mode were discussed by determining the activation and surface energies of the films before and after the thermal scans. The kinetic observation was correlated with the morphological investigations. An abnormal growth tendency of the grains was found past the normal growth.

Investigations into the polymorphic properties of N,N-dimethyltryptamine by X-ray diffraction and differential scanning calorimetry

The powerful psychoactive features of N,N-dimethyltryptamine (DMT) have sparked the imagination of many research disciplines for several decades. One of the key chemical features associated with compound identity is the determination of melting points. The descriptions of both melting points and morphology associated with DMT free base have long been a source of interest and discussion, especially when considering that these values encountered in the scientific literature range dramatically between 38–40°C and 73–74°C, respectively. Such variations in reported melting points suggest that DMT may exist in two or more polymorphic forms and it was the aim of this study to examine the potential polymorphism of DMT via X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC), including fast scan DSC. DMT samples were prepared following extraction from Mimosa tenuiflora inner barks or by laboratory synthesis and then its crystals were recrystallized from solutions of the alkaloid using either hexane or acetonitrile. Irrespective of source, crystals originating from synthesis were predominantly white crystals obtained using crystallization from hexane, whereas yellow samples following recrystallization with acetonitrile. Irrespective of source or solvent, two polymorphs appeared to exist with melting points, determined by DSC, of 57°C to 58°C for Form I and 45°C to 46°C for Form II. Estimates for their enthalpies were 91.9±2.4Jg−1 for Form I and 98.3±2.8Jg−1 for Form II. Form II converted to Form I during DSC; conversion was thus prevented by fast scanning rates of 100°Cmin−1. A transition temperature (Tg) in the range −21°C (2°Cmin−1) to −13°C (100°Cmin−1) was determined depending on DSC scanning rate. Its closeness to the melting point indicates a tendency of Form II to convert to Form I on storage, a phenomenon that was also facilitated by grinding. This study indicates that the presence of differently colored DMT free base crystals obtained from recrystallization might also point towards the existence of polymorphs rather than just the presence of impurities.

Comparison of thermal characteristics of degenerated and inflamed human collagen structures with differential scanning calorimetry

Collagen is the primary structural protein of the human body and the main component of connective tissue. In the form of elongated fibrils, collagen is mostly found in fibrous tissues such as tendon, ligament, and skin. We have already demonstrated that pathologic changes of human collagen structures could be monitored by differential scanning calorimetry (DSC), besides the classical histological methods. The aim of the study was to find whether there is a consistent increase or decrease of the thermal parameters, if we compare the changes of calorimetric enthalpy and denaturation temperature of (1) group: degenerative with (2) group: inflamed collagen structures. The degenerative samples were collected from ruptured Quadriceps, Achilles, patellar and anterior cruciate ligament, and degenerated joint capsule of the shoulder. The inflamed tissue samples were collected from palmar aponeurosis in Dupuytren disease, transverse carpal ligament in carpal tunnel syndrome (CTS), and transverse ligament of the first dorsal compartment in De Quervain disease. The thermal denaturation of human samples was monitored by a SETARAM Micro DSC-II calorimeter. All the experiments were performed between 0 and 100 °C. The heating rate was 0.3 K min−1. DSC scans clearly demonstrated significant differences between the two groups, proving that the thermal stability of the degenerative and inflamed pathologic collagens is significantly different. In cases of degenerative samples, the enthalpy decreased, while the melting temperature showed an increase. On the contrary, inflamed samples demonstrated a significant increase in the enthalpy and the melting temperature decreased. Our results indicate that DSC may be a clinically relevant method in the diagnosis of different collagen diseases.

Thermal Properties of the Polyolefin Based Elastic Filament DOW XLA<sup>TM</sup>

Thermal properties of the elastic filament DOW XLATMwere analyzed by differential scanning calorimetry (DSC) and thermogravimetry analysis (TG). Besides, the elastic recovery characteristics after heat treatment were also discussed. The DSC scan shows typical endotherms and its melting temperature (Tm) ranges from 28 °C- 65 °C. TG analysis indicates that the thermal degradation begins at 285 °C and the highest weight loss rate occurs at 461.9 oC. When the filaments are heat treated under relaxation or at constant elongatiSuperscript texton, their elastic recovery ratios all decrease with the increase of the heat treatment temperature except for 50 °C.

Study on curing kinetics of a diglycidyl ether of bisphenol A epoxy resin/microencapsulated curing agent system

A modified imidazole curing agent, EMI-g-BGE, was encapsulated for one-package of diglycidyl ether of bisphenol A (DGEBA) epoxy resin system. Polyetherimide (PEI) was used as the wall material, and the emulsion solvent evaporation method was used to form the microcapsules. The morphology and particle size distribution of microcapsules were evaluated by scanning electron microscopy (SEM), mastersizer analyzer. Microcapsules exhibited spherical shapes and the mean particle size was about 745 nm. The curing kinetic of DGEBA/microcapsules curing agent was studied by nonisothermal differential scanning calorimetry (DSC) technique at different heating rates. Dynamic DSC scans indicated the microcapsule was an effective curing agent of epoxy resin. The apparent activation energy Ea was 88.03 kJ/mol calculated through Kissinger method, more than DGEBA/EMI-g-BGE system. This microcapsule of EMI-g-BGE exhibited a long shelf life, and the curing did not occur in this epoxy-microcapsule resin system for more than 3months at room temperature. The kinetic parameters were determined by Málek method and a two-parameter ( m, n) autocatalytic model (Šesták–Berggren equation) was found to be the most adequate selected kinetic model, which showed the encapsulation of the curing agent EMI-g-BGE did not change the cure reaction mechanism of the epoxy resin system. From the experimental data, the nonisothermal DSC curves show the results being in accordant with those theoretically calculated.

Effects of alkaline-soluble okra gum on rheological and thermal properties of systems with wheat or corn starch

The effect of okra extract (OE) on the flowing and thermal properties of wheat and corn starch was investigated using rapid visco-analyzer (RVA), Brookfield viscometer, differential scanning calorimetry (DSC), and light microscopy. Starch-OE blends were prepared by replacing 5, 10, 15% of the starch. The RVA data showed that OE reduced the peak viscosity of both starches relative to the control. That was expected because of the reduction in the amount of starch that was replaced by OE. However, the drop in starch setback was more than just the omitted starch in the blend. The DSC scan data of the blends showed higher peak temperature compared to the control, indicating slower starch-granules gelatinization in the presence of OE. Brookfield profiles (performed at 50 °C) demonstrated increase in shear stress as a function of shear rate, but at high OE content, the shear stress of the blends showed resistant to change which was confirmed by lower slope of shear stress as a function of shear rate at higher OE content. Overall, it can be concluded that OE has influenced the investigated properties of the starches, either by indirectly controlling water movement, or by interacting with amylose as indicated by starch-gel setback outcome.

Effect of two different lipid sources on glass transition temperatures and tensile properties of corn semolina

The effect of adding corn oil (CO) and corn germ (CG) on the thermal and mechanical properties of corn semolina (CS) was investigated. The lipids concentration employed were 2% and 3% of CO or CG. The thermal transitions were studied in a moisture content range of 3–27% (d.b.), by means of dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) techniques. Wide angle X-ray scattering (WAXS) experiments showed that type-V amylose–lipid complexes were formed with the native lipids within the corn semolina during thermo-moulding and that re-crystallization to a type-A structure, favored by the added lipids, occurred upon storage in high relative humidity (RH) environments. Two thermal events were observed during the first DSC scan and tanδ DMTA curves. The first one appearing at around 55–60°C was attributed to a possible phase separation or ageing phenomenon taking place during storage of the samples, while the second was ascribed to the glass transition temperature of CS. It was found that addition of both, CO and CG, reduced the moisture content required for these transitions to appear. The expected decrease in the glass transition temperatures with moisture content was well described by the Gordon–Taylor equation. The addition of CO and CG also causes plasticization of CS. Hence, corn germ meal can be used as a lipid source that is more convenient to handle than liquid fats. However, the CS Tg values were independent of the lipids content. Tensile properties of CS and CS-lipid systems were found to be influenced by the moisture content, the physical state of the samples, and their composition.

Gelling and curing behaviors of benzoxazine/epoxy formulations containing 4,4′-thiodiphenol accelerator

Benzoxazine (BOX)/diglycidyl ether of bisphenol A (DGEBA) based epoxy resins (BOX/DGEBA = 100/0, 75/25 and 50/50 wt.%) with and without 4,4′-thiodiphenol accelerator (DT300) were prepared. The gelling and curing behaviors of the BOX and BOX/DGEBA mixtures in presence and absence of DT300 (10 parts per hundred resin, phr) were investigated using plate–plate rheometry and differential scanning calorimetry (DSC). The gel time was determined in isothermal scans at three different temperatures (T = 180, 200, and 220 °C). Dynamic DSC scans were registered at four heating rates (β = 5, 10, 15, and 20 °C min−1, respectively). The activation energy of gelling was assessed by an Arrhenius, whereas that of the curing by the Kissinger and Ozawa methods. Combination of BOX with DGEBA delayed the gel formation and increased the activation energy of both gelling and curing processes compared to neat BOX resin. By contrast, addition of 4,4′-thiodiphenol as co-reactive accelerator markedly reduced the gel time and the activation energy of both gelling and curing of BOX and BOX/DGEBA formulations.

Thermal stability up to 800 °C of a Ni–4 wt% Al nanocomposite

The thermal stability up to 800 °C of a nanocrystalline (NC) Ni (mean grain size ~25 nm) with ~4 wt% Al dispersed in the form of ~160-nm-sized particles, which was fabricated by co-electrodeposition from a nickel sulfate bath, has been investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that microstructural evolution of the composite is temperature dependent, i.e., normal grain growth of the NC Ni, ~0.6 wt% Al solution into the Ni matrix and direct reaction between Al and Ni to form Ni3Al precipitates occurred at ~290, ~325 and ~575 °C, respectively. The distribution of Al in Ni matrix with temperature is fully discussed. A DSC scanning up to 800 °C of a nanocrystalline Ni matrix dispersing ~4 wt% Al particles (mean size: 160 nm) shows the particles did not significantly affect the normal grain growth of NC Ni and they have been converted into Ni3Al and Al solute atoms.

Glassy Behavior of Denatured DNA Films Studied by Differential Scanning Calorimetry

We use differential scanning calorimetry (DSC) to study the properties of DNA films, made of oriented fibers, heated above the thermal denaturation temperature of the double helical form. The films show glassy properties that we investigate in two series of experiments, a slow cooling at different rates followed by a DSC scan upon heating and aging at a temperature below the glass transition. Introducing the fictive temperature to characterize the glass allows us to derive quantitative information on the relaxations of the DNA films, in particular to evaluate their enthalpy barrier. A comparison with similar aging studies on PVAc highlights some specificities of the DNA samples.

Termination of crystallization or ordering of flexible, linear macromolecules

This review concerns the “termination of crystallization or ordering of flexible, linear macromolecules” before the transition from the amorphous phase reaches thermodynamic equilibrium. It makes use of the precision of hindsight in interpretation of old experiments and the back-integration of more recent experiments into the knowledge gained from the well-known older experiments which had led to the paradox: Once the semi-ordered sample is produced, its disordering frequently follows a zero-entropy-production path, i.e., its latent heat is linked to the free enthalpy of the non-equilibrium phase, while on ordering, there exists a metastable temperature region of the polymer melt which cannot be broken by nuclei of the ordered phase. The classic scheme of crystallization via nucleation and growth is used to set the stage for the discussion. This scheme has been used for many years to describe the motion of single motifs to crystallize small, rigid molecules and its slow-down when approaching the glass transition. For flexible macromolecules, the ordering mechanism needs to be expanded to the description of cooperative ordering schemes of more than one motif of the molecular segments and a more complicated, multiple-step slow down when approaching the much wider glass transition region. The structural features causing the incomplete ordering of flexible macromolecules are the three-dimensional defects created at the phase boundaries between ordered and disordered phases, initially called the amorphous defects. The matter contained in these amorphous defects possesses a much broader glass transition. If this glass transition lies above the glass transition of the unrestrained, amorphous phase, the amorphous defects represent a separate nanophase, called a rigid-amorphous fraction. Modern differential scanning calorimetry (DSC), temperature-modulated DSC, and differential fast scanning calorimetry permit the study of latent heats and heat-capacity changes involved in the liquid–solid transitions of amorphous phases, crystals, and mesophases. In this more complex framework, the “termination of crystallization of flexible, linear macromolecules” is described together with the possibility of molar mass segregation by long-range and local diffusion instead of a thermodynamic mechanism.

Isothermal Crystallization Kinetics and Melting Behavior of a Luminescent Conjugated Polymer, Poly(9,9-Dihexylfluorene-Alt-2,5-Didodecyloxybenzene)

A study of the isothermal crystallization behaviors of poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. The Avrami exponent n ranges from 3.43 to 3.71 for PF6OC12 at crystallization temperatures between 100.0°C and 90.0°C, indicating a three-dimensional spherical crystal growth with homogeneous nucleation in the primary crystallization stage for the isothermal melt crystallization process. In the DSC scan, after the isothermal crystallization, multiple melting behavior was found. The multiple endotherms could be attributed to melting of recrystallized materials produced originally during different crystallization processes. According to the Arrhenius equation, the activation energy was determined to be 211.29 kJmol−1 for the isothermal melt crystallization of PF6OC12.

Influence of cellulose content on thermal properties of poly(lactic) acid/cellulose and low-density polyethylene/cellulose composites

Crystallization behaviour of polylactic acid/cellulose (PLA/CELL) and linear low-density polyethylene/cellulose (LDPE/CELL) composites was studied by differential scanning calorimetry (DSC) and polarized light microscopy equipped with hot-stage. The effect of addition of cellulose on thermal properties of PLA/CELL and LDPE/CELL composites was considered. The DSC experiments were performed at different scanning rates. For pure PLA the crystallization peak at T = 98.8 °C was observed in DSC scans at 20 °C/min with the corresponding melting peak at 110.1 °C. With addition of cellulose no crystallization peaks and melting peaks related to them were found. For all samples cold crystallization peaks at around 130 °C and corresponding melting peaks at 152–153 °C were observed in endotherms. Cold crystallinity is strongly affected by cellulose content: the higher the cellulose content, the higher is the cold crystallinity of the samples. At the same time overall crystallinity for all PLA/cellulose composites is negligible contrary to pure PLA, which is slightly crystalline. Unlike PLA, LDPE and its composites have no cold crystallization, which is a usual behaviour for LDPE materials. A general crystallization/melting behaviour of LDPE/cellulose composites is identical to that of pure LDPE. However, the crystallinity of LDPE/composites decreases with increasing cellulose content.

Thermosetting resin compositions based on novolac and modified novolac

AbstractNovel formaldehyde novolac resins at various molar ratios of monomers (4,4′‐methylenedianiline/p‐nonylphenol/p‐formaldehyde) were synthesized in the presence of an acid catalyst. The obtained resins were characterized by using elemental analysis, FT IR, and 1H NMR spectroscopic methods. Subsequently, these resins may further be modified by allylation and methacrylation and may be used as cross‐linking agents for epoxy resin/bismaleimide resin formulations. The curing of epoxy and bismaleimide resins with formaldehyde resins (FR) and modified FR and the thermal decomposition behavior of cross‐linked resins were studied by differential scanning calorimetry (DSC) and thermogravimetric (TGA) techniques. DSC scans for the curing of epoxy resins with FR show a single exothermic peak, which implied only the occurrence of cure reactions between epoxy ring and amine protons, whereas the DSC scans for the epoxy resins, bismaleimide resins, and modified FR systems have two exothermic peaks. The cured products possess a good thermal stability and low water absorption. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 219–233, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20218

Investigation of melting behaviors and crystallinity of linear polyamide with high‐aliphatic content

AbstractThe melting behaviors and crystal structures of a long alkyl chain polyamide and nylon 18 18, were investigated under annealing and isothermal crystallization conditions. Nylon 18 18 showed multiple melting peaks in differential scanning calorimetry (DSC) thermograms depending on thermal history of the samples. The origin of the multiple melting peaks may be a result of a melting and recrystallization mechanism during DSC scans. Wide‐angle X‐ray diffraction patterns showed two new diffraction peaks, which appeared at 0.44 and 0.37 nm, and are characteristic peaks of α‐form (triclinic structure) of even–even nylons with increasing annealing temperature. The intensities of these peaks increased, and they split further apart, with elevated annealing temperatures. The solid‐state 15N CP/MAS NMR spectra of the nylon 18 18 samples that had been quenched and annealed also confirmed the α‐crystalline form. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Preparation and Characterization of Polypropylene/Clay Nanocomposites

Polypropylene(PP)/clay nanocomposites were prepared by solution blending. The microstructure of PP/clay nanocomposites was studied by wide-angle X-ray diffraction (XRD) analysis. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to investigate thermal properties of PP/clay nanocomposites. XRD pattern prove that clay layers were exfoliated into nanometer size in PP matrix and that α-Phase crystallite was the main crystallite of PP in PP/clay nanocomposites. TGA examinations confirmed that the maximum decomposition temperature of PP/clay nanocomposites was higher than that of neat PP and that the thermal stability of PP/clay nanocomposites rose noticeably. Results of DSC scans showed the crystalliztion temperature of nanocomposites was slightly bigger than that of pure PP due to the efficient nucleating effects of clay layers.

Nonisothermal Crystallization and Melting Behavior of in-situ Polymerized Nylon 11/Nylon 66 Composites

Nylon-11/nylon-66 composites were prepared via in-situ polymerization. The nonisothermal crystallization behavior of neat nylon-11 and its composites was carried out using differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa theory, the modified Ozawa equation and an equation combining the Avrami and Ozawa equation were employed to study the crystallization behavior. It is found that the Ozawa analysis fails to provide an adequate description of the nonisothermal crystallization process in both neat nylon-11 and its composites. While the combination of Avrami and Ozawa equations is effective to analyze the nonisothermal crystallization kinetics. The activation energies were determined by the Kissinger method for nonisothermal crystallization. The activation energies for composites are greater than that for neat nylon-11. In addition, the subsequent DSC scans have also been performed to investigate the melting behaviors of the nonisothermally crystallized samples. Results reveal that the nonisothermally crystallized samples exhibit two melting endotherms, and the lower endotherm is dependent on the cooling rate.

Encapsulation of ethylene gas into α-cyclodextrin and characterisation of the inclusion complexes

Molecular encapsulation of various apolar compounds with α-cyclodextrin (α-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an α-CD under 0.2–1.5MPa for 12–120h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-α-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP–MAS 13C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C4, C3 and C5 in NMR spectra, intensity changes of C–H bending and CC stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans.

Effect of mixed glass formers on the crystallization kinetics in AgI–Ag2O–V2O5–MoO3 glassy superionic system

The crystallization and glass transition kinetics using differential scanning calorimetry (DSC) in 50AgI–33.33Ag2O–16.67[(V2O5)1−x–(MoO3)x] superionic glassy system is discussed. Thermal stability of glass, studied using various criteria, does not vary significantly with glass former variation. However, the activation energies for structural relaxation (Es) at glass transition temperature and crystallization (Ec) obtained using Moynihan and Kissinger, Matusita-Sakka formulations found to exhibit interesting trends with MoO3 substitution in the glass matrix. It is noticed that the electrical conductivity (σ)–temperature (T) cycles obtained at a typical heating rate of 1 °C/min do exhibit significant thermal events. The conductivity after first heating cycle at room temperature is found to be increasing with MoO3 content and maximum for x = 0.3 (~10−3 Ω−1 cm−1 at 30 °C) which is comparable to that of the host 50AgI–33.33Ag2O–16.67V2O5 glassy system. The parameters obtained from σ–T plots and DSC scans do complement each other in a particular range of composition.