Differential Scanning Calorimetry Crystallization Research Articles

Influence of Seeds' Age and Clarification of Cold-Pressed Raspberry (Rubus idaeus L.) Oil on the DSC Oxidative Stability and Phase Transition Profiles.

After cold-pressing, small particles of seed residue remain in raspberry seed oil (RSO), even after passing it through cold filtration. The removal of the remaining seed residue is rather an alternative option to improve the visual properties of RSO. This study investigated the influence that the seeds' age (0, 10, 20 months) and clarification process after pressing has on the oxidative stability and phase transition of RSO by means of differential scanning calorimetry (DSC). The results proved that the oil centrifugation process reduces the DPPH radical scavenging activity and oxidative stability measured by p-anisidine value (p-AnV) and DSC oxidation induction time (OIT) at 120 °C of all RSO samples, regardless of the age of the seeds (p ≤ 0.05). No significant differences were observed on the DSC melting and crystallization properties at 1 °C/min after the oil clarification by centrifugation (p > 0.05). The storage time of raspberry seeds, i.e., 10 and 20 months after expiry date, influenced the quality deterioration of RSO, as measured by higher p-AnV, lower DPPH, and OIT values (p ≤ 0.05). The results presented provide new information about oil production processing, suggesting that producers should reconsider giving up the clarification process of oil, since it lowers all quality parameters.

Single‐run DSC method for determining surface crystal growth rate in glasses generalized for samples of different shapes

AbstractWe propose a new generalized method for the determination of surface crystallization growth rates in a wide temperature range using a single Differential Scanning Calorimetry (DSC) experiment. It can be applied to different sample geometries—we have tested the method for powdered and millimetric cubic samples. The crystal growth rate is calculated from the DSC crystallization peak profile and the average particle size. The method was successfully tested using diopside (MgO·CaO·SiO2) glass powders and a sodium disilicate glass (Na2O·2SiO2) millimetric cube, which undergoes exclusive stoichiometric surface crystallization. The resulting crystal growth rates spanned ranges of approximately 60 K for diopside glass and 170 K for sodium disilicate. The method is very convenient, requiring a single DSC run and simple sample preparation. The crystal growth rates, , proved to be accurate when compared to literature optical microscopy measurements, with a root mean square deviation of 0.22 in for diopside glass.

Nonisothermal Crystallization Kinetics of an Ethylene‐Vinyl‐Acetate: I Calorimetry Versus Rheology

The knowledge of the thermo‐mechanical response of polymers during crystallization is of seminal importance for process control and modeling. Among the other subtle findings, the crystallinity‐rheological simplicity, resembling the thermo‐rheological one, was frequently reported, based on the observation that the same amount of crystallinity induces the same rheological hardening to the polymer, regardless the crystallization conditions. The crystallization kinetics, which is a fundamental issue in polymer science, is investigated with differential scanning calorimetry (DSC) measurements. However, the poor agreement of calorimetric data with data coming from rheological investigation remains a debated issue. The crystallization kinetics of a commercial poly‐ethylene‐vinyl‐acetate copolymer (EVA) is here investigated both with DSC and rheological measurements. EVA is a nice model system since its melting point is below 100°C, thus allowing avoiding all the experimental shortcomings related to thermal degradation. We show that DSC and rheological crystallization data satisfactorily agree for the investigated copolymer and thus we conclude that all the discrepancies found in the literature must be principally due to experimental artifacts. Moreover, the observed agreement between DSC and rheological data confirms that the rheological hardening is proportional to the volume of crystallites only and not to the modality in which the crystallization takes place. POLYM. ENG. SCI., 59:2557–2563, 2019. © 2019 Society of Plastics Engineers

Simulation and experimental study of the particle size distribution and pore effect on the crystallization of glass powders

Surface nucleation is a frequent phenomenon and plays an essential role in the crystallization of most glasses, especially glass powders used in sintered glass-ceramics, for example. A technique often employed to study the crystallization kinetics of glassy powders is Differential Scanning Calorimetry (DSC). However, the shape of the crystallization peak profile is usually very complex. For instance, in certain cases of surface nucleation, the crystal growth dimensionality may change during crystallization after crystal impingement, and a large density difference between the parent glass and the resulting crystalline phases may produce cavitation pores in the particle volume. Finally, crushed glass particles are not regularly shaped, as assumed in most models. Hence, to evaluate the crystallization kinetics of glass powders by DSC experiments, in this work, we modified and tested a particle crystallization model using the DSC crystallization peaks of jagged powders of a non-stoichiometric (0.95CaO·0.73MgO·2SiO2) diopside glass having different granulometries and a large crystal/glass density difference. The Reis-Zanotto model was adapted to include two complex variables: particle size distribution and crystallization-induced porosity. As predicted by the modified model, we confirmed the radical change of the DSC peak shape for some particle sizes as a result of crystal impingement and pore formation. This combined experimental-simulation study demonstrates that the adapted model can describe this type of complex and yet frequent crystallization case.

Crystallization kinetics study of silver-doped germanium glasses

A series of germanium glasses in the systems (100-x)[40GeO2-30Bi2O3-20PbO-10TiO2] – (x) AgCl with x = 0, 1, 3 and 5 (mol%) was prepared using the melt-quenching method and then characterized taking into account their crystallization kinetics mechanisms and microstructural analysis. Through Differential Scanning Calorimetry (DSC) performed in different linear heating rate programs, the experimental data obtained were based on non-isothermal models of phase transformation, since their versatility allows us to calculate kinetic parameters, for example, activation energy for crystallization (Ec) and Avrami index n. Thus, it is possible to obtain information on the crystallization mechanism of these glasses. Independent of the model, the values of the Avrami index for each composition are the same, considering the uncertainty attributed to them. It is safe to affirm that bulk and surface nucleation contribute to the crystallization of compositions containing 0 and 1 mol% of AgCl, whereas internal and surface crystallization with one-dimensional growth occur in samples with 3 and 5 mol% of AgCl, respectively. These results were supported by a microstructural analysis from bulk samples that underwent non-isothermal heat treatment at different temperatures according to DSC crystallization peak.

Investigation on crystallization kinetics and luminescent properties of Eu2+/Eu3+-coactivated hexacelsian based glass ceramics

The thermal properties and crystallization behavior of MgOBaOSiO2B2O3Al2O3 glass have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). After crystallization at temperature (800 °C) close to the DSC crystallization peak, dendritic hexacelsian crystals are found to form as the major crystalline phase among glass. The crystallization kinetics was studied by analyzing DSC curves with Chen's and Ozawa's equations. The mean crystallization activation energy and Avrami's parameter are evaluated to be 229 kJ/mol and 1.4, indicating that the crystallization process occurs predominantly by surface crystallization as consistent with experimental data. Concurrent emissions of Eu2+ and Eu3+ under 304 nm excitation demonstrate that partial reduction of Eu3+ to Eu2+ occurs, which could be ascribed to the partition of Eu3+ into the precipitated hexacelsian crystals during the sintering process of glass ceramics. These results indicate that glass ceramic route may serve as an intriguing way for synthesis of phosphors applicable to lighting and display fields.

Effects of process parameters on thermal properties of glass fiber reinforced polyamide 6 composites throughout the direct long‐fiber‐reinforced thermoplastics process

The direct long‐fiber‐reinforced thermoplastic (D‐LFT) process is an efficient, one‐stop manufacturing process starting from raw materials to a final product, and includes various types of equipment. Tandem twin‐screw extruders are the main components of the D‐LFT process, and their control dictates productivity and properties of products. This study investigates the effects of extruder temperature and screw speed on molecular weight and thermal properties of glass fiber‐reinforced polyamide 6 (PA6) composites throughout the D‐LFT process. Viscosity number measurements, thermogravimetric analyses (TGA), and differential scanning calorimetry (DSC) analyses were performed on samples taken from different locations along the D‐LFT process. It was found that viscosity number, which is a measure of molecular weight of the PA6 base resin, decreased with increasing extruder temperature and decreasing screw speed. In contrast, TGA results showed that the low screw speed of the extruders increased apparent activation energy of the final product. Non‐isothermal DSC crystallization analysis revealed no substantial changes to the material's degree of crystallinity with the variations in extruder temperature and screw speed; however, isothermal DSC crystallization analysis showed that the low screw speed of the extruders increased crystallization half‐time of the final material. POLYM. ENG. SCI., 58:E114–E123, 2018. © 2017 Society of Plastics Engineers

Se-doped GeTe4 glasses for far-infrared optical fibers

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study thermokinetic behavior of Ge21SeyTe79−y infrared glasses (for y up to 8 at.% of Se). Glass transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. Both enthalpy and volume relaxation kinetics were found to be uninfluenced by Se addition. On the other hand, DSC crystallization behavior changed significantly with increasing Se content: initial addition of Se partially delays and decelerates both the initial Te precipitation and the consequent volume-located crystallization of GeTe and Te; additional increase of Se content then further delays and separates the volume-located crystallization processes but the initial surface Te precipitation is no longer affected. From this point of view the fine compositional tuning of basic thermal stability of GeTeSe infrared glasses appears meaningless. On the contrary, glass workability window (determined by means of the TMA crystallization experiments) was found to be significantly affected by Se addition, emphasizing the importance of this type of measurements for the glass technology and material science. The 4 at.% Se content was found optimal with respect to fiber-drawing procedure.

Characterization, thermal properties and phase transitions of amazonian vegetable oils

Thermal profiles of buriti pulp oil (Mauritia flexuosa Mart.), tucuma pulp and kernel oils (Astrocarium vulgare Mart.), rubber seed oil (Hevea brasiliensis), passion fruit oil (Passiflora edulis) and ucuuba butter (Virola surinamensis) were analyzed by thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). Gas chromatography and calculated iodine values were performed to determine the fatty acid profile and to measure the degree of unsaturation in these oils, respectively. The TG curves showed three steps of mass loss, which can be attributed to the degradation of polyunsaturated, monounsaturated and saturated fatty acids. The DSC crystallization and melting curves are reported and depended on the fatty acid composition. Usually, oil samples with a high degree of saturation showed crystallization and melting profiles at higher temperatures than the oils with a high degree of unsaturation. The data obtained by physicochemical analysis of oil samples were analyzed by principal component analysis and hierarchical cluster analysis to increase understanding of the data set, examining the presence or absence of natural groupings between samples.

Influence of a commercial monoacylglycerol on the crystallization mechanism of palm oil as compared to its pure constituents

The effect of a commercial monoacylglycerol (MAG), Myverol™ 18 04-PK (Myverol), on the non-isothermal crystallization mechanism of palm oil (PO) was investigated and compared to the effect of the two main constituents of Myverol, monopalmitin and monostearin. The MAGs were added to PO in concentrations up to 8% and the blends were studied using different techniques (differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized light microscopy (PLM)). The DSC crystallization profiles revealed an earlier onset of crystallization along with extra crystallization peaks when MAGs were added to PO. Combined with X-ray results, it could be concluded that the crystallization process of the blends is initiated by the MAGs crystallizing in the α form and then transforming to sub-α. The effect on the non-isothermal crystallization of the PO TAGs is confined to an earlier onset of crystallization, probably through a template effect, and an effect on the crystal structure coarseness.

On the Determination of the Concentration of Crystal Nuclei in Glasses by DSC

An interesting technique was proposed by Ray et al. over a decade ago to determine the number density of nucleation sites, Nq, or the nucleation rate, I(T), in glasses that exhibit internal nucleation. Their approach is based on the measurement of the areas under the differential scanning calorimetry (DSC) crystallization peaks of partially crystallized glass samples. In this study, we review their method and test a modified equation recently proposed by some of us, which also takes into account the crystal morphology and impingement. We compare Nq obtained with both methods for a Li2O·2SiO2 glass. Small glass monoliths were treated at 620°C for different time periods for crystal growth, without any nucleation treatment, and subsequently analyzed by DSC up to 800°C. We thus estimated Nq from the area under the DSC crystallization peaks. The corrected approach resulted in Nq values which were not affected by the pair of growth times chosen, as expected, but the obtained values were two‐ to fivefold lower than those calculated with the Ray model. Taking into account previously reported nucleation rates and the corresponding induction periods as a function of temperature (for specimens of the same glass batch), we estimated the number of nuclei formed during the DSC heating/cooling steps, and also measured them by optical microscopy (OM). Finally, we compared the obtained values from OM with the Nq values determined by the DSC method. The Nq resulting from the original and new equations were approximately two orders of magnitude larger than those experimentally determined for the same glass using optical microscopy. This difference is attributed to the formation of new nuclei during the heating and cooling paths of the DSC runs and to surface crystallization, which are not taken into account in the DSC expressions.

Compatibility and physical properties of poly(lactic acid)/poly(ethylene terephthalate glycol) blends

Blends of poly(lactic acid) (PLA) and poly(ethylene terephthalate glycol) (PETG) of various compositions were prepared by melt compounding and their compatibilities, physical properties, and isothermal crystallization behaviors were investigated. The calculated solubility parameters of PETG are similar to those of PLA. The interaction parameter between PLA and PETG was derived from the Flory-Huggins theory and predicted that PLA and PETG are miscible when PETG contents are below 22 wt%. In accordance with this result, the tan δ peak and glass transition temperatures of blends determined from dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed a single peak at PETG contents lower than 22 wt%. Tensile test results showed that the elongation at the break of blends increased with an increase in PETG content. DSC and isothermal crystallization results showed that PETG accelerates the crystallization rate of PLA at PETG contents lower than 22 wt%, indicating that PETG acts as a nucleation agent in the crystallization of PLA. Wide angle X-ray diffraction results (WAXD) showed that the crystalline structure of PLA is not affected by the incorporation of PETG. Open image in new window

Characterization of Five Natural Resins and Waxes by Differential Scanning Calorimetry (DSC)

Thermal properties of 5 natural resin and wax samples (shellac, rosin, shellac wax, beeswax, Chinese insect wax) were examined by differential scanning calorimetry (DSC). The DSC melting and crystallization curves of the samples were presented in this paper. Three DSC parameters, To, Tf and ΔT (difference between To and Tf), were selected from each curve. Evaluation results of the parameters showed that they were statistically significant with individual excellent reproducibility. Information was provided by evaluation of changes among thermal absorption or release peaks of the curves in differentiating the five resins and waxes. It was demonstrated in this paper that DSC is rapid, convenient, reliable and accurate to qualitatively identify the resins and waxes mentioned above.

Controlled crystallization and ionic conductivity of a nanostructured LiAlGePO 4 glass–ceramic

A Li 1.5[Al 0.5Ge 1.5(PO 4) 3] glass composition was subjected to several crystallization treatments to obtain glass–ceramics with controlled microstructures. The glass transition ( T g), crystallization onset ( T x ) and melting ( T m) temperatures of the parent glass were characterized by differential scanning calorimetry (DSC). The glass has a reduced glass transition temperature T gr = T g/ T m = 0.57 indicating the possibility of internal nucleation. This assumption was corroborated by the similar DSC crystallization peaks from monolithic and powder samples. The temperature of the maximum nucleation rate was estimated by DSC. Different microstructures were produced by double heat treatments, in which crystal nucleation was processed at the estimated temperature of maximum nucleation rate for different lengths of time. Crystals were subsequently grown at an intermediate temperature between T g and T x . Single phase glass–ceramics with Nasicon structures and grain sizes ranging from 220 nm to 8 μm were then synthesized and the influence of the microstructure on the electrical conductivity was analysed. The results showed that the larger the average grain size, the higher the electrical conductivity. Controlled glass crystallization allowed for the synthesis of glass–ceramics with fine microstructures and higher electrical conductivity than those of ceramics with the same composition obtained by the classical sintering route and reported in literature.

Perfectly Controlled Lamella Thickness and Thickness Distribution: A Morphological Study on ADMET Polyolefins

AbstractSummary: Lamella thickness distribution (LTD) plays a critical role in determining the mechanical properties of polyethylene. LTD is predominantly governed by the intermolecular chemical composition distribution, but intrachain heterogeneity also results in a broadened LTD. Polyethylene synthesized by acyclic diene metathesis (ADMET) contains pristine microstructures free from inter and intrachain heterogeneity and therefore represent ideal models to investigate these phenomena. The crystalline structures of ADMET polyethylene with ethyl or n‐hexyl branches every 21st backbone carbon (EB21and EO21, respectively) were characterized by transmission electron microscopy (TEM), small X‐ray scattering and wide angle X‐ray diffraction (SAXS and WAXD), and differential scanning calorimetry (DSC). The samples were crystallized for various periods at temperatures near the DSC crystallization peak temperatures: 10 °C for EB21 and 0 °C for EO21. TEM observation exhibited that EB21 displays straight lamellar crystals with axialitic organization and an average thickness of about 55 Å. This corresponds to twice the ethylene sequence length between branches, suggesting that one lamellar stem spans three branches and includes one ethyl branch within the lamella. The lamella thickness distribution was very narrow compared with that of the cross‐fraction of ethylene/1‐butene copolymer prepared via Ziegler‐Natta polymerization. Similarly it was found from the same characterization methods that EO21 also displays a narrow lamella thickness distribution albeit with thinner lamellae, averaging 25–26Å thick. Judging from this lamella thickness, EO21 is considered to have a lamella stem composed of a single ethylene sequence between two braches, suggesting that the n‐hexyl branch is entirely excluded from a crystalline phase.

Isoconversional kinetic analysis of the crystallization phases of amorphous selenium thin films

The crystallization kinetics of Se thin films were determined under nonisothermal conditions using a differential scanning calorimetry (DSC) technique. The development of crystal phases by thermal treatment of the film at various temperatures was analyzed by X-ray diffraction. Microstructures were identified by studying the morphology of the films using scanning electron microscopy and atomic force microscopy. This study reveals the simultaneous presence of distinct hexagonal and monoclinic phases; the DSC crystallization curve is formed by overlapping the exothermic crystallization curves of both phases. Two isoconversional methods, the Kissinger–Akahira–Sunose and Vyazovkin methods, were used to determine the variation of the activation energy for crystallization with temperature. The results show that the crystallization activation energy decreases with the extent of crystallization or temperature, which suggests that the examined phases follow multi-step kinetics.

Estimation of the nucleation and crystal growth contributions to the overall crystallization energy barrier

AbstractClassical kinetic theories of polymer crystallization were applied to isothermal crystallization kinetics data obtained by polarized optical microscopy (PLOM) and differential scanning calorimetry (DSC). The fitted parameters that were proportional to the energy barriers obtained allow us to quantitatively estimate the nucleation and crystal growth contributions to the overall energy barrier associated to the crystallization process. It was shown that the spherulitic growth rate energy barrier found by fitting PLOM data is almost identical to that obtained by fitting the isothermal DSC crystallization data of previously self‐nucleated samples. Therefore, we demonstrated that by self‐nucleating the material at the ideal self‐nucleation (SN) temperature, the primary nucleation step can be entirely completed and the data obtained after subsequent isothermal crystallization by DSC contains only contributions from crystal growth or secondary nucleation. In this way, by employing SN followed by isothermal crystallization, we propose a simple method to obtain separate contributions of energy barriers for primary nucleation and for crystal growth, even in the case of polymers where PLOM data are very difficult to obtain (because they exhibit very small spherulites). Comparing the results obtained with poly(p‐dioxanone), poly(ε‐caprolactone), and a high 1,4 model hydrogenated polybutadiene, we have interpreted the differences in primary nucleation energy barriers as arising from differences in nuclei density. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1478–1487, 2008

Non-isothermal crystallization and melting of ethylene-vinyl acetate copolymers with different vinyl acetate contents

Non-isothermal crystallization and subsequent melting of three grades of ethylene-vinyl acetate copolymer were investigated by differential scanning calorimetry (DSC) technique. The DSC crystallization curves show that vinyl acetate (VAc) content has the same effect on the onset, peak and final crystallization temperatures, and these copolymers have almost the same spacing of thermal windows under identical crystallization condition. Subsequent melting DSC results suggest that EVA14 (14 wt% VAc) has the narrowest distribution of lamellar thickness and the most perfect crystals. Though the instantaneous nucleation was preferred, non-isothermal crystallization kinetics shows that EVA14 could form tridimensional crystallites, whereas EVA18 (18 wt% VAc) and EVA28 (28 wt% VAc) are prone to crystallize two-dimen- sionally, as a result of more noncrystallizable VAc co-monomers introduced in the crystallizable ethylene segments. The growth rate falls on the following sequence: EVA14>EVA18>EVA28. Moreover, the kinetic crystallizability G also well characterizes the variation of the non-isothermal crystallization of these EVA materials, in the view of structural impedi- ment caused by the VAc content.

NIR luminescence from Er 3+/Yb 3+, Tm 3+/Yb 3+, Er 3+/Tm 3+ and Nd 3+ ions-doped zincborotellurite glasses for optical amplification

In this paper, we report the near-infrared luminescence from the Er 3+/Yb 3+, Tm 3+/Yb 3+, Er 3+/Tm 3+ and Nd 3+ ions-doped TeO 2–ZnO–B 2O 3–Li 2O–Na 2O glasses for optical amplification. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) profiles of the host glass matrix have been carried out. From the DSC thermogram, glass transition ( T g), crystallization ( T c) and melting ( T m) temperatures have been evaluated. The near-infrared spectra of Er 3+/Yb 3+, Tm 3+/Yb 3+, Er 3+/Tm 3+ and Nd 3+ ions-doped glasses have shown full-width at half-maxima (FWHM) around 58, 127, 87 and 35 nm, respectively. These glasses with better thermal stability and broad near-infrared emissions should have potential applications in broadly tunable laser sources and broadband optical amplification at low-loss telecommunication windows.

Emission analysis of Dy 3+ and Pr 3+:Bi 2O 3–ZnF 2–B 2O 3–Li 2O–Na 2O glasses

In this paper, we present the spectral results of Dy 3+ and Pr 3+ (1.0 mol%) ions doped Bi 2O 3–ZnF 2–B 2O 3–Li 2O–Na 2O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition ( T g), crystallization ( T c) and melting ( T m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy 3+:glass has shown two emission transitions 4F 7/2→ 6H 15/2 (482 nm) and 4F 7/2→ 6H 13/2 (576 nm) with an excitation at 390 nm wavelength and Pr 3+:glass has shown a strong emission transition 1D 2→ 3H 4 (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy 3+ and Pr 3+ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.