Conventional Differential Scanning Calorimetry Research Articles

Crystallization of Polymers Investigated by Temperature-Modulated DSC.

The aim of this review is to summarize studies conducted by temperature-modulated differential scanning calorimetry (TMDSC) on polymer crystallization. This technique can provide several advantages for the analysis of polymers with respect to conventional differential scanning calorimetry. Crystallizations conducted by TMDSC in different experimental conditions are analysed and discussed, in order to illustrate the type of information that can be deduced. Isothermal and non-isothermal crystallizations upon heating and cooling are examined separately, together with the relevant mathematical treatments that allow the evolution of the crystalline, mobile amorphous and rigid amorphous fractions to be determined. The phenomena of ‘reversing’ and ‘reversible‘ melting are explicated through the analysis of the thermal response of various semi-crystalline polymers to temperature modulation.

Measuring the Glass Transition Temperature of Conjugated Polymer Films with Ultraviolet–Visible Spectroscopy

The glass transition temperature (Tg) of a conjugated polymer can be used to predict its morphological stability and mechanical properties. Despite the importance of this parameter in applications from organic solar cells to wearable electronics, it is not easy to measure. The Tg is often too weak to detect using conventional differential scanning calorimetry (DSC). Alternative methods—e.g., variable temperature ellipsometry—require specialized equipment. This paper describes a technique for measuring the Tg of thin films of semicrystalline conjugated polymers using only a hot plate and an ultraviolet–visible (UV–vis) spectrometer. UV–vis spectroscopy is used to measure changes in the absorption spectrum due to molecular-scale rearrangement of polymers when heated past Tg, corresponding to the onset of the formation of photophysical aggregates. A deviation metric, defined as the sum of the squared deviation in absorbance between as-cast and annealed films, is used to quantify shifts in the absorption spec...

Continuous gradient temperature Raman spectroscopy and differential scanning calorimetry of N-3DPA and DHA from −100 to 10 °C

Docosahexaenoic acid (DHA, 22:6n-3) is exclusively utilized in fast signal processing tissues such as retinal, neural and cardiac. N-3 docosapentaenoic acid (n-3DPA, 22:5n-3), with just one less double bond, is also found in the marine food chain yet cannot substitute for DHA. Gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near and at phase transitions. Herein we apply GTRS and both conventional and modulated DSC to n-3DPA and DHA from −100 to 20°C. Three-dimensional data arrays with 0.2°C increments and first derivatives allowed complete assignment of solid, liquid and transition state vibrational modes. Melting temperatures n-3DPA (−45°C) and DHA (−46°C) are similar and show evidence for solid-state phase transitions not seen in n-6DPA (−27°C melt). The C6H2 site is an elastic marker for temperature perturbation of all three lipids, each of which has a distinct three dimensional structure. N-3 DPA shows the spectroscopic signature of saturated fatty acids from C1 to C6. DHA does not have three aliphatic carbons in sequence; n-6DPA does but they occur at the methyl end, and do not yield the characteristic signal. DHA appears to have uniform twisting from C6H2 to C12H2 to C18H2 whereas n-6DPA bends from C12 to C18, centered at C15H2. For n-3DPA, twisting is centered at C6H2 adjacent to the C2-C3-C4-C5 aliphatic moiety. These molecular sites are the most elastic in the solid phase and during premelting.

Comparison of different tanning agents on the stabilization of collagen via differential scanning calorimetry

Leather is composed of a three-dimensional weave of collagen fiber bundles. Collagen is a fibrous protein well organized in the formation of skin as building blocks. Leather production involves serial operations where the tanning plays the major role in improving the durability of leather products by stabilizing the triple helical structure of collagen matrix. In the leather-making industry, different tanning agents are used to produce different kind of leather goods. These tanning agents have varied efficiency on the stabilization of collagen. In this study, thermal stability of the leathers tanned with most commonly used tanning agents was evaluated by conventional shrinking test (CST) and differential scanning calorimetry (DSC) methods. The results showed that the thermal stability of leathers varied by the type of tanning agent which were in accordance with theoretical approaches. A distinct correlation was also observed between CST and DSC results of the tanned leathers.

On the nature of the KH2PO4 high-temperature transformation

For over two decades, the high-temperature phase transition (HTPT) at around T p = 180 °C on KH2PO4 (KDP), which involves an ionic conductivity increase, constitutes a controversial subject; while most authors ratify a physical transformation (tetragonal → monoclinic phase transition), others defend the chemical transformation. A careful high-temperature phase behavior examination of this acid salt by means of modulated and conventional differential scanning calorimetry, thermogravimetric analysis, simultaneous thermogravimetric and differential scanning calorimetry, impedance spectroscopy, and temperature evolution of X-ray diffraction was performed to provide a possible solution to this long-standing issue. We found that the structural phase transition does not take place. Instead, a chemical transformation occurs at T p. When KDP is heated through this temperature, the sample initially corresponding to a single phase (tetragonal) transforms to a sample composed of two solid phases: tetragonal KDP, located at its bulk, and monoclinic potassium metaphosphate (KPO3), located at its surface. Most of the water produced evaporates, but a small portion of liquid water bonds to KPO3. Because this is of polymeric nature, it takes the role of a host matrix that contains liquid water regions. Consequently, given that part of the water dissolves a portion of surface salt (providing protons), the surface sample system behaves in a similar manner to a polymer electrolyte membrane where the proton transport mechanism includes the vehicle type, using hydronium (H3O+) as a charge carrier. On further heating, the bulk tetragonal KDP phase reduced to its total decomposition. The metastability of the high-temperature phase below T p is also explained.

Enthalpy relaxation of the glass of poly (l-lactic acid) of different d-isomer content and its effect on mechanical properties

The relaxation of the glass of poly (l-lactic acid) (PLLA) and its random copolymers with 2 and 4 mol% d-isomer co-units has been analyzed by conventional differential scanning calorimetry. It was found that the presence of up to 4% d-isomer co-units in the PLLA chain has no measurable effect on the glass relaxation kinetics in fully amorphous samples. At ambient temperature, after rapid cooling of the melt at a rate of 50 K/min, to avoid crystallization, the glass relaxation begins after about 10 min and is not finished within 5000 min. The relaxation of the glass is accompanied by a major change of mechanical properties as it was revealed by time-resolved measurements of the micro-indentation hardness and Young’s modulus. During annealing of amorphous PLLA at ambient temperature, the microhardness and Young’s modulus increase by more than 40 and 10%, respectively, within a time period of about one month, and with an equilibrium value not yet achieved even after such a long annealing time. As in case of the enthalpy-relaxation kinetics, both, absolute values and the time evolution of the analyzed mechanical properties are independent on the presence of d-isomer co-units in the PLLA chain within the investigated concentration range.

Detection of Quench Induced Precipitation in Al Alloys by Dilatometry

Quenching is a critical step during the strengthening age hardening of Aluminium alloys. To obtain optimal technological results, parts should be quenched with the upper critical cooling rate. The precipitation behaviour of Al alloys during cooling from solution annealing and thereby the critical cooling rates are typically investigated by in-situ measurements with differential scanning calorimetry (DSC). Conventional DSCs are limited at cooling rates below 10 Ks-1. Unfortunately, medium to high strength Al alloys typically have critical cooling rates between 10 and some 100 Ks-1. Recently it was shown that dilatometry is generally able for in-situ detection of precipitation in Al alloys. Dilatometry allows controlled cooling up to some 100 Ks-1 and therefore covers the cooling rate range relevant. In this work, we aim to show up and discuss possibilities and limitations of dilatometric detection of quench induced precipitates in 2xxx, and 7xxx Al alloys. The basic method will be presented and results will be compared with DSC work.

Features of colloidal disperse structure formation in petroleum bitumen

Temperature-modulated differential scanning calorimetry has been employed to analyze the structure-related thermal properties of petroleum bitumen. This method enables one to distinguish between “order–disorder” and glass transitions, thereby making it possible to monitor and identify structure-related phase transformations, the signals from which are invisible or overlapped in the thermograms of conventional differential scanning calorimetry. Bitumen has been shown to be a colloidal disperse system only under certain temperature–time conditions. Its dispersed phase may be represented by aggregates of two types with colloidal sizes. Saturated hydrocarbons form a solid crystalline phase in accordance with the regularities of first-order structural phase transitions and nucleation mechanism of phase separation. Asphaltenes and resins form a solid amorphous phase for a relatively long time as a result of a structural relaxation glass transition by the spinodal mechanism of phase separation.

Continuous cooling precipitation diagram of aluminium alloy AA7150 based on a new fast scanning calorimetry and interrupted quenching method

Differential fast scanning calorimetry (DFSC) has been combined with a novel differential reheating method (DRM). Interrupted quenching at different temperatures followed by overcritical cooling enables both time- and temperature-dependent investigations of precipitation reactions in aluminium alloys during cooling from solution annealing at cooling rates between 1K/s and 105K/s. Together with conventional differential scanning calorimetry (DSC) results, for the very first time, a full continuous cooling precipitation (CCP) diagram for a highly concentrated wrought AlZnMgCu alloy has been developed. For alloy AA7150, three precipitation reactions with their respective start and end temperatures were observed by DFSC. The critical cooling rate for suppressing the high-temperature precipitation of S-Al2CuMg was found to be ~10K/s, whereas for the medium-temperature precipitation of η-Mg(Zn,Al,Cu)2 it is ~100K/s and for the low-temperature precipitation of Y-phase plates enriched in Zn and Cu it is ~300K/s. The method can potentially be transferred to similar precipitate-forming metallic systems or related solid-state phase transformation systems also beyond the particular system analysed in the present study.

Probing the early stages of thermal fractionation by successive self-nucleation and annealing performed with fast scanning chip-calorimetry

The thermal fractionation kinetics of a linear low-density polyethylene (LLDPE) during Successive Self-Nucleation and Annealing (SSA) is investigated by fast scanning chip-calorimetry (FSC), by systematically varying the holding times (ts) at each fractionation temperature (Ts). The range of explored fractionation times spans four orders of magnitude, from 0.001 to 10 s. Discernible thermal fractions are already detected in the very early stages of the process, at ts shorter than one second. As ts increases, the melting endotherm after SSA indicates a progressive lamellar thickening and narrowing of the thicknesses distribution of the various crystalline fractions. The largest variations are observed for the families of crystals containing the longest crystallizable sequences, which also undergo a change of their relative content as a consequence of self-nucleated crystallization at Ts. The quality of the thermal fractionation obtained in 10 seconds with FSC is equivalent to that of conventional differential scanning calorimetry SSA (ts = 300 s). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2200–2209

Heat transfer performance of paraffin wax based phase change materials applicable in building industry

Thermal characterization of phase change materials (PCMs) compose of linear low-density polyethylene (LLDPE), paraffin wax (W) with a melting point of 25°C, and expanded graphite (EG), that are highly effective in thermal energy storage systems in the building industry, is reported.Thermal investigation of PCMs with various compositions of LLDPE, W and EG has been performed by nonconventional transient guarded hot plane technique (TGHPT) and compared with conventional differential scanning calorimetry (DSC) measurements. An excellent agreement in determination of thermal characteristics by both methods was found.The highest values of the total amount of stored energy, sensible heat for solid and liquid states (Qtotal, Qs(solid) and Qs(liquid), respectively) were found for the PCMs with composition LLDPE/W/EG=40/50/10 and 35/50/15w/w/w.Moreover, thermal conductivity and diffusivity of PCMs have been significantly improved by adding EG.Additionally, life cycle assessment was performed to evaluate the environmental impact of three different materials as glass wool, rock wool and PCM used with brick wall.

Influence of TiO2 nanoparticles on nonisothermal crystallization of PP in a wide range of cooling rates analyzed by fast scanning DSC

ABSTRACTThe influence of titanium dioxide (TiO2) nanoparticles on the crystallization behavior of polypropylene was investigated by conventional differential scanning calorimetry (DSC) and fast scanning DSC measurements. The data obtained from both methods were estimated for the first time using the Lauritzen‐Hoffmann equation to analyze the behavior over a wide cooling range under nonisothermal conditions. This provides more reliable values of nucleation parameters (Kg) and surface free energy (σe). The variation of the effective energy (ΔE) was determined with the Kissinger method. Regardless of the cooling rate, both Kg and σe indicate the role of titania as a nucleating agent enhances the crystallization rate. However, the ΔE denotes that TiO2 acts as an obstacle to the mobility of chain segments at cooling rates below 150 °C/s, while, in contrast, the presence of titania enhances the chain mobility at cooling rates above 150 °C/s. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43944.

Crystallization kinetics of polyamide 11 in the presence of sepiolite and montmorillonite nanofillers

The crystallization kinetics of polyamide 11 (PA 11) in the presence of sepiolite and organo-modified montmorillonite nanofillers has been studied in a wide range of temperatures and cooling rates by conventional differential scanning calorimetry (DSC) and fast scanning chip calorimetry (FSC). The presence of the nanofillers has a negligible effect on the crystallization temperature of PA 11 at low cooling rates. However, at rapid cooling conditions a distinct nucleating effect of the nanofillers is detected. The critical cooling rate to suppress crystallization increases from 600 K s−1 to about 1000 and 3000 K s−1 in nanocomposites containing sepiolite and montmorillonite, respectively. Regardless of the cooling rate applied for solidification of the melt, in the nanocomposites the crystallinity of PA 11 is 5–10 % higher than in neat PA 11, with the highest values obtained for the montmorillonite-containing system. The nucleating effect of the nanofillers onto the crystallization of the PA 11 is confirmed by analysis of the half-times of isothermal crystallization and by analysis of the spherulitic superstructure. All measurements proved a saturation of the nucleation efficiency at a loading of the nanofiller of 2.5 m%.

A novel approach to study the isothermal and non-isothermal crystallization kinetics of Poly(Ethylene Terephthalate) by Raman spectroscopy

This paper focuses on the study of the crystallization kinetics of an initially quasi-amorphous Poly(Ethylene Terephthalate) (PET) during controlled heating treatments using Raman Spectroscopy. Characteristic vibrational bands of both crystalline and amorphous phases are then investigated in terms of wavenumber values, full widths at half maximum and integrated intensities variations which led to the establishment of a more accurate crystallinity ratio criterion than the one obtained by standard differential scanning calorimetry (DSC) analysis too much dependent on the low polymer thermal conductivity. Applying this last criterion, isothermal and non-isothermal crystallization kinetics were investigated following the Avrami’s and Ozawa’s theories in order to identify the germination and growth modes of the triclinic crystals of PET as a function of thermal treatment. Moreover, all the specific microstructural transitions such as cold crystallization, crystallization from the melt, melting and glass transition are detected and characterized. Similar thermal behaviors were obtained from Raman results and conventional differential scanning calorimetry measurements.

Signatures of Structural Recovery in Polystyrene by Nanocalorimetry

The intrinsic isotherm, asymmetry of approach, and memory effect experiments are performed for a high fictive temperature polystyrene glass in enthalpy space using nanocalorimetry. Using aging at times as short as 0.01 s and relatively high aging temperatures allows the complete evolution of all three of the signatures of structural recovery to be obtained for the first time in enthalpy space. The results from down jump experiments are compared to those obtained at lower temperatures using conventional differential scanning calorimetry (DSC) with respect to the time required to reach equilibrium, the apparent activation energy, and the Tool–Narayanaswamy–Moynihan (TNM) model parameters, and these results are independent of the measurement method being used; on the other hand, the physical aging rate is higher for the high fictive temperature glass.

Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal-Organic Frameworks.

Water adsorption is becoming increasingly important for many applications including thermal energy storage, desalination, and water harvesting. To develop such applications, it is essential to understand both adsorbent-adsorbate and adsorbate-adsorbate interactions, and also the energy required for adsorption/desorption processes of porous material-adsorbate systems, such as zeolites and metal-organic frameworks (MOFs). In this study, we present a technique to characterize the enthalpy of adsorption/desorption of zeolites and MOF-801 with water as an adsorbate by conducting desorption experiments with conventional differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). With this method, the enthalpies of adsorption of previously uncharacterized adsorbents were estimated as a function of both uptake and temperature. Our characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorption enthalpies of MOF-801 are nearly constant for a wide range of vapor uptakes.

Thermal Analysis by Structural Characterization as a Method for Assessing Heterogeneity in Complex Solid Pharmaceutical Dosage Forms.

Characterizing inter- and intrasample heterogeneity of solid and semisolid pharmaceutical products is important both for rational design of dosage forms and subsequent quality control during manufacture; however, most pharmaceutical products are multicomponent formulations that are challenging in this regard. Thermal analysis, in particular differential scanning calorimetry, is commonly used to obtain structural information, such as degree of crystallinity, or identify the presence of a particular polymorph, but the results are an average over the whole sample; it cannot directly provide information about the spatial distribution of phases. This study demonstrates the use of a new thermo-optical technique, thermal analysis by structural characterization (TASC), that can provide spatially resolved information on thermal transitions by applying a novel algorithm to images acquired by hot stage microscopy. We determined that TASC can be a low cost, relatively rapid method of characterizing heterogeneity and other aspects of structure. In the examples studied, it was found that high heating rates enabled screening times of 3-5 min per sample. In addition, this study demonstrated the higher sensitivity of TASC for detecting the metastable form of polyethylene glycol (PEG) compared to conventional differential scanning calorimetry (DSC). This preliminary work suggests that TASC will be a worthwhile additional tool for characterizing a broad range of materials.

Thermal behavior of raspberry and blackberry seed flours and oils

This survey was conducted on thermal properties of flours obtained by grinding of blackberry (Rubus fruticosus L., Čačak Thornless cultivar) and raspberry (Rubus idaeus L., Willamette cultivar) seeds, as well as oils extracted from berry seeds. Thermal behavior and stability of berry seed flours were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). Crystallization and melting points of oils were determined using a conventional and modulated DSC techniques. Oils present in the blackberry and raspberry seeds start melting (Ton) at −24.02 and −26.44°C, respectively. Both berry seeds thermo-oxidatively decompose at temperatures above 210°C. Thermo-oxidative decomposition of these seed flours takes place in two stages, as TG/DTG curves have two thermal decomposition steps. Polymorphism was detected in both seed oils during heating.

Morphology, thermal properties and crystallization kinetics of ternary blends of the polylactide and starch biopolymers and nanoclay: The role of nanoclay hydrophobicity

Polylactide/butylated-starch/nanoclay (70/25.5/4.5 wt%) composites were prepared by melt blending with nanoclays of varying hydrophobicity. Electron microscopy studies indicated that the interphase boundary interaction was highest in the clay with intermediate hydrophobicity but decreased with clays of higher or lower hydrophobicity. Conventional and modulated differential scanning calorimetry studies showed that, in the case of composites, the change in the ratio of rigid and mobile amorphous fractions depends on the hydrophobicity of clays used for the preparation of blend composites. The mobile amorphous fraction related to the polylactide phase decreases in the case of intermediate hydrophobic clay compared with less and more hydrophobic clays or neat blend samples. Avrami bulk crystallization analysis and polarized optical microscopic observation demonstrated that hydrophobic clays hindered the crystallization of the PLA phase into the formation of disc-shaped spherulites. On the basis of obtained results, we propose a general understanding on how the morphology and thermal properties of the blend composites are related to the hydrophobicity of the nanoclays.

Detection of incipient self-ignition process in solid fuels through gas emissions methodology

The aim of this study is to propose an experimental methodology to detect incipient self-ignition processes in solid fuels. This methodology is based on the gases emissions of different solid fuels, varying the degree of compaction and the grain size of the materials. To achieve this goal, a procedure for the collection and analysis of the gases emitted by samples of various fuels has been developed, analysing the temperatures at which these emissions begin. The results obtained for different materials show that it is possible to detect incipient spontaneous combustion processes using measurements of CO and CO2 emissions during heating process, and then to set alarm thresholds based on the concentrations of these gases. Those results have been compared with results from conventional thermogravimetry and differential scanning calorimetry tests and it is shown that the proposed methodology detect the self-ignition process start point in advance.