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In present study, based on the two polymorphs (α and β form) of azelnidipine (AZE), 12 complexes of AZE and oxalic acid (OXA) were prepared by solvent-assisted grinding (SG) and neat powder grinding (NG) methods at the AZE/OXA molar ratios of 2:1, 1:1, and 1:2. The effect of the different polymorphs of AZE on the micro-structure of the complexes were investigated by powder X-ray diffraction (PXRD), tempreture modulated differential scanning calorimetry and thermogravimetric analysis, cryo-field emission scanning electron microscope system, fourier transform infrared (FTIR), and solid-state nuclear magnetic resonance spectroscopy. β-AZE-OXA co-crystal was produced at β-AZE/OXA molar ratio of 2:1 when SG method was used; while α-AZE was used to produce α-AZE-OXA co-crystal at same condition. However, the other 10 combinations were in co-amorphous forms, including the NG samples with α (or β)-AZE/OXA molar ratios of 2:1, 1:1 (SG and NG), and 1:2 (SG and NG). Although the XRD pattern and IR spectra of the two co-crystals showed no difference, the melting enthalpy and specific heat c p of the β-AZE-OXA co-crystal was higher than that of the α-AZE-OXA co-crystal, indicating that the numbers of solvent molecules which entered the two co-crystal lattices were different. Interestingly, obvious difference occurred in the IR spectra between the α-AZE-OXA and β-AZE-OXA co-amorphous systems. 1745 cm −1 wave-numbers, which were assigned to the free C O groups, appeared in the α-AZE-OXA co-amorphous systems even when just a small amount of OXA was introduced, thereby indicating the presence of different intermolecular forces in the two series of co-amorphous forms. The solubility in different media and the dissolution rate in 0.1 mol L −1 HCl of the 12 complexes were determined. The dramatically improved dissolution rates of the α- and β-AZE-OXA 1:2 (NG) combinations in vitro showed potential in improving the physicochemical properties of AZE by co-amorphous complex formation. [ABSTRACT FROM AUTHOR]

Common temperature modulated DSCs are limited in the accessible frequency range to about 0.1–0.001 Hz. We describe an extension of this frequency range towards lower and higher frequencies by using conventional DSCs (without TMDSC option). By applying steps in the temperature-time profile a simultaneous multi frequency analysis of the heating rate and the heat flow rate response yields heat capacity data over about 2 orders of magnitude in frequency from one single measurement. Based on this step response analysis we show on the example of a Calvet calorimeter, Setaram BT 2.15, an extension down to 10 −5 Hz and on the example of a chip calorimeter, Mettler Toledo Flash DSC 1, an extension up to 150 Hz. Details of the experimental procedures are provided and the influence of sample size on the obtained data and general limitations, particularly regarding temperature assignment, are discussed. A relaxation map is used to combine all calorimetric data and to compare them with dielectric data. [ABSTRACT FROM AUTHOR]

Reversible melting is a phenomenon unique to polymer crystals, which raises an excess reversing heat capacity near their melting points. By means of temperature-modulated differential scanning calorimetry (TMDSC) measurements with an expanded frequency range in chip-calorimeter, we studied reversing heat capacities of alpha- and beta-form crystals of isotactic polypropylene. We attributed their differences at high temperatures and low frequencies to variable chain mobility in these two crystals. We further performed parallel dynamic Monte Carlo simulations of lattice polymers with variable chain mobility in the crystals to confirm this attribution. Our observations provide the first evidence on the role of chain mobility in the microscopic mechanism of reversible melting at the fold-end surfaces of lamellar polymer crystals. [ABSTRACT FROM AUTHOR]

Post-consumer plastic waste contains blends of numerous types of polyethylene (PE) and isotactic polypropylene (i-PP), whose recycling is challenging due to the complexity of this waste stream. A comprehensive knowledge of the composition of these recyclates is essential to understand the structure-property relationship of these systems and therefore upcycle them for high-value applications. To this aim, we used Temperature Modulated DSC (TM-DSC) to develop a quantitative method to evaluate PE and Low-density PE (LDPE) content in recycled polyolefin blends. TM-DSC was carried out on 29 virgin PE materials, spanning densities between 960 and 862 kg/m3, characterizing a wide range of PE microstructures. Moreover, several PE/i-PP model blends were prepared by selecting LDPE, High-density PE (HDPE) and Linear Low-density PE (LLDPE) materials to blend them with i-PP of three types: homopolymer (PP–H), block copolymer (PP–B) and random copolymer (PP-R), mimicking the composition of real recyclates. Results from the TM-DSC analysis of these blends allowed us to establish methods for quantifying the amount of overall PE content and also the LDPE fraction within recyclates. The developed methods were applied to real post- consumer recycled grades, and results were compared with the ones obtained from Cross-Fractionation Chromatography (CFC) analysis and Nuclear Magnetic Resonance (NMR) spectroscopy, displaying good agreement between the latter and the TM-DSC method. • Thermal behaviour of different PE was investigated by standard DSC and temperature modulated DSC. • Quantitative methods developed to determine the amounts of PE in recycled polyolefin blends. • Soundness of these methods was tested on actual recycled grades from municipal waste. [ABSTRACT FROM AUTHOR]

Phase-structural changes and enthalpic relaxation behavior of poly( d , l -lactide) (PDLLA), poly( l -lactide) (PLLA) and poly( l -lactide-co-ε-caprolactone) (PLCL) copolymers with a lactide molar content ∼70% and having different randomness character (PLCL r 1 : R = 0.69; PLCL r 2 : R = 0.92) were evaluated over 7 days in phosphate buffered saline (PBS) at 37 °C. Results obtained by Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamic Mechanical Analysis (DMA) showed an increase in the value of enthalpic relaxation ( δ ) and the narrowing of the tan δ peak, respectively, indicating the reduction in molecular mobility and a more uniform distribution of the entropic states as the aging time increased. The results obtained for PLCLs were clearly affected by chain microstructural magnitudes, l LA (PLCL r 1 = 4.35 and PLCL r 2 = 3.45). Both showed a crystallization process accompanied by amorphous phase separation during the early stage in PBS. DSC and DMA results also revealed faster structural changes as a result of new supramolecular arrangements as well as a higher tendency to crystallize for PLCL r 1 regarding PLCL r 2 . [ABSTRACT FROM AUTHOR]

Carbon-fibre prepregs have found widespread use in lightweight applications. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. Prepreg materials are generally pre-cured so that they have a higher molecular weight than typical resins in order to reduce resin flow, which facilitates storage and later processing properties. The measurements were carried out using commercially available materials and follow the published DMA investigations of the same material [1]. TMDSC was used to find the correlation between curing conditions, the degree of cure and glass transition temperature. TMDSC has the advantage over standard DSC that it enables better determination of the glass transition temperature, which is often accompanied by an exothermic curing reaction, and thus overshadowed. The influence of the amplitude of temperature modulation was tested in preliminary experiments. For non-cured material a glass transition temperature of approximately 0 °C was determined; whereas for the totally cured material it was approximately 230 °C. The changes in degree of cure, temperature of actual glass transition and post-reaction are given as a function of curing time at 180 °C. The correlation between actual glass transition temperature and degree of cure is derived. [ABSTRACT FROM AUTHOR]

Highlights: [•] [Co(AIP)(BPY)0.5·H2O] n ·2nH2O was synthesized. [•] It is characterized by powder X-ray diffraction, FT-IR spectra. [•] Molar heat capacities of [Co(AIP)(BPY)0.5·H2O] n ·2nH2O were measured. [•] Its thermodynamic parameters (entropy and enthalpy) were derived. [•] Its thermal decomposition mechanism for the material was investigated. [ABSTRACT FROM AUTHOR]

Abstract: Various polyethylenes (PEs) and the effects of high-energy radiation on their structures were widely studied in the past using conventional Differential Scanning Calorimetry (DSC) measurements. In this work, we used the Temperature Modulated Differential Scanning Calorimetry (TMDSC) technique in order to obtain more information about the influence of the initial structural differences and gamma radiation on the evolution in structure and thermal properties of different polyethylenes. For this reason, low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) samples were exposed to gamma radiation, in air, to a wide range of absorbed doses (up to 2400kGy). The separation of the total heat flow TMDSC signal into a reversing and non-reversing part enabled us to observe the low-temperature enthalpy relaxation (related to the existence of the “rigid amorphous phase”) and recrystallisation processes, as well as to follow their radiation-induced evolution and/or that of melting in a more revealing manner compared to the case of the conventional DSC. Consequently, our results indicate that TMDSC could improve the understanding of radiation-induced effects in polymers. [Copyright &y& Elsevier]

Abstract: Gelatinisation of waxy maize starch (WMS) in excess glycerol was investigated by a temperature modulated DSC in quasi-isothermal and non-isothermal mode. By using the measured specific heat capacities (c p ) at different stages of gelatinisation and the hypothetical enthalpy of melting for 100% crystalline amylopectin, a method was developed to reveal the amorphous fraction which remains glassy in the presence of excess glycerol what can be called “rigid amorphous”. It was suggested that the amorphous part of starch was plasticised at around 40°C whereas, rigid amorphous fraction underwent a second stage glass transition which showed itself by an increase in c p under the gelatinisation endotherm. It was also shown that holding WMS in excess glycerol at 100°C (10°C above the gelatinisation onset temperature) for 10 days was not enough to gelatinise the whole WMS implicating that the most stable crystals did not melt before the required threshold temperature was reached. [Copyright &y& Elsevier]

Abstract: Measurements of the glass transition temperature obtained by dynamic mechanical analysis (DMA) and temperature modulated differential scanning calorimetry (TMDSC) are reported to be different. This was mainly attributed to the frequency effect. To obtain comparable measurements, experimental conditions were studied. Although some experimental issues had to be fixed, it was possible to apply the same frequency and temperature using quasi-isothermal conditions in both instruments. The method was tested with three different polymer samples. It was then found that when choosing a suitable response parameter, i.e. the phase angle, the dynamic glass transition temperature values obtained by both methods are practically the same. [ABSTRACT FROM AUTHOR]

Abstract: To develop constitutive models to represent the thermomechanically chemically coupled behaviour of curing resins, vulcanizing elastomers or melting and crystallizing polymers the technique of DSC is extremely helpful. In the present study, the method of TMDSC is interpreted and evaluated in the context of thermodynamics with internal state variables. The balance equation of energy and the dissipation principle in the form of the Clausius–Duhem inequality form the theoretical basis of our study. Since the pressure and the temperature are the external variables in DSC, the specific Gibbs free energy is used as thermodynamic potential. It depends on temperature, stress and a set of internal state variables to represent the microstructure of the material on a phenomenological basis. The temperature- and internal variable-induced changes in the Gibbs free energy are approximated by a Taylor series up to second order terms. As a substantial result of this work, closed-form expressions for the dynamic calorimetric response due to harmonic temperature perturbations and the frequency-dependent complex heat capacity are derived. The theory allows a physical interpretation of the complex heat capacity and its underlying phenomena and is in accordance with experimental observations from literature. [Copyright &y& Elsevier]

Abstract: The compositional variations of the fragility of lithium borate binary glasses have been investigated over a wide composition range up to 64 mol% of Li2O. The frequency dependences of the dynamic heat capacity C p(ω) above the dynamic glass transition temperature T g have been observed by Temperature-Modulated DSC. The fragility or steepness index m has been determined. The composition dependence has been discussed on the basis of the fragility model proposed by Vilgis, and it has been revealed that the trends of the fragility and the fluctuation of the coordination number of boron atom have the correlation over a wide composition range. The result indicates the origin of the fragility relates to the degree of the fluctuation of the coordination number. The formation of the 4-coordinated boron atom plays the dominant role in the fragility of the borate glassy system. [Copyright &y& Elsevier]

Abstract: In this work, we determined the Cooperative Rearranging Region (CRR) average sizes at the glass transition temperature according to Donth’s approach. From Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamical Mechanical Analysis (DMA) investigations, the CRR average size has been estimated for drawn poly(ethylene terephthalate) (PET) with various draw ratios ranging from λ =1 to λ =4. We show that the CRR size becomes anisotropic as a function of a specific molecular orientation induced by drawing effect. [Copyright &y& Elsevier]

Abstract: Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The properties of nanocomposites may vary between those of a simple mixture of independent components and those of a system, where specific interfacial interactions between the constituting parts lead to ‘new’ properties. Depending on the type of the nanoparticles filled into the matrix, the resulting properties might be closer to one or to the other extreme. We used temperature modulated differential scanning calorimetry (TMDSC) to investigate a matrix of the oligomer diglycidyl ether of bisphenol A (DGEBA) filled either with SiO2- or Al2O3-nanoparticles. The dependence of the complex specific heat capacity () on the concentration of nanoparticles shows a clear difference between the two systems as far as the glass transition of the oligomer is concerned. The SiO2 composite seems to behave more like a simple mixture, whereas the Al2O3 composite shows ‘new’ properties. [Copyright &y& Elsevier]

Abstract: Phase change materials (PCM) provide thermoregulation originating from the latent heat exchanged during melting or crystallisation. Linear hydrocarbons have weak interactions, but high symmetry, providing an effective quantity of latent heat over the most acceptable temperature range for applications. The ability to both melt and crystallise over a narrow range is made complex by nucleation, polymorphism and the kinetic nature of these changes. Differential scanning calorimetry (DSC), optical microscopy and temperature modulated DSC (TMDSC) was used to study the melting of n-eicosane. This PCM has a low degree of supercooling and conversion to the most stable crystalline state (triclinic) that occurs rapidly from a metastable phase (rotator) state on cooling. TMDSC revealed a small, yet similar degree of thermodynamic reversibility in the melting of each of the crystalline phases. [Copyright &y& Elsevier]

Abstract: The temperature-modulated differential scanning calorimetry (TMDSC) responses during cure of both epoxy/aromatic amine and dicyanate ester/polycyanurate systems are modeled using chemical reaction kinetics with diffusion control. Physical aging effects are incorporated into the model using the Tool–Narayanaswamy–Moynihan (TNM) equation. We investigate the assumption that the mobility factor, which may be obtained from experimental temperature-modulated differential scanning calorimetry reversing heat flow data, is related to the diffusion factor for the two systems. [Copyright &y& Elsevier]

Abstract: The compositions of a series of copolyesters of ethylene- and trimethylene- terephthalate were determined by NMR. The values of randomness parameter revealed these copolyesters were random copolymers with average-number sequence lengths varied from 1 to 10. These copolyesters were investigated using temperature-modulated differential scanning calorimeter (TMDSC) and wide angle X-ray diffractometer (WAXD). The crystallization behavior was evidenced from the non-isothermal DSC thermograms and WAXD patterns. The crystallization rate and the intensity of diffraction peaks decrease with increasing the minor co-monomer content. The copolyester with equal amounts of monomers is still crystallizable even though the average sequence length is only 2.0, and its WAXD pattern is quite different from those of homopolymers. In the melting study, three distinct peaks of reversing melting were observed. Two peaks in the high temperature side are due to remelting of the recrystallized crystals formed during the heating scan, whereas the highest temperature peak is attributed to the melting of the crystals that are formed in relatively high temperature. The results of WAXD and TMDSC support the mechanism of melting-recrystallization-remelting for the multiple melting behaviors. [Copyright &y& Elsevier]

Abstract: The crystallization and melting process of poly(l-lactic acid), PLLA, is investigated by temperature modulated differential scanning calorimetry, TMDSC. The sample is cooled from the melt to different temperatures and the crystallization process is followed by subjecting the material to a modulated quasi-isothermal stage. From the average component of the heat flow and the application of the Lauritzen–Hoffman theory two crystallization regimes are identified with a transition temperature around 118°C. Besides, the oscillating heat flow allows calculating the crystal growth rate via the model proposed by Toda et al., what gives, in addition, an independent determination of the transition temperature from modulated experiments. Further, the kinetics of melting is studied by modulated heating scans at different frequencies. A strong frequency dependence is found both in the real and imaginary part of the complex heat capacity in the transition region. The kinetic response of the material to the temperature modulation is analyzed with the model proposed by Toda et al. Finally, step-wise quasi-isothermal TMDSC was used to investigate the reversible surface crystallization and melting both on cooling and heating and a small excess heat capacity is observed. [Copyright &y& Elsevier]

The effect of thermal history on morphology, melting and crystallisation behaviour of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated by using differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC) and hot stage optical microscopy (HSOM). Various thermal histories were imparted by crystallisation with different continuous and modulated cooling techniques that involve cool–heat and cool–isothermal segments. The subsequent melting behaviour revealed that all samples experienced secondary crystallisation during heating and the extent of secondary crystallisation was varied depending on the treatment. PHB samples crystallised under slow to moderate continuous cooling rates were found to exhibit double melting behaviour due to melting of DSC scan-induced secondary crystals, but to a lesser extent. Samples subjected to a fast cooling rate gave amorphous PHB, while considerable secondary crystallisation/annealing took place under modulated cooling conditions. Additionally, the effect of melting conditions was also investigated by applying various continuous and modulated programs. The overall melting behaviour was rationalised in terms of recrystallisation and/or annealing of crystals. Interestingly, the samples analysed by temperature modulation programs showed a broad exotherm before the melting peak in the non-reversing curve and a multiple melting reversing curve, verifying that the melting–recrystallisation and remelting process is also operative. HSOM studies supported that the radial growth rate of the PHB spherulites was significantly varied upon the crystallisation conditions. [Copyright &y& Elsevier]

The melting and crystallization of gel-spun, ultrahigh molar mass polyethylene (UHMM-PE) fiber is analyzed with both, standard differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) to identify the differences to extended-chain crystals of polyethylene. The analyzed samples were studied before with respect to their molecular mobility, morphology, and crystal and phase structure. The UHMM-PE contains a mobile, oriented mesophase and only few folded chains. The truly amorphous fraction is about 3%. Reversing melting and crystallization is observed for these fibers. It increases in amount on recrystallization after melting. Difficulties in measuring the original fibers arose from the shrinkage of the fibers and a resulting deformation of the sample pan. The new data are compared to literature information on other polyethylenes and linked to reversible melting of decoupled segments of the polymer chains contained in small, nanometer-size phases within the crystalline phase and the oriented-intermediate fractions. [Copyright &y& Elsevier]

This paper provides an analysis of contributions to the apparent, reversing heat capacity when measured by temperature-modulated differential scanning analysis (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur. To deconvolute the data of a TMDSC scan into a total and reversing part, it is common practice to use the sliding averages and the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces erroneous reversing contributions which are detailed by experiment and simulation. Unless the response to the temperature modulation is linear, the total heat-flow rate is stationary, and the transition is truly reversible and occurs only once during the temperature scan, one cannot expect a true deconvolution of total and reversible effects. In the presence of multiple, irreversible transitions within a modulation period, however, each process involving latent heat can increase the modulation amplitude, as demonstrated by computer-simulation of polymer melting. As a result, the multiple transitions may give erroneously high latent heats when integrating the apparent reversing heat capacity with respect to temperature. [Copyright &y& Elsevier]

Linear, flexible macromolecules are long recognized as phase structures limited to micrometer and nanometer dimensions with covalent bonds crossing the interfaces. This special, usually non-equilibrium structure leads to unique properties and a multitude of changes for different thermal and mechanical histories. Analyses that enable the study of these properties are temperature-modulated calorimetry and related techniques which allow the separation of equilibrium and non-equilibrium responses. Research on these topics is reviewed and combined to a model for the nanophases. The new approach to the complex nanophase systems yields a better understanding of the relationship between structure and thermodynamic properties. Special emphasis is placed on the size and surface effects on the glass and melting transitions, the development of rigid-amorphous phases, and the reversible melting within the globally metastable structure. [Copyright &y& Elsevier]

Micro-thermal analysis (μTA™) and temperature-modulated differential scanning calorimetry (TMDSC) are emerging as powerful instruments for identifying the existence and quantities of phases in multi-component systems, as well as interfacial properties. In this study, these two complimentary techniques are utilised to probe the interphase behaviour of a polycarbonate/acrylonitrile–styrene–acrylate (PC/ASA) blend as they develop during injection molding. Micro-thermal analysis revealed that parts manufactured at high injection time, pack pressure and melt temperature show a densely packed bulk morphology, a significant amount of particle agglomeration as well as the formation of styrene–acrylonitrile/PC (SAN/PC) interphases. TMDSC qualitatively and quantitatively characterized the PC/ASA''s multi-phase morphology and its interfacial properties both before and after injection molding, indicating a greater amount of PC entering the interphase than SAN. [Copyright &y& Elsevier]

For semicrystalline polymers the observed relaxation strength at glass transition is often significantly smaller than expected from the non-crystalline fraction. This observation leads to the introduction of a rigid amorphous fraction (RAF) which does not contribute to the heat of fusion or X-ray crystallinity nor to the relaxation strength at glass transition. The RAF is non-crystalline and in a glassy state at temperatures above the common glass transition. Complex heat capacity in the high frequency limit allows for the measurement of base-line heat capacity also at temperatures above the glass transition. From that the temperature and time dependence of the RAF can be obtained. For PC, PHB and syndiotactic polypropylene (sPP) it is possible to study the creation and disappearance of the RAF in situ during isothermal crystallization and on stepwise melting. If crystallization is not limited by the stability (melting point) of the crystals to be formed the total RAF is created during the isothermal crystallization. Simultaneously with the melting of the smallest crystals the RAF disappears. For these polymers vitrification and devitrification of the non-crystalline material detected as the RAF at glass transition is structural (conformational) and not temperature induced. The formation of the last growing crystals, which melt first, are responsible for the vitrification of the amorphous material around them and, consequently, by that they limit their own growth. [Copyright &y& Elsevier]

Temperature-modulated differential scanning calorimetric (TMDSC) measurements on nascent ultrahigh molecular mass polyethylene (UHMMPE) in scanning as well as quasi-isothermal mode are presented. From these measurements different processes, which contribute to the modulated heat flow in the pre-melting region, both exothermic and endothermic in character, can be separated. One of them only occur on the first heating of the nascent material. Analysis of quasi-isothermal measurements, performed between 90 and 130 °C, show that there are two slow (exponential) relaxation processes with time constants of 2–5 and 10–100 min, respectively. One, exothermic in character, seems to be connected with irreversible structural changes (crystal thickening and ordering). The low activation energy (ca 40 kJ mol−1) points to a chain diffusion process rather than melting and crystallization. The other process (activation energy 60 kJ mol−1) seems to be endothermic. In the melting region, a slow (>100 min) 3rd relaxation process with high activation energy (300 kJ mol−1) can be separated. [Copyright &y& Elsevier]

The reversing heat capacity of polystyrene has been measured in the glass transition region as a function of frequency by temperature-modulated DSC using infra-red light for the modulation. The mean temperature was controlled by the calorimeter operating in the standard DSC mode. The additional power transferred to the specimens is obtained by infra-red diodes with their mean power controlled by a pulse-width modulation method. This method allows to synthesize sinusoidal temperature-profiles with negligible distortion with frequencies of up to 0.125 Hz. The experiments were carried out using multi-frequency temperature-profiles composed by superposition of four sinusoidal modulations of periods of 243, 81, 27, and 9 s, which cover the frequency range from the 1st to the 27th harmonic. To study the kinetics in the glass transition region, the thermal history was produced by cooling the samples at different rates. The results and the advantages of the new method are discussed and compared to a series of less-precise separate single-frequency analyses. [Copyright &y& Elsevier]

Linear, flexible macromolecules have long been recognized as being distributed between different metastable phases limited to micrometer and nanometer dimensions with their strong, covalent bonds crossing the phase boundaries. This structure leads to special properties and a multitude of changes are caused by differing thermal and mechanical histories. Temperature-modulated differential scanning calorimetry (TMDSC) and related thermal analysis techniques which can separate equilibrium and non-equilibrium responses within a sample are ideal for the analysis of such systems. A surprising observation in the last 5 years has been that there are some local, reversible ordering and disordering processes within this overall metastable aggregate. Three different reversible processes with latent heats have been identified and will be discussed using the example of polyethylene crystals: (1) The formation of larger concentrations of defects within the crystals. (2) The melting of small, paraffin-like crystals existing within the metastable arrangement. (3) The reversible, partial melting of chains at high-temperature which avoids molecular nucleation. [Copyright &y& Elsevier]

Heat capacity of semi-crystalline polymers shows frequency dependence not only in the glass transition range. Also above glass transition and below melting temperature a frequency dependent heat capacity can be observed. The asymptotic value of heat capacity at high frequencies equals base-line heat capacity while the asymptotic value at low frequencies yield information about reversing melting. For polycarbonate (PC), poly(3-hydroxybutyrate) (PHB) and syndiotactic polypropylene (sPP) the asymptotic value at high frequencies can be measured by temperature-modulated DSC (TMDSC). For polycaprolactone (PCL) and sPP the frequency dependence of heat capacity can be studied in quasi-isothermal TMDSC experiments. The heat capacity spectra were obtained from single measurements applying multi-frequency perturbations (spikes in heating rate) like in StepScan™ DSC or rectangular temperature–time profiles. Actually, the dynamic range of commercial TMDSC apparatuses is limited and only a small part of the heat capacity spectrum can be measured by TMDSC. Nevertheless, comparison of measured base-line heat capacity with expected values from mixing rules for semi-crystalline polymers yield information about the formation (vitrification) and disappearance (devitrification) of the rigid amorphous fraction (RAF). For PC and PHB the RAF is established during isothermal crystallization while for sPP only a part of the RAF is vitrified during crystallization. Devitrification of the RAF seems to be related to the lowest endotherm. [Copyright &y& Elsevier]

The heat capacities of sapphire (Al2O3) and sodium chloride (NaCl), have been measured to establish the accuracy and precision of two different temperature-modulated differential scanning calorimeters operated in diverse multi-frequency modes. The calorimeters have then been applied to find the apparent, reversing heat capacity of polystyrene as a function of frequency in the glass transition region. The first modulation mode consisted of a series of linear heating and cooling segments and produced four harmonics with practically equal temperature amplitudes (1st, 3rd, 5th, and 7th), one of lower amplitude (9th), and almost negligible higher harmonics. The second modulation mode is a rather sharp step ending in an isotherm or slow temperature-decrease and leads to a controlled spike in the heat-flow rate response which produces Fourier components of similar amplitudes for all harmonics of the rates of changes of temperature. The apparent, reversing heat capacity is evaluated from the amplitudes of the heat-flow rates and the corresponding sample temperatures or heating-rates. A time-constant or calibration constant which accounts for thermal conductivities and resistances within the calorimeters can be evaluated from the different harmonics of each run. Measurements in the glass transition region have a slow response of the sample. They are evaluated by separating the sample effect from the calorimeter response which can be extrapolated from data gained outside the transition. One measurement is thus sufficient for the evaluation of the frequency dependence of the heat capacity in the glass transition region. [Copyright &y& Elsevier]

The basic principle of heat transfer in temperature-modulated differential scanning calorimetry (TMDSC) and its influence on the measured signals is presented. Fundamentals of transfer theory are given within the framework of linear response. On this basis different calibration methods are suggested which enable to correct for the influence of heat transfer on the measured (effective) complex heat capacity in TMDSC. It is shown, that the complex calibration function is the reciprocal transfer function, which in turn is the product of the instrumental transfer function and the transfer function of the sample and its thermal connection to the TMDSC. Methods are given how to determine the transfer functions and how to correct the measured complex heat capacity properly. [Copyright &y& Elsevier]

In the first part of this paper we have discussed the influence of heat transfer in temperature-modulated differential scanning calorimetry (TMDSC) and its influence on the measured signals, in particular, magnitude and phase angle of effective complex heat capacity. Fundamentals of transfer theory were given within the framework of linear response. On this basis different calibration methods were suggested which enable to correct the influence of heat transfer on the measured (effective) complex heat capacity in TMDSC. In the second part of the paper, we apply the different calibration methods to a single set of experimental data to compare the results with the expected ones, and to draw conclusion concerning the calibration method in question and the frequency range where the calibration algorithm works. The example has shown that the more simple calibration procedures lead to nearly the same uncertainties of the results in everyday measurements as the more sophisticated “third order” calibration procedure does. However, we recommend the “third order” calibration procedure in all cases where the heat transfer conditions could change during the measurement. [Copyright &y& Elsevier]

Abstract: The goal is to quantify the respective influence on relaxation dynamics of the molecular orientation and of the crystallinity in uniaxially drawn polyethylene terephthalate and poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) films, the last one presenting a lower ability to crystallize under drawing. Combining Temperature Modulated Differential Scanning Calorimetry and Dynamical Mechanical Analysis investigations we evidenced that cooperativity length scale becomes anisotropic with the molecular orientation induced by drawing. [Copyright &y& Elsevier]