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Abstract  

The thermally induced phase separation behavior of hydrogen bonded polymer blends, poly(n-hexyl methacrylate) (PHMA) blended with poly(styrene-co-vinyl phenol) (STVPh) random copolymers having various vinyl phenol contents, was studied by temperature modulated differential scanning calorimetry (TMDSC).The enthalpy of phase separation was determined to be about 0.5 cal g–1 for one of the blends. A phase diagram was constructed from the TMDSC data for one of the blends. The kinetics of phase separation was studied by determining the phase compositions from the glass transition temperatures of quenched samples after phase separation. Subsequently, the phase separated samples were annealed at temperatures below the phase boundary to observe the return to the homogeneous state.

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Abstract  

The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on the symmetry of the twin calorimeters. This symmetry is of particular importance for the temperature-modulated DSC (TMDSC) since positive and negative deviations from symmetry cannot be distinguished in the most popular analysis methods. Three different DSC instruments capable of modulation have been calibrated for asymmetry using standard non-modulated measurements and a simple method is described that avoids potentially large errors when using the reversing heat capacity as the measured quantity. It consists of overcompensating the temperature-dependent asymmetry by increasing the mass of the sample pan.

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Abstract  

The determination of heat capacity data with sawtooth-type, temperature-modulated differential scanning calorimetry is analyzed using the Mettler-Toledo 820 ADSC™temperature-modulated differential scanning calorimeter (TMDSC). Heat capacities were calculated via the amplitudes of the first and higher harmonics of the Fourier series of the heat flow and heating rates. At modulation periods lower than about 150 s, the heat capacity deviates increasingly to smaller values and requires a calibration as function of frequency. An earlier derived correction function which was applied to the sample temperature-controlled power compensation calorimeter enables an empirical correction down to modulation periods of about 20 s. The correction function is determined by analysis of the higher harmonics of the Fourier transform from a single measurement of sufficient long modulation period. The correction function reveals that the time constant of the instrument is about 5 s rad−1 when a standard aluminum pan is used. The influence of pan type and sample mass on the time constant is determined, the correction for the asymmetry of the system is described, and the effect of smoothing of the modulated heat flow rate data is discussed.

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Abstract  

A newly developed Micro-Thermal Analyzer affords images based on thermal properties such as thermal conductivity, thermal diffusivity, and permits localized thermal analyses on samples of a square micrometer area by combining the imaging ability of the atomic force microscope and the thermal characterization ability of temperature-modulated differential scanning calorimetry. Since thermal penetration depth depends on frequency, one can obtain depth profiles of thermal conductivity and thermal diffusivity by varying the modulation frequency. Also, the analyzer can be used to characterize phase-transition temperatures, such as glass and melting transitions, of small sample regions with a precision of about ±3 K. Heating rates can be varied between 1 and 1500 K min–1. Modulation frequencies can be applied in the range from 2 to 100 kHz. We applied this new type of instrument to characterize microscopic thermal and structural properties of various polymer systems. The operation principles of the instrument are described, application examples are presented, and the future of the technique is discussed.

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Abstract  

The measured signal of the temperature-modulated differential scanning calorimetry (TMDSC) is discussed in the case of polymer melting. The common data evaluation procedure of TMDSC-signals is the Fourier analysis. The resulting information is the amplitude and the phase shift of the first harmonic of the periodic heat flow component. It is shown that this procedure is not sufficient for quantitative discussions if deviations from the symmetric curve shape occur in the measured heat flow curves. For polymer melting it is demonstrated that asymmetric curves will be measured if the experimental temperature amplitude is too large. In this paper a data evaluation method is presented, which is based on the Fourier transform of the measured curves. The peaks of the first and second harmonics in the resulting spectra are used for the analysis of the asymmetry of the measured curves. In the case of polymer melting this analysis yields the maximum temperature amplitude which follows a correct linear data evaluation. This maximum temperature amplitude depends on the material.

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Journal of Thermal Analysis and Calorimetry
Authors: Yanni Qi, Jian Zhang, Shujun Qiu, Lixian Sun, Fen Xu, Min Zhu, Liuzhang Ouyang, and Dalin Sun

Abstract  

Polyaniline/NiO (PANI/NiO) composites were synthesized by in situ polymerization at the presence of HCl (as dopant). FTIR, TEM and XRD were used to characterize the composites. Thermogravimetry (TG)–mass spectrometer (MS) and temperature modulated differential scanning calorimetry (TMDSC) were used to study the thermal stability, decomposition and glass transition temperature (T g) of the composites, respectively. FTIR and XRD results showed that NiO nanoparticles connected with PANI chains in the PANI/NiO composites. TEM results exhibited that the morphologies of PANI/NiO composites were mostly spherical, which were different from the wirelike PANI. TG–MS curves indicated that the products for oxidative degradation of both PANI and PANI/NiO composite were H2O, CO2, NO and NO2. TG curves showed that with NiO contents increased in PANI/NiO composites, thermal stability of PANI/NiO composites increased firstly and then decreased when the NiO content was higher than 66.2 wt%. T g of PANI/NiO composites also increased from 163.19 to 252.36 °C with NiO content increasing from 0 to 50 wt%, and then decreased with NiO content increasing continuously.

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Journal of Thermal Analysis and Calorimetry
Authors: Li-Fang Song, Chun-Hong Jiang, Jian Zhang, Li-Xian Sun, Fen Xu, Yun-Qi Tian, Wan-Sheng You, Zhong Cao, Ling Zhang, and Dao-Wu Yang

Abstract  

A novel two-dimensional metal organic framework MgBTC [MgBTC(OCN)2·2H2O, where BTC = 1,3,5-benzenetricarboxylate] has been synthesized solvothermally and characterized by single crystal XRD, powder XRD, FT-IR spectra. The low-temperature molar heat capacities of MgBTC were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 190 to 350 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range. The thermodynamic parameters of MgBTC such as entropy and enthalpy relative to reference temperature of 298.15 K were derived based on the above molar heat capacities data. Moreover, the thermal stability and decomposition of MgBTC was further investigated through thermogravimetry (TG)-mass spectrometer (MS). Four stages of mass loss were observed in the TG curve. TG-MS curve indicated that the products of oxidative degradation of MgBTC are H2O, N2, CO2 and CO. The powder XRD showed that the mixture after TG contains MgO and graphite.

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Abstract  

Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in a commercial size twin-screw reactive extrusion system. Temperature-modulated differential scanning calorimetry (TMDSC) was used to evaluate the effect of the chain extension process on the thermal transitions and crystallinity of R-PET. Reactive extruded recycled PET (RER-PET) samples were tested based on different PMDA concentration and reactive extrusion residence times. The glass transition temperature (T g) did not show a significant change as a function of PMDA addition or the extrusion residence time. Melting temperature (T m) and crystallisation temperature (T c) decreased with increasing PMDA concentration and with increasing extrusion residence time. RER-PET samples showed double melting peaks, it is believed that different melting mechanism is the reason behind this phenomenon. The crystallinity of RER-PET samples is lower than that of R-PET. RER-PET samples at constant PMDA concentration showed a decrease in crystallinity with increasing extrusion residence time. Results suggest that the reactive extrusion process is more dependent on PMDA concentration rather than reactive extrusion process residence time.

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Abstract  

The low-temperature molar heat capacities of CoPc and CoTMPP were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 223 to 413 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range for CoPc. However, a structural change was found to be nonreversible for CoTMPP in the temperature range of 368–403 K, which was further validated by the results of IR and XRD. The molar enthalpy ΔH m and entropy ΔS m of phase transition of the CoTMPP were determined to be 3.301 kJ mol−1 and 8.596 J K−1 mol−1, respectively. The thermodynamic parameters of CoPc and CoTMPP such as entropy and enthalpy relative to reference temperature 298.15 K were derived based on the above molar heat capacity data. Moreover, the thermal stability of these two compounds was further investigated through TG measurements. Three steps of mass loss were observed in the TG curve for CoPc and five steps for CoTMPP.

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Abstract  

Zinc formate dihydrate has been synthesized and characterized by powder X-ray diffraction, elemental analysis, FTIR spectra and thermal analysis. The molar heat capacity of the coordination compound was measured by a temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 200 to 330 K for the first time. The thermodynamic parameters such as entropy and enthalpy vs. 298.15 K based on the above molar heat capacity were calculated. The thermal decomposition characteristics of this compound were investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG curve showed that the thermal decomposition occurred in two stages. The first step was the dehydration process of the coordination compound, and the second step corresponded to the decomposition of the anhydrous zinc formate. The apparent activation energy of the dehydration step of the compound was calculated by the Kissinger method using experimental data of TG analysis. There are three sharply endothermic peaks in the temperature range from 300 to 650 K in DSC curve.

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