of experimental techniques are employed to characterize physical and thermal
properties of poly(lactic acid), PLA. To characterize PLA in terms of molecular
mass and molecular mass distribution, size exclusion chromatography was used.
The value of the specific refractive index increment was measured by differential
refractometry. The thermal properties of semicrystalline PLA were measured
by standard and temperature-modulated differential scanning calorimetry. The
thermal stability of PLA was monitored by measuring the changes of mass using
thermogravimetric analysis. The mechanical properties of amorphous PLA were
measured by dynamic mechanical analysis and the results were discussed and
compared with DSC in the glass transition region.
Authors:E. Orozco-Guareño, A. Campos Almaraz, G. Reyes, L. López-Ureta, and A. Gonzalez-Alvarez
The thermal behavior
of hydrogels synthesized by solution polymerization between acrylamide, acrylic
acid and diglycidyl acrylate (DGA) as a crosslinking agent was investigated.
The structure of the hydrogel can be tightly controlled with the reaction
temperature. This method produces a new type of hydrogels, which exhibit well
defined structures at various scales of length simultaneously. These multi-structured
hydrogels are hydrophilic, elastic, water insoluble, and soft polymers with
an anisotropic optical response. The structure was observed by scanning electron
microscopy (SEM), polarized light microscopy (PLM) and macroscopic visualization
(CCD camera). In addition, structural transitions in the hydrogels were monitored
by temperature modulated differential scanning calorimetry (TMDSC). Severe
heating tests in an adiabatic oven were performed to analyze decomposition
of the material. Fourier transform infrared (FTIR) spectroscopy was used to
qualitatively analyze the hydrogels samples exposed to a sudden thermal treatment.
To treat data from temperature modulated differential scanning calorimetry (TMDSC) in terms of complex or reversing heat capacity
firstly one should pay attention that the response is linear and stationary because this is a prerequisite for data evaluation.
The reason for non-linear and non-stationary thermal response is discussed and its influence on complex (reversing) heat capacity
determination is shown. The criterion for linear and stationary response is proposed. This allows to choose correct experimental
conditions for any complex heat capacity measurement. In the case when these conditions can not be fulfilled because of experimental
restrictions one can estimate the influence of non-linearity and non-stationarity on measured value of complex or reversing
Melting behaviours of poly(oxytetramethylene)glycols (POTMGs) with different molar masses were investigated by temperature-modulated
differential scanning calorimetry (TMDSC) and relaxation times within the melting range were estimated from the modulation-frequency
dependence of phase angle δ. An Arrhenius plot of the relaxation times exhibited a plateau in the lower melting peak region
of POTMGs with molar masses of 1400, 1000 and 650. This plot was compared with the standard DSC curve. The apparent activation
energy was estimated from the relaxation time in the upper and lower sides of a melting temperature region: slight dependence
on the molar mass was observed for the former region whereas the maximum value was obtained for a molar mass 1400 for the
Authors:Allisson Saiter, H. Couderc, and J. Grenet
Measurements have been performed
on poly(ethylene terephthalate)glycol/montmorillonite nanocomposites with
different filler contents using differential scanning calorimetry (DSC) and
temperature modulated differential scanning calorimetry (TMDSC). According
to the strong-fragile concept proposed by Angell, we have determined the values
of the fragility index m. In a second time,
we have calculated the average size of a cooperative rearranging region (CRR) z(Tg)
at the glass transition according to the definition proposed by Solunov. However, z(Tg
is a dimensionless quantity and then only allows a comparative study between
different samples. To calculate the average number of monomer units by CRR
we have used the method developed by Donth. The results show that the presence
of montmorillonite in PETg matrice implies modifications
on structural relaxation phenomena. Furthermore, we have shown that z(Tg
and Nα values
have the same evolution in function of filler content.
The response of temperature-modulated differential scanning calorimetry (TMDSC) to irreversible crystallization of linear polymers was investigated by model calculations and compared to a number of measurements. Four different exotherms were added to a typical modulated, reversible heat-flow rate in order to simulate irreversible crystallization. It was found that the reversing heat-flow rate of the TMDSC in response to such irreversible crystallization exotherms is strongly affected by tbe shape of the transition and the phase-angle where the exotherm occurs. A comparison with the experimental data gave valuable insight into the transitions, as well as the nature of the TMDSC response which is usually limited to an analysis of the first harmonic term of the Fourier series that describes the heat-flow rate.
Authors:M. Viciosa, J. Quiles Hoyo, M. Dionísio, and J. Gómez Ribelles
Temperature modulated differential scanning calorimetry (TMDSC) is used to study the kinetics of the free radical isothermal
polymerization of triethyleneglycol dimethacrylate (TEGDMA). Azo-bis-isobutironitrile was used as initiator. The polymerization’s temperature is lower than the final glass transition temperature
of the polymer network. The measurement of the average heat flow released and the heat capacity during the reaction allows
identifying the different stages of the reaction. The presence of double peaks in the heat flow is ascribed to the autoacceleration.
The influence of temperature, measuring conditions and oxygen are described. Vitrification is detected by the drop in heat
capacity. It occurs at increasing conversion rates for increasing temperatures. After vitrification, the diffusion-controlled
Authors:A. Toda, C. Tomita, T. Arita, and M. Hikosaka
The application of a periodically modulated driving force has been examined in the melting and crystallization kinetics of
ice crystals confined in a porous media. The kinetic response of transformation gives the real and imaginary parts of the
‘apparent’ heat capacity obtained with a temperature modulated differential scanning calorimetry (TMDSC). Based on a modelling
of the kinetics, the detailed examination of the frequency dispersion and its dependence on underlying heating/cooling rate
enables us to evaluate the transformation rate and the dependence of the rate coefficient on the driving force, i.e. the degree
of supercooling or superheating. The experimental results indicate that the transformation processes are limited by heat diffusion
from the growth interface of each crystallite to surroundings.
A novel metal-organic frameworks [Cu2(OH)(2,2′-bpy)2(BTC) · 2H2O]n (CuMOF, BTC = benzene-1,3,5-tricarboxylic acid, 2,2′-bpy = 2,2′-bipyridine) has been synthesized hydrothermally and characterized
by single crystal XRD, FT-IR spectra. The low-temperature molar heat capacities were measured by temperature modulated differential
scanning calorimetry (TMDSC) for the first time. The thermodynamic parameters 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 and the decomposition
mechanism of CuMOF were investigated by TG-MS (thermogravimetry-mass spectrometer). A four-stage mass loss was observed in
the TG curve. MS curve indicated that the gas products for oxidative degradation of CuMOF were H2O, CO2, NO and NO2.
Authors:Li-Fang Song, Cheng-Li Jiao, Chun-Hong Jiang, Jian Zhang, Li-Xian Sun, Fen Xu, Qing-Zhu Jiao, Yong-Heng Xing, F. L. Huang, Yong Du, Zhong Cao, Fen Li, and Jijun Zhao
One-three-dimensional metal-organic frameworks Mg1.5(C12H6O4)1.5(C3H7NO)2 (MgNDC) has been synthesized solvothermally and characterized by single crystal XRD, powder XRD, FT-IR spectra. The low-temperature molar heat capacities of MgNDC were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 205 to 470 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range. The thermodynamic parameters of MgNDC 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 MgNDC was further investigated through thermogravimetry (TG)–mass spectrometer (MS). Three stages of mass loss were observed in the TG curve. TG–MS curve indicated that the oxidative degradation products of MgNDC are mainly H2O, CO2, NO, and NO2.