2 3 Journal of Thermal Analysis and Calorimetry An International Forum for Thermal Studies Applications of some thermo-analytical techniques to glasses and polymers (original) (raw)
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Temperature Modulated Calorimetry of Glassy Polymers and Polymer Blends
Macromolecules, 1998
The theoretical modeling of the relaxation behavior of polymers in the glass transition region, advocated by Moynihan and co-workers, has been used to analyze the heat flow and the relaxation of polymer systems during isothermal modulated DSC experiments in the glass transition region. An analytic solution for the frequency dependent fictive temperature is obtained, which takes a particularly simple form in the high-frequency region. The maximal phase lag of the fictive temperature T f is π/2, where the exponent of the stretched-exponential characterizing the enthalpy relaxation, , is on the order of 0.1-0.7. The corresponding maximal phase lag in the heat flow is much smaller, on the order of 2-5 deg. It is once more iterated that, as observed long ago by Birge and Nagel, the loss heat capacity corresponds to the entropy production due to a redistribution of energy over the heat baths. The possibility of using specific-heat spectroscopy as a tool to determine miscibility in polymer blends whose constituents possess similar glass transition temperatures is discussed. Compared to conventional differential scanning calorimetry, the resolution is enhanced. However, in many cases an unambiguous conclusion still requires additional enthalpy relaxation of the blend induced by physical aging in the glassy state.
Abstract Using the thermal analyzer STA 449 F3 Jupiter (NETZSCH – Germany), the effect of the conditions of calibration and experiment on the values of the enthalpies of the polymorphous transition and melting of КNO3, as well as the enthalpies of melting and, respectively, the degree of crystallinity of poly(ethylene oxide)(PEO) used a model solutions for DSC analyses were studied. For comparison, similar data were obtained for a number of commercial crystallizing polymers (PP 6631, Hostaflon 1502, etc.). The thermo physical characteristics obtained by several types of DSC curve calibration by enthalpy are discussed: 1) by the enthalpy of melting of standardized metals in corundum crucibles; 2) by the specific heat capacity of sapphire in corundum crucibles and 3) by the specific heat capacity of sapphire in Pt crucibles. The following experimental conditions were varied: heating rate – 5, 10 and 20 deg/min; crucibles – corundum or platinum; gaseous medium – air (static) or nitroge...
Polymer International, 2016
Thermal analysis has been utilized in polymer research for a long time and its usefulness is widely recognized. High‐performance commercial instruments have driven significant progress in the thermal studies of polymers. On the other hand, new experimental instruments have been developed in laboratories as well. In this paper attention is paid to the latter category. The laboratory‐made instrument focused on the target material and/or phenomena provides data that are not available from other techniques. Experiments using the temperature modulation technique, which has been successfully utilized in laboratory‐made instruments, are introduced in this paper. The temperature modulation technique reveals a new aspect of temperature useful for studies of material properties. © 2016 Society of Chemical Industry
Thermal properties of polymers by non-steady-state techniques
Polymer Testing, 2007
The nature of the molecular structure of polymers makes the properties of such materials markedly temperature dependant. Modelling heat transfer under steady-state or transient conditions is of fundamental importance in engineering design as well as for the tailoring of thermal and mechanical behaviour of materials. Thermal conductivity, thermal diffusivity and specific heat, namely the thermal properties, are the three most important physical properties of a material that are needed for heattransfer calculations. Nowadays, several different techniques for the determination of the thermal diffusivity and thermal conductivity may be found in the literature. Recently, transient techniques have become the preferable way for measuring thermal properties of materials. In this work, two absolute and non-steady-state methods are employed in the experimental determination of thermal properties of some selected polymers: the laser flash technique and the hot-wire technique. In the hotwire technique, samples were prepared from the extrusion process in the shape of a rectangular parallelepiped, with the molten mass for each sample being approximately 1500 g. Thermal conductivity, thermal diffusivity and specific heat were simultaneously determined from the same experimentally determined thermal transient. In the laser flash technique, disc shaped samples were prepared, either by hot pressing approximately 50 mg of material, or by cutting the discs from long cylindrical bars. In this technique, only the thermal diffusivity is determined from the experimentally determined thermal transient. The thermal conductivity was derived from the thermal diffusivity with the knowledge of the bulk density and the specific heat. Specific heat was experimentally determined using a modulated differential scanning calorimeter, and the density was obtained from the PVT curve at each temperature. Since the sample mass ratio between both techniques is approximately 3 Â 10 4 , and the speed of the cooling process may generate different morphologies, this phenomenon may be partially responsible for any discrepancy between both techniques for a specific polymer. Experimental results obtained by both techniques are checked against each other, as well as, when possible, with data found in literature.
Short Review on Thermal and Mechanical Properties of Polymers
Journal of emerging technologies and innovative research, 2019
In recent years the importance about the use of the polymeric materials in various fields has been growing fastly.The thermal and mechanical properties plays a important role in determining their glass transition temperature (Tg), degradation temperature, melting temperature, crystallinity, tensile strength, stress, elongation at break, stiffness, hardness, toughness, embrittlement etc. The aim of this review is to understand how these properties changes with the different preparation methods, reaction conditions including temperature, pressure and catalyst. The current review also highlighted on characterization techniques for measurements of these properties.
Journal of Thermal Analysis, 1996
The results from temperature modulated DSC in the glass transition region of amorphous and semicrystalline polymers are described with the linear response approach. The real and the imaginary part of the eomplex heat capacity are discussed. The findings are compared with those of dielectric spectroscopy. The frequency dependent glass transition temperature can be fitted with a VFT-equation. The transition frequencies are decreased by 0.5 to 1 orders of magnitude compared to dielectric measurements. Cooling rates from standard DSC are transformed into frequencies. The glass transition temperatures are also approximated by the VFT-fit from the temperature modulated measurements. The differences in the shape of the curves from amorphous and semicrystalline samples are discussed.
Differential scanning calorimetry (DSC) of semicrystalline polymers
Analytical and Bioanalytical Chemistry, 2009
Differential scanning calorimetry (DSC) is an effective analytical tool to characterize the physical properties of a polymer. DSC enables determination of melting, crystallization, and mesomorphic transition temperatures, and the corresponding enthalpy and entropy changes, and characterization of glass transition and other effects that show either changes in heat capacity or a latent heat. Calorimetry takes a special place among other methods. In addition to its simplicity and universality, the energy characteristics (heat capacity C P and its integral over temperature T-enthalpy H ), measured via calorimetry, have a clear physical meaning even though sometimes interpretation may be difficult. With introduction of differential scanning calorimeters (DSC) in the early 1960s calorimetry became a standard tool in polymer science. The advantage of DSC compared with other calorimetric techniques lies in the broad dynamic range regarding heating and cooling rates, including isothermal and temperature-modulated operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of DSCs. Rates as low as 1 μK s −1 are possible and at the other extreme heating and cooling at 1 MK s −1 and higher is possible. The broad dynamic range is especially of interest for semicrystalline polymers because they are commonly far from equilibrium and phase transitions are strongly time (rate) dependent. Nevertheless, there are still several unsolved problems regarding calorimetry of polymers. I try to address a few of these, for example determination of baseline heat capacity, which is related to the problem of crystallinity determination by DSC, or the occurrence of multiple melting peaks. Possible solutions by using advanced calorimetric techniques, for example fast scanning and high frequency AC (temperature-modulated) calorimetry are discussed.
Identification of temperature-dependent thermal properties of solid materials
Journal of The Brazilian Society of Mechanical Sciences and Engineering, 2008
This work proposes an experimental technique for the simultaneous estimation of temperature-dependent thermal diffusivity, α, and thermal conductivity, λ, of insulation materials. The thermal model used considers a transient one-dimensional heat transfer problem. The determination of these properties is done by using the principle of the Mixed technique. In this technique two objective functions are defined, one in the frequency domain and the other in the time domain. The objective function in the frequency domain is based on the square difference between experimental and calculated values of the phase angle, while the other objective function is the least square error function of experimental and calculated signals of temperature. The properties α and λ are obtained by using an experimental apparatus that basically consists of a Polyvinyl Chloride (PVC) sample exposed to different temperatures inside an oven. The temperature inside the oven is controlled by a PID temperature controller. The properties α and λ were estimated for 7 (seven) points of average temperature in a range from 20 ºC to 66 ºC. The properties were determined with an additional heating of approximately 4.5 K on the frontal surface. Analyses of sensitivity, sensors location and sample dimensions were also made.
Effect of cooling rate and frequency on the calorimetric measurement of the glass transition
2005
The glass transition of thermoplastics of different polydispersity and thermosets of different network structure has been studied by conventional differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC). The cooling rate dependence of the thermal glass transition temperature T g measured by DSC, and the frequency dependence of the dynamic glass transition temperature T a measured by TMDSC have been investigated. The relation between the cooling rate and the frequency necessary to achieve the same glass transition temperature has been quantified in terms of a logarithmic difference DZlog 10 [jqj]Klog 10 (u), where jqj is the absolute value of the cooling rate in K s K1 and u is the angular frequency in rad s K1 necessary to obtain T g (q)ZT a (u). The values of D obtained for various polymers at a modulation period of 120 s (frequency of 8.3 mHz) are between 0.14 and 0.81. These values agree reasonably well with the theoretical prediction [Hutchinson JM, Montserrat S. Thermochim Acta 2001;377:63 [6]] based on the model of Tool-Narayanaswamy-Moynihan with a distribution of relaxation times. The results are discussed and compared with those obtained by other authors in polymeric and other glass-forming systems.
Thermal lens scanning of the glass transition in polymers
Journal of Applied Physics, 2001
In this article we discuss the use of the thermal lens technique for investigating the thermal properties of polymers as a function of temperature. It is also discussed how the experimentally determined thermal lens parameters can be used to locate the glass transition in polymers. The methodology is tested using a solution casted films of poly͑vinyl chloride͒ as a testing sample. A comparison with conventional differential scanning calorimetry data is made. It is proposed that the current transient thermal lens methodology, with minor changes in its experimental configuration, could be adapted to develop a new methodology called differential thermal lens scanning especially designed for the investigation of the phase transitions in polymers. It is shown that this new methodology could be equally used for the measurement of the thermal expansion coefficient, above and below the glass transition.