Characterisation techniques thermal analysis

The procedures of measuring changes in some physical or mechanical property as a sample is heated, or alternatively as it is held at constant temperature, constitute the family of thermoanalytical methods of characterisation. A partial list of these procedures is differential thermal analysis, differential scanning calorimetry, dilatometry, thermogravimetry. A detailed overview of these and several related techniques is by Gallagher (1992). 

Thermogravimetric analysis has also been used in conjunction with other techniques, such as differential thermal analysis (DTA), gas chromatography, and mass spectrometry, for the study and characterisation of complex materials such as clays, soils and polymers.35... 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

Several methods have been developed over the years for the thermochemical characterisation of compounds and reactions, and the assessment of thermal safety, e.g. differential scanning calorimetry (DSC) and differential thermal analysis (DTA), as well as reaction calorimetry. Of these, reaction calorimetry is the most directly applicable to reaction characterisation and, as the heat-flow rate during a chemical reaction is proportional to the rate of conversion, it represents a differential kinetic analysis technique. Consequently, calorimetry is uniquely able to provide kinetics as well as thermodynamics information to be exploited in mechanism studies as well as process development and optimisation [21]. 

Thermal analysis is a group of techniques in which a physical property of a substance is measured as a function of temperature when the sample is subjected to a controlled temperature program. Single techniques, such as thermogravimetry (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric thermal analysis, etc., provide important information on the thermal behaviour of materials. However, for polymer characterisation, for instance in case of degradation, further analysis is required, particularly because all of the techniques listed above mainly describe materials only from a physical point of view. A hyphenated thermal analyser is a powerful tool to yield the much-needed additional chemical information. In this paper we will concentrate on simultaneous thermogravimetric techniques. 

The thermal characterisation of elastomers has recently been reviewed by Sircar [28] from which it appears that DSC followed by TG/DTG are the most popular thermal analysis techniques for elastomer applications. The TG/differential thermal gravimetry (DTG) method remains the method of choice for compositional analysis of uncured and cured elastomer compounds. Sircar s comprehensive review [28] was based on single thermal methods (TG, DSC, differential thermal analysis (DTA), thermomechanical analysis (TMA), DMA) and excluded combined (TG-DSC, TG-DTA) and simultaneous (TG-fourier transform infrared (TG-FTIR), TG-mass spectroscopy (TG-MS)) techniques. In this chapter the emphasis is on those multiple and hyphenated thermogravimetric analysis techniques which have had an impact on the characterisation of elastomers. The review is based mainly on Chemical Abstracts records corresponding to the keywords elastomers, thermogravimetry, differential scanning calorimetry, differential thermal analysis, infrared and mass spectrometry over the period 1979-1999. Table 1.1 contains the references to the various combined techniques. 

This book contains papers from the Fourth International Conference on Computational Methods and Experiments in Materials Characterisation which brought researchers who use computational methods, those who perform experiments, and of course those who do both, in all areas of materials characterisation, to discuss their recent results and ideas, in order to foster the multidisciplinary approach that has become necessary for the study of complex phenomena. The papers in the book cover the follow topics Advances in Composites Ceramics and Advanced Materials Alloys Cements Biomaterials Thin Films and Coatings Imaging and Image Analysis Thermal Analysis New Methods Surface Chemistry Nano Materials Damage Mechanics Fatigue and Fracture Innovative Computational Techniques Computational Models and Experiments Mechanical Characterisation and Testing. 

Over the years, quantitative structure/property relationships have been developed by various workers in the polymer research field. Hell known are for example the important contributions made by D.W. van Krevelen in Properties of polymers [3] and by J. Bicerano in Prediction of Polymer Properties [4]. An endeavour is made in chapter seven (and eight) to improve some of such correlations by using consistently measured, reproducible TA data. Chapter nine shows the contribution of TA to the characterisation effort necessary for the technical and commercial development of a new polymer system. Chapter ten finally, provides information about different polymers obtained during special case studies. This book illustrates in this way, applications of a wide variety of thermal analysis techniques. The author hopes that this monograph will be useful especially to those who are going to work in the thermal analysis area in the context of polymer research. 

Chapter 9. Characterisation of polyketone polymer systems by Thermal Analysis Techniques... 

CHAPTER 9 CHARACTERISATION OF POLYKETONE POLYMER SYSTEMS BY THERMAL ANALYSIS TECHNIQUES... 

The introduction and development of Micro-Thermal Analysis are described and discussed by Duncan Price in Chapter 3. The atomic force microscope (AFM) forms the basis of both scanning thermal microscopy (SThM) and instruments for performing localised thermal analysis. The principles and operation of these techniques, which exploit the abilities of a thermal probe to act both as a very small heater and as a thermometer, in the surface characterisation of materials are described in detail. The... 

MTDSC is a powerful thermal analysis technique to characterise important events along the reaction path of reacting polymer systems. An empirical modelling of both heat flow and heat capacity MTDSC signals in quasi-isothermal and/or non-isothermal reaction conditions enables the quantification of the influence of vitrification and devitrification on the reaction kinetics. In this way, the ciure kinetics can be determined more accurately than with conventional DSC, even up to high overall reaction conversion. 

Several qualitative and quantitive techniques have been evolved to characterise blowing agents in polymers. These methods include EGA [28-30], differential thermal analysis (DTA) [31, 32] and TGA [31, 32]. The EGA technique limitations are well-described by Jaafer and Sims [28] where rate of gas evolved is dependent on type of additive and... 

The smaller number of techniques used for the study of polymer sohds are broad band dielectric relaxation, dynamic mechanical thermal analysis, smaU angle inelastic neutron scattering and NMR, which together span a frequency range of 10 to 10 Hz. So, they can be used to study aU the correlation frequencies that characterise the motions of interest. 

Macroscopic properties, alternatively referred to as bulk properties or simply performance , are of the utmost importance in material selection. For any application it is essential that the material provides the properties desired, under the conditions of use. In addition, it is wise to characterise the material more fully in order to understand what the effect might be, for example, of changing the temperature. Consideration should also be given to time-related phenomena, such as creep or stress relaxation. What are the consequences of dimensional instability Techniques that can provide this type of information directly include mechanical testing, rheology and thermal analysis. In cases where knowledge of the relationship between structure and properties is desirable, then obviously the techniques described here must be used in combination with those which follow. 

Here we consider those aspects of characterisation which fall between measurement of molecular structure and the bulk properties described above. A typical example might include the overall degree of crystallinity in a partially crystalline polymer, which could be determined by thermal analysis, scattering techniques or microscopy. The most appropriate method will of course be determined by the particular system of interest. Another example is taken from the area of polymer blends. In many cases the component materials are immiscible at the molecular level, and a phase-separated structure is formed. The morphology of this structure largely determines the way in which the blend will perform. Again, any of the above techniques could be used. Microscopy, in conjunction with preferential staining of one component, has proved particularly powerful in this area. 

A valuable approach for measuring thermal degradation kinetic parameters is controlled-transformation-rate thermal analysis (CRTA) - a stepwise isothermal analysis and quasi-isothermal and quasi-isobaric method. In this method, some parameters follow a predetermined programme as functions of time, this being achieved by adjusting the sample temperature. This technique maintains a constant reaction rate, and controls the pressure of the evolved species in the reaction environment. CRTA is, therefore, characterised by the fact that it does not reqnire the predetermined temperature programmes that are indispensable for TG. This method eliminates the nnderestimation and/or overestimation of kinetic effects, which may resnlt from an incomplete understanding of the kinetics of the solid-state reactions normally associated with non-isothermal methods. 

The techniques of thermal analysis are very significant to the whole field of polymers in that they provide essential information relating both to their characterisation and their degradation. Table 2a lists areas where Thermal Analysis (TA) provides information for characterisation while Table 2b lists areas where TA provides information on the degradation processes. 

Photoacoustic spectroscopy and related photothermal products [7] are well-established spectroscopic techniques. The photoacoustic technique, apart from providing direct optical absorption spectra, can also be used to perform depth profile analysis, and characterisation of thermal properties. In addition, there has been a substantial development of new versatile and competitive instrumentation and experimental methodologies suitable for use in daily practice [6,7]. Further details on the photothermal wave phenomenon and its applications can be found in the books by Rosencwaig [6] and Almond [7] and in some of many published reviews on the subject [8-10]. 

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