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Thermomechanical analysis (TMA)
TMA or static force-TMA (sf-TMA) is a technique that derives from thermomechanometry. It is a very important tool for studying materials that are to be subjected to a wide variation in temperature during their usage. An illustrative example is food packaging which has to undergo thermal processes such as heating, pasteurisation, freezing, etc. (Brown, 2001; Haines, 2002). In TMA the sample’s dimension or length is measured as a function of temperature (heating, cooling or held at a constant temperature) while it is under constant mechanical stress. Usually, the results are evaluated by examining the changes in the thermal expansion coefficients with temperature and/or time (Haines, 2002; Crompton, 2006; Gabbott, 2008).
Modern TMA instruments are designed to measure: (i) penetration; (ii) extension; (iii) flexure; and (iv) torsion (Brown, 2001). For extension measurements, a flat-ended probe is inserted and rested on the top surface of the sample, and a static force is applied. A sensor then measures the movement of the probe (Haines, 2002).
Differential scanning calorimetry (DSC)
DSC is an analytical technique that is used to determine composition, chemical and thermal stability, as well as decomposition kinetics. It does not require sample preparation (just a few milligrams of a powder, pellet or fibre) and measures the amount of energy absorbed or released by an analyte during heating, cooling or even at a constant temperature. The heat flow, associated with transitions, provides quantitative and qualitative information about physical or chemical changes related to exothermic or endothermic processes or changes in heat capacity (Crompton, 2006).
The glass transition (Tg), melting temperature (Tm), crystallisation temperature, specific heat, thermal and oxidative stability, and reaction kinetics, etc. can be determined directly, rapidly and accurately by a DSC instrument using appropriate software.
X-ray diffraction (XRD)
The XRD technique has been extensively used to identify and distinguish vermiculite from other clay minerals (e.g. chlorite and smectites). In fact, the definition of vermiculite is based on its ca. 1.45 nm basal spacing for Mg-vermiculite treated with glycerol and on the characteristic 1.0 nm spacing for the K-vermiculite form on heating at 300 °C (Brindley and Brown, 1980; Bergaya et al., 2006). XRD is also used to distinguish the dioctahedral (d060 = 0.149–0.150 nm) from the trioctahedral (d060 = 0.151–0.153 nm) clay minerals (Brindley and Brown, 1980). It is a versatile and also non-destructive technique that reveals detailed information about the phases contained, as well as their crystallographic features (Cullity, 1978; Moore and Reynolds, 1989).
Scanning electron microscopy (SEM)
Nowadays SEM (along with TEM) is one of the most important characterisation techniques as a result of the huge technological improvements made since its invention and the relatively easy interpretation of data. This technique has also been used by some researchers to study the surface changes in vermiculite resulting from physical or chemical modification.
In a SEM, the electron gun bombards the sample with electrons of a specific wavelength. Deflected electrons, commonly elastically scattered electrons, are collected as signals for imaging. Different topographies and different chemical compositions bring about different signal intensities, thereby giving different contrasts on the SEM screen (Lawes, 1987).
Dynamic mechanical analysis (DMA)
DMA is a mechanical testing method used to measure the elastic (modulus) and viscous (damping) properties of polymeric materials as a function of temperature, time, frequency, stress or a combination of these parameters. As a thermal method, it is also used to study the degradation mechanisms, chemical reactions, etc. of materials (Crompton, 2006;2012).
CHAPTER 1 GENERAL INTRODUCTION
1.1 BACKGROUND
1.2 RESEARCH OBJECTIVES
1.3 RESEARCH METHODOLOGY
REFERENCES
CHAPTER 2 LITERATURE SURVEY
2.1 CLAYS AND CLAY MINERALS
2.2 VERMICULITE
2.3 VERMICULITE/POLYMER COMPOSITES
2.4 FLAME RETARDANCY .
2.5 ANALYTICAL AND CHARACTERISATION TECHNIQUES
REFERENCES
CHAPTER 3 CHARACTERISATION OF NEAT PALABORA VERMICULITE
3.1 INTRODUCTION
3.2 EXPERIMENTAL
3.3 RESULTS AND DISCUSSION
3.4 CONCLUSIONS
REFERENCES
CHAPTER 4 INORGANIC MODIFICATION OF PALABORA VERMICULITE .
4.1 INTRODUCTION
4.2 EXPERIMENTA
4.2.1 Starting material .
4.2.2 Ion-exchange reaction of vermiculite .
4.2.3 Characterisation of inorganically modified vermiculites
4.3 RESULTS AND DISCUSSION
4.4 CONCLUSIONS.
REFERENCES
CHAPTER 5 ORGANIC INTERCALATION OF PALABORA VERMICULITE
CHAPTER 6 THERMAL EXPANSION BEHAVIOUR OF VERMICULITE
CHAPTER 7 MODIFIED VERMICULITE/POLYMER COMPOSITES
CHAPTER 8 GENERAL CONCLUSIONS AND RECOMMENDATIONS
APPENDICES .
