Analysis thermomechanical

Thermomechanical analysis involves measuring variations in a sample s volume or length as a function of temperature and/or time. The method is commonly used to determine thermal expansion coefficients as well as the glass-transition temperature of polymer or composite materials. A weighted probe is placed on the specimen surface, and the probe s vertical movement is monitored continuously while the sample is heated at a controlled rate. 

Thermomechanical analysis (TMA) predates the use of dynamic mechanical analysis techniques. TMA is used for 7 determination, but is significantly less sensitive than DMA and cannot be used for studying the weaker p relaxations, as seen in many polymers. In many respects TMA is the simplest form of thermal analysis equipment. A small sample is mounted in the instrument, which is surrounded by a furnace and the variation of sample length is recorded as a function of time or temperature. 

One important application area is the derivation of the coefficient of thermal expansion (GTE). This is usually performed using tension or compression geometries and measuring the expansion although modern TMAs generally have the same range of deformation geometries as used by DMA, described in Section 4.3.2. 

Another variant of TMAs is the dynamic TMA. These function with half the facilities of a DMA, in that they apply a small constant dynamic load throughout a thermal scan, usually 

TMA is the measurement of dimensional changes (such as expansion, contraction, flexure, extension, and volumetric expansion and contraction) in a material by movement of a probe in contact with the sample in order to determine temperature-related mechanical behaviour in the temperature range -180 to 800 °C as the sample is heated, cooled (temperature plot), or held at a constant temperature (time plot). It also measures linear or volumetric changes in the dimensions of a sample as a function of time and force. 

Plots of sample temperature versus dimensional (or volume) changes enable the Tg to be obtained. The Tg is obtained from measurement of sudden changes in the slope of the expansion curve. However, the technique has much wider ranging applications than this in the measurement of the thermal (Chapter 16) and mechanical (Chapter 18) properties of polymers. 

A series of quartz probes are available that allow the TMA-7 to be used in a variety of different operating modes expansion, compression, flexure, extension, and dilatometer. 

Johnston [6, 7] studied the effects of sequence distribution on the Tg of alkyl methacrylate-vinyl chloride and a-methylstyrene-acrylonitrile copolymers by DSC, DTA, and TMA. 

When an elastomer was subjected to a penetration load of 0.03 N and a temperature range of -150 to 200 °C, the material showed a slight expansion below the Tg, before allowing penetration at -17.85 °C, resulting in a very marked Tg. The expansion that takes place after the Tg shows that the material is sturdy enough to resist further penetration, even in its rubbery state. 

For compression measurements (as illustrated) a flat-ended probe is rested on the top surface of the sample and a static force is applied by means of a weight or (more commonly in the case of modern instrumentation) an electromagnetic motor similar in principle to the coil of a 

The equipment must be calibrated before use. The manufacturers, as well as various standardisation agencies, usually provide recommended 

Plots of sample temperature versus dimensional (or volume) changes enable the to be obtained. The 7 is obtained from measurement of sudden changes in the slope of the expansion curve. 

FIGURE 4.6 Determination of 7 of epoxy printed circnit board. 

Wohitjen and Dessy [106, 107] described a surface acoustic wave (SAW) device for conducting a thermomechanical analysis measurement of the on polyethylene terephthalate, polytetrafluoroethylene bisphenol A, polysulfone, polycarbonate, and polymethyl methacrylate. There are several factors that distinguish the SAW device as a useful monitor of polymer T. The device is very sensitive, thereby permitting very small samples to be used. Preparation and mounting of the sample are simple and rapid. The device is quite rugged and possesses a small thermal mass, which permits fairly rapid temperature changes to be made. 

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The dynamic mechanical properties of VDC—VC copolymers have been studied in detail. The incorporation of VC units in the polymer results in a drop in dynamic modulus because of the reduction in crystallinity. However, the glass-transition temperature is raised therefore, the softening effect observed at room temperature is accompanied by increased brittleness at lower temperatures. These copolymers are normally plasticized in order to avoid this. Small amounts of plasticizer (2—10 wt %) depress T significantly without loss of strength at room temperature. At higher levels of VC, the T of the copolymer is above room temperature and the modulus rises again. A minimum in modulus or maximum in softness is usually observed in copolymers in which T is above room temperature. A thermomechanical analysis of VDC—AN (acrylonitrile) and VDC—MMA (methyl methacrylate) copolymer systems shows a minimum in softening point at 79.4 and 68.1 mol % VDC, respectively (86). 

The glass transition temperatures (Tg) of both modified and unmodified PSs were determined by DSC analysis, and thermomechanic analysis was controlled by TMK. The results are given in Table 8. It is seen from Table 8 that the highest glass transition temperature (410 K) was obtained with chlorohydrinated PS and that of the lowest (370 K) with olefinic PS. The lowest glass transition temperature in the alkenylated PS caused to elasticity properties on polybutadien and polyisopren fragments. 

Thermal analysis helps in measuring the various physical properties of the polymers. In this technique, a polymer sample is subjected to a controlled temperature program in a specific atmosphere and properties are measured as a function of temperature. The controlled temperature program may involve either isothermal or linear rise or fall of temperature. The most common thermoanalytical techniques are (1) differential scanning analysis (DSC), (2) thermomechanical analysis (TMA), and (3) thermogravimetry (TG). 

DSC helps in determining the glass-transition temperature, vulcanization, and oxidative stability. TG mainly is applied for the quantitative determination of major components of a polymer sample. TMA or DLTMA (dynamic load thermomechanical analysis) measures the elastic properties viz. modulus. 

Other parameters which have been used to provide a measure of a include physical dimensions (thermomechanical analysis, TMA) [126], magnetic susceptibility [178,179], light emission [180,181], reflectance spectra (dynamic reflectance spectroscopy, DRS) [182] and dielectric properties (dynamic scanning dielectrometry, DSD) [183,184], For completeness, we may make passing reference here to the extreme instances of non-isothermal behaviour which occur during self-sustained burning (studied from responses [185] of a thermocouple within the reactant) and detonation. Such behaviour is, however, beyond the scope of the present review. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

First-order phase transitions can be detected by various thermoanalytical techniques, such as DSC, thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) [31]. Phase transitions leading to visual changes can be detected by optical methods such as microscopy [3], Solid-solid transitions involving a change in the crystal structure can be detected by X-ray diffraction [32] or infrared spectroscopy [33], A combination of these techniques is usually employed to study the phase transitions in organic solids such as drugs. 

One of the more recently exploited forms of thermal analysis is the group of techniques known as thermomechanical analysis (TMA). These techniques are based on the measurement of mechanical properties such as expansion, contraction, extension or penetration of materials as a function of temperature. TMA curves obtained in this way are characteristic of the sample. The technique has obvious practical value in the study and assessment of the mechanical properties of materials. Measurements over the temperature range - 100°C to 1000°C may be made. Figure 11.19 shows a study of a polymeric material based upon linear expansion measurements. 

Carrington et al. [1.124] usd thermomechanical analysis (TMA) to study the ice-crystallization temperature of 30 % (w/w) fructose, sucrose and glucose with and without sodium carboxy methyl cellulose (CMC). TMA has been used to measure the expansion of... 

ASTM E 1545-00, ASTM Book of Standards 2002. Standard Test Method for Assignment of the Glass Transition Temperature by Thermomechanical Analysis . ASTM International, Conshohocken, PA. 

Dynamic mechanical anlaysis (DMA) measurements were done on a Rheometrics RDS-7700 rheometer in torsional rectangular geometry mode using 60 x 12 x 3 mm samples at 0.05% strain and 1 Hz. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) were performed on a Perkin-Elmer 7000 thermal analysis system. 

Thermomechanical analysis (tma), 79 573 Thermomechanical fatigue (TMF), 73 488 Thermomechanical finishing, 77 514-516 Thermomechanical properties, of... 

Thermomechanical analysis (TMA) helps to measure the mechanical response of a polymer system with the change of... 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

Figure 2. Thermomechanical analysis of T300/934. (Reproduced from reference 7.)...

Thermal expansion and contraction are reversible effects of temperature which may be very important in some applications. Usually expansion is measured using thermomechanical analysis (TMA) (see ISO 11359-2 [4]). 

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