TGA experiments isothermal

Table 2.1 Results of isothermal TGA experiments on non-stabilised PP powder samples...

The mass/time curves of a non-stabilised and a stabilised PP sample during isothermal TGA experiments at 250°C (nitrogen atm.)... 

Mass increase of a syndiotactic 1,2-polybutadiene (ex-JSR) sample during an isothermal TGA experiment at 240°C in air... 

Non-isothermal TGA experiments showed that sample B still contained 13.5 %wt. MIBK while sample C still contained 4 %wt. MIBK. The TGA experiments also showed that a temperature of about 250°C is necessary to remove the residual solvent from the samples B and C within a reasonable amount of time (l to 2 hour). 

As mentioned earlier, the reactivity of a prepared coal char is often measured with the sole purpose of char classification and compsu ison to known samples. Because of its simple determination, the CO2 reactivity is measured fi om an isothermal TGA experiment (e.g., at 1000 °C) [62]. The reactivity, as shown in Equation (3.22), is calculated where the carbon burn-off under a CO2 atmosphere is X = 0.5. 

In order to establish the optimum chemisorption temperature, a series of isothermal chemisorption experiments were performed at different temperatures between 200 and 300 °C. The sample was first outgassed in Ar (15 °C min, 1000 C, 5 hours). The temperature was then lowered to the chemisorption temperature, and a flow rate of 75 mL min of oxygen was introduced to the TGA. In this way, an optimised chemisorption temperature of 250 °C was found, so that equilibrium could be achieved in a reasonable period of time, and simultaneous carbon gasification could be avoided. 

To reversely check the kinetic model, the integral rate equation (for non-isothermal conditions) describing the As release during pyrolysis of CCA treated wood is used in combination with the measured temperature profiles T(t) in order to calculate the corresponding As content of the pyrolysis residues. The calculated arsenic content of the pyrolysis residues is compared with the experimental values labscale and TGA experiments) in the parity plot, presented in Figure 5. 

The TGA experiments at T(isothermal) > 190°C show a continuous, nearly linear with the time, decreasing sample mass after the first (non-linear) mass losses due to evaporation of the oligomers fraction. The slopes of the linear part of these curves increase with isothermal measuring temperatures. This effect is thought to be caused by the thermal degradation of the polymer matrix. The mass/time curves were extrapolated, subsequently, as indicated in Figure... 

Figures la and lb show the TGA-mass spectrometry data for water and NMP on the as-received poly(amide-imide), indicating that neither liquid was removed until five minutes into the run, which corresponded to approximately 220 C. The thermogravimetry showed that there was a total of approximately 2 weight percent of water and NMP in the polymer. Isothermal thermogravimetric experiments were conducted on the as-received sample between 145 and 165 C. Temperatures above 155X were enough to dry the sample in 3 hours. Although, further drying of the samples were done at 190 C, an intermediate value between 155 and 220°C. Even this simple experiment showed that there were strong associations of the water and NMP to the poly(amide-imide).

The purpose of this section is to provide guidance to the reader in the general design and implementation of a TGA experiment as well as to provide insight and practical examples of specific types of measurement, such as thermal stability, isothermal mass loss, and material composition. 

The main choices one has to decide on in performing a TGA experiment are the sample pans, the sample size, the temperature program, including possible isothermal steps and the gas environment—either inert or oxidative. Occasionally, it may be helpful to add moisture to the TGA s gas stream to measure moisture sorption/desorption properties (see Section 3.4.4 and Fig. 3.15) or to test a polymer s susceptibility to hydrolysis. Several manufacturers sell accessories that allow the operator to control the room temperature humidity of the purge gas (see Section 3.7 on instrumentation). A fritted glass bubbler can also be employed to saturate the purge gas with water. 

Under the conditions employed in running the PVC sample in Rg. 3.9, there is no sign of any mass loss until the sample is heated above 200 C. However, this behavior is reproducible only as long as the same heating rate of 5 °C/min is employed. With slower heating rates the first sign of mass loss will shift to lower temperatures. The maximum, positive effect on sensitivity to mass loss occurs if PVC is held for long periods of time under isothermal conditions. This type of TGA experiment is demonstrated in Fig. 3.10, where a neat PVC film, 0.31 mm thick with a mass of about 7 mg, is held at 78 °C for approximately one day (Salovey and Bair 1970). 

From Equation 1.12, it can be seen that, from a single TGA trace and from a single isothermal degradation experiment, the value of E may be readily obtained irrespective of reaction order. Equation 1.12 has been plotted for Teflon degradation in a vacuum using an isothermal temperature of 494 °C. From the slope of the linear... 

Thermal decomposition was performed using a SDT Q-600 simultaneous DSC-TGA instrument (TA Instruments). The samples (mass app. 10 mg) were heated in a standard alumina 90 il sample pan. All experiments were carried out under air with a flow rate of 0.1 dm3/min. Non-isothermal measurements were conducted at heating rates of 3, 6, 9, 12, and 16 K/min. Five experiments were done at each heating rate. 

All of the DBDPO and HBCD thermal degradation experiments reported here were carried out isothermally with a nitrogen purge in a thermal gravimetric analyzer (TGA) at temperatures between 390 and 410° C for DBDPO and 240° C for HBCD, respectively. 

Thermogravimetric analysis (TGA) has often been used to determine pyrolysis rates and activation energies (Ea). The technique is relatively fast, simple and convenient, and many experimental variables can be quickly examined. However for cellulose, as with most polymers, the kinetics of mass loss can be extremely complex (8 ) and isothermal experiments are often needed to separate and identify temperature effects (9. Also, the rate of mass loss should not be assumed to be related to the pyrolysis kinetic rate ( 6 ) since multiple competing reactions which result in different mass losses occur. Finally, kinetic rate values obtained from TGA can be dependent on the technique used to analyze the data. 

Thermal Analysis. The DuPont Instruments Model 9900, computer controlled thermal analyzer and Model 951 TGA module were used in the experiments, using a gas flow rate of 100 cc/min. Experiments were performed in dynamic and isothermal mode using air and argon. 

Following the isothermal curing cycle in Step 5 the sample was cooled to ambient temperarnre and then further isothermed on a thermogravimetric analyzer for 120 minutes at 200,250,300, and 350°C in an air atmosphere with a 50 cc/min flow rate. In this experiment the plastic sample exhibited only a3.69% weight loss as determinedby TGA. 

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