Thermal vacuum weight loss

Figure 3. Thermal vacuum weight loss of T300/934. (Reproduced from reference 7.)...

The previous conflicting investigations may now be rationalized. Red phosphorus is known to thermally convert to white phosphorus, which will burn in air. If white phosphorus is formed, a fire is expected and no flame retardant activity will be observed. On the other hand, if the phosphorus reacts with the polymer as in Scheme 1, then thermal stabilization is expected. The efficacy of red phosphorus seems to be closely related to the efficiency of mixing of the additive and the polymer, when they are well-mixed the phosphorus will react with the polymer and lead to flame retardant activity, if the mixing is poor then the phosphorus will be converted to the white allotrope and burning will result. Since all of the work reported herein was carried out in sealed tubes under vacuum, the phosphorus must react and lead to stabilization of the polymer against molecular weight loss and fuel production, i.e. thermal stabilization. 

The vacuum-thermal weight loss results presented in Figure 3 show a two-step weight loss pattern for the irradiated sample. Weight loss associated with volatilization of the first product begins before 100°C and the second near 150°C. No weight loss was observed below 225°C for the nonirradiated composite sample. 

The effect of temperature in an oxidising environment is discussed in the next section. In an inert gas or in vacuum molybdenum disulphide has very good thermal stability. Figure 4.3 shows the loss in weight as the powder at 10 to 10 Torr (0.13 to 1.3)t/Pa) was heated in stepwise fashion to 1260°C. Weight loss can be seen to begin at 930°C, and beyond that point the weight loss increased with temperature. 

The thermal decomposition studies were initially carried out by following weight-loss as functions of time and temperature of the sample when under vacuum. When the lowest temperature for rapid weight-loss had been established it was our practice to hold the sample at this temperature until constant weight was attained. The volatiles were trapped at -196° and were subsequently examined by gas-phase Infrared spectroscopy. The residual solids in the Monel tubes were examined by X-ray powder photography, Raman and Infrared spectroscopy and were also tested for para- or diamagnetism. 

Pure PP and blends with increasing proportions of PMMA were irradiated in vacuum at 20°C for 20 hours. The weight loss on subsequent heating for 3 hours at 354°C was used as a measure of the Influence of blend composition on stability and compared with the behavior of un-lrradlated materials. The results, which are illustrated in figure 9, demonstrate that while the thermal stability of pure PP is greatly reduced by pre-irradiation, the additional effect of the presence of PMMA is relatively minor. 

Dhawan and Trivedi [127] studied the thermal stability of conducting polypyrrole film, grown on the FeCU spray-coated polyvinylacetate film, exposed to pyrrole vapours under mild vacuum. The thermogravi-metric analysis data for the conductive polypyrrole composite showed its stability up to I50°C and after that a continuous weight loss was observed up to 450°C implying the breakdown of the host polymer, polyvinylacetate matrix. The differential thermal analysi.s of the composite also showed first inflection at 205°C followed by a major transformation at 296°C. 

Troare et al. [162] performed thermogravimetric analysis of emeraldine hydrochloride under high vacuum in conjunction with thermal volatilization analysis. The initial weight loss was attributed to the... 

The results of studies on the influence of molecular mass and molecular mass distribution of PIB on the kinetics of its thermal degradation are of interest because of the effect of chemical structure on the thermal stability of the polymer. Several high and low molecular mass fractions and non-fractionated samples of PIB with high and low molecular masses have been used in these studies. It has been found that the molecular mass of PIB sharply decreases from about two million to about 25,000 in the initial period (10% of weight loss) of polymer degradation under vacuum at 300 °C. Thereafter the decrease in molecular mass of the polymer decelerates. 

Thermal degradation of polymers is conveniently studied by pyrolytic methods. The polymer literature contains many reports on such studies conducted at various temperatures in inert atmospheres, in air, or in vacuum. The volatile products are usually monitored with accompanying measurements of the weight loss per unit time. The reaction rates are thus measured by ... 

Fig. 21.3 Weight loss curves for raw MWNTs (filled triangles), diamond (filled squares), annealed diamond (open circles), graphite (filled circles), annealed MWNTs (open diamonds), and annealed graphite (open triangles) thermal annealing at 2,800 °C in vacuum (Reprinted with permission from Bom et al. 2002, Copyright 2002 American Chemical Society)...

---