Pyrolysis volatile decomposition, products from

Gas theories. — These attribute the retardant action to modification of the behavior of the volatiles (from the pyrolysis) by gases evolved from the decomposition of the retardant. Two suggested modes of action are (a) prevention of the formation of inflammable mixtures of air and volatile compounds (derived from the cellulosic material), by dilution with noninflammable gases derived from decomposition of the retardant, and (b) inhibition of free-radical chain-reactions in the flame, by introduction of decomposition products (from the retardant) that act as chain breakers. 

The extent to which starch and cellulose form volatile decomposition products in the absence of inorganic material may be seen from the results shown in Table IV for the percentage weight of polysaccharide remaining after pyrolysis under vacuum. Although differences between starch and its components are small, cellulose is relatively more stable. The general order of thermal stability appears to be amylose < starch < amylo-pectin < cellulose. 

A more detailed analysis of the composition of the volatile portion by the method of mass spectrometry showed that the products liberated from polyvinyl chloride at 400°C under vacuum in 30 min contain not only hydrogen chloride, but also 26 different aliphatic and aromatic compounds saturated and unsaturated hydrocarbons, diehloroethane, allqrl-and alkylenebenzenes are detected ethylene, propylene, ethane, pentane, hexane, benzene, and toluene predominate quantitatively [30]. It has been found by the methods of chromatography and IR- and UV-spectrom-etry that when the pyrolysis temperature is raised to 450-500°C, substances with three to five condensed aromatic nuclei appear among the volatile decomposition products of polyvinyl chloride [31]. 

An example of the effect of source temperature is seen for TiF40xH 110), for which, at 180°C, the highest m/e corresponds to TiFsOX (i.e., P—HF), whereas at 240°C the thermal decomposition product, TiF20X2, is observed. Compound Cu(NOs)2 shows a parent ion 111, 112) [unlike Sn(NOs)4 (79)], but thermal decomposition occurs even at source temperatures of 100°C resulting in much of the N02 and NO observed. As samples are volatilized from the probe at temperatures of up to 350°C, serious thermal decomposition or polymerization may result 8,113-116). Even with the source at a low temperature, there is still the very hot region in the vicinity of the filament that can cause pyrolysis. 

Polysaccharide pyrolysis at 375-520°C is accompanied by a higher rate of weight loss and evolution of a complex mixture of vapor-phase compounds preponderantly of HsO, CO, C02, levoglucosan, furans, lactones, and phenols (Shafizadeh, 1968). The volatile and involatile phase compositions are conditional on the rate of removal of the vapor phase from the heated chamber (Irwin, 1979), inasmuch as the primary decomposition products are themselves secondary reactants. The reaction kinetics is described as pseudo zero order (Tang and Neill, 1964) and zero order initially, followed by pseudo first order and first order (Lipska and Parker, 1966), suggesting an... 

Hydrogen sulfide is the main decomposition product seen from the pyrolysis of poly(thiophene-2,5-diyl). Some 2,2 -bithiophene (17.4% of pyrolysate) and only a small proportion of thiophene are generated (less than 5% of pyrolysate). However, the pyrolysis in He also forms char, which is not volatile and cannot be seen in the pyrogram. The bonds that appear to cleave more easily are the S-C bonds and the bonds between the thiophene units (C-C type). Since the hydrogen content of the polymer is low, the formation of SH2 is associated with the formation of char. The elimination of some carbon and sulfur as CS2 or S explains the formation of benzene, thiophene, etc. 

A study of the cumulative yields of volatile products at various temperatures showed that, after pyrolysis for 18 hours at 156 and 188°, although water was the main product from the starches, carbon dioxide and carbon monoxide were also formed. Limited, pyrolytic degradation must, therefore, have occurred at these temperatures. There was a large increase in all three products at 218.6°, indicating that major decomposition occurs near this temperature. In contrast, cellulose did not form comparable quantities of carbon dioxide and carbon monoxide until temperatures of 260-270° were reached. 

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