Study of the thermal decomposition of polymers by on-line cross-correlation gas chromatography

The possibilities of on-line cross-correlation gas chromatography for analytical studies of polymer degradation are demonstrated. Temperature-resolved pyrolysis gas chromatograms and monomer evolution rate curves show the applications of the technique. Data on the linearly programmed system also permit calculations of the kinetic parameters of the reaction (frequency factor, activation energy and reaction order).     

Analysis of thermal decomposition products arising from polyvinyl chloride analogs by supersonic jet/multiphoton ionization/mass spectrometry

Polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) were thermally decomposed at 200-500 degrees C, and the reaction products measured by supersonic jet/multiphoton ionization/mass spectrometry. No precursor molecules of dioxins, such as chlorobenzene, were observed from PVC, although benzene was produced as one of the major components. On the other hand, a large peak corresponding to chlorobenzene was observed, when CPVC was used as a sample. These results suggest that the release of hydrogen chloride and aromatic ring formation occur efficiently and produce chlorinated aromatic hydrocarbons only when excess chlorine atoms are present in the chain of PVC. This method, which has very high selectivity is preferred for trace analysis of specific compounds such as dioxin precursors in a complex mixture. Isomer-selective analysis, e.g. detection of o-, m-, and p-dichlorobenzenes, is also demonstrated in this study.     

Thermal decomposition of polybutadienes by pyrolysis gas chromatography

The thermal decomposition of cis-1,4-, trans-1,4-, and 1,2-polybutadienes (PBD) in the temperature range 450–900°C was investigated by pyrolysis gas chromatography (PGC). The cis- and trans-PBDs have closely similar product distribution and can be readily distinguished at lower temperatures of pyrolysis from the 1,2-PBD by the low amount of vinyl cyclohexene (VCH) produced by the 1,2 species. The amount of butadiene (BD) produced by 1,2-PBD varies with the tacticity of the polymer; the greater syndiotactic yields a lesser amount of BD. A method of determining the 1,4 and the 1,2 contents of PBD based on the ratios of peak heights of ethylene (C2) to VCH, propylene (C3) to VCH, and BD to VCH is presented. The advantages of this method are discussed. The nature and composition of the products of pyrolysis in the temperature range 540–900°C are presented and the mechanism of degradation at these elevated temperatures is explained.     

Investigations on poly(vinyl chloride). IV. Effects of metal chlorides on the thermal decomposition of poly(vinyl chloride)

The effects of various metal oxides upon the thermal decomposition of poly(vinyl chloride) (PVC) were previously reported. In this work, 23 metal chlorides were investigated to determine their effects on the thermal decomposition of PVC by pyrolysis–gas chromatography at 500°C. Each metal chloride exhibits influences on the course of thermal decomposition of PVC almost similar to the corresponding metal oxide except for a few elements; the metal chlorides from acidic metal oxides accelerate the thermal decomposition of PVC, but the metal chlorides from basic metal oxides do not. On comparing the effects of metal oxides and metal chlorides on the thermal decomposition of PVC, most metal chlorides were found to accelerate the thermal decomposition of PVC more than the corresponding metal oxides, owing to ease of addition of the chlorine atoms released from metal chloride to the dehydrochlorinated chains. It is concluded from these results that the thermal decomposition of PVC containing metal salts is markedly influenced by the ease with which chlorine atoms are released from the corresponding metal chloride.     

Investigations on the thermal decomposition of 1,2-dioxetanes via DSC

Reproducible measurements, reliable results and 1^st order kinetics for the whole reaction are obtained during the thermal decomposition of dioxetanes only, if inclusions of impurities in commercial sample pans are blocked by additional thick (magnitude of 100 ?m) and close Al₂O₃ protective layers. As a rule, nearly the same activation parameters are then found both for the decomposition of solvent-free dioxetanes and diluted solutions in several solvents. Mixtures of different dioxetanes in the same solvent contribute independently to the overall heat flow rate.

     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

Investigations on poly(vinyl chloride). III. Effects of metal oxides upon thermal decomposition of poly(vinyl chloride)

Thermal decomposition mechanisms of poly(vinyl chloride) (PVC) and the effects of a few metal oxides on the pyrolysis of PVC were previously reported. In the present work, 33 metal oxides were investigated to determine their effects on the thermal decomposition of PVC, by using a pyrolysis gas chromatograph. Most acidic oxides accelerate the recombination of chlorine atoms with double bonds, since PVC containing these metal oxides easily release lower aliphatics, toluene, ethylbenzene, o-xylene, and chlorobenzenes. On the other hand, most basic metal oxides, such as oxides of alkaline earths or silver, inhibit the recombination. These tendencies observed in the thermal decomposition of PVC agree with the contributions of corresponding metal salts to the dehydrochlorination of PVC proposed by other workers. This means that thermal decomposition or dehydrochlorination of PVC is affected by irregularities in head-to-tail linkages formed by the recombination of chlorine atoms during heat treatment of PVC.     

可反应性纳米二氧化硅填充聚氯乙烯树脂在空气中的热分解行为

利用热重分析和差热重量分析(TG/DTG)技术研究了可反应性纳米二氧化硅填充聚氯乙烯(PVC/n-SiO2)树脂在空气气氛中的热分解行为,利用Ozawa-Flynn-Wall (OFW)方程和Friedman方程对其热分解进行了动力学分析.结果表明,可反应性纳米SiO2对PVC树脂热分解的第一阶段影响比较明显,当纳米S...     

气相色谱法研究配位化合物的热稳定性 II.草酸配位化合物的热分解动力学

In this paper kinetics of thermal decomposition of oxalato coordination is stuided by gas chromatography. A kinetic equation of thermal decomposition is proposed. A computer program which was written in FORTRAN-IV language has been worked out to evaluate the activation energy and the Arrhenius pre-exponential factor. The results of calculation show that the equation is better agreement with the experimantal data. The activation step in decomposition of Fe(C2H4)3 is discussed on basis of calculation by EHMO method.     

Sulfur speciation in hard coal by means of a thermal decomposition method

A new method for the determination of organic and pyritic sulfur in hard coal is presented. The method is based on controlled thermal decomposition of coal sample in oxygen-free and oxygen atmospheres. The results for sulfur liberated in an argon atmosphere at temperatures up to 773 K were close to organic sulfur contents (Sorg), although owing to the definition of 'organic sulfur' the values were not directly comparable. Sorg contents are calculated from the difference between total sulfur content in coal and contents of this element in the form of sulfides, sulfates and pyrites. Sulfur contents, found in the second stage of analysis, were close to pyritic sulfur contents. The difference between total sulfur content and the sum of sulfur values obtained in stages I and II corresponded to sulfur contents in those samples which were neither decomposed nor oxidized at temperatures up to 1173 K. Although not comparable with such conventional concepts for industrial purposes these data are attractive due to the ease and rapidity of the new method for the control of sulfur streams in industrial processes.     

Characterization of differently bound water by means of the constants of thermal decomposition kinetics

Summary Compounds containing differently strong bound water molecules were investigated by thermogravimetry and derivative thermogravimetry. The following models were used: inorganic adsorbents, salts containing water of crystallization and a compound with structural water. The temperature interval, the stoichiometry of the water release were determined and kinetic parameters of the processes were calculated. These results could be brought into connection with the nature of the adsorption and crystallization water.

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Charakterisierung von verschieden gebundenem Wasser mit Hilfe der kinetischen Konstanten der thermischen Zersetzung

Zusammenfassung Thermogravimetrisch und durch derivative Thermogravinietrie wurden Verbindungen untersucht, die mit verschiedener Stärke gebundene Wassermoleküle enthalten: anorganische und organische Adsorbentien, Kristallwasser enthaltende Salze und Verbindungen mit Strukturwasser. Die Temperaturgebiete sowie die Stöchiometrie der Wasserfreisetzung wurden bestimmt und die kinetischen Parameter der Vorgänge ermittelt. Die Ergebnisse ließen sich zu der Natur des adsorptiven oder Kristallwassers in Beziehung bringen.

The authors thank Mr. P. Töke and Mr. M. Matula for running the computer program and Mrs. E. Borsay for the technical assistance.