Showing papers on "Thermogravimetric analysis published in 1970"

Thermogravimetric and differential thermal analysis of cellulose, hemicellulose, and lignin

Abstract: The thermal degradation of samples of cellulose, hemicellulose, and lignin have been investigated using the techniques of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) between room temperature and 600°C. The results calculated from static and dynamic TGA indicated that the activation energy E for thermal degradation for different cellulosic, hemicellulose, and lignin samples is in the range 36–60, 15–26, and 13–19 kcal/mole, respectively. DTA of all the wood components studied showed an endothermic tendency around 100°C in an atmosphere of flowing nitrogen and stationary air. However, in the presence of flowing oxygen this endothermic effect was absent. In the active pyrolysis temperature range in flowing nitrogen and stationary air atmospheres, thermal degradation of Avicel cellulose occurred via a sharp endothermic and a sharp exothermic process, the endothermic nadir and exothermic peak being at 320° and 360°C, respectively. In the presence of oxygen, combustion of Avicel cellulose occurred via two sharp exothermic processes. DTA studies of different cellulose samples in the presence of air showed that the shape of the curve depends on the sources from which the samples were prepared as well as on the presence of noncellulosic impurities. Potassium xylan recorded a sharp exothermic peak at 290°C in a nitrogen atmosphere, and in a stationary air atmosphere it yielded an additional peak at 410°C, while in the presence of oxygen the curve showed two sharp exothermic peaks. DTA traces of periodate lignin in flowing nitrogen and air were the same and showed two exothermic peaks at 320° and 410°C, while in the presence of oxygen there were two exothermic peaks in the temperature range 200°–500°C.

Thermal degradation of wood components: a review of the literature.

Abstract: This review of the literature focused on thermal methods of analysis of the degradation of wood, cellulose, hemicelluloses, and lignin. The methods included thermogravimetric analysis (TGA) and differential thermal analysis (DTA). A discussion of the general thermal degradation process for wood is followed by a more specific review of the use of these methods to analyze the thermal degradation of wood and its components. 11 figures, 2 tables. (DP)

Degradation of poly(vinyl chloride)

Abstract: The decomposition of poly(vinyl chloride) below 155°C has been examined by thermogravimetric analysis. Degradation is enhanced by irradiation with 1 MeV electrons. Later stages of isothermal weight loss for thermal and radiolytic decomposition follow 3/2-order kinetics and a similar reaction scheme is inferred. A free radical mechanism for dehydrochlorination involving allyl and polyenyl radicals is postulated.

Thermogravimetric Analysis of Ammonia-Swelled Cellulose

Abstract: Cellulose decrystallized by swelling in liquid ammonia produced a simpler thermogravimetric analysis curve than obtained from ordinary cellulose—presumably because of a decrease in the intermolecular char-forming reactions. By using a graphical procedure which permits a linear plot of the thermogram, it was possible to resolve the overall curve into two components: the principal reaction by which more than 90% of the weight loss occurred (activation energy = 54.9 kcal/mole; pre-exponential factor = 3.15 × 1019/min), and a second component which may be approximated by a first-order reaction leading to an ultimate 4% char.

Kinetic analysis of thermogravimetric data, III: Improvement of Doyle's isothermal method

Abstract: Doyle's isothermal method is analysed by using it for deriving activation energies from theoretical curves. Empirical formulae are given for the time correctiontc, as well as for the factorr in the following equation:Ea=−rm cal/mole. An iterative procedure is suggested, which eliminates the inaccuracy of Doyle's method and permits the derivation of activation energies with an accuracy of ±0.1 kcal/mole in ideal cases.RésuméOn analyse la méthode isotherme de Doyle en l'employant pour le calcul des énergies d'activation sur des courbes théoriques. On donne des formules empiriques pour la correction du tempstc, ainsi que pour le facteurr dans l'équationEa=−rm cal/mole. On propose un procédé itératif éliminant l'incertitude de la méthode de Doyle et permettant le calcul des énergies d'activation à±0.1 kcal/mole dans les cas idéals.ZusammenfassungDie Doylesche isothermische Methode wurde analysiert, indem man sie zur Ableitung der Aktivierungsenergiewerte aus theoretischen Kurven heranzog. Empirische Formeln für die Zeitkorrekturtc und für den Faktorr in der GleichungEa=−rm cal/Mol wurden gegeben. Eine Iterationsmethode durch welche die Ungenauigkeit der Doyleschen Methode beseitigt und die Werte der Aktivierungsenergien auf ±0.1 Kcal/Mol Genauigkeit für den Idealfall bestimmt werden können, wurde vorgeschlagen.РезюмеПроанализирован изо термический метод До йля при его использовани и для расчета энергии акти вации по теоретическ ой кривой. Приведены эмпиричес кие формулы для коррекции времен иtc и для фактораr в сле дующем уравнении: Ea=−rm кал/мол. Предлагается прибли женный метод, исключа ющий неточность метода До йля и дающий возможность расчита ть энергию активации с точностью ±0,1 ккал/мол в идеальном случае.

Thermogravimetric analysis of Ontario limestones and dolomites. II. Reactivity of sulfur dioxide with calcined samples

Abstract: Thermogravimetric analysis was done for representative calcined samples of Ontario limestones and dolomites in a 5% SO2 controlled atmosphere. The SO2 absorption vs. temperature curves showed three...

Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) Studies of Flame-Retardant Rayon Fibers:

Abstract: The thermal behavior of flame-retardant fibers in which the flame-retardant chemical trapped inside the regenerated cellulose has now been studied, by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The thermograms obtained in a dynamic air atmosphere resemble those previously reported elsewhere for cellulosic materials treated with flame retardants in the conventional manner. In all cases, it has been found that the thermal degradation of the flame-retardant fibers begins at a lower temperature than for the control. A smaller quantity of flammable volatile matter is evolved and a much larger residue remains when the pyrolysis is complete. The total area of the exothermic peaks is, therefore, much smaller for the flame-retardant fibers than for the control.When the same flame-retardant fibers are heated in a nitrogen atmosphere, it can be easily seen that the onset of decomposition occurs quite suddenly at a definite temperature and clearly involves a reaction between the flame r...

Poly‐2‐oxazolidones: Preparation and characterization

Abstract: Poly-2-oxazolidones were synthesized by the 1,3-cycloaddition of bisglycidyl ethers to diisocyanates with the use of N,N-dimethylformamide and lithium chloride as solvent and catalyst, respectively. A variety of arylene and alkylene diisocyanates and coreactant bisepoxides were used in the polymer-forming reaction. The polymers, obtained in high yield, were generally soluble in methylene dichloride, chloroform, N,N-dimethylformamide, and dimethyl sulfoxide. They had intrinsie viscosities up to 0.42 dl/g and could be cast into films. In several cases molecular weights were determined by vapor pressure osmometry. The poly-2-oxazolidone based upon 1,6-hexamethylene diisocyanate and the bisglycidyl ether of isopropylidene diphenol gave the highest molecular weight. Confirmation that the base unit of the polymers contains the 2-oxazolidone ring was obtained by elemental analysis, infrared and NMR spectroscopy. The poly-2-oxazolidones synthesized were found to be amorphous by x-ray diffraction. Thermogravimetric analyses indicated that a majority of the poly-2-oxazolidones were stable in dry air up to 300°C. In a number of cases Tg's were also determined by using differential scanning calorimetry.

Reactions near the burning surface of double- base propellants

Abstract: Reaction heat for flameless combustion of double- base propellant using differential scanning calorimetry and thermogravimetric analysis, noting pressure effects

The Effect of Impurities upon the Physical Properties of Silica Gel by the Heat-Treatment

Abstract: The effects of various kinds of inorganic salts upon the physical properties of silica gel heated in the range up to 1200°C were studied. We measured the polymorphic behavior by means of X-ray diffraction, the simultaneous measurement of the differential thermal analysis, and the thermogravimetric analysis, and the specific surface area by means of the BET N2 method and by means of studying the water-adsorption capacity. The cationic impurities which were found to have strong effects upon the physical properties mentioned above are Na+, K+, Ca2+, Pb2+, Cd2+, Zn2+, and Sb3+. Cations such as Al3+, Cr3+, Mn3+, and Co2+ were shown to have weak but positive effects upon the physical properties of silica gel.

A Thermochemical Investigation of Cotton Flame Retardance

Abstract: Differential scanning calorimetry and thermogravimetric analysis curves were obtained for cotton cellulose in the presence of both flame-retarding and nonflame-retarding compounds and evaluated quantitatively for ΔH, activation energy, total weight loss, and char remaining after pyrolysis. Twenty-three compounds were tested and were found to fall roughly into three groups: (I) those which do not undergo decomposition in the temperature interval in which cellulose decomposes (200-400°C); (II) those which decompose appreciably during or preceding this temperature range; and (III) those which do not interact in any way with cellulose. It was found that, with increasing molar add-on, heat liberated from cellulose decreased for group I, increased for group II, and was not a function of molar add-on for III.A study of the kinetics of decomposition for these systems indicates that, while the majority of reactions proceeded as a pseudo first-order process, there are several exceptions to the trend. As would be ex...

A thermogravimetric method for the analysis of mixtures of brushite and monetite

Abstract: A thermogravimetric method is described for the quantitative analysis of mixtures of calcium hydrogen orthophosphate dihydrate (brushite) and anhydrous calcium hydrogen orthophosphate (monetite) based on their loss of water on heating. An extension to the method when the above system contains a third component of known weight loss is also discussed.

Thermogravimetric analysis of Ontario limestones and dolomites I. Calcination, surface area, and porosity

Abstract: The calcination of natural Ontario limestones and dolomites in a flow of 100 cm3/min of nitrogen at 745 °C required from 0.43 ± 0.03 to 0.35 ± 0.05 min/mg of 100 mesh samples, respectively. The nit...

Structure and properties of poly‐2,5‐distyrylpyrazine

Abstract: Poly-2,5-distyrylpyrazine (poly-DSP) was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and measurements of dynamic viscoelastic and electrical properties. From DTA and TGA studies it was confirmed that poly-DSP melts at 321°C and depolymerizes rapidly to the monomer at temperatures between 335°C and 345°C in helium. The polymer is affected by oxygen above 200°C. The E′ value from dynamic viscoelasticity measurements on amorphous film is 2 × 1011 dyne/cm2 at room temperature. It decrease abruptly in the temperature range 140–150°C; but the net decrease of E′ within this temperature range is relatively small. The electrical properties of amorphous poly-DSP are characterized by a small temperature dependence of the dielectric constant between room temperature and 100°C. The dielectric loss tangent was observed to be small, and the dc conductivity was extremely small. It is concluded that rotation of the phenyl branches in the polymer occurs above −30°C and the glass transition occurs at about 150°C. These properties are discussed in some detail in relation to the polymer structure.

Synthesis and characterization of polyiminobenzothiazoles

Abstract: A series of polyiminobenzothiazoles was synthesized by the polymerization of either 2,6-dichloro- or 2,6-diphenoxybenzobisthiazole with a number of aromatic diamines. A polymer was also obtained from the self-condensation of either 2-chloro- or 2-phenoxy-6-aminobenzothiazole. The polymers were characterized by their elemental analysis and infrared spectra. Thermogravimetric analysis, differential thermal analysis, and softening under load were used to evaluate their thermal properties. The polymers were found to be light tan to brown powders which showed only slight softening below their decomposition temperatures. Onset of breakdown under thermogravimetric analysis in a nitrogen atmosphere generally occurred at 375–400°C. The polymers were sparingly soluble in organic solvents and had inherent viscosities in the range of 0.11–0.55.