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Journal ArticleDOI

Kinetics of thermal degradation of char-forming plastics from thermogravimetry. Application to a phenolic plastic

07 Mar 2007-Journal of Polymer Science Part C: Polymer Symposia (John Wiley & Sons, Ltd)-Vol. 6, Iss: 1, pp 183-195

Abstract: A technique was devised for obtaining rate laws and kinetic parameters which describe the thermal degradation of plastics from TGA data. The method is based on the inter-comparison of experiments which were performed at different linear rates of heating. By this method it is possible to determine the activation energy of certain professes without knowing the form of the kinetic equation. This technique was applied to fiberglass-reinforced CTL 91-LD phenolic resin, where the rate law - (1/we)(dw/dt) = 1018e−55,000/RT [(w - wf)/w0,]5, nr.−1, was found to apply to a major part of the degradation. The equation was successfully tested by several techniques, including a comparison with constant temperature data that were available in the literature. The activation energy was thought to be correct within 10 kcal.
Topics: Thermogravimetry (53%), Activation energy (51%), Rate equation (51%)
Citations
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Journal ArticleDOI
10 Jun 2011-Thermochimica Acta
Abstract: The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations offer guidance for reliable evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) from the data obtained by means of thermal analysis methods such as thermogravimetry (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). The recommendations cover the most common kinetic methods, model-free (isoconversional) as well as model-fitting. The focus is on the problems faced by various kinetic methods and on the ways how these problems can be resolved. Recommendations on making reliable kinetic predictions are also provided. The objective of these recommendations is to help a non-expert with efficiently performing analysis and interpreting its results.

3,232 citations


Journal ArticleDOI
D. K. Chattopadhyay1, Dean C. Webster1Institutions (1)
Abstract: The thermal stability and flame retardancy of polyurethanes is reviewed. Polyurethanes (PUs) are an important class of polymers that have wide application in a number of different industrial sectors. More than 70% of the literature that deals with PUs evaluates their thermal stability or flame retardancy and attempts to provide a structure–property correlation. The importance of studying thermal degradation, understanding the processes occurring during thermal stress as well as the parameters affecting the thermal stability of PUs are essential in order to effectively design polyurethanes having tailor-made properties suitable for the particular environment where they are to be used. A detailed description of TGA, TGA-MS and TGA-FTIR methods for studying the decomposition mechanism and kinetics is also a part of this review. In general, thermal decomposition of PUs begins with the hard segment (HS) and a number of parameters govern a polyurethane's thermal stability. Detailed description of the parameters such as HS, soft segment (SS) and chain extender (CE) structure and molecular weight, NCO:OH ratio, catalyst nature and crosslink density that affect the nature of PU degradation is given. Descriptions of approaches to improve the thermal stability in PUs such as formation of poly(urethane-isocyanurate), poly(urethane-oxazolidone) and poly(urethane-imide) in addition to other methods such as PUs with an s-triazine ring or increased aromatic ring concentration, azomethane linkages as well as use of hyperbranched polyols as crosslinking agents is given. A part of the review is also concentrated on the improvement of thermal stability via hybrid formation such as the incorporation of appropriate amounts of fillers, e.g., nano-silica; Fe 2 O 3 ; TiO 2 ; silica grafting; nanocomposite formation using organically modified layered silicates; incorporation of Si–O–Si crosslinked structures via sol–gel processes; and the incorporation of polyhedral oligomeric silsesquioxane (POSS) structures into the PU backbone or side chain. Incorporation of carbon nanotubes (CNT) into PUs and the use of functionalized fullerenes in PUs are also described as these are the newest tools to obtain good thermal stability and flame retardancy. Part of the review also concentrates on the process that occurs during burning of PUs, flame retardant mechanisms and different additives or reactive type flame retardants used in the PU industry. The use and working function of expandable graphite and melamine as additive type flame retardants are shown. Description of the use of different reactive type organophosphorus compounds, cyclotriphosphazenes, aziridinyl curing agents in aqueous polyurethane dispersions (PUDs), organoboron compounds and organosilicon compounds for improving flame retardancy is also given.

1,159 citations


Journal ArticleDOI
Marco J. Starink1Institutions (1)
04 Sep 2003-Thermochimica Acta
Abstract: Model-free isoconversion methods are the most reliable methods for the calculation of activation energies of thermally activated reactions. A large number of these isoconversion methods have been proposed in the literature. A classification of these methods is proposed. Type A methods such as Friedman methods make no mathematical approximations, and Type B methods, such as the generalised Kissinger equation, apply a range of approximations for the temperature integral. The accuracy of these methods is investigated, by deriving expressions for the main sources of error which includes the inaccuracy in reaction rate measurement, approximations for the temperature integral and inaccuracies in determination of temperature for equivalent fraction transformed. Both highly inaccurate and highly accurate Type B methods are identified. In cases where some uncertainty over baselines of the thermal analysis data exists or where accuracy of determination of transformation rates is limited, type B methods will often be more accurate than type A methods.

1,115 citations


Journal ArticleDOI
Abstract: The past decades have seen increasing interest in developing pyrolysis pathways to produce biofuels and bio-based chemicals from lignocellulosic biomass. Pyrolysis is a key stage in other thermochemical conversion processes, such as combustion and gasification. Understanding the reaction mechanisms of biomass pyrolysis will facilitate the process optimization and reactor design of commercial-scale biorefineries. However, the multiscale complexity of the biomass structures and reactions involved in pyrolysis make it challenging to elucidate the mechanism. This article provides a broad review of the state-of-art biomass pyrolysis research. Considering the complexity of the biomass structure, the pyrolysis characteristics of its three major individual components (cellulose, hemicellulose and lignin) are discussed in detail. Recently developed experimental technologies, such as Py-GC–MS/FID, TG-MS/TG-FTIR, in situ spectroscopy, 2D-PCIS, isotopic labeling method, in situ EPR and PIMS have been employed for biomass pyrolysis research, including online monitoring of the evolution of key intermediate products and the qualitative and quantitative measurement of the pyrolysis products. Based on experimental results, many macroscopic kinetic modeling methods with comprehensive mechanism schemes, such as the distributed activation energy model (DAEM), isoconversional method, detailed lumped kinetic model, kinetic Monte Carlo model, have been developed to simulate the mass loss behavior during biomass pyrolysis and to predict the resulting product distribution. Combined with molecular simulations of the elemental reaction routes, an in-depth understanding of the biomass pyrolysis mechanism may be obtained. Aiming to further improve the quality of pyrolysis products, the effects of various catalytic methods and feedstock pretreatment technologies on the pyrolysis behavior are also reviewed. At last, a brief conclusion for the challenge and perspectives of biomass pyrolysis is provided.

1,054 citations


Journal ArticleDOI
Sergey Vyazovkin1Institutions (1)
Abstract: Integral isoconversional methods may give rise to noticeable systematic error in the activation energy when the latter strongly varies with the extent of conversion. This error is eliminated by using an integration technique that properly accounts for the variation in the activation energy. The technique is implemented as a modification of the earlier proposed advanced isoconversional method [Vyazovkin, S. J Comput Chem 1997, 18, 393]. The applications of the modified method are illustrated by simulations as well as by processing of data on the thermal decomposition of calcium oxalate monohydrate and ammonium nitrate. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 178–183, 2001

863 citations


References
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Journal ArticleDOI
C. D. Doyle1Institutions (1)
Abstract: Thermogravimetric data are generally more extensive than are comparable isothermal aging data, and therefore afford preliminary kinetic information in greater abundance. The kinetic analysis of the thermogram, by use of either its exact equation or a more convenient approximation formula, is straightforward in cases of volatilization via simple kinetics. Application of the analytical procedure to the thermogram for the zero-order volatilization of octamethylcyclotetrasiloxane yielded an estimate of 11.65 kcal./mole as the average heat of vaporization in the temperature range of 80 to 145°C. The apparent activation energy for the first-order pyrolytic volatilization of 200-mg. samples of pulverized polytetrafluoroethylene was estimated to be 66 to 68 kcal./mole in the temperature range of 520 to 610°C.

1,065 citations


Journal ArticleDOI
David A. Anderson1, Eli S. Freeman1Institutions (1)
Abstract: The nonisothermal method of Freeman and Carroll is used to investigate the kinetics of the thermal degradation of polyethylene and polystyrene. The reactions were studied thermogravimetrically under a vacuum of 1 mm Hg. Decomposition appears to occur in stages. The rate parameters were determined for each region of reaction. Mechanisms of degradation are suggested. The results of this investigation are compared with the kinetic parameters reported by other investigators for the decompostion of these polymers.

239 citations


Journal ArticleDOI
David A. Anderson1, Eli S. Freeman1Institutions (1)
Abstract: The kinetics of the thermal decomposition of the polyester, Laminac 4116, were investigated in air and argon at atmospheric pressure by means of a continuous recording thermobalance and by differential thermal analysis. Samples were heated from ambient temperature to 600°C. at rates of 5°/min. and 15°/min. In air and argon, decompostion commences at 200°C. and is complete at 550 and 450°C., respectively. Four modes of degradation in oxygen and two in argon are indicated from derivative plots of the thermogravimetric curves. The kinetics of reaction were evaluated by the method of Freeman and Carroll. In the presence of air, the initial stage of reaction appears to involve formation of an unstable hydroperoxide intermediate which undergoes rearrangement and degradation. The energy of activation was calculated to be 19 kcal./mole. An exotherm corresponding to this first stage of degradation is observed by differential thermal analysis. The second and third stages of reaction in air correspond approximately to the two stages in argon with respect to their endothermal nature and to the temperature regions over which they occur. Mass spectrometric and infrared analysis were employed for identification of gaseous and volatile products. The fourth stage of reaction in air appears to involve the oxidation of carbon to carbon dioxide. Mechanisms of reaction are proposed and discussed.

41 citations



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