Thermal analysis, degradation

This technique has many applications in qualitative and quantitive thermal analysis degradation studies and polymer microstructure studies [1-3]. 

Levi, Literature Survey on Thermal Degradation, Thermal Oxidation, and Thermal Analysis of High Polymers , PLASTEC Note 7 (1963)... 

Literature Survey on Thermal Degradation, Thermal Oxidation, and Thermal Analysis of High Polymers. Ill , PLASTEC Note 20 (1969) 29) N T. Baldanza, Literature Search Injection Molding Processing Parameters , PLASTEC Note 21 (1969) 30) A.H. Landrock, Polyurethane... 

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

A comprehensive review of compositional and failure analysis of polymers, which includes many further examples of analysis of contaminants, inclusions, chemical attack, degradation, etc., was published in 2000 [2], It includes details on methodologies, sampling, and sample preparation, and microscopy, infrared spectroscopy, and thermal analysis techniques. 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

Measurements of thermal analysis are conducted for the purpose of evaluating the physical and chemical changes that may take place in a heated sample. This requires that the operator interpret the observed events in a thermogram in terms of plausible reaction processes. The reactions normally monitored can be endothermic (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, chemical degradation, etc.) or exothermic (crystallization, oxidative decomposition, etc.) in nature. 

On the basis of the data obtained from the early thermal analysis and tube furnace pyrolysis experiments performed during the initial phases of this investigation, it became apparent that in order to establish the principal reaction pathways to the generation of volatile antimony species, the volatile degradation products of the DBDPO itself would need to be characterized (24, 25). 

From the results of the small scale thermal analysis experiments previously reported (23,25), it was concluded that the antimony volatilization and bromide release observed for ternary mixtures containing organobromine compounds, which did not undergo intermolecular dehydrohalogenation, could not be accounted for solely on the basis of HBr formation during degradation. 

Thermal analysis, in the form of TG, has been employed extensively in the area of polymer flammability to characterize polymer degradation. 

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

Thermal analysis has proved useful in determining the number of sulfoxide moieties which are lattice-held in a given complex. For example, the thorium and zirconyl perchlorate complexes of Me2SO undergo thermal degradation (Eqs. (2) and (3)]. 

In the polymer industry, the melting or degradation behaviors of polymers are important to determine. For example, when a polymer is extruded (i.e., when polymer pellets are converted to film by heating them and drawing them through an extruder), the thermal analysis of the polymer material determines the amount of heat needed in the extruder to make the material pliable. Given the large number of polymer formulations that have been developed and continue to be developed, thermal analysis procedures can be quite important. 

B.A. Howell and B.B.S. Sastry, Degradation ofVinylidene Chloride / Methyl Acrylate Copolymers in the Presence of Phosphines , Proceedings, 22nd North American Thermal Analysis Society Meeting, pp. 122- 127, (1993). 

An easy method for investigating the thermal-oxidative degradation of PET is differential thermal analysis (DTA), which indicates thermal degradation by the appearance of an exothermic peak in the range of the melting temperature. This approach also can be used to assess the efficiency of stabilizers [40],... 

Thirdly, PMMI starts thermally degrading at about 154 C to form an anhydride [65,74]. Thermal analysis showed that the onset temperatures for degradation of the complexes PMMI/PDMA, PMMI/PEOX and PEMl/PVPo was substantially higher than those of the corresponding poly(monoalkyl itaconates), and the difference was attributed to the fact that hydrogen bonds in the complexes need to be broken before anhydride formation takes place. 

In DSC the measured energy differential corresponds to the heat content (enthalpy) or the specific heat of the sample. DSC is often used in conjunction with TA to determine if a reaction is endothermic, such as melting, vaporization and sublimation, or exothermic, such as oxidative degradation. It is also used to determine the glass transition temperature of polymers. Liquids and solids can be analyzed by both methods of thermal analysis. The sample size is usually limited to 10-20 mg. 

While physicochemical and spectroscopic techniques elucidate valuable physical and structural information, thermal analysis techniques offer an additional approach to characterize NOM with respect to thermal stability, thermal transitions, and even interactions with solvents. Information such as thermal degradation temperature (or peak temperature), glass transition temperature, heat capacity, thermal expansion coefficient, and enthalpy can be readily obtained from thermal analysis these properties, when correlated with structural information, may serve to provide additional insights into NOM s environmental reactivity. 

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