Polymeric materials, thermal decomposition studies

Plasma-polymerized materials differ significantly from those polymerized by conventional methods in their surface properties, and surface tension values do not correspond. This difference may be due to the highly cross-linked nature of plasma polymers or to the incorporation of other entities from the carrier gas. These effects are more important than the intrinsic differences in backbone fiexibility. Wrobel (88) presents ATR-IR (attenuated total reflection infrared) spectroscopic data indicating that silazanes and silanes cross-link more readily than do siloxanes under plasma conditions. Wrobel and his co-workers (89) have also used contact angles to study the thermal decomposition of plasma-polymerized organosilicon polymers. 

Thermogravimetric Analysis (TG). TG involves weighing a sample while it is exposed to heat. The chief use of this technique has been to study the thermal decomposition of polymeric materials and to accumulate kinetic information about such decomposition. A sample is suspended on a sensitive balance that measures the weight (Figure 1) as it is exposed to a furnace. Air, nitrogen, or another gas flows around the sample to remove the pyrolysis or combustion prod-... 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

Interesting supports are the polymeric materials, notwithstanding their thermal instability at high temperatures. In the electrocatalysis field, the use of polypyrrole, polythiophene and polyaniline as heteropolyanion supports was reported [2]. The catalytically active species were introduced, in this case, via electrochemical polymerization. Hasik et al. [3] studied the behavior of polyaniline supported tungstophosphoric acid in the isopropanol decomposition reaction. The authors established that a HPA molecular dispersion can be attained via a protonation reaction. The different behavior of the supported catalysts with respect to bulk acid, namely, predominantly redox activity versus acid-base activity, was attributed to that effect. 

Pyrolysis (thermal degradation) is used extensively with mass spectrometry for (i) elucidation of chemical structures of unknown polymers, (ii) assessing the thermal behavior of polymeric materials (e.g., in thermal processing or combustibility studies), and (iii) investigation of polymer decomposition kinetics and mechanisms. Pyrolysis field ionization (Py-FI-MS) turns out to be a very informative method for use in polymer decomposition studies, for several reasons. 

TG-DTA-MS has obvious synthetic polymer applications. TA-MS has been appHed to study the thermal behavior of homopolymers, copolymers, polymeric blends, composites, residual monomers, solvents, additives, and toxic degradation products. In the latter context, FICl evolution from heated polyfvinyl chloride) materials is readily quantified by TA-MS and such data are of major significance in the design of fire-resistant polymeric materials. Pyrotechnic materials have been studied by TA-MS. A complex sequence of thermal events relates to the decomposition of these materials involving interactions between the nitrocellulose, perchlorate, and metal components with periodic release of carbon dioxide and oxygen. Only by EGA is it possible to rationalize the thermal behavior of such materials. TA-FTIR has also been applied extensively to study the thermal characteristics of synthetic polymers... 

Thermogravimetry (or thermogravimetic analysis, TGA) is one of the oldest thermo-analytical procedures and has been used extensively in the study of polymeric systems. The technique involves monitoring the weight loss of the sample in a chosen atmosphere (usually nitrogen or air) as a function of temperature. It is a popular technique for the evaluation of the thermal decomposition kinetics of polymeric materials and hence provides information on thermal stability and shelf life. However, it is well known for its ability to provide information on the bulk composition of polymer compounds. 

Stability can be said as the protection of polymeric materials from which lead to deterioration of properties [9]. In literature, there are different and sometimes contradictory reported papers concerning the effect of the nanoparticles on polymer thermal stability. There are papers suggesting that nanoparticles have no obviously effect on thermal stability, some of them suggested a small to substantial enhancement and some others suggested acceleration of thermal decomposition. In a study performed by Ollier et al. [10], the author incorporated 5 % weight of bentonite in unsaturated polyester (UP) matrix. They noted that the addition of bentonite... 

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo-oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one-dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behavior compared with neat PP. Evidently, the mechanism of nanocomposite flame retardancy is based on shielding role of high-performance carbonaceous-silicate char which insulates the underlying polymeric material and slows down the mass loss rate of decomposition products. 

In this regard, thermogravimetric analysis (TGA) is known to be a powerful technique in the study of the thermal decomposition and thermal stability of polymeric materials [38, 39]. However, the potential of TGA to evaluate the thermo-oxidative stability of contemporary UHMWPE for orthopedic use remains mostly to be unveiled. 

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