Thermal volatilization analysis degradation

The degradation behaviour of polymethylmethacrylate is easily characterized by thermal volatilization analysis [87] (Fig. 29). Monomer is obtained in very high yield in all cases. A polymer sample prepared by a free radical reaction undergoes a rapid depolymerization at about 275°C as indicated by the first peak. The second peak, situated between 350 and 400°C, corresponds to a second mode of initiation of chain depolymerization. For samples prepared by anionic polymerization, the first peak is not observed. Depolymerization of the whole sample occurs above 350°C. 

A thermal volatilization analysis of polyvinylacetate degradation has been reported by Gardner and McNeill [200] (Fig. 54). Two maxima are observed at 322 and 435°C. The Pirani gauge situated after the 0°C trap responds to all volatile products, while the gauge situated after the —196°C trap responds only to non-condensable gases. Infrared analysis has shown the presence of carbon monoxide and methane in this last fraction. The... 

The rates of production of volatile material from polyvinylacetate, polyvinylchloride and vinylacetate vinylchloride copolymers, covering the entire composition range, have been compared by thermal volatilization analysis. It has been found that, at both extremes of the composition range, incorporation of the comonomer unit induces de-stabilization. Minimum stability occurs for composition of approximately 40—50 mole % vinylacetate. The rate of volatilization as a function of the composition of the copolymers is given in Fig. 74. The results were confirmed by a study of the thermal degradation in tritolylphosphate solution. The stability of the copolymers is a minimum at 30—40 mole % vinylacetate. HC1 and acetic acid catalyse the degradation of the... 

The thermal degradation of poly(vinyl bromide), of blends of this polymer with polyfmethyl methacrylate) and of the copolymer of vinyl bromide and methyl methacrylate have been investigated by sub-ambient thermal volatilization analysis and thermogravimetry. The results are discussed in relation to the use of the vinyl bromide unit as a Are retardant. 

With respect to apparatus, the design and operation of a sub-ambient thermal volatilization analysis (TVA) system has been described. A technique, which is essentially TVA, has also been used for the qualitative and quantitative analysis of trace amounts of volatiles produced during polymer degradation. A pyrolytic mass spectrometric method has also been developed which gives information on the yield of volatile degradation products, on their nature and on the kinetics of their formation. 

The volatile products from the decomposition of blends of polystyrene with polybutadiene have been examined by thermal volatilization analysis. Compared with the pure homopolymers there was no change in the nature of the degradation products, but the rate of polystyrene degradation was markedly reduced. The polybutadiene broke down first and its decomposition products diffused into and inhibited the subsequent breakdown of the polystyrene. 

A very detailed study of thermal PLA degradation was carried out by McNeill and Leiper [17,18]. They used TG, DSC and thermal volatilization analysis (TVA) in combination with H-NMR, IR and MS for product identification. Jamshidi et al. [19] and Zhang et al. [20] discussed inter- and intramolecular transesterfications as causes for tiie reduction of the molar mass when heated above the melting point. Five mechanisms have been postulated (Fig. 8.3). 

Early applications of what would later become analytical pyrolysis of silicone systems include work by Wacholtz et al. [61] in which the pyrolysis products of the thermal degradation of a silicone system were sampled and analyzed in-line using a combination of FTIR and GC/MS. Such early in-line pyrolysis studies of silicone degradation would later form the basis of modern microanalytical pyrolysis methodologies for the analysis of silicone degradation. However, until comparatively recent times the field of analytical deg-radative analysis of sihcones was almost entirely dominated by the vacuum pyrolysis technique—thermal volatilization analysis (TVA). 

Subambient thermal volatilization analysis can also be used to probe the effects of physical fillers in silicone materials. In 2008 Lewicki et al. [51] studied the degradation profiles and product speciation of a series of montmorillonite clay filled silicone elastomers which had been characterized using SATVA. Shown in Figure 13.17 are a series of TVA thermal degradation profiles for the non-oxidative degradation of a bimodal-condensation-cured silicone matrix, filled with 0-8 wt% of organically modified montmorillonite (0-MMT) exfoliated nanoclay platelets. 

Rincon, A. and McNeill, I. C., Thermal degradation of polycarbonate-poly(methyl methacrylate) blends by thermal volatilization analysis, Polym. Degrad. Stabil, 18(2), 99-110 (1987). 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

Thermal evolution analysis is an excellent tool for polymer studies complementary to other thermal techniques such as DTA, TG and pyrolysis. Its applications include thermal degradation studies, determination of additives and contaminants, polymer composition and structure identifications. With small variations, the apparatus can also be used for vapour pressure measurements, and for determination of odorous materials in polymer systems. Coupling of TEA to GC for the identification of effluents is practicable and useful. TEA-CT-GC was used for the analysis of volatiles from ABS 10 ppb of styrene but negligible acrylonitrile was detected in the headspace of a typical ABS resin [42]. 

Thermal volatilisation analysis (TVA) is a common method invented in the early 1970s that allows examination of the volatile products of degradation and gives the rate of volatilisation versus temperature (or time), as shown in Figure 3 for poly(isoprenyl acetate) (PIPA) [a.l5] 687290. ... 

Thermal volatilisation analysis (TVA) and sub-ambient thermal volatilisation analysis (SATVA) techniques are described. In addition to rate profiling of the volatile product flux of thermal degradation under high-vacuum conditions through measurement of pressure in the vacuum line as a function of sample temperature, the TVA technique is shown to afford a convenient method for an on the basis of volatility under high-vacuum conditions, of product fractions of thermal degradation for subsequent spectroscopic analysis. The capacity and flexibility of TVA as a platform for these analyses are illustrated in a case study format by degrading poly(bisphenol A, 2-... 

The thermal stability of a material is characterized mainly by thermogravi-metric analysis (TGA), where the sample mass loss due to volatilization of degraded by-products is monitored as a function of temperature. Usually, polymer-LDH nanocomposites have enhanced thermal stability compared with virgin polymers and conventional composites because the well-dispersed LDH layers can act as a superior thermal insulator and mass transport barrier to the volatile products generated during decomposition. 

Although the majority of studies focus on the solid state, many applications focus more or additionally on the volatile products arising from polymer degradation. Evolved gas analysis (EGA) from thermal analysers and pyrolysers by spectroscopic and coupled chromatography-spectroscopy techniques can be particularly important from a safety and hazard viewpoint, since data from such measurements can be used to predict toxic or polluting gases from fires, incinerators, etc. 

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