The porous nature of alumina has been investigated using various techniques. The values obtained for moisture content, surface area, pore volume, average particle size and porosity were 22%, 116 m2/g, 0.76 cm3/g, 17.0±0.5 μm and 68.0%, respectively. The adsorption isotherms of NdIII, PrIII and ErIII on alumina from aqueous solution have been obtained at different temperatures. All these adsorption isotherms obey the Langmuir, Freundlich and Dubinin-Radushkevich isotherm equations. Thermodynamic parameters such as the free energy, entropy and enthalpy of adsorption have been computed and interpreted. It is noteworthy that the adsorption of PrIII and NdIII increases with decreasing temperature while the reverse is observed for ErIII.
ABSTRACT:Mass spectrometric studies of thermal-nonoxidative degradation of poly(vinyl chloride) (PVC) were carried out in the temperature range of 473-523 K. The population of various series of polyene linkages at different temperatures was studied. Concentration of polyene linkages with odd numbers of carbon atoms were found to be minimal as compared to polyene linkages containing the adjacent even numbers of carbon atoms. These results are explained on the basis of strain on the valence angle and permissible ring formation and agree with those of Spanagel and Carother on depolymerization of polyesters.KEY WORDS Poly(vinyl chloride)/ Thermal Non-oxidative Degradation/ Mass Spectrometry Polyenes Yield / Spanagel Carother Theory / Poly(vinyl chloride) (PVC) is the second most important plastic used in the world both in rigid and flexible forms. Although it has numerous excellent properties thermal degradation of PVC occurs during processing, or when it is subjected to high temperature while in use. In the early stages, dehydrochlorination of PVC takes place and long conjugated polyene linkages are formed. Rapid growth of a polyene sequence takes place probably as a consequence of allylic activation of monomeric units in the vicinity of the C = C bond. The growth of polyene sequence ceases after reaching a certain length. This process is often called zip reaction and has been studied by various techniques including dehydrochlorination, 1 -3 TGA, 4 • 5 IR, 6 NMR, 7 ESR, 8 UV, 9 -11 and mass spectrometry. 12 In the later stages, long polyene linkages further decompose into smaller ones and these small polyene linkages may cyclize to form cyclic compounds as shown by many workers. 13 • 14 This paper discusses the second stage of degradation in which long polyene linkages break down into smaller ones and cyclize via intra or intermolecular interactions. The relatively large amount of polyene linkage containing even numbers of carbon atoms rather than odd numbers has been explained on the basis of a theory due to Spanagel and Carother. 15
EXPERIMENT ALAnalytical grade PVC powder (BDH, England) (MW= 100000 ± 20), (100% of the powder passes through 60 mesh and 74% through 200 mesh) was used as such. PVC was dissolved in peroxide-free spectrograde tetrahydrofuran.For mass spectrometric measurements, a sample was degraded in the pyrolysis unit of GC/MS for 15 min in a N 2 atmosphere at the desired temperature. The volatile products of degradation were introduced to the mass spectrometer (Shimadzu GCMS QP 1000) by the vacuum system of the spectrometer. The species formed were passed through the gas chromatograph column OV-17 and were detected by the molybedinum hyperbolic quadrupole of mass spectrometer. The software of GC/MS displayed the spectra of the sample. Yields of different polyenes were differentiated by pattern recognition analysis.
RESULTS AND DISCUSSIONThe results of mass spectrometeric studies shows that dehydrochlorination of PVC occurs with the formation of polyene linkages and is followed by the breaking o...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.