Mass Spectrometric Studies of Thermal-Nonoxidative Degradation of Poly(vinyl chloride)

Abstract

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...

Effects of MgAlCe‐CO3 layered double hydroxides on the thermal stability of PVC resin

“…Compared with the PVC strips containing MgAl‐CO 3 ‐LDH, the long‐term stabilization effect of PVC composites containing MgAlCe‐CO 3 ‐LDHs are more excellent although the early coloring maintains just a little better. The effect about thermal stabilization of rare earth on PVC is attributed to the strong complexation property of rare earth elements, which have longer atom radius and more coordination numbers 24. According to the conception of Lewis' acid and alkali, rare earth ions belong to hard‐acid, and they are inclined to coordinate with the hard‐alkali chloride ions in PVC main chains 25.…”

Pyro-GC/MS and thermal degradation studies in polystyrene–poly(vinyl chloride) blends

“…But with higher PVC contents (20 wt.%) three DTGA peaks are observed and it seems (phase separated) PVC component decomposes earlier than PS. The pure PVC generally degrades [24][25][26] in two steps. The first step, in the temperature range of 220-320 8C, involves a dehydrochlorination reaction.…”

“…In these blends, whereas PVC firststep degradation is not affected by PS, the degradation of PS is affected by the degraded components of PVC. The third DTGA peak is around 500 8C and due to second degradation step of PVC where the polyene linkages are formed as a result of dehydrochlorination ultimately giving volatile aromatic products [24][25][26]. These results show that blends with higher PVC loading degrade predominantly within their phase-separated regions.…”

“…5) it is found that PVC degrades earlier (around 220 8C). The initial degrading products from PVC [24][25][26] are chlorine radical (reaction 1) as shown in Scheme 1. The chlorine radicals, however, can interact with the PVC polymer chain (reaction 2) abstracting hydrogen from the chain thus forming HCl or these can also interact with the PS chain.…”

“…4 and 5, respectively, where the mass of the residual content in the blends retained after 400 8C is much higher in comparison to pure PS. The cross-linked products, which are relatively more stable formed by the reaction of two macroradicals from PS and PVC has also increased the T max for the second stage of degradation in blends (Table 1) which is mainly due to aromatization of polyene linkages formed by the dehydrochlorination of PVC [24,25]. In the pure PVC such weight loss due to formation of volatile aromatics was around 440 8C but in the presence of PS this either occurs at higher temperature or this stage is not detected as the cross-linked network structures may not be able form volatile aromatics in the blends ( Table 1).…”