Vinyl chloride, sampling

Supercritical fluid extraction (SFE), microwave-assisted extraction (MAE) and Soxhlet extraction under various experimental conditions were applied for spiked poly(vinyl) chloride samples. Extracted dyes were separated in an ODS column (250 X 4.6 mm i.d. particle size 5 jum) using methanol as the mobile phase. Dyes are well separated by this method as demonstrated in Fig. 3.59. The optimal parameters of the extraction methods are compiled in Table 3.23. Recoveries depended on both the type of extraction method and the chemical structure of the dye. It was found that the highest recovery can be obtained by MAE and the extraction efficacy was the lowest for Solvent red 24 [129],... 

The Russian workers (12) also noted a significant effect of time of exposure to the radiation field before stress application on the resultant creep rate of poly (vinyl chloride) samples (Figure 8). 

The tan 5 curve at 1 Hz for a poly(vinyl chloride) sample shows two distinct relaxations (1) one at 210 K, attributed to main chain motion, and (2) a main tan 5 peak at 343 K, associated with the glass-rubber transition. 

Aoki et al. prepered PVC gels from well-characterised p>oly(vinyl chloride) samples and the solvent of bis(2-ethyUiexyl) phthalate (EXDP). In the experiment, four PVC samples were used and the gelation of the solution was examined with PVC concentration as the variable... 

Commercially available poly(vinyl chloride) contains small amounts of different abnormal structures (defects) which may originate from synthesis. Such groups are random unsaturation (allylic chlorines) [316, 317,710,956,957] chain end groups [2, 3, 357, 710, 955, 1431, 2052] branch points (tertiary-bonded chlorine atoms) [2,3, 319, 357, 995,1514,2052-2054] head-to-head units [3,309,357,710] and oxidized structures [3,317,357,700]. It has been estimated that the number of defects per 1000 monomer units in commercial poly(vinyl chloride) samples are [357] 4-6 chloromethyl branches, 0.4-2.4 chloroethyl branches, 0.4-1.6 butyl branches (value uncertain), 0.18-2.4 long branches (value uncertain), 6-7 head-to-head structures (values uncertain), 1.4-3 total double bonds and 0.08-0.27 internal double bonds. Labile chloride atoms have been estimated at 0.6-2.5 per 1000 monomer units of which 0.5-2.5 are allylic chlorine or ketochloroallylic chlorine and 0.16-1.0 are chlorine at tertiary carbon (value uncertain). The possible structures of these defects are given in Table 3.12. 

Table 3,13 Bromine double bond contents of some commercial poly(vinyl chloride) samples [271]...

Poly(vinyl chloride) samples can also contain traces of catalysts or products of their decomposition. 

Study of the kinetics of HCl evolution during UV, thermal and photo-thermal degradation shows that the amounts of produced HCl differ significantly depending on the treatment of the poly(vinyl chloride) samples [1792]. 

The constant quantum yield measured at room temperature implies that the degradation quantum efficiency is not dependent on the amount of these unsaturations in the commercial sample [407]. When the double bonds initially present in the poly(vinyl chloride) sample were removed by catalytic hydrogenation, before they induced photo-oxidation, the quantum yield of dehydrochlorination remained the same, (/>hci = 0.015, whereas the rates of degradation and discoloration were sharply reduced [552]. 

Polyene structures formed during the photodehydrochlorination of poly(vinyl chloride) samples are bleached in the dark as well under UV/VIS irradiation. Bleaching in the dark is a much slower process that in the presence of light. Oxygen plays an important role in bleaching processes in the dark and during light irradiation [771, 1674, 1791, 1881, 1882]. 

The initial rates of both thermal and photo-oxidative degradations are linearly related to the concentration of hydroperoxide groups in poly(vinyl chloride) samples, but not to the unsaturated groups and carbonyl concentration. 

Figure 10.79 shows a typical photoacoustic spectrum obtained for poly(vinyl chloride) samples exposed to different periods of UV irradiation. This spectrum shows the formation of polyene structures during the photodegradation process. 

This experiment describes a simple gravimetric procedure for determining the %w/w Cl in samples of poly(vinyl chloride). 

Automated analyzers may be used for continuous monitoring of ambient poUutants and EPA has developed continuous procedures (23) as alternatives to the referenced methods. Eor source sampling, EPA has specified extractive sampling trains and analytical methods for poUutants such as SO2 and SO [7446-11-9] sulfuric acid [7664-93-9] mists, NO, mercury [7439-97-6], beryUium [7440-41-7], vinyl chloride, and VOCs (volatile organic compounds). Some EPA New Source Performance Standards requite continuous monitors on specified sources. 

Molybdenum trioxide is a condensed-phase flame retardant (26). Its decomposition products ate nonvolatile and tend to increase chat yields. Two parts of molybdic oxide added to flexible poly(vinyl chloride) that contains 30 parts of plasticizer have been shown to increase the chat yield from 9.9 to 23.5%. Ninety percent of the molybdenum was recovered from the chat after the sample was burned. A reaction between the flame retardant and the chlorine to form M0O2 012 H20, a nonvolatile compound, was assumed. This compound was assumed to promote chat formation (26,27). 

There are numerous misconceptions about the sources of various chemical elements in waste, particularly those that are potential acid formers when the waste is incinerated or mechanically converted and used as a refuse-derived fuel. For example, it is often mistakenly stated that the source of chlorine in waste, hence a potential source of HCl emissions, is poly(vinyl chloride). The relative contents of selected, potentially acid-forming elements in the organic portion of a sample of waste collected from various households in one U.S. East Coast city is given in Table 2 (17). In this city, a chief source of chlorine in the waste is NaCl, probably from food waste. 

Vinyhdene chloride is hepatotoxic, but does not appear to be a carcinogen (13—18). Pharmacokinetic studies indicate that the behavior of vinyl chloride and vinyhdene chloride in rats and mice is substantially different (19). No unusual health problems have been observed in workers exposed to vinyhdene chloride monomer over varying periods (20). Because vinyhdene chloride degrades rapidly in the atmosphere, air pollution is not likely to be a problem (21). Worker exposure is the main concern. Sampling techniques for monitoring worker exposure to vinyhdene chloride vapor are being developed (22). 

Much work has been carried out in order to elucidate the molecular structure of poly(vinyl chloride). In 1939, Marvel, Sample and Roy dechlorinated PVC with zinc dust to give linked cyclic structures (Figure 12.9). 

From the results obtained by thermal decomposition of both low-molecular weight vicinal dichlorides in the gas phase [74,75] and of the copolymers of vinyl chloride and /rthermal instability of PVC to the individual head-to-head structures. Crawley and McNeill [76] chlorinated m-1,4-polybutadiene in methylene chloride, leading to a head-to-head, and a tail-to-tail PVC. They found, for powder samples under programmed heating conditions, that head-to-head polymers had a lower threshold temperature of degradation than normal PVC, but reached its maximum rate of degradation at higher temperatures. 

Marvel, Sample, and Roy concluded that cyclopropane rings were formed when a dilute solution of poly-(vinyl chloride) in dioxane was treated with zinc, which removes halogen atoms from alternate carbon atoms. Only 84 to 86 percent of the chlorine could be removed, however, a result which was attributed to the occasional isolation of a lone substituent between reacted neighbors. The structure of the product was presumed to be... 

Suitable PLOT columns for the determination of vinyl chloride monomer in PVC include 15.00 m, 0.53 mm bonded polystyrene-divinyl benzene and 30 m, 0.53 mm porous divinyl benzene homopolymer types. Typical responses for vinyl chloride monomer standards (0.06, 0.19 and 0.31 mg/1) in N,N-d imethylaceta-mide expressed as mg/kg vinyl chloride (PVC sample) using the 30 m homopolymer column and flame ionisation detection are shown in Figure 38. An automatic static headspace sampler was employed. 

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