Laser-induced decomposition of PVC

A laser probe–molecular beam experimental technique devised to investigate the dynamic characteristics of polymer decomposition processes is described. Results are presented from application of the technique to the laser vaporization of pure poly(vinyl chloride) (PVC). Vaporization products are sampled directly from the source cell using modulated molecular beam mass spectrometry. Only signals arising from the PVC species in the molecular beam appear in the modulated mass spectra; background species from the residual gas are automatically rejected. Time-resolved spectra provide information on the relative evolution characteristics of the PVC decomposition products. Hydrogen chloride, benzene, and toluene are found to evolve concurrently from the irradiated PVC sample. PVC monomer species are not detected in the laser-vaporized products. The presence of loosely bound water in the sample is distinguished from the evolution of volatile decomposition products by its burst-like release mode. The effect of plasticizer and flame retardant additives on the evolution characteristics of the laser-vaporized species from PVC are also presented.     

Toxicity of the pyrolysis and combustion products of poly(vinyl chlorides): A literature assessment

Poly(vinyl chlorides) (PVC) constitute a major class of synthetic plastics, Many surveys of the voluminous literature have been performed. This report reviews the literature published in English from 1969 through 1984 and endeavors to be more interpretive than comprehensive. PVC compounds, in general, are among the more fire resistant common organic polymers, natural or synthetic. The major products of thermal decomposition include hydrogen chloride, benzene and unsaturated hydrocarbons. In the presence of oxygen, carbon monoxide, carbon dioxide and water are included among the common combustion products. The main toxic products from PVC fires are hydrogen chloride (a sensory and pulmonary irritant) and carbon monoxide (an asphyxiant). The LC₅₀ value calculated for a series of natural and synthetic materials thermally decomposed according to the NBS toxicity test method ranged from 0.045 to 57 mg l^?1 in the flaming mode and from 0.045 to > 40 mg l^?1 in the non-flaming mode. The LC₅₀ results for a PVC resin decomposed under the same conditions were 17 mg l^?1 in the flaming mode and 20 mg l^?1 in the non-flaming mode. These results indicate that PVC decomposition products are not extremely toxic when compared with those from other common building materials. When the combustion toxicity (based on their HCI content) of PVC materials in compared with pure HCI experiments, it appears that much of the post-exposure toxicity can be explained by the HCI that is generated.     

异氰酸酯的合成研究进展

异氰酸酯是一种重要的有机中间体,综述了异氰酸酯的合成方法,并对各种方法的优缺点作了简要评价。目前,工业上的主流方法为光气法,但业内一直在积极探索新的绿色合成方法,其中,三光气法和氨基甲酸酯热分解法是具有开发前景的工业合成方法。     

Sulfur containing polymers

Summary Copolymers containing -S-CO-S-and/or -O-CO-S-groups have been synthesized mainly by interfacial polycondensation.Different chemical structures were obtained by reacting 1,3-benzene dithiol (BDT) respectively with phosgene alone, phosgene and bisphenol-A (BPA), bischloroformate of BPA, BPA polycarbonate oligomers and by reacting phosgene with the products of BPA polycarbonate degraded with BDT. The chemical structures of the copolymers were investigated by IR, ¹H-NMR and ¹³C-NMR; molecular weights were determined by viscometry and vapor pressure osmometry. Although no attempt was made to find the optimum conditions for high molecular weight, some copolymers with fairly high mol. weight were obtained.     

气相色谱-质谱法研究聚氯乙烯的热裂解行为

采用气相色谱-质谱法并结合热重分析法对聚氯乙烯(PVC)的热裂解行为进行了研究。首先对PVC的热失重行为进行考察,确定最佳裂解温度;然后分别在350℃和600℃下对PVC进行热裂解,并用气相色谱-质谱联用仪对裂解产物进行定性和半定量分析。结果表明:在350℃下,PVC裂解产物主要以HCl和苯等易挥发物质为主;在600℃下,裂解产物为多环芳烃,但未检测到HCl。根据裂解产物的种类及相对含量的变化,确定PVC的分段裂解回收工艺,从而提高了热裂解产物的回收率和热裂解效率。     

STUDY ON THE PYROLYSIS AND RECYCLING OF PVC WASTE AS AN ENERGY SOURCE

The pyrolysis dechlorination of PVC (polyvinyl chloride) has been carried out by batch operation under atmospheric pressure. The kinetics involved in the PVC thermal decomposition was studied by using thermogravimetric technique. Several tests were carried out at the heating rate of 5-10℃/min, the yields of products and the distribution of chlorine were also studied. The kinetic parameters such as activation energies, reaction orders and preexponential factors under nitrogen atmosphere were calculated by applying Friedmans method. The results showed that the PVC thermal degradation is substantially a two-step process. The first step mainly involves dechlorination of the polymers. HCI is the main volatile product and this reaction can be seen as a first-order reaction. A kinetic model for the thermal dechlorination of PVC has been developed.     

Nitrogen-containing products from the thermal decomposition of flexible polyurethane foams

The thermal decomposition of a polyester and a polyether flexible foam in a nitrogen atmosphere has been studied by gas chromatography, mass spec-trometry and elemental ultramicroanalysis. It is shown that the decomposition behaviours of the two foams are similar. At low temperatures (200 to 300 °C) there is a rapid and complete loss of the tolylene diisocyanate unit of each foam as a volatile yellow smoke leaving a polyol residue. The smoke has been isolated as a yellow solid (common to both foams) which contains virtually all of the nitrogen of the original foams and, under the conditions of test, is stable at temperatures up to 750 °C. Nitrogen-containing products of low molecular weight (mainly hydrogen cyanide, acetonitrile, acrylonitrile, pyridine and benzonitrile) observed during the high temperature decomposition (over 800 °C) of the foams are shown to be derived from the yellow smokes. At 1000 °C, approximately 70% of the available nitrogen has been recovered as hydrogen cyanide.     

Liquid-phase degradation of poly(vinyl chloride)

The main kinetic regularities of the thermal and thermal-oxidative degradation of poly(vinyl chloride) (PVC) in the liquid phase have been analyzed in comparison with the solid-phase degradation of PVC. The thermal (in an N₂ atmosphere) degradation of PVC in the form of dilute solutions is characterized by a number of essential distinctions, the primary peculiarity consisting of a lower dehydrochlorination rate due to the retarded reaction of the formation of bond polyconjugated systems. The same is observed for the thermal degradation of PVC plasticized with di- and polyesters. On the contrary, in an oxygen-containing atmosphere the solvents promote PVC decomposition. Accelerated PVC degradation under such conditions is due to the solvent oxidation that causes the appearance, within the system, of products activating the PVC macromolecular decomposition. The intensified degradation processes are accounted for, in the first place, by an increased reaction rate of the statistical (by the random law) detachment of HCl from normal macromolecular units. In general, the kinetics of the thermal-oxidative liquid-phase degradation of PVC is determined by the partial pressure of oxygen in the reaction zone, by the quantity of the solvent introduced into the polymer, as well as by the oxidative stability of the solvent. It has been shown that an effective stabilization of PVC in the liquid phase, particularly in the systems highly plasticized with esters, can be achieved through stabilizing the solvent, first of all, rather than the polymer, against oxidative decomposition. In this case the PVC dehydrochlorination rate decreases sharply and may reach an essentially lower value than under similar conditions of the solid-phase thermal degradation of PVC. PVC stabilization with respect to the reaction of HCl elimination achieved through the solvent stabilization against thermal-oxidative decomposition has been called the effect of “echo-stabilization” of PVC.     

A review of products evolved from heated coal,wood and PVC

A review is presented of the gaseous combustion and pyrolysis products evolved from coal, wood and PVC. Information has been collated on the range of products evolved, the temperatures of evolution and the effect of different ambient conditions (e.g. oxidizing of inert conditions). The data for coal have been subdivided into those from which rates of gas evolution have been or can be derived and those from which this is not possible. Probable decomposition routes for PVC and for wood are discussed. Although all three materials have been widely studied, the correlation between the work of different authors in not always good. The data obtained are dependent on the form of the experiment, and there are gaps in the information available, especially information on the rates of evolution of products of products as a function of temperature.     

Gamma radiation stabilization of PVC

A new class of additives combining heat and radiation stabilization has been shown to prevent the discoloration and associated undesirable hydrogen chloride formation encountered when PVC is exposed to sterilizing doses of gamma radiation. Various mechanisms that lead to the decomposition are described and the free radical processes that cause changes in physical and mechanical properties are discussed. The performance of the new additives demonstrates that rigid PVC can be exposed to high (> 5MRad) radiation with little or no discoloration and loss of physical properties.     

Thermal Decomposition of Polymer Mixtures Containing Poly(vinyl chloride)

Thermal decomposition of a series of 1 : 1 mixtures of typical polymer waste materials [polyethylene (PE), poly(propylene) (PP), polystyrene (PS), polyacrylonitrile (PAN), polyisoprene, poly(methyl methacrylate) (PMMA), polyamide‐6 (PA‐6), polyamide‐12 (PA‐12), polyamide‐6,6 (PA‐6,6), and poly(1,4‐phenylene terephthalamide) (Kevlar)] with poly(vinyl chloride) (PVC) was examined using thermal analysis and analytical pyrolysis techniques. It was found that the presence of polyamides and PAN promotes the dehydrochlorination of PVC, but PVC has no effect on the main decomposition temperature of polyamides. The hydrogen chloride evolution from PVC is not altered when other vinyl polymers or polyolefins are present. The thermal degradation of PAN is retarded significantly, whereas that of the other vinyl polymers is shifted to a slightly higher temperature in the presence of PVC. Among the pyrolysis products of PAN‐PVC mixture methyl chloride was found in comparable amount to the other gaseous products at 500°C pyrolysis temperature.     

Role of poly(vinylchloride) and Di-2-ethyl hexyl-phthalate in the smoke formation from plasticized poly(vinylchloride)

The increase of the smoke level from PVC plasticized with di-2-ethyl hexyl phthalate with respect to the rigid PVC is caused mainly by interaction of the plasticizer with HCl evolved from the polymer when the temperature is higher than 200°C. This interaction causes the increase of the yield of phthalic anhydride probably through HCl as catalyst for DOP decomposition but phthalic anhydride formation parallels the formation of products enabled to increase the smoke level such as phthalic acid. In the presence of metallic compounds (iron, zinc, aluminium) it is possible to favor the formation of phthalic anhydride with respect to these products which are responsible for the smoke production. Then phthalic anhydride can be used as a tracer to estimate the efficiency of an additive or a combination of additives as smoke suppressant for DOP because its smoke level varies inversely with the yield of phthalic anhydride. The best combination to reduce the smoke level from plasticized PVC is obtained with the binary systems based upon copper compound, mainly efficient as smoke suppressant for PVC and either zinc or aluminium compounds, mainly efficient as smoke suppressant for DOP.     

建立PVC料浆测定法,确定汽提系统最佳操作条件

利用气相色谱法对PVC料浆中残留VCM含量进行测定。此方法简便、快捷,并具有较好的精密度与准确度。残留VCM的回收率为95%～103%,精密度为0.2%～2.5%。该方法的建立对提高PVC产品的质量具有积极的指导意义。     

Update on smoke toxicity of vinyl compounds

All organic materials burn and give off toxic products. These always include water, carbon dioxide, and the single gas causing the greatest hazard in fires—carbon monoxide (CO). The intrinsic toxicity of the smoke of all combustible materials, including PVC, is very similar in terms of lethality, with very few exceptions. Toxicity of vinyl compounds is due to two major gases: CO and hydrogen chloride (HCI). Since natural combustible materials are not chlorinated, speculation has arisen about the toxicity of HCl and of PVC smoke. Recent studies have shown that it takes similar doses of HCl and CO to kill rats. Furthermore, rats and baboons will tolerate the same levels of HCl. However, mice are much more sensitive than either rats or baboons towards HCl. Baboons are a very good model for humans; therefore, mice will be killed by exposure to much lower HCl levels than those required to kill humans. HCl concentrations in real fires are quite low: HCl decays rapidly by reacting with wall materials such as gypsum, cement, or ceiling tile. It does not, however, react rapidly with plastic or glass walls, which is where toxicity tests are carried out. Therefore PVC smoke is less hazardous in reality than it appears to be from toxicity test results. Since most products have similar intrinsic toxicities, as regards lethality, the real toxicity in a fire is a consequence of the rate of generation of gases. PVC is a difficult polymer to ignite and burns very slowly, so that it will give off less toxic products per unit time than many other common materials and cause lower fire hazard.     

Poly(vinyl chloride) polymerization performance-enhancing initiators with emphasis on high activity grades and water-based dispersions

Vinyl chloride is most commonly polymerized by suspension processes, where surface active materials as granulating agents and organic peroxides as free radical initiators are the crucial additives, which may affect PVC qualities substantially. Among the wide variety of usable and commercially available organic peroxides, the most suitable types for an individual process need to be selected with specific regard to reactivity, polymerization performance, storage, and handling. Currently, high activity types are subject of continuously growing interest to many PVC manufacturers who are trying to achieve higher productivity and to expand their product range mainly by focusing on PVC grades of higher molecular mass. A short comparison between the different alternatives of highly active initiators is given, showing the potential for further improvement by using a new difunctional peroxyneodecanoate. Among the manifold formulations of organic peroxides, which have been developed, particular importance is attached to water-based grades. Dispersions of solid peroxydicarbonates are explained in detail, and their outstanding benefits on performance and safety are covered.     

Vinyl chloride formation from the thermal degradation of poly(vinyl chloride)

The volatile products from the thermal degradation of poly(vinyl chloride) (PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 210°C, vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry.     

Synthesis and some properties of anthracene and anthraquinone incorporated poly(vinyl chloride) and the ion exchange resin therefrom

Poly(vinyl chloride) has been modified by chlorine displacement reaction with 2-anthrol and anthraquinone-2-ol. The condensates (PVC-ACOL and PVC-AQOL) are insoluble in all solvents common to PVC and have been characterized by elemental and IR spectra analysis. The initial decomposition temperature of these condensates follow the trend: PVC-AQOL (250°C) > PVC-ACOL (200°C) > PVC(190°C) and the overall thermal stabilities beyond 60% decomposition follows the same trend. Permittivity and dielectric loss of these condensates sharply fall with increasing applied frequency (10–1.3 ×10⁷ Hz) to a limiting constant value. In contrast, for unmodified PVC these values are low and remain independent of frequency in the same range. Sulfonation of these PVC condensates affords a weak acid resin with ? COOH and ? OH ionogenic groups, but no strong sulfonic acid groups due presumably to oxidative degradation of the PVC matrix.     

Vinyl chloride formation from the thermal degradation of poly(vinyl chloride)

The volatile products from the thermal degradation of poly(vinyl chloride) (PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 210°C., vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry.     

A study of the reaction of dry hydrogen chloride with white lead suspended in di—2—ethyl hexyl phthalate at 182 °C

In order to test certain ideas which have recently been formulated on the way in which basic lead compounds stabilise polyvinyl chloride against thermal decomposition, the reaction of dry hydrogen chloride with a suspension of white lead in hot di-2-ethyl hexyl phthalate was studied by withdrawing samples and examining the solids by X-ray diffraction. Normal lead phthalate, and an uncharacterised substance which has been called “basic lead chloride X”, were formed initially. Subsequently, this basic lead chloride X was converted to normal lead chloride. The continuous formation of normal lead phthalate in this experiment contrasts with observations made on the crystalline products of stabilising reactions in PVC blends containing basic lead carbonates, and suggests that there are fundamental differences between the reaction mechanisms which prevail in these two systems. It is proposed that the results obtained with PVC blends are best explained in terms of free-radical mechanisms for thermal decomposition and stabilisation of this polymer, whereas the results obtained in the present experiment can be explained by a simple acid—base type reaction. X-ray powder diffraction data are tabulated for normal lead phthalate.     

Stabilizers for peroxydicarbonate initiator solutions

Liquid dialkyl peroxydicarbonates are used as initiators in the PVC industry. Because of the thermal reactivity of these initiators, they require very low temperature storage, shipment, and handling. At temperatures above 10°C, most undergo autoaccelerated self-induced decomposition. In other words, their self-accelerating decomposition temperature (SADT) is exceeded. New additives have been discovered which increase the SADT of the initiators. These additives effectively stabilize the products, making them safer to handle, store, and ship. The proprietary additives and a mechanism of stabilization are discussed. We also include a section concerning the implications these products have for future initiator formulation.