Hydrogen Halide-Catalyzed Thermal Decomposition of Poly(vinyl Chloride)

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Protective Effect of Water against Toxicity of Pyroiysis and Combustion Products of Wood and Polyvinyl Chloride)

The toxicity by inhalation of combustion and pyroiysis products of a PVC and a wood (Douglas Fir) has been studied by the physiogram method, in the rabbit in controlled ventilation and by the mask cage method in spontaneous ventilation. The protecting effect of water was evaluated by trapping the gases and vapors with an impinger placed on the air flow just before the animals. Combustion and pyrolysis products were generated by an annular furnace moving along a strip of samples. The temperature of the furnace was 400°C for smoldering conditions and 850°C for flaming conditions. CO, CO₂, 0₂, and HC1 were determined in the atmospheres; pO₂, pCO₂, pH, CO, COHb in the animals' blood and EEG, EKG, and arterial pressure were recorded. The animals are very significantly protected by water against PVC fumes (HC1 is very soluble in water) and in part protected against fumes from combustion of wood. In both cases, CO is not trapped and seems to be then the determinant toxicant.     

Heat Degradation of PVC Stabilized by Treatment with Alkylaluminum Compounds

Thermal degradation of PVC treated with alkylaluminum compounds has been studied. Four PVC samples of different molecular weights have been treated with Me₃Al, and Et₃A₁, and the dehydrochlorination rates of the polymers were determined at 190 and 220°C under a nitrogen atmosphere. The alkylaluminum-treated low molecular weight samples show marked increase in thermal stability, i. e., slower rate of dehydrochlorination right from the beginning of degradation, whereas with the higher molecular weight samples stabilization becomes pronounced only after a few percent of dehydrochlorination. The color of R₃Al-treated samples was much lighter (yellowish) than those of controls (dark brown) at 1% HCl loss. The average polyene sequence lengths formed during the early stages of dehydrochlorination are found to be much shorter with RsAl-treated PVC than with virgin samples. It appears as though polyene sequences which arose by zipping- initiation from allylic and/or tertiary chlorine sites are longer than those which form by random initiation along the chain. The autocatalytic (i. e., HC1-catalyzed) dehydrochlorination observed with virgin PVC disappears after treatment with R3A1. The HCl-catalyzed dehydrochlorination is minimized when thin films are used instead of powdery samples, which may be due to higher rates of HC1 diffusion through thin films. Autocatalysis of dehydrochlorination is affected by the concentrations of double bonds and HCl and the length of polyene sequences. Interaction between polyenes and HC1 by hydrogen transfer may lead to the re-initiation of unzipping, thus lengthening the polyene sequences.     

Mechanical and dielectric absorption of poly(vinyl chloride) and some related polymers

The mechanical and dielectric low temperature absorptions of poly(vinyl chloride) (PVC) and several modified PVC's have been studied over the temperature range from ?60 to +60°C. with some tests extending to ?150°C. and others to +170°C. The results indicate that the low-temperature absorption near ?50°C (β₂ absorption) decreases in intensity with chlorination, while the absorption at a higher temperature near 0°C (β₁ absorption) decreases in intensity with hydrogenation. The apparent activation energies of the β₁ and β₂ absorptions were calculated to be 16 kcal/mole and 10.7 kcal/mole, respectively. Besides, the β₂ absorption markedly decreases in intensity with addition of plasticizer, while the intensity of β₁ absorption is not much affected by increasing plasticizer content. From these results, the β₁ and β₂ processes are concluded to be the results of molecular motion in crystalline and amorphous region in PVC, respectively. For samples of reduced Cl content, another low-temperature absorption was located near ?120°C (γ absorption) and attributed to the presence of short sequences of ethylene units. It has also been observed that the temperature location of the high temperature absorption near 100°C (α absorption) shifts linearly to higher temperature with increasing chlorine content and to lower temperature with increasing hydrogen content.     

Radical block polymerization of vinyl chloride. II. Synthesis and characterization of vinyl chloride block copolymers

Peroxidized polypropylene has been used as a heterofunctional initiator for a two-step emulsion polymerization of a vinyl monomer (M₁) and vinyl chloride with the production of vinyl chloride block copolymers. Styrene, methyl-, and n-butyl methacrylate and methyl-, ethyl-, n-butyl-, and 2-ethyl-hexyl acrylate have been used as M₁ and polymerized at 30–40°C. In the second step vinyl chloride was polymerized at 50°C. The range of chemical composition of the block copolymers depends on the rate of the first-step polymerization of M₁ and the duration of the second step; e.g., with 2-ethyl-hexyl acrylate block copolymers could be obtained with a vinyl chloride content of 25–90%. The block copolymers have been submitted to precipitation fractionation and GPC analysis. Noteworthy is the absence of any significant amount of homopolymers, as well as poly(M₁)n as PVC. The absence of homo-PVC was interpreted by an intra- and intermolecular tertiary hydrogen atom transfer from polypropylene residue to growing PVC sequences. The presence of saturated end groups on the PVC chains is responsible for the improved thermal stability of these block polymers, as well as their low rate of dehydrochlorination (180°C). Molecular aggregation in solution has been shown by molecular weight determination in benzene and tetrahydrofuran.     

Studies of the photooxidation mechanism of polymers. III. Role of tetrahydrofuran in the photooxidative degradation of poly(vinyl chloride)

The influence of tetrahydrofuran (THF) on photooxidative degradation of poly(vinyl chloride) in films cast from THF solution was studied. THF is partially retained in the polymer matrix in amounts of 6–8% after casting and drying the film. The last 2–3% is very difficult to remove. By use of thermogravimetric analysis, density measurements, and gas permeability measurements, it was shown that THF residues can be removed by preheating the PVC samples to 80°C. THF forms a charge-transfer complex with oxygen which is easily photolyzed. During this reaction hydroperoxide radicals are formed. Molecular weight distribution curves by gel-permeation chromatography (GPC) show that THF in the presence of air promotes the photodegradation of PVC. Attention has been given to the correct interpretation of the infrared absorption spectra of PVC films containing THF residues and ultraviolet-irradiated in air.     

Nonenzymatic glucose sensing at ruthenium dioxide–poly(vinyl chloride)–Nafion composite electrode

Development of nonenzymatic glucose sensors with high reproducibility and stability is an urgent need to reduce cost of regular diabetic monitoring. Here, we have fabricated ruthenium dioxide–poly(vinyl chloride)–Nafion (RuO₂–PVC–Nafion) composite for direct glucose sensing in sodium hydroxide and phosphate buffer nonenzymatically for the first time. The restricted activity of the RuO₂–PVC film electrode in alkaline pH is extended to neutral pH using Nafion as an outer membrane, which reduces the distance between Ru active sites by bridging effect and improves the electrode stability. The catalytic rate, measured in terms of change of RuO₂ resistance, is similar irrespective of the medium for the high temperature annealed RuO₂ (700 °C), whereas the low temperature annealed RuO₂ (300 °C) is highly sensitive for the change in the pH of the solution. This is revealed by observing large Michaelis–Menten kinetic constant K _M for the RuO₂ (700 °C) than the low temperature annealed RuO₂ (300 °C) due to effective increase in the catalytic active sites similar to oxygen evolution reaction. Contrast to this, the buffer solution does not influence significantly the apparent K _M observed for RuO₂ (300 °C) and has greater impact on the high temperature 500 and 700 °C annealed RuO₂ samples. Cyclic voltammetry, chrono amperommetry, and electrochemical impedance spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction techniques are used for characterization of the sensor behavior. The RuO₂–PVC–Nafion senses glucose selectively in the presence of potential interferences like fructose, galactose, mannose, sucrose, starch, uric acid, ascorbic acid, dopamine, and catechol in NaOH and phosphate buffer. Glucose sensing in the blood serum of the diabetic and nondiabetic patients is made. The results suggest that the RuO₂–PVC–Nafion is a promising candidate for the development of nonenzymatic glucose sensors.     

Evolution of HCN by thermal oxidative degradation from nylon 66 at high temperatures including burning

Work on the evolution of HCN from nylon 66 was extended to temperatures from ca. 300 to 695°C. Below ca. 300°C the evolution of HCN is governed by chemical decomposition, and above 300°C the evolution is controlled by diffusion. Above 530°C oxidation of HCN becomes noticeable and ignition occurs at 590°C. The rate constants for all of the temperature ranges and for the oxidation of HCN are given in terms of Arrhenius equations. The activation energy for the oxidation of HCN before ignition (590°C) is reached is 47 kcal/mole, and beyond this point, the oxidation is controlled by diffusion. The rate constants increase linearly with oxygen concentration as long as HCN oxidation is negligible; however, they pass through maxima if HCN oxidation is appreciable (some HCN is evolved even in the absence of oxygen). A new flash degradation apparatus has been constructed for these high-temperature ranges and a degradation mechanism has been proposed which is in satisfactory agreement with the experimental results.     

Mathematical models of the initial stage of the thermal degradation of poly(vinyl chloride). II. The thermal degradation of poly(vinyl chloride) with effective removal of HCl

The dehydrochlorination of different samples of PVC under vacuum with continuous removal of HCl by freezing, has been studied at 180–210°C. The comparison of the kinetic curves of the dehydrochlorination of various samples of PVC which were obtained by us and other investigators, with the theoretical curves for the thermal degradation of idealized PVC in the absence of HCl has been carried out. This had made it possible to evaluate the influence of unstable fragments present in the original polymer on the initial rate of PVC degradation quantitatively. It has been shown that the distinction between the stationary rates of the dehydrochlorination of various samples of PVC is determined by the difference of the values of the average length of dehydrochlorination chain, l_av. The most probable interval of the values of l_av has been ascertained to be 4–12. It is established that the most probable value of the constant of the rate of dehydrochlorination of normal links of PVC, k₀, is 2.1 × 10^?7?2.5 × 10^?7 s^?1 at 200°C. © 1993 John Wiley & Sons, Inc.     

Intralaboratory validation of an analytical method for determining the migration of bis(2-ethylhexyl) adipate from packaging to fat foods

Polyvinylchloride (PVC) has been widely used in the packaging industry in the form of flexible films for food packaging. Among the main plasticizers used in flexible PVC films is bis(2-ethylhexyl) adipate, DEHA. Brazilian law provides a specific migration limit for DEHA of 18 mg kg^?1 of food simulant. Although Brazilian Sanitary Surveillance Agency Resolution no. 51 (passed on November 26, 2010) establishes conditions for the migration test, there is a need for intralaboratory validation of the method involved. This paper presents the validation of a method for determining the migration of DEHA from food packaging using fatty food simulant. The DEHA migration test was performed through contact between a 1 dm² PVC film cutout and 100 ml of a food simulant, 2,2,4-trimethylpentane (isooctane), for 48 h at 20 °C. The mass fraction of DEHA in the migration solutions was determined by gas chromatography with a flame ionization detector. The method was validated and determined to be well suited to the intended purpose. The working range was defined as 5–25 mg kg^?1 and was determined to be linear, with no observed lack of fit to the model. There was no matrix effect, and the selectivity of the method was considered adequate. The method showed adequate repeatability, intermediate precision, and robust results for migration temperature and migration time: 20 °C with tolerance limit of ±3 °C and 48 h with tolerance limit of ±30 min, respectively.     

Physico-Chemical Characterization of Poly(vinyl Chloride). IV. Branching

Degree of branching in PVC as a function of its temperature of polymerization has been determined by the catalytic hydrogenation (LiAlH₄) of the polymer followed by IR measurements. The samples used were prepared at 55, 90, 130, and 160°C. A branching calibration curve (ACH₃ /ACH₂ vs CH₃/CH₂) was established for linear hydrocarbons, and was found to follow the relation, ACH₃/ACH₂ = 20(CH₃ /CH₂). This equation was used to characterize the branching indices of PVC samples studied. Branching values in units of 100(CH₃ /CH₂) were as follows: 55°C (1.92), 90°C (1.95), 130°C (2.61), and 160°C (2.96). These results are in agreement with the theoretical prediction that the degree of branching in PVC should decrease with the lowering of its temperature of polymerization because the energy of activation for the propagation step is smaller than that for chain the transfer step.     

Etude de la chloration du PVC en masse—II. Influence et evolution de la stereoregularite de la chaine en rapport avec les mecanismes de reaction

Bulk chlorination of PVC has been studied by i.r. and NMR. The evolution of chain stereoregularity during reaction and its significance to reaction mechanism have been specified. In particular, for temperatures <80°, the ratio Cl/C cannot exceed 0.75 because changes of conformation are impossible. To exceed this ratio, additional energy is necessary but then there is a parallel loss of hydrogen chloride. In all cases isotactic diads of TG conformation would be first chlorinated. At temperature above 100°, the microstructure of bulk chlorinated products is similar to that of products prepared in solution while their configuration and conformation are different.     

Characterization of poly(vinyl chloride) powder produced by emulsion polymerization

The effect of emulsion process formulation ingredients on the morphology, structure, and properties of polyvinyl chloride (PVC) powder has been considered in this study. PVC powder was extracted with ethanol and films were obtained by solvent casting from tetrahydrofurane. Characterization of powders, films, and ethanol extract was performed through FTIR spectroscopy, DSC, AFM, SEM, EDX analysis, methylene blue, and nitrogen adsorption. PVC powder was composed of spheres of a large particle size range from 10 nm to 20 μm as shown by SEM. The specific surface area of the PVC powder was determined as 16 and 12 m² g⁻¹ from methylene blue adsorption at 25 °C and from N₂ adsorption at −196 °C, respectively. AFM indicated the surface roughness of the films obtained by pressing the particles was 25.9 nm. Density of PVC powder was determined by helium pycnometry as 1.39 g cm⁻³. FTIR spectroscopy indicated that it contained carbonyl and carboxylate groups belonging to additives such as surface active agents, plasticizers, and antioxidants used in production of PVC. These additives were 1.6% in mass of PVC as determined by ethanol extraction. EDX analysis showed PVC particles surfaces were coated with carbon-rich materials. The coatings had plasticizer effect since, glass transition temperature was lower than 25 °C for PVC powder and it was 80 °C for ethanol extracted powders as found by using differential scanning calorimetry. These additives from polymerization process made PVC powder more thermally stable as understood from Metrom PVC thermomat tests as well.     

NMR spectrum of poly(vinyl chloride)

The 100-MHz proton NMR spectra of commercial and laboratory-prepared poly(vinyl chloride) (PVC) have been measured in various solvents at high temperature (80–150°C). Tacticity in PVC was determined by the analysis of the β-proton spectrum. The spectrum was calculated assuming that the PVC chain consists of tetrad sequences of monomer units and that their distribution in the chain is described by a simple Bernoulli-sequence statistics with a P_m (the probability of isotactic placement) of 0.45 for commercial PVC polymerized at 50°C. Tacticity calibration curves based on measurements made for the polymer in pentachloroethane and β-dichlorobenzene were established, and they provide a simple method for the measurement of tacticity in PVC directly from the observed spectra. Excluding samples prepared in butyraldehyde solution, the formation of syndiotactic structures in PVC (prepared by free-radical polymerization) was found to be favored by lowering the polymerization temperature. This preference is due to an increase in the activation enthalpy of 510 cal/mole which is required for forming an isotactic placement in the chain during the propagation step.     

Using cone calorimeter to study thermal degradation of flexible PVC filled with zinc ferrite and Mg(OH)2

Flame-retarded poly(vinyl chloride) (PVC) materials have been prepared by using zinc ferrite (ZnFe₂O₄ (ZFO)) combined with magnesium hydroxide (Mg(OH)₂ (MH)). The effects of these additives on the combustion and thermal degradation of PVC samples were studied using the limiting oxygen index test, the smoke density rating test, thermogravimetric–differential thermogravimetry, and the cone calorimeter test. The results showed that ZFO and MH were good synergists for improving the flame retardancy and smoke-suppressing of PVC/MH/ZFO blends. ZFO can significantly improve the maximum mass loss velocity in the first stage, and reduce the initial decomposition temperature and the decomposition range in the PVC/MH/ZFO blends. The char yield at 700 °C of flame-retarded PVC clearly decreased below theoretical values due to the cationic cracking reactions in the presence of ZFO. Furthermore, the PVC/10MH/10ZFO showed strong flame-retarding synergism since the decreased average heat release rate value. And the PVC/19MH/1ZFO presented a significant smoke-suppressing effect by the least average specific extinction area, peak smoke production rate, and total smoke produce. Moreover, the CO and CO₂ production was increased because of a large amount of fragment of char residue in contact air in the presence of ZFO.     

Anionic polymerization of vinyl chloride

Anionic polymerization of vinyl chloride has been studied. Of the organometallic compounds tested as initiators, only butyllithium was found to initiate polymerization. Polymerization in bulk at 0°C and with tert-butyllithium as initiator gave poly(vinyl chloride) in a yield of 38% with M _n = 55,000. Tacticity of the anionic PVC was similar to that of conventional PVC prepared at similar temperatures. Anionic PVC was found to be less branched and more heat-stable than the conventional polymer.     

Thermal degradation of PVC cable insulation studied by simultaneous TG-FTIR and TG-EGA methods

Thermogravimetry (TG/DTG) coupled with evolved gas analysis (MS detection) of volatiles was used to characterize the thermal behavior of commercial PVC cable insulation material during heating in the range 20-800°C in air and nitrogen, respectively. In addition, simultaneous TG/FTIR was used to elucidate chemical processes that caused the thermal degradation of the sample. A good agreement between results of the methods was found. The thermal degradation of the sample took place in three temperature ranges, namely 200-340, 360-530 and 530-770°C. The degradation of PVC backbone started in the range 200-340°C accompanied by the release of HCl, H₂O, CO₂ and benzene. The non-isothermal kinetics of thermal degradation of the PVC cable insulation in the temperature range 200-340°C was determined from TG results measured at heating rates of 1.5, 5, 10, 15 and 20 K min^-1 in nitrogen and air, respectively. The activation energy values of the thermal degradation process in the range 200-340°C of the PVC cable insulation sample were determined from TG results by ASTM method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of oxygen on the polymerization of vinyl chloride. I. Kinetic features

The effect of oxygen on the liquid-phase polymerization of vinyl chloride at 55°C in the presence of an added initiator, bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16), has been studied by the technique of tumbled dilatometry. With this method, at constant initiator concentration, the induction period showed a half-order dependence on the initial oxygen concentration. At a constant initial oxygen concentration, the induction period varied inversely as the square root of the initiator concentration. Under the experimental conditions empolyed, the polyperoxy radicals with chloroalkyl (～CH₂?HCl) endgroups were not wholly scavenged by molecular oxygen but could undergo various decomposition reactions. The degree of conversion of the initial oxygen to peroxidic compounds did not exceed 30% by weight and was dependent on the shape of the reaction vessel empolyed. The existence of other oxidation products has been demonstrated. At 55°C, the average velocity constant for decomposition of the peroxide products from vinyl chloride, measured in dichloromethane solution, was found to be 8 × 10^?5 sec^?1. A kinetic scheme involving a predominant cross-termination reaction is proposed to explain the experimental results.     

Dehydration of lithium iodide crystal hydrate in vacuum

Dehydration of the LiI · 3H₂O crystal hydrate in vacuum has been investigated at 20–25°C. The decomposition of the LiI · 3H₂O crystal hydrate in vacuum proceeds to monohydrate. During heating of lithium iodide monohydrate, evolution of water vapor is observed at 30–100 and 100–170°C. Above 200°C, evolution of molecular oxygen is observed, possibly, because of the decomposition of lithium peroxide that is formed in side reactions during the decomposition of lithium iodide crystal hydrate.