DEVELOPMENT OF SYNERGISTIC HEAT STABILIZERS FOR PVC FROM ZINC BORATE-ZINC PHOSPHATE

The importance of flame-retardant and smoke-suppressed poly(vinyl chloride) (PVC) compositions is increasing gradually in the polymer industry since PVC releases smoke and toxic gases (hydrogen chloride, HCl) during heating at temperatures above 140°C with the result of dehydrochlorination reaction. In this study, the synergistic effects of zinc borate (ZB)-zinc phosphate (ZP) on the thermal stability of PVC were investigated using thermal techniques. The induction and stability time values of PVC plastigels were obtained at 140° and 160°C. The results revealed that PVC plastigels having only ZP and ZB retarded dehydrochlorination of PVC compared with the unstabilized sample. However, the plastigels with both ZB and ZP had a superior synergistic effect on char formation of PVC. Since the induction periods of the samples having both ZB and ZP were higher than those of the unstabilized samples having only ZB or only ZP, the synergistic effect was observed.     

Thermal dehydrochlorination of poly(vinyl chloride). I. Effect of iron oxide on the rate of dehydrochlorination

The thermal degradation of poly(vinyl chloride) (PVC) was studied by following the rates of dehydrochlorination at temperatures between 180°C in pure nitrogen and air flow. Iron oxide accelerates the elimination of hydrogen chloride from PVC. The accelerating effect depends on the concentration of the oxide, and it has a maximum. This work tried to explain these behaviors. A mechanism of dehydrochlorination is suggested for polymer containing iron oxide.     

Chemical modification of rigid poly(vinyl chloride) by the substitution with nucleophiles

The reaction of rigid poly(vinyl chloride) (PVC) with iodide, hydroxide, azide, and thiocyanate as nucleophiles (Nu) in ethylene glycol (EG) resulted in the substitution of Cl by Nu additional to the elimination of HCl, leading to the dehydrochlorination of the rigid PVC. High substitution rates were observed for hydroxide, azide and thiocyanate, while the addition of iodide accelerated predominately the elimination of HCl. The substitution by thiocyanate resulted at 150°C in both thiocyanate and isothiocyanate structures, whereas at 190°C, only isothiocyanate was observed in the polymer. The dehydrochlorination yield increased with an increasing molar SCN/Cl ratio, resulting in a maximum substitution at high molar SCN/Cl ratios. When EG was replaced by diethylene glycol (DEG) as solvent, the dehydrochlorination was found to be accelerated. It was assumed that DEG has a higher compatibility with PVC, making it easier to penetrate the rigid PVC particle. For triethylene glycol (TEG), the rapid dehydrochlorination resulted probably in the coverage of the surface of the PVC particle by methyl methacrylate/butadiene/styrene (MBS), preventing the penetration by the solution. The substitution/dehydrochlorination ratio decreased in the order of EG > DEG > TEG because of the declining polarity of the solvent, stabilizing the activated S_N2 complex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(ethylene glycol)–polyhedral oligomeric silsesquioxane as a novel plasticizer and thermal stabilizer for poly(vinyl chloride) nanocomposites

The plasticizing and thermostabilizing effect of poly(ethylene glycol)–polyhedral oligomeric silsesquioxane (PEG‐POSS) on poly(vinyl chloride) (PVC) is discussed thoroughly in this work. As PEG‐POSS content increases, PVC becomes more flexible and the decomposition temperature of PVC increases slightly. Meanwhile, the temperature of maximum HCl emission is elevated from 265.3 °C in neat PVC to 285.7 °C in PVC nanocomposites, with the peak intensity of HCl emission decreased by 30.8%, and a new lower intensity of HCl emission peak appearing at much higher temperature (around 370 °C), which is in accordance with the maximum degradation temperature of PEG‐POSS. Thereby, a possible dehydrochlorination mechanism is suggested according to the fact that the electron donor effect of ether groups would stabilize the C? Cl bonds by means of more electron cloud stacked in those bonds, which agrees with Fourier transform infrared and X‐ray photoelectron spectroscopy experiments in terms of hydrogen bonds. © 2016 Society of Chemical Industry     

Degradation kinetics of PVC plasticized with different plasticizers under isothermal conditions

The aim of the present work is to elucidate the degradation kinetics of polyvinyl chloride (PVC) plasticized with some phthalate and nonphthalate plasticizers. A PVC thermomat instrument was utilized to maintain the isothermal degradation conditions at 140 and 160°C, and to suppress the oxidative degradation by means of nitrogen flow. The conductivity measurements were performed to follow hydrogen chloride (HCl) gas which is released upon PVC degradation and trapped in water. Dehydrochlorination of plasticized PVC films occurred with activation energies of about 23–160 and 26–117 kJ mol^?1 and the isokinetic temperatures, at which the dehydrochlorination rate constants of all p‐PVC films would have the same value, were found to be 171 and 128°C for initial and linear regions of dehydrochlorination curve, respectively. Plasticizer incorporation contributes to the stability of the films particularly after the consumption of stabilizer due to the dehydrochlorination. Influence of temperature rise by 20°C on the degradation rate constant is the lowest for DINCH having p‐PVC films as 0.36 and 0.42% increment at the initial region and linear region, respectively. On the other hand, DOTP reveals greater stability than the others do since the compensation ratio of the PVC film having DOTP is greater than the other films. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41579.     

Synergistic effect of metal soaps and natural zeolite on poly(vinyl chloride) thermal stability

The synergistic effect of metal soaps (zinc stearate and calcium stearate) and/or natural zeolite (clinoptilolite) on PVC thermal stability was investigated. For this purpose, PVC plastisol was prepared by mixing poly(vinyl chloride) (PVC) and dioctyl phthalate (DOP) and stabilized with different amounts of metal soaps and zeolite. Kinetic studies of dehydrochlorination at 140 and 160°C were done for unstabilized and stabilized PVC plastigels using 763 PVC Thermomat equipment. The stabilizing effect of zeolite on the increase in the induction period of the sample was considered to result from the absorption of HCl, a property that was thought to reduce the autocatalytic effect of HCl evolved at the initial stages of dehydrochlorination. Since the induction time of the sample having 0.53% of zinc stearate and 0.53% of zeolite was higher than those of the PVC plastigels having only zinc stearate or zeolite, the synergistic effect on thermal stability was observed at low levels of these additives. J. VINYL. ADDIT. TECHNOL., 11:47–56, 2005. © 2005 Society of Plastics Engineers     

Studies on photodegradation of poly(vinyl chloride), part 3

PVC films were degraded by outdoor exposure, irradiation by a weatherometer and heating by an electric oven. In PVC films subjected to outdoor exposure and to irradiation by the weatherometer at a low temperature, e. g. sample surface temperature of 0°C, photo-oxidation and scission of the main chain were caused, but dehydrochlorination or formation of solvent-insoluble substances were not observed. In contrast, PVC subjected to irradiation by the weatherometer at a high temperature, e. g. sample surface temperature of 80°C, showed a degradation tendency similar to that of PVC heated at 200°C in the electric oven, and decomposition of the thermal degradation type characterized by dehydrochlorination, formation of polyenes and formation of solvent-insoluble substances were observed.     

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.     

Degradation of poly(vinyl chloride). I. Kinetics of thermal and radiation-induced dehydrochlorination reactions at low temperatures

The dehydrochlorination reaction arising thermally and from exposure to γ-radiation has been followed, under vacuum, in the temperature range from 80° to 130°C by measuring the pressure of the evolved volatiles. The catalytic action of HCl, which was recently established, has been observed also at these low temperatures. In agreement with previous data, a free-radical mechanism has been accepted to be operating in the radiation-induced reaction, which has been found to be linearly dependent on dose rate and essentially independent of temperature. Assuming the thermal dehydrochlorination to proceed according to the same mechanism, its activation energy, lying within the range of values reported in the literature, represents the activation energy for the thermal process of radical formation by dissociation of normal and anomalous structures in PVC macromolecular chains. Since this value appears to be substantially constant in the temperature range from 90° to 240°C, it can be established whether the dissociation reactions of all the PVC structures are regulated by the same activation energy or, more simply, only one of these structures is concerned.     

Reaction between HC1 and orthophthalates of lead in hot DOP without PVC,and stabilization in plasticized PVC

Reactions between hydrogen chloride, HCl, and either hydrocerussite, 2PbCO₃. Pb(OH)₂, or an orthophthalate of lead suspended in di(2-ethylhexyl)phthalate, DOP, at 180°C are discussed as models of what should happen during the stabilization of PVC if thermal dehydrochlorination were to yield HCl. There is a sharp contrast between the products of these model reactions and those actually found in plasticized PVC containing basic lead compounds. This is taken to show that basic lead stabilizing regimes inhibit PVC thermal dehydrochlorination, actually preventing the formation of HCl. It is proposed that these stabilizing regimes function by a free-radical mechanism which has been called “true stabilization” for ease of reference.     

Dehydrochlorination of poly(vinyl chloride) with Ca(OH)2 in ethylene glycol and the effect of ball milling

The dehydrochlorination behavior of pure and flexible PVC in ethylene glycol was studied in the presence of Ca(OH)₂ at temperatures between 170 °C and 190 °C. Although the dehydrochlorination proceeded slower in Ca(OH)₂ than in NaOH, similar dehydrochlorination yields were obtained. It was assumed that the slower reaction rate was a result of the low solubility of Ca(OH)₂ and the larger solvation shell of the Ca²⁺ ion. The dehydrochlorination rate and yield were improved by employing a ball mill. Additionally, diisononyl phthalate and CaCO₃ were quantitatively separated from flexible PVC during the ball-milling process. The maximum dehydrochlorination yield of pure PVC after 7 h at 190 °C was 74%. After 8 h at the same temperature, a comparable dehydrochlorination yield of 77% was achieved for flexible PVC, which could be increased by ball milling to 86%.     

Thermal stabilization of PVC with khaya seed oil: Thermogravimetric studies

Thermal degradation of PVC stabilized with barium and cadmium soaps of Khaya senegalensis seed oil was studied by thermogravimetry up to 500°C using a constant heating rate of 10°C min⁻¹. At temperatures below 300°C, the extents of dehydrochlorination of both the unstabilized and stabilized PVC samples were low (less than 6% conversion). It was found from the values of weight loss that HCl was the only volatile product of degradation of PVC between 170 and 200°C. The rates of dehydrochlorination at about 200°C was of the order of 10⁻²% min⁻¹, about the same order of magnitude as the values obtained from kinetic studies. The temperatures at which maximum rates of degradation were attained, t_dmax, and the temperatures at which various extents of degradation were attained were used to assess the effectiveness of the metal soaps of Khaya seed oil in stabilizing PVC against thermal degradation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1432–1438, 2000     

The effect of amines on the dehydrochlorination of poly(vinyl chloride)

A study has been made of the effect of amines, particularly those used as catalysts in the preparation of polyurethane foams, on the dehydrochlorination of poly(vinyl chloride) (PVC). It has been shown that when PVC is heated at a temperature of 80°C in the presence of amines the levels of dehydrochlorination produced are considerably greater than those found if no amine is present. This has been attributed to a chemical dehydrochlorination reaction and could well have implications with respect to the physical and mechanical properties of the polymer for certain of its commercial applications.     

Isothermal and Dynamic Thermogravimetric Degradation of Rigid and Plasticized Poly(Vinyl Chloride)/Poly(Methyl Methacrylate) Blends

The thermal degradation of rigid and plasticized poly(vinyl chloride) (PVC)/poly (methyl methacrylate) (PMMA) blends was investigated by means of isothermal and dynamic thermogravimetric analysis in a flowing atmosphere of air. For that purpose, blends of variable composition from 0 to 100 wt% were prepared in the presence (15, 30 and 50 wt%) and in the absence of di-(2-ethyl hexyl) phthalate (DEHP) as plasticizer. The thermal degradation of the blends was investigated by isothermal thermogravimetry at 180°C during 120 min. It was found that the main processes are the dehydrochlorination of PVC and depolymerization of PMMA. The dynamic thermogravimetric experiments were carried out in the temperature range of 30 ? 550°C. The results showed that the thermal degradation of rigid and plasticized PVC/PMMA blends in this broad range of temperatures is a three-step process and that PMMA exerted a stabilizing effect on the thermal degradation of PVC during the first step by reducing the dehydrochlorination.     

Thermooxidative degradation of poly(vinyl chloride)/acrylonitrile–butadiene–styrene blends

The thermal degradation process of poly(vinyl chloride)/acrylonitrile–butadiene–styrene (PVC/ABS) blends was investigated by dynamic thermogravimetric analysis in the temperature range 50–650°C in air. The thermooxidative degradation of PVC/ABS blends of different composition takes place in three steps. In this multistep process of degradation the first step, dehydrochlorination, is the most rapid. The maximal rate of dehydrochlorination for the PVC blends containing up to 20% ABS-modifier is achieved at average conversions of 23.5–20.0%, i.e., at 13.5% for the 50/50 blend. The apparent activation energies (E = 103–116 kJ mol⁻¹) and preexponential factors (Z = 2.11 × 10⁹−3.45 × 10¹⁰min⁻¹) for the first step of the degradation process were calculated after the Kissinger method. © 1996 John Wiley © Sons, Inc.     

Comparative study of the effects of chlorinated polyethylene and acrylic impact modifier on the thermal degradation of poly(vinyl chloride) compounds and poly(vinyl chloride)/(oil palm empty fruit bunch) composites

The effects of chlorinated polyethylene (CPE) and acrylic impact modifier (AIM) on the thermal degradation of poly(vinyl chloride) (PVC) compounds and composites were investigated. The amounts of AIM and CPE used were fixed at 9 parts per hundred parts of resin (phr), while oil palm empty fruit bunch (OPEFB) fiber content was increased from 0 to 40 phr. To produce composites, the PVC formulations were dry‐blended by using a laboratory blender before being milled into sheets on a two‐roll mill at 165°C. The milled sheets were then hot‐pressed at 180°C. The thermal degradation of the specimens was evaluated by using thermogravimetry in a nitrogen environment. Thermal stability of the PVC/CPE compounds and PVC/CPE/OPEFB composites was improved by the addition of CPE. The CPE retarded the dehydrochlorination of PVC. However, the stabilization effect was reduced by the incorporation of OPEFB at levels of 30 and 40 phr. The presence of AIM accelerated the dehydrochlorination of PVC/AIM compounds and PVC/AIM/OPEFB composites. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

The copolymerization of vinyl chloride with 1-olefins. V. Heat stability of copolymers of vinyl chloride with propene, 1-butene,and 1-pentene

Copolymers of vinyl chloride with propene, 1-butene, and 1-pentene containing 2–15 mol % of 1-olefinic structural units were prepared. The copolymers were dehydrochlorinated at 180°C in an inert atmosphere; the amount of hydrogen chloride split off was determined by continuous potentiometry. The results show that the heat stability of propene, 1-butene, and 1-pentene copolymers containing the same amount of 1-olefinic structural units does not differ significantly. Compared with the homopolymer of vinyl chloride, it is favorably affected by the presence of 1-olefinic structural units in poly(vinyl chloride) (PVC) chains. On the other hand, however, the heat stability of copolymers is impaired by the higher content of structural defects able to initiate the dehydrochlorination reaction. These structural defects, probably represented by chloroallyl groups, are formed in the copolymers during their synthesis. At the beginning of heating, structural defects produce intensive dehydrochlorination and, therefore, copolymers of vinyl chloride with 1-olefins if processed appear to be less thermally stable than does PVC.     

Catalytic dehydrochlorination of the solid poly(vinyl chloride) in the presence of aluminium chloride (friedel-crafts) catalyst: Studies of the structure by spectroscopical methods

Catalytic dehydrochlorination (100%) of solid poly(vinyl chloride) (PVC) in the presence of AlCl₃ at 200°C gives a product which has a similar structure to the product of catalytic dehydrochlorination of 1,2-dichloroethane in the presence of AlCl₃ at 60°C. Both products have brown-black color, are completely insoluble, thermally resistant up to more than 400°C, and exhibit conductivities in the range 10^?6 S cm^?1 (after doping with FeCl₃ or I₂ conductivities: 10^?5 S cm^?1). Different spectroscopical methods such as UV/VIS, IR, Raman, ESCA, and ¹³C-NMR were employed to the structure study of both products, which are crosslinked polyenes with a number of aromatic rings.     

Kinetics and mechanism of the thermal degradation of poly(vinyl chloride)

The kinetics of the thermal degradation of solid powdered poly(vinyl chloride) (PVC) under nitrogen was studied by thermogravimetry, rate of hydrogen chloride evolution, and rate of polyene sequence formation. These results are accommodated by a chain mechanism involving initiation by random dehydrochlorination at normal monomer residues of PVC, and a series of intermediates, each leaking to a stable conjugated polyene sequence. Structural irregularities such as allylic and tertiary chlorine are responsible for a fast initiation process at the very beginning of the degradation. Mean rate constants and activation parameters for random initiation, propagation, and termination reactions of the PVC degradation chain were calculated by simulation. Activation enthalpy/entropy correlations for the experimental data available for dehydrochlorination of chloroalkanes and chloroalkenes in the gas and in the liquid phase or nonpolar solvents and elementary reactions of PVC degradation show that initiation is an HCl elimination through a transition state of four centers requiring a synperiplanar conformation of the >CH–CCl< group, whereas propagation is a dehydrochlorination through a transition state of six centers requiring a cis configuration of the double bond.     

Thermal stability of blends of poly(vinyl chloride) with polyester elastomer

The thermal stability of poly(vinyl chloride) (PVC) under air atmosphere was improved by blending with PETE (polyester elastomer). Its enhanced stability could be explained by a reaction between the ester component of PETE and HCl from dehydrochlorination of PVC, which was identified by IR- and ¹H-NMR spectroscopy. The best result of thermal stability was shown at a composition of 100 parts of PVC with 4 parts of PETE. By surveys of glass transition temperatures, it was found that all PVC/PETE blends were ununiformly distributed. During processing, the fusion time and torque at fusion decreased as the quantity of PETE increased. The mechanical properties of the blends were also changed; as the quantity of PETE increased, tensile strength of the blends decreased, while impact strength increased.