Thermal Degradation Of Polyvinyl Chloride Research Articles

Thermal degradation of polyvinyl chloride in the presence of lead oxide: A kinetic and mechanistic investigation

The elimination of toxic heavy metals from metallurgical wastes before its recycling to steel furnaces is essential. Lead oxide (PbO) is a major toxic heavy metal present in electric arc furnace dust (EAFD). The co-recycling of EAFD with Polyvinyl chloride (PVC) followed by water leaching allows the elimination of this material. Herein, an experimental and theoretical kinetic investigation was conducted on the thermal degradation of PVC in the presence of PbO. An inhibiting effect of PbO on the thermal degradation of PVC was observed; the onset PVC de-hydrochlorination temperature increased from 273 to 293 °C. PbO addition also increased the activation energy of PVC mass loss from 148 kJ/mol (PVC) to 173 kJ/mol (PbO-PVC) in the conversion window 5–45 %. The theoretical Density Function Theory (DFT) suggested that the intramolecular hydrogen transfer (IHT) to form H2O on PbO surface exhibited the highest energy barrier at 251.01 kJ/mol, which aligns with the experimental data. The kinetic parameters generated here can be utilised to calculate the appropriate holding temperature and time for the effective removal of PbO from waste EAFD using PVC as a chlorinating additive. This should contribute towards optimising process economics and efficiency.

Investigation of the uptake and catalytic effect of calcium and potassium‐based additives under low‐temperature pyrolysis of polyvinyl chloride

AbstractManaging plastic waste containing polyvinyl chloride is difficult due to the release of hazardous substances such as hydrogen chloride. Alkaline metal has been proven to minimize the release of hydrogen chloride during thermal degradation of polyvinyl chloride. However, most past studies conducted heating experiments under a high temperature which promotes the production of aromatic hydrocarbons. In this study, low‐temperature pyrolysis was utilized which focuses on the dehydrochlorination stage while minimizing further degradation of hydrocarbons. The effectiveness of calcium oxide, calcium carbonate and potassium carbonate in minimizing the release of hydrogen chloride was also evaluated. Among those three additives, calcium oxide and potassium carbonate have shown some potential in uptaking hydrogen chloride. Especially when the molar ratio of additive to PVC is 1:1.6, calcium oxide reduced the generation of hydrogen chloride to as low as 20%. Potassium carbonate also exhibits an uptake effect but has a slight catalytic effect when the molar ratio is less than 1:1. On the other hand, calcium carbonate not only shows little to no uptake effect, but also promotes the thermal degradation of hydrocarbon.

Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment

Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C1–C4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C1–C4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes.

Chlorine Fixing Ability of Electric Arc Furnace Dust During the Thermal Degradation of Polyvinyl Chloride under Oxidative Conditions

Electric arc furnace dust (EAFD) and polyvinyl chloride (PVC) are two hazardous wastes that are accumulated world-wide at an alarming rate. Utilising these two wastes simultaneously towards a sustainable recycling loop can greatly mitigate their environmental impact. Herein, EAFD was studied as a potential emission fixator of evolved gaseous HCl generated from the thermal decomposition of PVC under different operational conditions: EAFD-PVC mass ratio, solid reactants geometry, O2 partial pressure, holding temperature, holding time and heating rate. The highest chlorine fixation percentage was calculated to be 78.9% and was obtained at an EAFD-PVC mass ratio of 1:1 (thin disks geometry), while the rest escaped in the form of HCl/Cl2. No significant variation was observed on the percentage of fixed chlorine when the thermal treatment was performed using different geometries: long cylinder, thin disks, and powder forms with a maximum difference in fixation of only 5.6% between extremities. Increasing O2 partial pressure positively affected the chlorine fixation percentage increasing it from 39.9 to 48.4% at 0 and 21 kPa partial pressures, respectively. Increasing both the holding temperature and holding time under oxidative conditions negatively affected the percentage of fixed chlorine due to oxidation of formed FeCl2 back to Fe2O3. The heating rate did not show any significant effect on the amount of fixed HCl, suggesting that the speed of chlorination reactions can be identical to or faster than the decomposition rate of PVC. Overall, EAFD is believed to be an excellent candidate for capturing HCl contained in PVC upon thermal degradation.

A thermo-kinetic investigation on the thermal degradation of polyvinyl chloride in the presence of magnetite and hematite

Electric arc furnace dust (EAFD) which is accumulated in large amounts world-wide contains hematite (Fe2O3) and significant quantities of magnetite (Fe3O4). Waste polyvinyl chloride (PVC) also poses a great environmental threat aside to accumulated EAFD. Both of these wastes have shown a great potential for their co-thermal treatment for metal extraction, thus minimising their environmental footprint. Herein, an investigation on the thermal degradation behaviour, reaction products, thermodynamics and the decomposition kinetics of PVC and its stoichiometric mixtures with Fe3O4 and Fe2O3 was conducted using non-isothermal thermogravimetric scans. The kinetic data suggests a significant increase in the average activation energy of PVC de-hydrochlorination from 122.6 ± 24.2 kJ/mol (pure PVC) to 177.0 ± 28.0 and 199.0 ± 77.0 kJ/mol when stoichiometric quantities of Fe3O4 and Fe2O3 were mixed with PVC. The inhibiting effect of both Fe3O4 and Fe2O3 on the degradation of PVC might be assigned to the capturing of emitted gaseous HCl which is known for its catalytic effect. This result suggests that EAFDs containing both Fe3O4 (in large amounts) and Fe2O3 can have an inhibiting effect on the de-hydrochlorination of PVC resulting in longer processing times or the requirement of higher processing temperatures for achieving reasonable reaction rates.

Raman spectroscopic detection of polyene-length distribution for high-sensitivity monitoring of photo- and thermal degradation of polyvinylchloride

The degradation of the ubiquitous polyvinylchloride (PVC) material under the influence of various factors is known to result commonly in polyene formation. Such polyene defects occur in the form of conjugated aliphatic chains with different lengths and contents, and their sensitive and length-specific monitoring is important for the assessment of PVC degradation. Here, we report on the resonance-enhanced Raman signatures of polyene sequences of varying lengths in photo- and thermally degraded PVC films. The lengths of polyene segments have been estimated based on their selectively enhanced and spectrally resolved contributions to the Raman bands assigned to the stretching vibrations of conjugated double carbon bonds. Using deconvolution analysis of a characteristic Raman band of polyenes, we especially demonstrate that the spectral signatures of polyene segments corresponding to other various electronic resonances contribute to the Raman spectral envelope observed at a given resonant excitation. In most cases, we observe an asymmetric band profile, indicating an asymmetric length distribution of polyene defects formed in PVC films upon a mild degradation extent less than 1% mass loss. We also demonstrate that the wavenumber (ν1) of the stretching vibrations of single carbon bonds in the polyene sequences of degraded PVC is inversely related to the number (n) of double carbon bonds by an empirical equation n=476·cm-1/ν1-1082·cm-1. To the best of our knowledge, while considering different laser excitations spanning the range of possible electronic resonances from blue to near-infrared for Raman investigations, the present work includes (i) the first Raman spectral deconvolution study for the 532.0 nm excitation wavelength used in most portable Raman probes nowadays and (ii) the screening of polyene defects also beyond the red edge of the visible spectrum and the evidence of a resonance-enhanced polyene signal at 647.1 nm. Important new information has been obtained about polyene lengths and spectral distribution for PVC, whose critical physical properties ranging from flexibility to electrical resistance are severely affected by polyene formation.

Comprehensive kinetic study of thermal degradation of polyvinylchloride (PVC)

The plastic waste accumulation has been increasing and a solution other than landfilling is required. Due to the high cost of recycling, thermal treatment could be an option. However, the existence of polyvinyl chloride (PVC) would release hydrochloric acid which would cause emission problems as well as damage to the reactor systems. The thermal degradation of PVC has been studied over the years. However, the mechanism of the PVC thermal degradation is not fully developed. Specifically, the mechanism of the PVC thermal degradation at medium temperatures, which is more practical for industries, is still lacking. A degradation temperature of 300 °C was used to study the dehydrochlorination behavior of PVC. A rather comprehensive mechanism with four consecutive reactions has been developed based on the micro-pyrolysis experiments and has been validated and proved by predicting the mass loss, chlorine content, heat content and elemental composition with high precision experimental data in different reactors with/without heat transfer coupling.

The Self-Degradation Mechanism of Polyvinyl Chloride-Modified Slag/Fly Ash Binder for Geothermal Wells

Polyvinyl chloride (PVC) releases hydrochloric acid (HCl) during its thermal degradation, and hydrochloric acid can react with hydration products of alkali-activated binders. According to this characteristic of PVC and the temperature change that occurs during the development of a geothermal well, the PVC was added into slag/fly ash binder to develop self-degradable materials. The thermal degradation properties of PVC, compressive strength, hydration products, and microstructure of binders at different stages were tested, in order to study the degradation mechanism of the material. It was found that 20% PVC reduced the compressive strength, decreasing the level of binder from 13.95% to 76.63%. The mechanism of PVC promoting the material degradation mainly includes the following: (1) the thermal degradation of PVC increases the number of multiple damage pores in the material, at a high temperature; (2) HCl generated by the PVC thermal degradation reacts with the binder gels, and breaks them into particles; and (3) HCl also reacts with other substances in the binder, including CaCO3 and NaOH in the pore solution.

Controlling generation of benzenes and polycyclic aromatic hydrocarbons in thermolysis of polyvinyl chloride in CO2

This study emphasizes the control of benzene derivatives and polycyclic aromatic hydrocarbons (PAHs) in thermolysis of polyvinyl chloride (PVC) using CO2. To this end, the generation of benzenes and PAHs from the thermolysis of PVC in N2 was characterized and all experimental findings from the thermolysis of PVC in N2 were used as the reference value to configure the role of CO2 in the thermolysis of PVC. The formation of hydrogen chloride (HCl) followed by the subsequent dechlorination in the thermolysis of PVC in N2 resulted in the high yield of charring compounds, providing a favorable condition for forming benzene derivatives and PAHs. However, the thermal degradation of PVC in CO2 showed the genuine thermal degradation patterns. For instance, despite the presence of the source for oxygen, the formation of CO at temperatures higher than 600 °C was observed in the thermolysis of PVC in CO2, suggesting that some unknown reactions between hydrocarbons from the thermolysis of PVC and CO2 are initiated to form CO. In addition to these unknown reactions, the enhanced thermal cracking induced by CO2 was observed. Two identified roles of CO2 during the thermolysis of CO2 was only limited at temperatures higher than 600 °C. However, despite no precise description for the mechanistic role of CO2 at this stage of study, the formation of benzene derivatives and PAHs was effectively controlled in the presence of CO2 at temperatures higher than 480 °C. Thus, these empirical findings in this study are necessary to further be investigated in the future, which offers a great venue offering a new means for modifying and/or controlling the harmful chemical species.

Thermal degradation, dynamic mechanical and morphological properties of PVC stabilized with natural polyphenol-based epoxy resin

In this study, the thermal degradation, dynamic mechanical and morphological properties of polyvinyl chloride (PVC) stabilized with tannin-based epoxy resin and with Ca/Zn-based thermal stabilizers were studied. The efficiency of tannin epoxy resin as thermal stabilizer and additive for PVC was explored in this work using thermogravimetric analysis, dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM) techniques. The obtained TG results reveal that the tannin-based epoxy resin as well as Ca/Zn-based thermal stabilizer has a significant effect on the thermal stability of PVC. The viscoelastic properties of PVC with and without tannin epoxy resin were evaluated by dynamic mechanical thermal analysis technique (DMTA). It was observed that the tannin derivative has an improvement effect on the viscoelastic properties of PVC. The glass transition temperature of PVC/tannin epoxy resin occurs at about 90–93 °C and it is close to that of PVC formulated with Ca/Zn-based commercial thermal stabilizer and without using a plasticizer. DMTA properties show that PVC incorporated with tannin epoxy resin have relatively more recognized flowing stage which occurs smoothly at 160 °C. Other analytical techniques such as SEM and energy dispersive X-ray spectroscopy are employed on PVC morphological properties. Experimental results confirm that the tannin epoxy increase thermal stability of PVC which exhibits smooth and homogenous surface properties compared to the commercial thermal stabilizer.

Utilizing CO2 to suppress the generation of harmful chemicals from thermal degradation of polyvinyl chloride

This study put a great emphasis on the role of carbon dioxide (CO2) in thermal decomposition of polyvinyl chloride (PVC). To do this, systematic experimental works were carried out to explore the influence of CO2 on pyrolysis of PVC by comparing with that in N2. First of all, a series of thermo-gravimetric analysis (TGA) of PVC in N2 and CO2 was performed to characterize the thermal deconstruction of PVC in N2 and CO2, which confirmed that any physical aspect (i.e., onset and end temperature of depolymerization of PVC) attributed by CO2 was nearly negligible as compared to the case in N2. This phenomenon was also fully evidenced by differential thermogram (DTG) and differential scanning calorimeter (DSC) because both DTG and DSC curves in N2 and CO2 were identical. However, the concentration profiles of CO evolved from the thermal degradation of PVC in N2 and CO2 was significantly different: the enhanced generation of CO occurred in the presence of CO2. This observation suggested that the genuine role of CO2 is to consume carbon source (i.e., acting as a carbon scavenger) for pyrolysis of PVC. It also provided a favorable condition for suppressing the formation of harmful chemical compounds such as benzene derivatives and polycyclic aromatic hydrocarbons (PAHs). Therefore, the mass portion of the oil in pyrolytic products produced from pyrolysis of PVC in CO2 was lower than that in N2. These particular thermal degradation behaviors may be explained by the genuine role of CO2: the enhanced thermal cracking of volatile organic carbons (VOCs) evolved from the pyrolysis of PVC. The findings of this study strongly suggest that CO2 can be effectively applied to thermal disposal of recalcitrant wastes since employing CO2 in thermal treatment provides a means for in-situ mitigation and/or reduction of harmful chemical species.

Reactions of products from thermal degradation of PVC with nanoclusters of α-Fe2O3 (hematite)

Polyvinyl chloride (PVC) plastics constitute a large fraction of buildings, packaging and electronic devices, whereas, the annual emission electric arc furnace dust (EAFD) from steel manufacturing operations has recently peaked at nearly 6Mt. Co-pyrolysis of PVC with EAFD currently represents a focal abatement technology for both categories of pollutants. However, despite of several experimental investigations; the mechanisms underlying interaction between EAFD and PVC remain largely speculative. Herein, we examine theoretically reactions of major products from thermal degradation of PVC with nanoclusters of iron (III) oxide, α-Fe2O3 (hematite) as a representative model for the various metal oxides in EAFD. The facile nature for the H-Cl bond fission over hematite is in line with experimental findings, pointing out to formation of iron chlorides from pyrolysis of Fe2O3-PVC mixtures. Interaction of selected chlorinated C1-C3 cuts with the hematite structure preferentially proceeds via a dissociative adsorption pathway. Results from this study shall be instrumental to understand, on a precise molecular basis, fixation of halogens on transitional metal oxides; a viable thermal recycling approach for polymeric materials laden with halogenated constituents.

Synthesis and characterization of iron(III) oxide/polyvinyl chloride/poly(methyl methacrylate) nanocomposites

ABSTRACTPolyvinyl chloride/poly(methyl methacrylate) blended and iron(III) nanoparticle polyvinyl chloride/poly(methyl methacrylate) nanocomposites were prepared by solution casting. The iron(III) oxide nanoparticles were prepared using a sol-gel procedure and their particle size was less than 200 nm. Scanning electron microscopy showed that no phase separation occurred and polyvinyl chloride and poly(methyl methacrylate) were miscible. Scanning electron microscopy also showed that the iron(III) oxide nanoparticles were dispersed well within the polymer blend. Thermogravimetric analysis showed three stages for the thermal degradation for polyvinyl chloride/poly(methyl methacrylate) blend and the iron(III) oxide/polyvinyl chloride/poly(methyl methacrylate). The second degradation was possibly due to dehydrochlorination during the thermal degradation of polyvinyl chloride in the blend system. Young’s modulus of the iron(III) oxide nanoparticle filled nanocomposites was from 1987.7–2471.6 MPa, which was higher than polyvinyl chloride/poly(methyl methacrylate) blend (1955.5 MPa). The stress yield (47.9–51.8 MPa) of the iron(III) oxide nanoparticle composites was higher than pure polyvinyl chloride/poly(methyl methacrylate) (47.0 MPa). The cyclic voltammograms of the pure blend and the nanocomposites were compared.

Evaluation of the thermal stabilization effect of polymeric dioctyltin maleate on polyvinyl chloride

Polyvinyl chloride (PVC) is a major plastic material with widespread applications. When PVC is heated during the processing period, it presents very low thermal stability and will decomposed to polyene byproducts. To increase the thermal decomposition temperature of PVC and broaden the narrow temperature ranges of related molding products, efficient thermal stabilizers are required to ensure its functionality. Herein, a series of novel polymeric thermal stabilizers, the dioctyltin maleate/styrene/methyl acrylate {P (DOTM/St/ MA)}, dioctyltin maleat/styrene/N-phenylmaleimide {P(DOTM/St/NPMI)}, dioctyltin maleate/styrene/N-pchlorophenyl maleimide {P(DOTM/ St/NClPMI)} and dioctyltin maleate/styrene/N-p-nitrophenyl maleimide {P(DOTM/St/NNOPMI)} copolymers, composing of mature primary heat stabilizing unit dioctyltin maleate, auxiliary heat stabilizing unit N-phenyl maleimide that is able to inhibit the thermal degradation of PVC, as well as methyl acrylate and styrene that have better compatibility with PVC, have been synthesized to improve the thermal stabilization efficiency, taking advantages of their excellent compatibility and dispersibility. The influences of these compounds on the thermal stability of PVC were estimated by Congo red test, pH-meter, and thermal degradation assay in hot oven. The effect of the compatibility on the thermal stability of the PVC stabilizing system was thoroughly explored. It was found that thermal stability was increased with excellent compatibility, demonstrating the effectiveness of these PVC stabilizers. Furthermore, the mechanism of thermal stabilization was discussed through FT-IR and compared with previous studies conducted by other researchers.

Kinetics of thermal degradation of poly(vinyl chloride)

Extensively studied thermal degradation of polyvinyl chloride (PVC) occurs with formation of free hydrogen chloride and conjugated double bonds absorbing light in visible region. Thermogravimetric monitoring of PVC blends degradation kinetics by the loss of HCl is often complicated by evaporation and degradation of plasticizers and additives. Spectroscopic PVC degradation kinetics monitoring by absorbance of forming conjugated polyenes is specific and should not be affected by plasticizers loss. The kinetics of isothermal degradation monitored by thermal gravimetric analysis in real time was compared with batch data obtained by UV/Visible absorption spectroscopy. Effects of plasticizer on kinetics of polyene formation were examined. Thermal degradation of PVC films plasticized with di-(2-ethylhexyl) phthalate (DEHP) and 1,2,4-benzenedicarboxylic acid, tri-(3-ethylhexyl) ester (TOTM) was monitored by conjugated double bonds light absorption at 350 nm at 160, 180, and 200 °C. Plasticizer-free PVC powder degradation kinetics and that of plasticized films were also obtained thermogravimetrically at temperatures ranging from 160 to 220 °C. Plasticizer-free PVC powder degradation and spectroscopically monitored degradation of plasticized PVC films occurred with the same apparent activation energy of ≈150 kJ mol−1. No difference in degradation kinetics of films plasticized with DEHP and TOTM was detected.

Determination of HCl and VOC Emission from Thermal Degradation of PVC in the Absence and Presence of Copper, Copper(II) Oxide and Copper(II) Chloride

Polyvinyl chloride (PVC) has played a key role in the development of the plastic industry over the past 40 years. Thermal degradation of PVC leads to formation of many toxic pollutants such as HCl, aromatic and volatile organic carbon vapors. Thermal degradation of PVC and PVC in the present of copper, cupric oxide and copper(II) chloride were investigated in this study using a laboratory scale electrical furnace. HCl and Cl- ion were analyzed by a Dionex ion chromatograph and VOCs compounds were analyzed using GC or GC‐MS. The results showed that HCl plus Cl- ion and benzene formed about 99% and 80% respectively in the first step of thermal degradation under air atmosphere. The presence of cupric oxide increases the percentage of short chain hydrocarbons more than 184% and decreases the amount of the major aromatic hydrocarbon and HCl plus Cl- ion to 90% and 65% respectively. The total aromatic hydrocarbon emitted less than when atmosphere was air and difference was statistically significant (Pvalue<0.000)

TG-FTIR analysis of PVC thermal degradation and HCl removal

The pyrolysis of polyvinyl chloride (PVC) was qualitatively analyzed by TG-FTIR, and HCl removal efficiency of Ca-based additives were semi-quantitatively studied also by means of TG-FTIR. Additionally, the thermodynamic equilibrium modeling was also carried out to understand the formation of HCl from PVC and from mixtures of PVC with different additives. Experimental results showed that the pyrolysis of PVC took place in two steps accompanied by the release of HCl and hydrocarbon, respectively. Almost all Cl transformed to HCl, and hardly any other kinds of Cl compounds were detected. The addition of Ca-based additives extended the second weight loss step of PVC, but they did not affect the release time when the maximum HCl concentration appeared. The maximum HCl concentration decreased according to the increase of additive amount, that is to say, the HCl removal efficiency increased as the Ca/Cl molar ratio increased, however when the Ca/Cl ratio increased to a certain value, the increase of HCl removal efficiency was not proportional to the increase of additive amount. For different additives, different Ca/Cl ratios should be chosen based on the cost, HCl removal efficiency and utilization efficiency of additive.

Temperature Dependence on the Activation Energy of Dechlorination in Thermal Degradation of Polyvinylchloride

Abstract The dechlorination of polyvinylchloride (PVC) powder initially progressed on an apparent zero order reaction, and proceeded in higher dechlorination range by an apparent first order reaction. The apparent activation energies indicate that the rate of the dehydrochlorination is controlled by the chemical reaction at low temperature, but that from 300 to 400 °C is controlled by heat transfer rate.

Crosslinking of Macrochains in the Thermal Degradation of Polyvinyl Chloride

Crosslinking of Macrochains in the Thermal Degradation of Polyvinyl Chloride

Studies in the utilisation of epoxidised vegetable oils as thermal stabiliser for polyvinyl chloride

Epoxidised Jatropha seed, Khaya seed and rubber seed oils were prepared at 29 °C by using peracetic acid generated in situ by reacting glacial acetic acid and hydrogen peroxide. The barium, cadmium and lead soaps of the epoxidised oils are prepared by metathesis in aqueous alcohol solution. The effects of the epoxidised vegetable oils and their metal soap derivatives on the rate of the thermal degradation of polyvinyl chloride and on the viscosity of the polymer samples degraded at 190 °C were studied. The effectiveness of the additives (epoxidised oils and their metal soaps) in stabilising polyvinyl chloride against thermal degradation was assessed by comparing the kinetic and viscosity data obtained for the degradation of the polymer in the presence of the additives with corresponding values obtained in the absence of the additives. It was found that the additives retard the rate of degradation and reduce the extent of polymer chain scission associated with the thermal degradation of polyvinyl chloride. The metal soaps of the epoxidised oils were found to be generally more effective than the epoxidised oils in stabilising polyvinyl chloride against thermal degradation.