Studies in the thermal degradation of poly(vinyl chloride)

Thermal degradation of poly(vinyl chloride) (PVC) was studied in nitrogen atmosphere in the presence of rubber seed oil and epoxidized rubber seed oil, barium and lead soaps of rubber seed oil, and epoxidized seed oil at various temperatures. The rate of dehydrochlorination at 1% degradation and the time required to attain 1% degradation were used to assess the effect of the thermal susceptibility of PVC to dehydrochlorination. It was found that epoxidized rubber seed oil, the metal soaps of rubber seed oil, and epoxidized rubber seed oil markedly enhance the thermal stability of PVC. The order of increasing stabilizing influence was metal soaps of epoxidized rubber seed oil > metal soaps of rubber seed oil > epoxidized rubber seed oil > rubber seed oil. © 1993 John Wiley & Sons, Inc.     

Studies in solid-solid reactions: Autocatalysis in the reduction of cuprous chloride by silicon

Reaction between silicon solid cuprous chloride constitutes a major step in preparing the catalyst for the manufacture of chlorosilanes. Experimental results on this reaction are reported. Data are analyzed based on the observed autocatalytic nature of the reaction. Rate constants activation energies for both the steps-non-catalytic and autocatalytic—are obtained. Finally, the effect of various process parameters on the reaction rate is discussed.     

On the thermal degradation of poly(vinyl chloride). I. An apparatus for investigation of early stages of thermal degradation

A dehydrochlorination apparatus is described for studies of the early stages of the thermal degradation of poly(vinyl chloride) (PVC), combining good reproducibility, high accuracy, and a low detection limit. The evolved hydrogen chloride is absorbed in water and the electrical conductivity is continuously recorded. Measurements of the rate of dehydrochlorination repeated over an extended period of time showed a standard deviation of 2% of the mean value. The activation energies for the dehydrochlorination in nitrogen for two commercial suspension-polymerized samples were found to be 27.9 ± 1.5 and 26.2 ± 0.6 kcal/mole.     

Volatiles from thermal degradation of PVC compounds

Several methods were developed to measure and identify the volatile species generated when PVC is heated to decomposition temperatures. PVC film compound containing various organotin stabilizers was processed under a range of typical conditions. The film samples were subjected to degradation temperatures of 210 to 230°C in both enclosed sampling systems (for optimum collection efficiency) and open systems that were designed to mimic working conditions. The collected samples were analyzed for amounts of hydrogen chloride, organotin compounds and organics in general. Variables such as type of stabilizer, degradation time and temperature, and sample thickness and fusion time were studied.     

Reversible crosslinking during thermal degradation of PVC

Summary PVC undergoes rapid crosslinking during thermal degradation. Diels-Alder addition of conjugated polyenes was proposed as a possible crosslinking mechanism by earlier authors. By the use of conditions favoring retro Diels-Alder reaction of crosslinks (treatment with maleic anhydride at elevated temperature) it was proved that crosslinks are largely reversible. Evidently Diels-Alder addition of the conjugated polyenes plays an important role in crosslinking during thermal degradation of PVC.     

Basic principles of thermal degradation and thermal stabilization of poly(vinyl chloride). Mathematical model of the action of PVC thermal stabilizers

A model of the action of chemically homogeneous thermal stabilizers of poly(vinyl chloride) is shown. Based on the described computer program and experimental data, the proposed model is confirmed and rate constants of the reaction of stabilizers with HCI and the effect of the products of this reaction on the kinetics of PVC degradation are calculated.     

Some aspects of the thermal degradation of PVC. Crosslinking of macromolecules

Direct experimental proof is presented that crosslinking of macromolecules during the thermal degradation of PVC proceeds with participation of blocks of conjugated double bonds formed upon activation by carbonylallyl groups.     

Kinetic analysis of the thermal degradation of PVC plastisols

The thermal degradation of plasticized polyvinyl chloride (plastisol) is reported here. Plastisols used in the present work were prepared with the plasticizer diethylhexyl phthalate in different proportions. Thermogravimetric analysis has been applied to study the behavior of plastisols at high temperatures and to evaluate their degradation kinetics. Several tests were carried out at different heating rates and the variation of the degree of reaction with time and temperature was calculated. The influence of the heating rate in dynamic measurements (5–40°C/min) on kinetic parameters, such as activation energies and reaction orders, has also been studied. These parameters were calculated from dynamic thermogravimetric analysis tests using Friedman analysis and a kinetic model for the degradation of poly(vinyl chloride) and plastisols has been then developed. The obtained model was able to simulate the thermal degradation process of plastisols in dynamic conditions and was used to evaluate the effects of additives in the degradation. The results of this study can be used to optimize the concentration of plasticizers and stabilizers in poly(vinyl chloride) formulations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1069–1079, 1999     

Evolution of hydrogen chloride from the surface of PVC wire-insulation

Long-term dark ageing in the temperature range 35 to 91°C, has shown that hydrogen chloride is released in small but measurable quantities from the surface of fully-stabilized PVC wire-insulating compounds. The rate of release is temperature- and time-dependent. For the particular formulations studied, there is an inverse dependence on the half-power of neutralizer content. Risks to electrical circuit components associated with PVC insulation in enclosed equipment are assessed and shown to be negligible for most normal operating conditions.     

Influence of tacticity on the thermal degradation of PVC. VI. New advances in the degradation process through the behavior of modified PVC samples

Three PVC samples having different tacticities, as well as the products resulting from their reaction with sodium thiophenate, which was previously found to occur selectively by some definite isotactic conformations, were degraded at 180°C in solid state up to 0.3%. In agreement with prior works, the stability of the substituted polymers was shown to be higher as the substitution extent increased up to a definite value, which depends on the overall isotactic content of the starting materials. On the other hand, the found changes in polyene distribution for the degraded samples with the substitution extent, as followed by UV-visible spectroscopy, demonstrate that the specific bands at 393, 416, and 437 nm, which are known to be characteristic for the most unstable PVCs, arise from the lability of some chlorine atoms located at GTTG′ (or TTTG) conformations, as prior results suggested. On the basis of the so-obtained correlation between the content of some isotactic triads (especially the GTTG′) and both the thermal instability and the formation of the above-indicated specific polyenes, new advances in the degradation mechanism are proposed.     

DSC investigation on the thermal degradation of PVC in blends

The thermal degradation of poly(vinyl chloride) (PVC) has been studied by differential scanning calorimetry (DSC). Due to crosslinking, the glass transition temperature (Tg) of PVC raises during the degradation. The thermal degradation of PVC has also been studied for heterogeneous 1:1 (w/w) blends of PVC with polystyrene (PC), poly(styrene-co-acrylonitrile) (SAN), high-impact PS (poly(styrene-g-butadiene)) (HIPS) and poly(SAN-g-butadiene) (ABS). Tg of the PVC phase raises slower during degradation in the PVC/PS-blend, whereas in the other blends the crosslinking is accelerated, due to a negative influence of the double bonds and/or the nitrile groups on the thermal stability of PVC. Since most methods use the determination of eliminated HCl to study the degradation of PVC, the DSC method is very useful in investigations on PVC-containing polymer blends, if there might be a reaction of HCl with one of the blend components.     

The influence of the tacticity on thermal degradation of PVC. III. Verification by ozonization of degraded samples

Two sets of ozonization reactions, for 1 h and 24 h respectively, have been carried out at ?20°C on degraded samples of PVC having different contents of tactic sequences. The evolution of the polyene sequences distribution with the ozonization was followed by UV-Visible spectroscopy. The number of chain scissions of ozonized samples was calculated from the number average molecular weight measurements before and after ozonization. The observed increase of short polyenes relative to the long polyenes with ozonization was found to depend markedly on the content of syndiotactic sequences. On the other hand, the number of chain scissions after total ozonization was found to be the higher the lower the content of tactic sequences in PVC samples is.     

Studies of rigid poly(vinyl chloride) (PVC) compounds. I. Morphological characteristics of poly(vinyl chloride)/chlorinated polyethylene (PVC/CPE) blends

Chlorinated polyethylene (CPE) is a commonly used impact modifier of poly(vinyl chloride) (PVC). The major goal of this research was to understand the fundamental morphological aspects of PVC/CPE blends. Scanning electron microscopy (SEM) was used to image the surface structure of these blends, and both transmission electron microscopy (TEM) and scanning-transmission electron microscopy (S-TEM) were used to image the morphological boundaries of the blends. TEM imaging distinguishes the boundaries between PVC and CPE more clearly or better than does S-TEM, but it is time-consuming. However, some CPE particles are not observed in TEM because of inefficient staining. S-TEM imaging is much faster and does not depend on staining for the imaging of the CPE phase. © 1995 John Wiley & Sons, Inc.     

Effect of thermal degradation on the impact properties of PVC compounds

An instrumented drop weight impact test was used to study the effect of thermal degradation on the impact properties of PVC compounds. The impact resistance of the aged compounds related well with their weight loss and hence, with thermal degradation. Each compound showed a specific weight loss percentage that correlated with a 50% loss in its impact properties (failure point), irrespective of the aging temperature. The results were also used to estimate a thermal index (TI) of each compound in a rapid and reliable way.     

Preventing thermal degradation of PVC insulation by mixtures of cross-linking agents and antioxidants

Poly(vinyl chloride) (PVC) is widely used—in spite of HCl formed from it at elevated temperatures. PVC wire and cable insulation has poor thermal stability, causing the plasticizer to separate from the PVC chains and produce an oily residue, lowering the tensile elongation at break and thus increasing brittleness. One uses cross-linking agents and antioxidants, as well as mixtures of both, to improve the thermal stability of the plasticizer and tensile properties of PVC after thermal exposure. We performed tensile tests, tribological tests, profilometry, scanning electron microscopy (SEM), and water absorption determination before and after thermal exposure at 136 °C for 1 week. After adding the agents, elongation at break increased by 10 to 20% while the wear rate and water absorption were lower than for the control sample. Less voids are seen in the SEM images after adding these two kinds of agents. The thermal resistance of the PVC cable insulation is best enhanced by combinations of cross-linking agents and antioxidants. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48816.     

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.     

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.     

The composition and structure of solid char residues after thermal degradation of polystyrene,PVC and polyamide. Part I

The study of char residues after thermal degradation of synthetic polymers, especially the identification of their morphology, structure and chemical composition is presented in this paper. Special attention was focused on the polystyrene, PVC and polyamide char residues. By means of microscopy in reflected light and reflected polarized light the manifestations of optical anisotropy were observed. X-ray analysis was used for the examination of the microstructure of PVC char residues carbonized at temperatures above 1000°C. For PVC char residues the electric resistivity was determined. The results have proved the close connection between the structure and properties of char residues and the intensity and course of thermal degradation of polymers.