Thermal Dehydrochlorination Of Poly Research Articles

Effects of steam on the thermal dehydrochlorination of poly(vinyl chloride) resin and flexible poly(vinyl chloride) under atmospheric pressure

A steam-based treatment for the dehydrochlorination of poly(vinyl chloride) (PVC) at atmospheric pressure was evaluated. Temperatures ranging from 170 to 250 °C and steam concentrations of up to 75 vol% were applied to PVC resin and flexible PVC. Overall, the addition of steam increased the dehydrochlorination ratios for both sample types, regardless of temperature. PVC resin reached a maximum dehydrochlorination ratio of 76% after 1 h of treating at 250 °C and at a steam concentration of 50 vol%; this compares favorably to the 61% achieved under nitrogen. Higher steam concentrations reduced the maximum dehydrochlorination ratio for PVC resin; this was shown to be the result of a shielding effect due to rapid, superficial dehydrochlorination. This effect was not observed for flexible PVC, which reached a maximum dehydrochlorination ratio of 69% after 1 h of treating at 250 °C and at a steam concentration of 75 vol%; again, this is a significant improvement over the 51% value obtained under nitrogen. Moreover, the loss of plasticizer was shown to account for the majority of the flexible PVC weight loss. The reaction kinetics was also investigated. The proposed treatment is of special interest for the treatment of PVC medical equipment, since it could fulfill the needs for both sterilization and dehydrochlorination which the disposal of this waste requires.

Mechanism of Autocatalysis in the Thermal Dehydrochlorination of Poly(vinyl chloride)

Autocatalysis during the thermal dehydrochlorination of poly(vinyl chloride) (PVC) is shown to be a free-radical process that converts the ordinary monomer units of the polymer into chloroallylic structures that have low thermal stabilities. In the first stage of dehydrochlorination, conjugated polyene sequences are created by a nonfree-radical route. They react with HCl to give cation monoradicals and/or excited cation diradicals. One or both of these species, or other radicals formed from them, can then abstract methylene hydrogen in order to produce new radicals that are also carbon-centered. These are converted by chlorine-atom β scission into the chloroallylic segments, which start the growth of new polyenes in the usual (nonradical) way. At 180 °C in solid PVC, autocatalysis was inhibited by free-radical scavengers (a hindered phenol, triphenylmethane, and metallic mercury) but greatly enhanced by an increased concentration of HCl when all-trans-β-carotene, a model for PVC polyene sequences, was int...

Effects of Oxygen on Thermal Dehydrochlorination of Poly(vinylidene chloride)

The early stages of thermal degradation below 1% dehydrochlorination poly(vinylidene chloride) (PVDC), can be divided into an induction period, period with conversion below 0.1% dehydrochlorination, and that with conversion ranging from 0.1 to 1%. The time of induction period increases with oxygen concentration due to retardation effect. The second and third stages of degradation follow the apparent zero-order reaction and rates of dehydrochlorination of both stages increase linearly with oxygen concentration. The melting points of samples with different degrees of degradation show a decreasing trend with degrading time regardless of annealing effect. By combination with our differential scanning calorimetry (DSC) thermograms and wide-angle X-ray diffraction (WAXD) patterns, in the presence of pure oxygen which first reacts with the PVDC dangling chains outside the crystalline, and cuts through the degraded crystalline along the backbones resulting in many pieces of small crystallite. A polarity change of PVDC characterized by solid-state nuclear magnetic resonance (NMR) due to degradation can be observed.

Thermal dehydrochlorination of poly(vinyl chloride)—epoxidized butadiene/styrene triblock copolymer blends

The effect of the type of epoxidized butadiene/styrene block copolymer [ESBS; linear (B/S) or radial (E(B/S) n ), containing 0–27% of epoxy groups] on the thermal dehydrochlorination of poly (vinyl chloride) (PVC)-ESBS blends (ESBS content 10%) was investigated in the temperature range 170–180 °C, under a non-oxygen atmosphere. Thermal stability of the PVC-ESBS blends was estimated on the basis of induction time, t 0, and maximum rate of hydrochloride emission, V max from the system. It was found that, for a similar degree of epoxidation of the SBS copolymer, the induction time i.e. the time after which emission of HCl begins, is longer in the series PVC < PVC-SBS < PVC-EB/S < PVC-E(B/S) n, and the same is true for thermal stability. However, the maximum rate of emission of HCl is lowest in the case of PVC-EB/S blends, in the range of molar ratios from 0.5 to 2.0 × 1 O −2. On the basis of the dependence V max = f( EB VC ), it was found that there is a certain content of epoxidized butadiene (EB) units in a mixture which causes the optimum stability of poly (vinyl chloride) during heating. During thermal destruction of the PVC-ESBS blends, the HC1 evolved undergoes addition both to epoxy fragments and to double bonds. The degree of conversion of EB units in time t 0 is 20% at 170 °C and 30% at 180 °C. The glass transition temperature, T g , of PVC in the PVC-ESBS blends shifts towards higher temperatures by about 6–8 °C, proving the existence of crosslinking processes during moulding of the blends. The epoxidized butadiene/styrene radial block copolymer, E(B/S) n , is a better thermal stabilizer of PVC than the linear EB/S copolymer.

Thermal dehydrochlorination of poly(vinyl chloride) in the presence of Jatropha seed oil

AbstractThermal degradation of poly(vinyl chloride) was studied in a nitrogen atmosphere in the presence of Jatropha seed oil, epoxidized Jatropha seed oil, and soaps (barium and cadmium) of Jatropha seed oil at various temperatures. The rate of dehydrochlorination measurement at 1% degradation, RDH, and the time required for dehydrochlorination to attain 1% conversion were used to assess the effect of the additives on the susceptibility of the polymer to dehydrochlorination. It was found from the kinetic studies and the results from viscosity measurements on degraded polymer samples that the Jatropha seed oil derivatives suppressed the initial loss of HCl from the polymer and the extent of polymer chain scission accompanying the dehydrochlorination process. Thermal degradation studies of poly(vinyl chloride) in the presence of mixtures of barium and cadmium soaps of Jatropha seed oil were also carried out. It was found that soap mixtures containing less than 80 wt% cadmium soap exerted a deleterious (antagonistic) effect on the degradation of poly(vinyl chloride) while in the presence of soaps containing more than 80 wt% cadmium soap, considerably lower values of RDH and higher values of tDH were observed. The soap mixture containing 90 wt% cadmium soap was found to exhibit a remarkedly improved stabilizing effect on the dehydrochlorination of poly(vinyl chloride). © 1995 John Wiley &amp; Sons, Inc.

Quantum Chemical Study of Thermal Dehydrochlorination of Poly(vinyl chloride) Containing Aldehyde Groups

Thermal dehydrochlorination of syndiotactic oligomeric models of PVC with aldehyde groups is studied using semiempirical quantum chemical methods AM1 and MNDO. The possibility of both radical and ionic mechanism of HCl elimination is examined. From the results it follows that the homolytic detachment of chlorine from the carbon in β-position to the aldehyde group is preferred, followed by hydrogen splitting off. Hydrogen atom detachment from the carbon in α-position to the aldehyde group as the first step is found energetically less convenient. The dehydrochlorination of aldehyde-containing PVC model, especially of the first molecule from the chain, is remarkably easier in comparison with regular PVC model. However, the energetical preference is smaller for further HCl splitting off and, from the kinetic point of view, this process seems to be slower. The influence of the aldehyde group inductive effect on the driving force potential m(Ca-Cw) is apparent from the partial charge distributions.

Medium effects on the thermal dehydrochlorination of poly(vinyl chloride)

In the light of polaron theory it is shown that, in the thermal dehydrochlorination (TDHC) of poly(vinylchloride) (PVC), the medium can, by its interaction with the double bonds existing in PVC, control the rate, the mechanisms of TDHC, the cis/trans configuration and the length distribution of conjugated polyene sequences developed in the polymer backbone. It also shows that the propagation of elimination of HCl in the TDHC of PVC can occur via allylic, as well as normal chlorine atoms.

Thermal Dehydrochlorination of Poly(vinyl chloride) in Syndiotactic Systems

The thermal dehydrochlorination of syndiotactic poly(vinyl chloride) sequences has been studied theoretically on low-molecular weight models ranging from vinyl chloride dimer to pentamer using the semiempirical quantum chemical MNDO method. Parameters obtained with saturated systems and their change caused by the proceeding elimination of hydrogen chloride accompanied by the formation of the corresponding unsaturated structures are discussed with respect to the repeated chloroallyl or α-chloropolyene activation of the dehydrochlorination process. The study of the assumed radical and ionic intermediates is used in discussing the reaction mechanism of dehydrochlorination, and the radical or ionic mechanism is supposed to be operative depending on the reaction conditions.

Metathesis ring opening polymerization of 5,6‐dimethylenebicyclo[2.2.1]hept‐2‐ene

Abstract5,6‐Dimethylenebicyclo[2.2.1]hept‐2‐ene (I) polymerizes in the presence of the two‐component ring opening metathesis polymerization (ROMP) initiators WCl6/(CH3)4Sn and MoCl5/(CH3)4Sn. The product polymers were insoluble in all of many solvents investigated and are presumably cross‐linked. The product polymers were investigated by IR and solid state 13C NMR spectroscopy, which established that the material consisted predominantly of poly(1,4‐(2,3‐dimethylene‐cyclopentylene)vinylene) (II). A possible alternative route to II via thermal dehydrochlorination of poly(1,4‐(2,3‐bis(chloromethyl)cyclopentylene) vinylene) (IV) was also examined.

Thermal Dehydrochlorination of Poly(vinyl chloride) Model Compounds. I.

The liquid phase (neat and solution) thermal degradation of a number of compounds which model the common defect groups found in pvc has been investigated. Compounds with halogen atoms at tertiary positions have stabilities similar to allylic halides. However, there was nearly a tenfold difference in the rate of reaction between the positionally isomeric 2-chloroalk-3-enes and 4-chloroalk-2-enes. Compounds with unsaturation within a longer chain or compounds lacking a terminal methyl group are somewhat less reactive. The dehydrochlorination reaction was confirmed to be accelerated by glass surfaces, hydrogen chloride and polar solvents.

Thermal Dehydrochlorination of Poly(vinyl chloride) Model Compounds. II. Computer Analysis of Kinetic Results

Computer simulation has been used to analyse the condensed-phase thermal degradation of a series of compounds with functional groups related to defects found in poly(vinyl chloride) ( pvc ). We have been able to estimate the relative significance of catalysed and non- catalysed processes and make some estimates of the significance of allylic rearrangement.

Kinetic Model of Thermal Dehydrochlorination of Poly(Vinyl Chloride)

Kinetic Model of Thermal Dehydrochlorination of Poly(Vinyl Chloride)

The effect of barium and cadmium stabilizers on the thermal dehydrochlorination of poly(vinyl chloride): A resonance Raman spectroscopic study

AbstractA laser Raman spectroscopic study has been made of the effect of barium and cadmium stabilizers on the thermal dehydrochlorination of poly(vinyl chloride) (PVC). The results obtained indicate that, in terms of the total level of dehydrochlorination, cadmium stearate is not as superior to barium stearate as the visual appearance of the polymer suggests. Also, the level of dehydrochlorination produced in the presence of a mixed stabilizer is not significantly lower than that produced in the presence of barium stearate alone, while samples of the latter exhibit much stronger color. It has also been shown that cadmium stearate can reduce the length of long polyene sequences, presumably by a reaction near the center of such a sequence.

Resonance Raman spectroscopic studies on dehydrochlorinated stretched poly(vinyl chloride)

AbstractResonance Raman spectroscopy has been used to assess the effect of streching on the formation of conjugated polyenes during the thermal dehydrochlorination of poly(vinyl chloride). Two samples, a commerical mass polymer and a material prepared at −30°C, have been examined, unplasticised and plasticised, at different draw ratios. Stretching prior to dehydrochlorination leads to an increase in the length of the polyene sequences, the effect being more marked with the low temperature polymer and with increasing draw ratio. Stretching after dehydrochlorination has no significant effect on the polyene distribution. These observations are consistent with the occurrence of chain orientation and alignment during stretching; this reduces the incidence of cross‐linking between polyene sequences in adjacent chains and leads to an increase in the average sequence length.

Thermal dehydrochlorination of poly(vinyl chloride), 2. Transiently and permanently acting structural defects

AbstractSamples with an increased content of chloroallyl structures were prepared by chemical degradation of poly(vinyl chloride) (PVC) using potassium tert‐butoxide. The samples were thermally dehydrochlorinated in an inert atmosphere, and their dehydrochlorination curves were determined by the continuous potentiometric method. The results show that the chloroallyl structures affect the dehydrochlorination of PVC only transiently. The same conclusion is obtained by an analysis of experimental data of the dehydrochlorination of PVC samples enriched in structures with the chlorine atom bound to the branching site (structures with the chlorine atom at the tertiary carbon atom). A general conclusion is that all structural defects, which facilitate the elimination of hydrogen chloride along the polymer chain and exist in the polymer before its heat stress, play only a transient role in the thermal dehydrochlorination of PVC. These structural defects initiate the splitting‐off of hydrogen chloride during the induction period of dehydrochlorination and form conditions for a gradually increasing effect of the basic initiation mechanism, which in the course of dehydrochlorination gives rise to chloroallyl structures. The formation of chloroallyl structures is brought about by a reaction between regular structural PVC units and s‐cis‐enone, dienone, or polyenone structures. A possible mechanism of this reaction, consisting in an interchain syn‐elimination of hydrogen chloride, is suggested.

Thermal dehydrochlorination of poly(vinyl chloride). I. Formation of ketone structures in the polymer

Thermal dehydrochlorination of poly(vinyl chloride). I. Formation of ketone structures in the polymer

Structure and stability of poly(vinyl chloride), 4. Unsaturated ketones and their role in the initiation of thermal degradation

AbstractThe thermal dehydrochlorination of poly(vinyl chloride) (PVC) in an inert atmosphere was investigated by the continuous potentiometric method. The effect of the structure of alicyclic and aliphatic α,β‐unsaturated ketones on the rate of dehydrochlorination was examined, and a new mechanism of initiation for the dehydrochlorination of PVC was suggested. The results obtained demonstrate that the basic cause of the thermal instability of PVC are structures of the type of cisoid α,β‐unsaturated ketone, dienone, or polyenone which by the dehydrochlorination of regular structural PVC units form isolated double bonds which, in turn, initiate the chain dehydrochlorination of PVC by allyl activation.

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.

Thermal dehydrochlorination of poly(vinyl chloride) models in the liquid phase

AbstractAn investigation was made of the kinetics of thermal dehydrochlorination of 8‐chlorohexadecane, 2,4‐dichloropentadecane, 4‐chloro‐2‐dodecene, 8‐chloro‐6‐tridecene, 6‐chloro‐2,4‐octadiene, and 7‐chloro‐3,5‐nonadiene in the liquid phase in an inert gas.The course of the reaction is accelerated by the presence of free hydrogen chloride and slowed down by conjugated dienes and trienes. Destruction of the model compounds leads to the formation of oligomers and telomers, some of which were isolated and their elementary composition and molecular weight determined. The reaction occurs much faster in nitrobenzene, compared with the dehydrochlorination of a model without solvent.With respect to its complicated mechanism, the dehydrochlorination reaction was characterized from the kinetic viewpoint by its initial rate kO. Parameters E and A were estimated from the temperature dependence kO = A exp(−E/RT).It follows from the experimental results and from the comparison of thermal dehydrochlorination reactions in the gas and liquid phases and in poly(vinyl chloride) that the reaction under investigation occurs by a ionic mechanism in the liquid phase, and most probably also in the polymer.

Investigations on thermal dehydrochlorination of poly(vinyl chloride)

AbstractThe thermal dehydrochlorination of PVC has been examined on some samples prepared by fractionation of a commercial PVC, and some other samples obtained by polymerization at different temperatures. The results disagree with the concept of a continuous dehydrochlorination from one side to the other of the chain, that necessitates initiating structural anomalies in the macromolecule itself.