The thermal degradation of polyvinylchloride in solution. I. The kinetics of the dehydrochlorination reaction

Abstract

The dehydrochlorination of polyvinylchloride in ethyl benzoate solution has been studied over the temperature range 178 to 212OC in an atmosphere of nitrogen. Over this temperature range the expression for the rate in moles HCl IiberatedIlitre. sec., is 5.7. 107e-229800/R.T*cn, where cn is the polymer concentration in polymoles/litre. Thus, for a fixed weight concentration of polymer, the rate is inversely proportional to the number average degree of polymerisation of the polymer.The presence of oxygen does not affect the rate of dehydrochlorination, but it causes a more rapid blackening of the polymer solution, and is accompanied by chain scission. The addition of free radical initiators increases the rate somewhat while quinone type compounds have no inhibiting effect. The addition of a commercial stabilizer (Stanclere 70) containing a dialkyl tin salt resulted in a retarded rate for a period proportional to the amount added. This was followed by the normal unretarded rate. The results, however, still leave undecided the mechanism of the dehydrochlorination reaction. Z US AM M E N F A S SUNG: Die Chlorwasserstoffabspaltung von Polyvinylchlorid wurde in Benzoesiureathylester-Losung unter Stickstoffatmosphare im Bereich von 178 bis 212OC untersucht. In diesem Bereich ist die Geschwindigkeit der Chlorwasserstoffentwicklung 5,7 .107.e-22800/RT.cn (cn = Polymerkonzentration in Polymolen /I). Fur eine bestimmte Gewichtskonzentration des Polymeren ist die Geschwindigkeit umgekehrt proportional dem Zahlenmittel des Polymerisationsgrades.Sauerstoff beeinflul3t nicht die Geschwindigkeit der Chlorwasserstoffabspaltung, verursacht aber ein rascheres Dunkelwerden der Losung, und daneben zeigt sich Kettenspaltung. Zugesetzte freie radikalische Initiatoren erhohen etwas die Geschwindigkeit, wahrend chinonartige Verbindungen keine inhibierende Wirkung zeigen. Ein handelsublicher, dialkylzinnsalzhaltiger Stabilisator (Stanclere 70) vermindert die Geschwindigkeit wahrend einer Zeit, die proportional der zugefiigten Menge ist. Jedoch erlauben die Ergebnisse keine Entscheidung iiber den Mechanismus der Chlorwasserstoff-Abspaltungsreaktion.Chain scission, crosslinking, and dehydrochlorination, are known to occur l) during the thermal degradation of polyvinylchloride at temperatures in the region of 200°C. The mechanisms of these processes are, 31

Increase of PVC thermal stability through chemical modification by dibutylester of malein acid

“…The beginning of PVC gel formation depends to a considerable degree on the concentration (13). The presence of oxygen causes the breaking of chains (14), but it may also lead to the formation of nonstable groups in split-off polymer. The speed of PVC dehydrochloration depends considerably on the type of solvent used (15-17) but at temperatures over 200°C it proceeds fairly fast already (16).…”

A review on photochemical effects of common plastics and their related applications

“…The main mechanism of photooxidation reaction of PVC is free radical reaction. [159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176][177] When the temperature is higher than 100 C or exposed to the sun for a long time, PVC decomposes into hydrogen chloride, 177 which further autocatalytically decomposes PVC, causing discoloration and rapid decline in physical and mechanical properties. Although HCl has an…”

“…After the molecular oxygen is fixed, the peroxidation reaction begins. The main mechanism of photooxidation reaction of PVC is free radical reaction 159–177 . When the temperature is higher than 100°C or exposed to the sun for a long time, PVC decomposes into hydrogen chloride, 177 which further autocatalytically decomposes PVC, causing discoloration and rapid decline in physical and mechanical properties.…”

Stabilization of gamma‐irradiated poly(vinyl chloride) by epoxy compounds. III. Conjugated double bonds and degree of unsaturation in gamma‐irradiated PVC–stabilizer mixtures

“…A nonlinear segments of this dependence indicate the appearance of secondary reactions. 18,21,22 On purpose, to illustrate better the action of a stabilizer on the formation of the conjugated polyene sequences, the total amount of polyene sequences. H, vs dose, for the pure and stabilized PVC, is presented in Figures 3 and 4.…”