M.I. Abdullin

The degradation of polyvinyl chloride in presence of phosphorus-containing plasticizers☆

Abstract The introduction of plasticizers based on orthophosphoric acid esters into PVC significantly changes the thermal and thermo-oxidative degradation processes occuring in the polymer, consisting in HCl elimination, and formation of a conjugated double bond system and of statistical, isolated, C=C double bonds. Phosphate plasticizers intensify the thermal decay of PVC. The thermo-oxidative degradation may be retarded or on the other hand, substantially accelerated by phosphates. The process kinetics are determined by the nature and amount of plasticizer in the polymer composition and also by the decomposition products. As a result, the efficiency of metal-containing thermostabilizer-HCl acceptors and antioxidant-stabilizers is determined to an appreciable extent by the nature of the phosphate plasticizer being used.

Effect of ozone on the breakdown of polyvinylchloride

A study was made of kinetic relations of hydrogen chloride liberation from PVC and the formation of peroxide compounds in the polymer during thermal decomposition of PVC in the presence of ozone. Rate constants of corresponding processes were determined. Ozone markedly intensifies the separation of HCl from PVC macromolecules; gross dehydrochlorination of the polymer in ozone mainly takes place by the statistical elimination of HCl, the process of forming polyconjugated systems being practically fully inhibited. By the action of ozone on PVC O3 rapidly interacts with internal and terminal double bonds 〉CC〈 and slow reaction takes place with saturated polymer structures. It was shown that labile groups containing oxygen, formed during the attack of saturated macromolecular sections of PVC by ozone reduce polymer stability to a greater extent than structures formed during the reaction of O3 with 〉CC〈 bonds.

Chemiluminescence during the oxidation of ester plasticizers of polyvinylchloride

Abstract The thermo-oxidative degradation of ester plasticizers of PVC, namely, the dialkyl esters of o -phthalic acid, is accompanied by chemiluminescence, a correlation being observed between the maximum intensity of the chemiluminescence and the rate of oxidative overall dehydrochlorination of the PVC in a medium consisting of the ester plasticizers mentioned. Intense oxidative thermal degradation of plasticized PVC is caused by the occurrence of processes involving the formation and decomposition of hydroperoxides of the dialkylphthalates. The kinetic parameters characterizing the auto-catalytic oxidation of the ester plasticizers have been measured.

Thermal oxidative breakdown of plasticized polyvinylchloride

The addition to PVC of ester plasticizers considerably changes the rate of breakdown processes—elimination of HCl, formation of statistical isolated >C=C< bonds and the formation of poly-conjugated systems of double bonds in the macro-molecules. The ratio of rates of these processes depends on the oxidative stability of the plasticizer its concentration and partial oxygen pressure in the reaction zone. Products of oxidation of esters intensify the formation of polyene systems, whereas actinometer coupled with an F-116/1 microvoltmeter. Within the wavelength interval specified the intensity was varied from 6 × 1014 to 1·5 × 1015 quantum cm−2sec−1. The exposure time was 10–300 sec. The electronic spectra were measured with an SP-700 spectrophotometer; an IKS-29 spectrophotometer was used for the IR spectra. The differential quantum yield of the PVCA oxidation product was measured by a standard method [5], using monochromatic light. The wavelength selected was in the interval 400–440 nm, such that the intensity of the light absorbed did not exceed 20% on that of the incident light. The amount of light absorbed was calculated in line with the Lambert-Beer law.

Quantitative evaluation of the effect of a plasticizer on the thermo-oxidative degradation of polyvinylchloride☆

Abstract It has been shown, with the oxidation by oxygen of PVC in esters of dicarboxylic acids and o -phosphoric acid as examples, that the rate of thermo-oxidative degradation of plasticized PVC is determined, in the first instance, by the oxidative stability of the plasticizer and by its concentration in the polymer. The change in the rate of thermo-oxidative degradation of PVC under the action of plasticizers is described quantitatively. The rate of thermo-oxidative degradation of plasticized PVC becomes greater than the rate of decomposition of the unplasticized polymer, beginning at a certain critical value of the oxidative stability of the plasticizing agent; independently of the chemical nature of the plasticizer, the rate depends linearly on the plasticizer concentration in the polymer.

Thermal and thermo-oxidative degradation of polyvinyl chloride in phosphorus-containing plasticizers☆

The kinetics of the degradation of PVC greatly changes on introducing phosphorus-containing plasticizers into the polymer system with a significant difference in the patterns of the processes of thermal and thermo-oxidative degradation. The main reason for the acceleration of thermodegradation of PVC in a medium of phosphorus-containing plasticizers is chiefly the high nucleophilicity of the esters of o-phosphoric acid governing the specific solvation interaction between the molecules of the plasticizer and the polymer macrochains. The rate of the thermo-oxidative degradation of PVC plasticized by o-phosphates is determined by the reactivity of the esters of o-phosphoric acid in relation to oxygen; the rate of breakdown of the polymer rises with fall in the oxidative stability of the plasticizer the quantitative characteristic of which is the parameter of oxidizability of o-phosphate k = k2k6−0.5k30.5.

Role of plasticizer in thermal-oxidative breakdown of polyvinylchloride in the presence of metal chlorides

Abstract The rate of thermal-oxidative breakdown of PVC, in relation to the presence in the polymer composition of metal chlorides—main products of the conversion of metal-containing heat-stabilizers of PVC, is determined by the presence of plasticizers in the polymer. The effect is due to the variation of oxidation kinetics of plasticizers by the action of metal chlorides and therefore, on differences in the effect of plasticizers and the intensification (or weakening) of the catalytic action of metal chlorides on the breakdown of PVC. Metal chlorides and plasticizers based on esters have a non-additive effect upon breakdown processes of PVC.

“Auto-echo” stabilization of polyvinyl chloride in blends of ester and phosphate plasticizers☆

Abstract Ester plasticizers and aryl-containing phosphates influence non-additively the rate of oxidative thermal breakdown of PVC. The interaction of aryl phosphates with oxygen on thermo-oxidative exposure of the plasticates is accompanied by the formation of products retarding oxidative degradation of the ester plasticizing agents and, a consequence, the thermo-oxidative breakdown of PVC (“auto-echo” effect of stabilization of PVC).

Methods of investigation Automatic equipment for measuring the low-temperature dehydrochlorination of chlorine-containing polymers☆

A high sensitivity automatic apparatus for measuring the rate of dehydrochlorination of chlorine-containing polymers is described.

The thermal degradation of vinyl chloride homo- and copolymers in solution☆

Abstract The mechanisms of thermal degradation of vinll chloride polymers in solution have been shown to be related to solvation effects i.e. to specific (donor-acceptor) and non-specific (Van der Waals) interactions of the macromolecules with solvent molecules. Specific interaction of the solvent with anomalous homo- and copolymer macrochain,, depending on the solvent basicity, causes a decrease or increase in the polymer dehydrochlorination rate, accompanied by formation of C=C bond polyconjugated systems, whereas non-specific solvation, in all cases, intensifies polymer decay.