Béla Turcsányi

Composition dependence of tensile yield stress in filled polymers

Examen de divers polymeres: ABS, polypropylene, polyethylene et diverses charges: verre, CaCO 3 , talc, silice, etc

Analysis of Linear Methods for Determining Copolymerization Reactivity Ratios. III. Linear Graphic Method for Evaluating Data Obtained at High Conversion Levels

Abstract If copolymerizations are carried to high conversions, the determination of copolymerization parameters involves significant computational difficulties because the exact integrated form of the copolymerization equation has to be applied. A simple method has been developed to transform experimental data, even at high conversions, to be used in the differential form of copolymerization equation. In this method an average monomer composition is assigned to the corresponding experimental average copolymer composition. The proposed approximation extends the use of our linearization technique previously developed for low conversions. It was established that this method yields highly reliable results for practically.

Polymer-analogous reactions of polyenes in poly(vinylchloride)

ABSTRACT The primary process in the thermal degradation of PVC in an inert atmosphere and at relatively low temperatures, is the elimination of hydrogen chloride molecules and the formation of polyene sequences of different lengths. The polyenes formed are highly reactive and participate in different secondary reactions. It has been shown for PVC samples degraded both in dilute solution and in the solid state that the amount of polyenes does not correspond to the degree of dehydrochlorination: proportionality may be observed only at the initial stage of degradation and, later on, the number of double bonds in the system is much lower than the amount of hydrogen chloride molecules split off. With the increase of conversion the increase in the amount of polyenes containing three or more double bonds gradually slows down and, later on, practically ceases. This phenomenon is also quantitatively well interpretable by intramolecular cyclization (backbiting) of polyenes. The reaction leads to cyclohexadiene structures. On completing the kinetic treatment of the process, we determined the relative rate constant of cyclization. Reactive dienophilic reagents readily react with the polyenes formed in degraded PVC. Based on the changes observed in the u.v. and visible spectra, a kinetic study was made on the Diels–Alder reaction with chloromaleic anhydride. The kinetic treatment, performed on the basis of a presumed mechanism, allowed the determination of the rate constants and their temperature dependence. Depending on the experimental conditions, the polyenes formed in the course of degradation may participate in other reactions as well. Some of the possible reaction routes are: the change in molecular weight, the formation of low molecular weight aromatic compounds (e.g. benzene) and the considerable proton exchange observed in the reaction of polyenes with hydrochloric acid.

Evaluation of high conversion copolymerization data by a linear graphical method

A method is presented by which experimental data for copolymerization can be treated also at high conversions to allow determination of copolymerization para meters by a simple, graphically evaluable linear equation.Compared to the usual experimental errors, the error of approximation is negligible up to 50% conversion and thus does not affect the reliability of the parameters determined.AbstractПриводится метод, с помощью которого экспериментальные данные по сополимеризации, включая также данные при высоких конверсиях, могут быть обработаны для определения параметров сополимериз ации с помощью простого, графически оцениваемого линейного уравнения.Сравнивая с сбычными ошибками измерений, погрешностью данного приближения можно пренебречь вплоть до конверсий 50%, что, т.о., не оказывает влияния на надежность параметров.

Reversible crosslinking during thermal degradation of PVC

SummaryPVC 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.

Crosslinking, scission and benzene formation during PVC degradation under various conditions

SummaryThe kinetics and mechanism of crosslinking and chain scission has been studied on several PVC samples during thermal thermooxidative, dynamic, and HCl catalyzed degradation. During pure thermal degradation crosslinking at a constant rate without scission occurs, while in the presence of oxygen and/or shear scission is not negligible. In the dynamic test, under shear both processes are fast, compared to static tests. The mechanism of benzene formation without main chain scission is discussed.

On the most significant processes of thermooxidative PVC degradation

In the thermooxidative degradation of PVC two processes are of decisive importance: the elimination of HCl in allyl-activated steps producing polyene sequences in the polymer backbone, and the radical chain oxidation of these polyenes. The two processes are closely interrelated as the carrier radicals of the oxidation chain initiate also sequential HCl elimination. This results in an enhanced rate of HCl elimination and a low steady-state concentration of polyenes.AbstractВ термоокислительной деградации ПВХ два процесса обладают решающей важностью: выделение HCl в аллил-активированной ступени, приводящее к образованию полиеновых сегментов в полимерном скелете, и радикальное окисление этих полиенов. Два процесса тесно связаны, т. к. носители радикалов цепей окисления инициируют также последующее выделение HCl. Это приводит к повышенной скорости выделения HCl и низкой стационарной концентрации полиенов.

Kinetics of initiation in reactive processing: Nonisothermal decomposition of initiators

For the complex radical reaction systems of reactive processing the kinetics of the rate determining initiator decomposition is of preeminent importance. Thermal decomposition of initiators takes place here in nonisothermal regime. Simplified kinetic treatment shows how the important characteristics—e.g. the temperature at which the initiation rate has maximum value—relate to the Arrhenius parameters of initiator decomposition and rate of temperature increase. The results give orientation for optimization of conditions in reactive processing.

Cross-linking and gel formation in the thermal degradation of PVC

Cross-linking in the thermal degradation of PVC was investigated by measuring the dependence of number-average molecular weight, gel fraction, molecular weight distribution and intrinsic viscosity on degradation time. A linear relationship was found between the cross-linking density and reaction time. Only one fifth of the polyene sequences formed participate in the cross-linking process.AbstractСшивка при термической деградации ПВХ была исследована измерением зависимости средне-числового молекулярного веса, гелевой фракции, распределения по молекулярным весам и истинной вязкости от времени деградации. Была найдена линейная зависимость между плотностью сшивки и временем реакции. Лишь одна пятая от всех образующихся полиеновых звенев принимает участие в сшивке.

Thermal Degradation of Vinylchloride/α-Olefin Copolymers

Abstract The preliminary results obtained for the thermal degradation of vinylchloride/α-olefin copolymers are, in part, unexpected. Decrease of the initial polyene length with the increase of comonomer content is a reasonable consequence of the shorter viny chloride sequence lengths, but the constancy of these lower values in the course of further degradation indicates, that some secondary reactions of the polyenes (e.g. cyclization) must be absent here. The decrease of the HCl elimination rate in case of copolymers differs from the dependence given by the weak sites model. Formally, the rate is proportional to a netative power of conversion, the value of the exponent depending on the composition. These results indicate the necessity of further research for clearing up the unknown details of PVC degradation mechanism.