Constantin Ciobanu

Cure kinetics of epoxy resins studied by non-isothermal DSC data

Abstract The curing kinetics of diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of hydroquinone (DGEHQ) epoxy resins in presence of diglycidyl aniline as a reactive diluent and triethylenetetramine (TETA) as the curing agent was studied by non-isothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Malek for the kinetic analysis of the data obtained by the thermal treatment. A two-parameter (m, n) autocatalytic model (Sestak–Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. Reactive diluent decreases both the activation energy and the cure kinetic parameters. Non-isothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated.

Thermal degradation of semi-interpenetrating polymer networks based on polyurethane and epoxy maleate of bisphenol A

Abstract Two polyurethane–epoxy maleate of bisphenol A semi-interpenetrating polymer networks were synthesized and their thermal behavior studied. The data obtained by thermogravimetry showed that the decomposition of the tested samples is complex, occurs in three steps, and depends on the degree of crosslinking. The main decomposition takes place between 290 and 480 °C, with weight losses between 62 and 66%. The apparent thermal stability of the sample synthesized with a low content of epoxy maleate of bisphenol-A (11.11 wt%) is lower compared with polyurethane, while the sample with high content of epoxy maleate of bisphenol-A (27.3 wt%) shows a higher stability.

Photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution. The role of some dyes in the degradation

The influence of some dyes on the photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution has been studied. It has been found that, among the dyes used, only riboflavin sensitizes and accelerates the degradation of the polymer. It is proposed that under ultraviolet irradiation riboflavin undergoes photoreduction to lumichrome, which sensitizes the photodegradation of the polymer. It is also possible that the mechanism of photodegradation involves the participation of singlet oxygen.

Thermal degradation of polyester precursors of polyurethanes modified with cesium cations

Abstract The effect of cesium cations on the thermal behaviour of two linear aliphatic polyesters, poly(butylene adipate)diol and poly-(hexamethylene adipate)diol, major precursors of polyesterurethanes, was studied by using thermogravimetric analysis. The activation energy for parent polyesters and for their interaction products with cesium was evaluated using the Coats–Redfern and Levi–Reich methods. The thermo-oxidative resistance of both polyesters is improved by modification with cesium cations. ©

Aspects of polyesterurethane interaction with metallic ions: II. Synthesis and thermal behavior of polyurethane interaction products with manganese and copper ions

Abstract The objective of this study was to investigate the effects of some transition metal ions on the thermal behavior of polyurethane materials. The interaction products of a segmented polyesterurethane prepared from 4,4′-diphenylmethane diisocyanate, poly(ethylene-co-diethylene adipate)diol and ethylene glycol, with manganese and copper ions were synthesized and their thermal decomposition was studied in comparison to that of the original polyurethane by using thermogravimetric analysis. The activation energy of the thermal degradation was evaluated by Coats–Redfern and Levi–Reich methods. It was revealed that the thermal decomposition of the polyurethane is affected by the presence of both metallic ions and that each ion has a specific influence on the process. By modification with manganese and copper ions, changes in the degradation mechanism of the polyurethane are induced. It was found that manganese ions have a catalytic effect on the overall decomposition process, whereas copper ions reduce the initial thermal stability of the polyurethane and catalyze the final stage of its decomposition, but enhance the thermal stability of the intermediate products. In general, the influence of metallic ions on the thermal behavior of the polyurethane becomes more significant as their proportion increases.

Aspects of polyesterurethane interaction with metallic ions. III. Thermal behavior of polyurethane interaction products with iron and chromium ions

Abstract The present study aimed to investigate the influence of some transition metal ions on the thermal behavior of polyurethane materials. To this purpose, the interaction products of a segmented polyesterurethane with iron and chromium ions were synthesized and their thermal decomposition was studied in comparison with that of the original polyurethane by using thermogravimetric analysis. The activation energy of the thermal degradation was evaluated by Coats–Redfern and Levi–Reich methods. It was revealed that the presence of both metallic ions affects the thermal decomposition of the polyurethane and that each ion has a specific influence on the process. The modification of polyurethane with iron and chromium ions induces changes in the degradation mechanism. It was shown that iron ions favor, generally, the decomposition, having a pronounced catalytic effect on the final stage. Chromium ions reduce the initial thermal stability of the polyurethane and strongly catalyze the final stage of its decomposition, but enhance the thermal stability of the intermediate products. In general, the influence of metallic ions on the thermal behavior of the polyurethane is increasingly pronounced as their amount is higher.

Thermal behaviour of polyurethane interaction products with cobalt ions

Abstract This study deals with the effects of a transition metal ion, cobalt on the thermal behaviour of polyurethane materials. A series of interaction products with cobalt ions of a segmented polyesterurethane prepared from 4,4′-diphenylmethane diisocyanate, poly-(ethylene-co-diethylene adipate)diol and ethylene glycol were synthesized and their thermal degradation investigated in comparison to that of the original polyurethane by thermogravimetric analysis. The activation energy of the thermal degradation was estimated from the thermogravimetric data by the Coats–Redfern and Levi–Reich methods. It was found that modification of the polyurethane with cobalt ions induces changes in its decomposition mechanism. All the steps of polyurethane decomposition are affected by the presence of cobalt ions and the modifications in mass loss, maximum rate of mass loss and corresponding temperature are specific for every step. It was shown that cobalt ions generally favour the degradation, having a significant catalytic effect on its final stage. In general, the favourable influence of cobalt ions on the processes involved in polyurethane decomposition tends to become more pronounced as their amount increases.

Thermal Stability of Polyesteric Precursors of Polyurethanes Interacted with Potassium Cations

Abstract The effect of potassium cations on the thermal stability of three aliphatic linear polyesters, i.e. poly(ethylene adipate)diol, poly(butylene adipate)diol and poly(hexamethylene adipate)diol, major precursors of polyesterurethanes, was investigated. The activation energy of the thermal decomposition processes of polymer/potassium ions interaction products and of parent polyesters was evaluated using the Levi-Reich thermal analysis method. It was found that the presence of potassium cations enhances the thermal stability of the studied polyesters.

Thermal degradation of some crosslinked acrylic copolymers functionalized as ion exchangers

Thermal degradation of some acrylic crosslinked copolymers based on divinyl benzene, ethyl acrylate and acrylonitrile as such, or functionalized with various amines was examined by thermogravimetry in the range of temperatures between 40 and 600°C. The original copolymers decompose in two stages, and the functionalized copolymers in three stages. In both cases the main decomposition is between 250 and 450°C. The decomposition of the crosslinked copolymers depends on the nature of copolymer, the amount of divinyl benzene used as the crosslinked agent and on the extent of conversion. The decomposition proper of the functionalized copolymers depends on the nature of both the copolymer and of the amine used in the aminolysis.

Photodegradation in Aqueous Solution of a Polyamidehydroxyurethane Type Polymer. Temperature Effect on the Process of Degradation

Abstract The present research shows some aspects of temperature effect on the process of photodegradation in aqueous solution of a polyamidehydroxyurethane type polymer. The process of photodegradation in aqueous solution of the studied polymer proceeds with chain scissions, what is promoted at elevated temperatures. At the temperatures 45°C and 65°C the values of the number average of chain scissions, S, and of the quantum yield of chain scission, φcs, are greater at the initial moments of the process than the correspondent values at 25°C and 35°C. At elevated temperatures there is an increase in the probability of the process of recombination of macroradicals, formed during chains scission. The values of S at 45°C and 65°C by the end of the process are smaller than those at 35°C and 25°C. It can also be noticed, that the values of φcs at 45 °C and 65°C continuously decrease after the initial moments of irradiation till the end of the process of degradation, while at 25°C the values of φcs increase pract...