Ion Mihalcea

Effects of some antioxidants on the stability of ethylene-propylene elastomers

Abstract The thermal-oxidative behaviour of ethylene-propylene elastomers EPDM and EPR, with the same ethylene/propylene ratio has been studied in experiments performed in the temperature range 140–180 °C. The antioxidants tested were sterically hindered phenols, bis-phenols containing either methylenic or sulphur bridges and triazines. Some main kinetic characteristics: induction time, relative activity and activation energy for degradation, were used to establish increasing orders of effect in relation to thermal ageing. IR spectroscopy and oxygen uptake were chosen for determination of chemical changes of the elastomers during their isothermal degradation. A discrepancy between EPR and EPDM was identified because of the presence of ethylidene-2-norbornene in the terpolymer structure, which decreases its thermal stability.

Chemiluminescence investigation of thermo-oxidative degradation of polyethylenes stabilized with fullerenes

The stabilization effect of various carbon materials: [C60]fullerene, three adducts with levopimaric acid, two sorts of carbon black and nanocarbon on HDPE, LDPE and LLDPE have been studied by chemiluminescence at 180, 190 and 200 °C. Kinetic parameters: oxidation induction time, rate of oxidation and activation energy were determined. On the basis of these results some considerations on oxidation prevention mechanism are revealed.

Effect of calixarenes on thermal stability of polyethylenes

The thermal degradation of some polyethylenes (one type of high density PE and two of low-density) was studied by isothermal chemiluminescence. Each polymer was stabilized by one of four phenolic additives: p-t-butylphenol (considered as reference), 2,4,6-tri-t-butylphenol, p-t-butylcalix[4]arene, and p-t-butylcalix[6]arene. Six kinetic parameters of thermal oxidation (induction period, maximum oxidation rate, half-period of ageing, maximum CL intensity, maximum degradation time, and activation energy) along with relative activity and stability were calculated. Protection efficiency of additives was evaluated by relative activity and relative stability indexes. Considerations of a stabilization mechanism involving calixarenes are presented.

Thermo-oxidative behaviour of halobutyl and butyl elastomers

The thermo-oxidative degradation of butyl and halobutyl elastomers has been studied by both IR spectroscopy and chemiluminescence methods. The kinetic parameters of degradation are similar for both methods and show that the chlorinated elastomer is less stable than the parent hydrocarbon, whereas the brominated elastomer is more stable. Degradation of the butyl rubber is mainly by chain scission, whereas the halobutyl elastomers undergo extensive cross-linking.

Behaviour of ethylene-propylene elastomers in salt solution—III. Gel content data

Abstract The effects induced by chloride ions in ethylene-propylene elastomers (EPR and EPDM) by gamma radiation are evaluated using gel content data. Charlesby-Pinner plots illustrate the competition of two antagonistic processes, scission and crosslinking, which take place in gamma irradiated polymers. Changes in gel content over large salt concentration (0–10%) at increasing absorbed doses up to 250 kGy were determined. A mechanism of formation and decay of oxygenated units is presented.

Behaviour of ethylene-propylene elastomers in salt solutions: I. SEM investigation of gamma irradiation effects

Changes of morphological structure of irradiated ethylene-propylene elastomers (EPDM and EPR with the same propylene content) in various conditions, air, distilled water, 0.1% and 10.0% NaCl solutions, at a total gamma dose of 0.5 MGy are discussed. Scanning electron microscopy was employed to reveal material alteration by the simultaneous action of ionizing radiation and environmental factors (oxygen, water chloride ions). Gel fraction determination showed the overall effect of polymer crosslinking. The main role of free radicals is shown to be in oxygen scavenging instead of their recombination. In contrast the presence of chloride ions in aqueous solutions promoted network development. A mechanism is proposed for radiation ageing of the tested polymers, which can explain the degradation effects.

The comparative effectiveness of some commercial antioxidants as studied by lyoluminescence

Abstract Lyoluminescence is an interesting tool to study the reactivity of different antioxidants towards the free RȮ 2 radicals which are frequently involved in the oxidative processes of different polymeric materials. In the present paper we have used lyoluminescence to characterize the effectiveness of the following commercial phenolic antioxidants: Topanol OC, Irganox 1076, Ionox 220, Etanox 330, Cyanox 2246 and Irganox 1010. The antioxidant efficiency of these products in the thermal oxidation of polyethylene was compared on the basis of the results of oxyluminescence and thermal analysis methods.

Irradiation of Polyethylene in Presence of Several Additives as Studied by Chemiluminescence

Abstract The protecting effect against radiation induced oxidation of poly-ethylene provided by several additives, namely pyrene, Irganox 1222 and Irganox 1010 has been investigated by mean of FTIR spectroscopy and chemiluminescence (CL) technique. Pyrene appears to be more effective and more stable to irradiation than phenolic antioxidants. Thus, about half of initial pyrene seems to remain unchanged after an exposure of the material to γ60Co rays at 240 kGy (dose rate 1 kGy/h) in presence of air. Under the same conditions, about 90% of initial Irganox 1010 seems to be consumed as indicate a comparison of induction oxidation times of initial and irradiated material. The stabilizing effect of the residues resulted by pyrolysis at 850°C in inert atmosphere of several polymers, such as polyacrylonitrile, polyvinylchloride and methyl cellulose is discussed as well.