Antioxidants and stabilizers, 116 Influence of the carbon black chezacarb EC on polyolefin thermooxidation: A model study with cyclohexene doped with chain‐breaking antioxidants

Abstract

The ageing of polyolefins is accelerated by carbon black Chezacarb EC used as a filler. Conditions for selection of suitable chain-breaking antioxidants protecting against degradation were simulated using cyclohexene doped with various amounts of carbon black and oxidized at 60°C. The results obtained reveal an acceleration of cyclohexene oxidation in the phase following the induction period (IP). The oxidation acceleration is similar to the effect caused by powdered copper(0) or copper(I1) ions. Polynuclear phenolic antioxidants are able to stabilize cyclohexene for periods longer than 120 h only in the presence of low amounts of Chezacarb (up to 0.5 wt.-"0). At higher Chezacarb concentrations, merely a prolongation of IP may be achieved. Arylene diamines are efficient stabilizers only if combined with a high concentration of Chezacarb (10 wt.4'0). None of the chain-breaking antioxidants used was able to diminish the oxidation rate of cyclohexene in the phase after IP. ZUSAMMENFASSUNG:Die oxidative Alterung von Polyolefinen wird durch RUB, Chezacarb EC, als Fullstoff beschleunigt. Die Bedingungen fur die Auswahl von geeigneten kettenabbrechenden Antioxidantien wurden mittels Cyclohexen, das mit verschiedenen Mengen von RUB versetzt und bei 60°C oxidiert wurde, simuliert. Die Resultate zeigen eine Beschleunigung der Oxidation des Cyclohexens in der Phase nach der Induktionsperiode (IP). Die Oxidationsbeschleunigung ist dem katalytischen Effekt von Kupfer (0)-Pulver oder Kupfer(I1)-Ionen ahnlich. Mehrkernige phenolische Antioxidantien konnen Cyclohexen fur einen langeren Zeitabschnitt als 120 h nur in Anwesenheit von kleinen Mengen Chezacarb (bis 0,5 Gew.-%) stabilisieren. Nur eine Verlangerung der IP wurde bei hoheren Konzentrationen von RUB beobachtet. Arylendiamine stabilisieren wirksam nur in Anwesenheit von einer hoheren Konzentration (10 Gew.-%) von Cheza-* Part 115 cf. ref.lg.

Environmental and Micro-Environmental Influences Affecting the Performance of Polymer Stabilisers

“…Rather complicated problems can be encountered in the determination of residual hindered amine stabilisers (HAS) in photooxidised polymers [21] . HAS do not absorb in the UV-A or UV-B regions and are designed to be rather unextractable.…”

Exploitation of the current knowledge of antioxidant mechanisms for efficient polymer stabilization

“…Polymers must also be appropriately protected against radical chain oxidation, and the application of CB A 0 and/or their combinations with secondary A 0 is obligatory. It has been shown under model conditions (autoxidation of cyclohexene at 60°C) that even very efficient hindered phenols and aromatic amines, when used without MD, were not able to stabilize the hydrocarbon system filled with carbon black contaminated with metal impurities after the induction period [43].…”