ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 11, pp. 1981–1986. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © D.G. Lin, E.V. Vorob’eva, N.V. Marchenko, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 11, pp. 1866–1871.
Oxidation of Polyethylene Inhibited with a Phenolic Antioxidant
under the Conditions of Contact with Metallic Zinc
D. G. Lin, E. V. Vorob’eva, and N. V. Marchenko
Skorina Gomel State University, Gomel, Belarus
Received March 25, 2008
Abstract—The inhibiting power of a phenolic antioxidant upon introduction into polyethylene contacting with
metallic zinc was examined. Conditions at which zinc enhances the inhibiting effect of the antioxidant were
determined, and the mechanism responsible for this effect was suggested.
It is well known that many variable-valence metals
accelerate oxidation of noninhibited polyethylene (PE)
owing to the transfer of soluble metal-containing com-
pounds formed by contact reactions [1, 2]. These com-
pounds exhibit high catalytic activity and transfer the
oxidation process from the layer adjacent to the metal
into the bulk of the polymeric material. Therefore, for
successful operation of metal–polymer materials and
articles containing active metals, it is necessary to en-
sure deactivation of the catalytic surface of metal-
containing compounds which in the course of oxida-
tive transformations migrate in a polymeric binder.
One of the ways to solve this problem is introduction
into a polymer of antioxidant (AO) additives. The most
common of them are amine and phenolic additives.
Previous studies [3–5] showed that the use of such
AOs for inhibiting the oxidation of polymers that are
in contact with active metals can lead to quite unex-
pected results. For example, Irganox 1010, an effective
AO for PE, in oxidative contact of the polymer with
copper (e.g., in case of a PE coating on a copper sup-
port or of PE filled with dispersed copper) is rapidly
consumed, and the induction period of the oxidation
(IPO) decreases by a factor of more than 7 [4, 5]. On
the contrary, relatively weak amine AO, Neozon D,
under the similar conditions becomes more effective,
and IPO of the polymer increases . Below we
briefly describe the mechanism  of the copper effect
on the inhibiting power of amine and phenolic AOs.
With a phenolic AO, the decisive factor is transfer
of copper-containing compounds from the zone of ad-
hesion contact to the bulk of the polymer [4–6]. This
transfer apparently occurs even during the IPO. The
transferred copper compounds catalyze the generation
of primary radicals which, in turn, accelerate the AO
consumption. In this step of the oxidation process, sta-
ble oxidation products (namely, carbonyl-containing
compounds) are not detected yet, and, according to IR
monitoring, this period can be considered as IPO. After
the majority of AO is consumed, the oxidation be-
comes autocatalytic, and specifically this moment is
fixed as the end of IPO.
AND POLYMERIC MATERIALS
Enhancement of the performance of an amine AO
in the presence of copper is attributed [3, 7] to direct
reaction of AO with copper (support surface or filler
particles) with the formation of stable nitroxyl radicals
whose inhibiting power is higher than that of the initial
AO. Effective oxidation inhibitors arising in the con-
tact zone suppress the formation and transfer of cop-
per-containing compounds. As a result, the onset of the
autocatalytic step of the oxidation process is delayed,
and IPO becomes longer.
As can be seen, the use of AOs of different classes
under the conditions of contact oxidation of PE on
copper can lead to opposite results. Therefore, solution
of the problem of suppressing the catalytic effect of
active metals that are components of metal–polymer
materials and of articles based on them will remain for
a long time on the level of experimental search and
discoveries. In this connection, we examined in this
study the oxidation of PE inhibited by a phenolic AO
and occurring in contact with metallic zinc.