Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressure

Abstract

Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80 C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 Â 10 À3 mol L À1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 Â 10 À3 mol L À1 . The results indicate the existence of a direct phenol-oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build-up and stabilizer consumption.

Polypropylene stabilization by hindered phenols – Kinetic aspects

“…1. Results obtained at 80 C were presented elsewhere [25]. It is well known that kinetics of thermal oxidation of hydrocarbon at moderate temperature are characterized by an induction period after which one observes hydroperoxides, alcohols and carbonyl build-up, oxygen uptake and mass variation, chemiluminescence emission and exothermal heat flow.…”

Polyethylene stabilization against thermal oxidation by a trimethylquinoleine oligomer

“…According to discussions in previous papers [45,46], we have assumed a two-step stabilization mechanism for the hindered di-tert-butyl-phenol:…”

Comparison of stabilization by Vitamin E and 2,6-di-tert-butylphenols during polyethylene radio-thermal-oxidation

“…According to this work, and other previous papers (Richaud et al, 2008, Richaud et al, 2011, Richaud, 2013, the action of stabilizers is can be described by adding the following equations to the general mechanistic scheme: Richaud et al, 2008, Richaud et al, 2011, Richaud, 2013. The following set of differential equations Figure 9 were [POOH] 0 was considered as an adjustable parameter expressing the level of unstable moiety in several PE from different sources).…”

“…In UHMWPE films thin enough (such those used in Costa et al (2009) to neglect all diffusion phenomena, k S1 … k S4 can be estimated "simply" by an inverse approach from ageing experiments (Richaud et al, 2008;Richaud et al, 2011;Richaud, 2013). For that purpose, Vitamin E stabilization reactions are added to the scheme previously established for additive free PE (Khelidj et al, 2006) …”