Modelling of thermal oxidation of phosphite stabilized polyethylene

Abstract

Modelling of thermal oxidation of phosphite stabilized polyethylene. Polymer Degradation and Stability, Elsevier, 2011, 96 (7), pp. a b s t r a c tThe thermal oxidation behaviour of polyethylene films stabilized by various weight ratios of organophosphites (Irgafos 168) has been studied at selected temperatures. The duration of the induction period was found to increase proportionally with the stabilizer concentration, even at temperatures as low as 80 C. Particular attention was paid to the phosphiteephosphate conversion during the induction period. A kinetic model, involving volatile and partially soluble hydroperoxide decomposers, was developed in order to simulate these results. With the use of kinetic parameters that can be at least tentatively justified from theoretical considerations, this model gave simulations in reasonable agreement with the experimental observations for stabilizer depletion and carbonyl formation. Of particular note is the fact that, even for non-trivial results such as the shape of the phosphite versus phosphate concentration plots, or phosphate build-up, there was also a quite good agreement.

Kinetic modelling of phenols consumption during polyethylene thermal oxidation

“…4). This conclusion can be drawn to each case where induction period duration increases linearly with initial stabilizer concentration [14]. Therefore, phenol depletion will be only considered as caused by chemical consumption in the following.…”

“…In previous papers [13,14], we successfully simulated the behavior of phosphites and sulfurs by supposing that stabilizer soluble part disappear by reaction and evaporation, and insoluble one works as a reservoir maintaining the amorphous phase at the saturation limit as long as it is not totally consumed:…”

“…-Estimation of solubility limit of stabilizers (being relatively polar molecules) in polyolefins from a theoretical approach is relatively complex: as observed for example by Billingham [9,14], regular solution theory (which is derived from Flory Huggins approach) is shown to give a good basis for extrapolation of data but cannot predict solubilities. This is not surprising first because approach derived from Flory's theory cannot be when polar interactions exist between polymer and stabilizer, and also because of the semi-crystalline nature of polyolefins [21].…”

“…Discuss on the ability of the model to simulate the shape of stabilizer residual concentration curve. We already obtained promising results in comparable studies for hydroperoxides decomposers [13,14] but it was in case of a major volatile loss so that it is not sure that the stabilizer depletion only due to chemical reaction is accurately simulated. Since Oxidation Induction Time measurement (by Chemiluminescence or DSC) is a commonly employed [4][5][6], we will try to discuss on the reliability of this method for determining the residual quantity of stabilizer in polymer after exposure.…”

Rheological and mechanical properties of recycled poly(ethylene terephtalate)/high density polyethylene blends

“…Phosphites react with hydroxyl and carboxyl end groups of PET to diminish the possibility of their reaction via hydrolysis. They can also reduce the hydroperoxides to alcohol in polyolefins [3][4][5][6] according to the following reaction:…”