Critical Temperature for Solubility of a Phenolic Antioxidant

Abstract

Antioxidants are commonly added to polyethylene to retard oxidative degradation. The effectiveness of these antioxidants is dependent on both their chemical and physical properties. Thus an antioxidant must possess the chemical capability to retard the oxidation of the polymer, and in addition must have the physical properties which allow it to remain in the polymer bulk at a sufficient concentration to insure long term stabilization. The amount of antioxidant remaining in the polymer bulk will be dependent on: the equilibrium solubility of the antioxidant in the polymer, the rate of diffusion of the antioxidant and the rate of volatilization of the antioxidant from the polymer surface.¹ For long term stability, an antioxidant should have a high equilibrium solubility, a low rate of diffusion and a low volatility. Knowledge of these three factors would be helpful in screening chemically similar antioxidants. How-ever, obtaining these data, especially near room temperature, is quite difficult because antioxidants usually have low solubilities (< 0.1 weight %) in hydrocarbon polymers and low vapor pressures (< 10^-3 mm). In the current work we have attempted to develop a simple method for the measurement of solubility.