Migration and blooming of stabilizing antioxidants in polypropylene

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Abstract
We have studied the migration of the hindered phenol, octadecyl‐3,5‐bis (1,1‐dimethylethyl)‐4‐hydroxybenzenepropanoate, and the phosphite co‐stabilizer tris 2,4‐bis(1,1‐dimethylethyl)phenylphosphite, out of films of polypropylene (nominal melt flow 3.5 g/10 min). Loss of additive from an initial 10% weight‐% level in the polymer was followed by FTIR bands in the appropriate regions. Temperatures of 298 K, 313 K and 333 K were used. An attempt was made to analyze migration data using Fick's law for diffusion by means of a least squares fit. Octadecyl‐3,5‐bis (1.1‐dim ethylethyl)‐4‐hydroxybenzenepropanoate diffused according to Fick's law with a temperature independent diffusion constant (D = 1.27 × 10−15 m2 S−1) to a steady state concentration of 7.2 % + −0.56 weight‐%. The phosphite did not diffuse at all at 298 K and 313 K, but diffused with D = 8.1 × 10−16 m2 S−1 to a steady level at 333 K. Our interpretation of the phosphite migration data assumes that most of the phosphite in the sample is immobilized. A subset of the total phosphite level is free to diffuse to the surface of the polymer.