Diffusion of di(2-ethylhexyl)phthalate in PVC quantified by ATR-IR spectroscopy

Di(2-ethylhexyl)phthalate (DEHP) is a commonly employed plasticizer for poly(vinyl chloride) (PVC). Diffusion of di(2-ethylhexyl)phthalate (DEHP) takes place when plasticized PVC is immersed in hexane. Rather than determining DEHP concentration in the immersion solvent, an IR window for PVC from 1500 to 1900 cm(-1) enabled direct measurement of HADD (hexane assisted DEHP diffusion) using ATR-IR by monitoring the DEHP carbonyl absorption at 1715 cm(-1). The present study employed PVC containing 45% plasticizer (PVC-45, tygon tubing). A fast diffusion process was observed for short times (<30 s) while a slower diffusion process occurred at longer immersion times (30 s < t < 6 min). A synergistic increase in mesosurface T-g toward that of PVC coupled with low solubility of hexane in PVC accounts for decreased DEHP diffusion rates (10(-12)-10(-13) cm(2) s(-1)) for immersion times > 30 s. Analysis by XPS shows the outermost surface is PVC free of plasticizer after 6 min immersion. After an induction period, back diffusion coefficients D-b were estimated from peak areas during a subsequent fast recovery period (10(-14) -10(-15) cm(2) sec(-1)). A model is proposed for the induction period associated with re-plasticization that involves a change from a mesosurface glass to a gel like solid. (C) 2015 Elsevier Ltd. All rights reserved.