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

• Published in: Polymer (Guilford) Vol. 76; pp. 70 - 79
• Main Authors: Wang, Chenyu, Johnson, Daniel, Suleman, M. Aziz, Suleman, M. Adil, Zhang, Wei, Pestov, Dmitry, Ramsinghani, Priyanka, Wickham, Rennisha, Wynne, Kenneth J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 12-10-2015
• Subjects: Diffusion; Diffusion rate; Hexanes; Immersion; Infrared spectroscopy; Phthalates; Plasticizer; Plasticizers; Polyvinyl chlorides; Surface; X-ray photoelectron spectroscopy; Diffusion; Plasticizer; Surface
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2015.08.048

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 Tg toward that of PVC coupled with low solubility of hexane in PVC accounts for decreased DEHP diffusion rates (10−12–10−13 cm2 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 Db were estimated from peak areas during a subsequent fast recovery period (10−14–10−15 cm2 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.
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•Di(2-ethylhexyl) phthalate (DEHP) diffusion into hexane was determined using ATR-IR spectroscopy.•An IR window for PVC enabled measurement of DEHP diffusion by by monitoring the DEHP CO absorption at 1715 cm−1.•Fast diffusion at short immersion times (<30 s); slower at longer times (30 s < t < 6 min).•The formation of a glassy domain in the outermost surface is proposed to explain HADD and back diffusion processes.