Phase transfer catalysed surface modification of plasticized poly(vinyl chloride) in aqueous media to retard plasticizer migration

Plasticized poly(vinyl chloride) (PVC) sheets were surface modified by nucleophilic substitution of chlorine by azide in aqueous media under phase transfer conditions. PVC was reacted with a 40% solution of sodium azide in water using tetrabutyl ammonium bromide as the phase transfer catalyst. The reaction was conducted at temperatures ranging from 50 to 80°C for various periods of time (1-4 h). The azidated PVC surface was then irradiated using u.v. light with a 125 W lamp for various time periods to crosslink the surface. Migration of the plasticizer di-(2-ethylhexyl phthalate) from surface modified and unmodified PVC was examined in a potential organic extractant such as hexane. It was found that considerable reduction in the migration of the plasticizer could be achieved by this technique depending on the extent of azidation of the PVC surface and the irradiation dose. Determination of the stress/strain properties of PVC sheets before and after modification showed that there was around 30% reduction in these properties after surface modification. However, the values were still much above the minimum prescribed for vinyl chloride polymers used in biomedical applications