Migration of plasticizers in flexible crosslinked PVC

Abstract

In this paper, the migration of three kinds of plasticizers (terephthalate, citrate, phthalate) in flexible crosslinked PVC was studied in 40°C olive oil. The results show that the migration ratio increases with time, and increases quickly in initial 24 h, and then tends to be gently after 192 h, which can be attributed to two reasons. The first, concentration gradient of plasticizers between the samples and solution is high at beginning, it is propitious to migration. The second, crosslinked net which is formed by peroxide is located at the inner of PVC sample and can't inhibit the migration of the plasticizers located at the edge of the sample, which consequently migrate quickly into solution in initial stage. As the soak time increasing, the concentration gradient of plasticizers between sample and solution is reduced. Moreover, crosslink structure of PVC could effectively inhibit the migration of plasticizers, and the higher gel content the sample has, the more effective inhibition it shows. The migration ratio can be reduced about 30% when the sample has the maximal gel content. In addition, the results reveal that the migration ratio of plasticizers is ranged in the order of citrate, phthalate, terephthalate from large to small, which can be attributed to the difference of molecular structure of plasticizers. The higher molecular polarity the plasticizer has, the smaller migration ratio is shown in 40°C olive oil environment. It was found that the effect of PVC crosslink on inhibiting the migration ratio among the three plasticizers has no obvious rule.