Research breakthrough keeps phthalates from migrating out of PVC

In an article entitled “Phthalate Plasticizers Covalently Bound to PVC: Plasticization with Suppressed Migration,” the research group led by Helmut Reinecke, a research scientist at Spain’s ICTP-CSIS (Institute of Polymer Science & Technology; Madrid), published the first report on a new way of preventing phthalate plasticizers from migrating from items made of PVC. These plasticizers are added to PVC to make it flexible.

Phthalate migration out of PVC products has been a topic of concern for years, particularly concerning toys or other items likely to be sucked or chewed by babies, as some research has shown common phthalates to be a factor in hormone disruption in rodents and, most likely, also in young children. The resulting outcry has in many cases led to bans or limitations on some phthalates' use, and often led brand owners to demand that items processed of PVC be replaced with comparable ones made from alternative materials. Even without the health concerns, phthalate migration is a serious problem as products over time will lose some of their pliability—think of PVC medical tubing.  

The scientists in their article describe development of a way to make phthalates permanently bond to the internal structure of PVC so that they will not migrate. Their laboratory tests showed that the method completely suppressed the migration of plasticizer to the surface of the plastic. The method involves covalently linking phthalate-based thiol additives, which the group developed, to the PVC molecular chain. The result, according to Reinecke, in answer to questions from MPW, was PVC only slightly less flexible than commercial PVC formulations plasticized with an equivalent amount of established phthalate plasticizer additives, but with the benefit of complete hindrance of phthalate migration. He adds that processors could obtain similar flexibilities for both systems using a higher quantity of the covalently linked additive.

Reinecke says the group has not yet measured the mechanical properties of its system. Current work in the group, he says, is focused on development of new plasticizers. “We are confident that these will have even better properties than our DOP-SH additives,” he commented, with the acronym referring to the ones it has developed so far.