Rebecca Braslau, a professor of chemistry and biochemistry at UC Santa Cruz, has received a $480,000 grant from the National Science Foundation to support her research to develop a safe and affordable alternative to phthalate plasticizers.
Phthalates are synthetic chemicals added to polyvinyl chloride (PVC) to make flexible plastics. Due to health concerns, phthalates have been banned from children's products in the United States and Europe, but they are still used in a wide range of consumer products, including food wrap, medical devices, automotive parts, and building materials.
Phthalates are readily absorbed by the body through inhalation, ingestion, or skin contact. Because phthalates are not chemically bound to the PVC polymer, they tend to migrate out of plastic products and into the environment. The same is true of alternative plasticizers currently on the market. Braslau's approach is to use compounds similar to phthalates that can be chemically attached to the PVC polymer chain.
"We want our phthalate mimics to be part of the polymer so they won't leak out, and even if they do, it would be as part of a larger molecule that wouldn't have the same health effects," Braslau said.
Phthalate exposure has been associated with reproductive and developmental abnormalities in animal studies. Epidemiological studies in humans also suggest that exposure to phthalates may have adverse health effects, including reproductive abnormalities that can lead to infertility. Phthalates are metabolized by the body into compounds that are considered "endocrine disruptors," chemicals that interfere with the body's hormone systems. Effects on wildlife of phthalates in the environment are also a concern.
Braslau first began studying phthalates several years ago and published a paper showing how a phthalate mimic could be incorporated into the PVC polymer. A key part of the process required an expensive chemical step, however, so she didn't pursue it any further. More recently, however, she realized that a similar target could be prepared using much simpler "click" chemistry. "It's called a click reaction because it's so easy it's like snapping your fingers," Braslau said.
First she found a click reaction that made most of the desired structure, but required a copper catalyst. She kept searching the literature and eventually found a reaction she could use that didn't require copper. After experimenting with the procedure in her lab, she and her students showed that the reaction works at room temperature to make a compound very similar to a phthalate, with a chemical bond to a PVC polymer. Those results were published earlier this year in a paper by Braslau and graduate student Aruna Earla in Macromolecular Rapid Communications.
"Now we have a process that could potentially be used by industry," Braslau said.
The NSF grant will fund ongoing work by Braslau's laboratory and several collaborators to further develop this process and test the properties of the resulting polymers. Polymerizing PVC requires special equipment, so Braslau's group prepares the chemical subunits and will send them to the laboratory of Virgil Percec at the University of Pennsylvania for polymerization. She will also be collaborating with the Polymers and Coatings Program at Cal Poly San Luis Obispo, where the material properties of the new polymers will be tested.
"We'll be going down there to measure the properties of our samples so we can tell whether it is working effectively as a plasticizer," Braslau said. "We need to explore how much to put in and how it changes the physical properties of the material."
Another area she wants to investigate, although it is not covered by the current grant, is how the new materials will break down in the environment. "Eventually it will biodegrade into something, and before we scale up it would be prudent to make sure it doesn't biodegrade into something toxic," she said.
Whether her approach will provide a commercially viable alternative to phthalate plasticizers remains to be seen, but Braslau said it's important to try because phthalates are so widely used.
"The amounts are astronomical, on the scale of a million tons per year," she said. "It could really make a big difference to both human and wildlife populations if we succeed in developing an affordable and safer replacement for phthalate plasticizers."