Hazardous chemical removal could boost plastic recycling
Polyvinyl chloride (PVC) is a widely produced synthetic plastic polymer, found in applications ranging from clothing to construction materials. “A key benefit of PVC is that it is durable, and is resistant to water and solvents,” explains REMADYL project co-coordinator Laurens Delva from Centexbel in Belgium. “This makes it suitable for demanding applications.” While efforts to recycle such material have increased, a major obstacle is that PVC materials sometimes contain what are known as legacy additives. “When these substances were used, often several decades ago, they were not considered as hazardous,” says Delva. “These substances are however now considered problematic. For example, phthalates were added to make PVC flexible, and some of these have been identified as posing health concerns.” In addition, lead compounds were sometimes added to rigid PVC as stabilisers. While they have been progressively replaced and fully phased out in PVC applications since 2015, some long-life PVC applications can still contain lead.
New innovations in chemical extraction
The REMADYL project set out with a number of ambitions. One of these was to find ways of extracting phthalates and lead from end-of-life PVC, in order to increase recycling rates. “We took three approaches to this,” notes Delva. “First, we added a scavenger chemical during the melt phase of end-of-life plastic. This works by capturing the lead, which can then be filtered out.” The project team also used supercritical carbon dioxide to remove phthalates. This technique is already used in the pharmaceutical and food industries to fight odours or extract caffeine. Finally, the team looked at using solvent-based technology, which swells the plastic and makes removing lead easier.
Sorting, detecting and recycling
“Alongside extraction, we also examined new sorting and detection methods,” explains Delva. “Not every PVC product contains dangerous chemicals. We therefore wanted to see if it would be possible to introduce in-line detection and sorting methods in recycling plants.” The prototype developed by the REMADYL project used spectroscopy to quantify how much lead is in a product. Theoretical studies were also carried out to assess the feasibility of implementing the technology in an actual recycling facility. The team additionally looked into what could be done with the removed lead and phthalates. The team applied already existing technology that changes the phthalate molecules in safe molecules, thus enabling the chemicals to be reused. The scavenger chemicals were used to turn the lead in PVC into lead salts which could be removed from the polymer matrix. A project partner that operates a lead refinery was able to turn these lead salts into pure lead, thus opening up potential new applications in products such as batteries.
New opportunities in plastics recycling
A key success of the project was demonstrating the feasibility of the methods being pioneered. The ability to remove phthalates and lead from waste PVC opens up huge opportunities to not only recycle more PVC material, but also give a second life to the chemicals removed. “This was all conducted at the research level,” says Delva. “We also carried out economic analyses to see how these methods could be scaled up to the industrial level. This work is still under discussion.” In collaboration with another EU-funded project, called CREAToR, the REMADYL project team recently published a policy brief. This identifies some of the main obstacles to developing a circular economy for plastics, and puts forward recommendations.
Keywords
REMADYL, plastic, recycling, PVC, polymer, phthalates
