The amount of plastic waste is enormous: worldwide, we throw away 350 million tons every year, which amounts to 40 kilograms per inhabitant of the earth. Scientists at the Faculty of Science and Engineering (FSE) of the RUG are working on new ways to recycle plastic waste and turn it into new, high-quality products. This is the second part in a series of four articles on plastic research within FSE.
Recycling plastics has several advantages: reuse reduces waste, and provides raw materials for new plastic. Moreover, by reusing the carbon atoms that make up plastics, they do not end up directly in the atmosphere in the form of the greenhouse gas carbon dioxide. But recycling is not easy: there are many different types of plastic that all require different approaches, says chemical engineering professor Francesco Picchioni.
“The University of Groningen has a unique position in recycling research: we work on the recycling of a large number of different plastics, together accounting for about 80 percent of all plastic produced. I know of no other institute where the research is so broad.” Just three types of plastic, polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) together already account for 75 percent of all plastic production worldwide. “And if you add to that the PET of plastic bottles and polyurethane used in foam you already exceed 80 percent.”
“We are working on recycling a large number of different plastics, together accounting for about 80 percent of all plastic produced,”
Picchioni himself works on different polymers, the long molecules that make up plastics. He recently made a breakthrough in recycling rubber. The polymers in rubber are linked together to form a kind of molecular network. It seemed impossible to take this network apart without damaging the polymers. This leads to shorter polymers, with which only lower quality rubber can be made. Picchioni found a way to connect the shorter polymers together in such a way as to create new rubber of ordinary quality. The company New Born Rubber uses this patented method to make new rubber for products such as driving plates.
Francesco Picchioni has a number of patents to his name. That sounds nice, but it is not always good for a scientific career. He says he could easily write 10 articles on the method of recycling rubber, but doesn’t. ‘The patent was granted eight years ago. If I publish about the method it would hurt the position of the company that wants to make products using the patented technology. For me it doesn’t matter; I am an established scientist and don’t need so many publications anymore. But it would be very bad for the career of a junior researcher.
“Our university is also unique because here we work on both ways to recycle plastic: material recycling and chemical recycling,” Picchioni says. Material recycling is a process where the plastic is directly reused. But this usually means the quality of the recycled product is reduced. In chemical recycling, the polymers are broken down into their building blocks, the monomers, or even into carbon dioxide and water. Those breakdown products can then be used as building blocks for new plastics. When you convert waste into new plastic, it’s called “upcycling. But it is usually easier to break down plastic into simple hydrocarbons that can be used as a low-grade fuel, for ships for example. This route is called” downcycling.
If at all possible, Picchioni tries to avoid “downcycling,” in which the recycled product is worth less than the original. Among other things, he is working on a project to recycle PVC using supercritical carbon dioxide. “This type of plastic contains a lot of excipients. Soft PVC consists of about 30 percent plasticizers, and these make it unsuitable for recycling,” he explains. In addition, PVC contains chloride, which is converted to the corrosive substance hydrochloric acid during recycling.
Supercritical carbon dioxide allows you to remove the admixtures and prevents the formation of hydrochloric acid. Picchioni: “We expect to have a pilot plant later this year in which we can clean five kilograms of PVC per hour. And we are in the process of patenting a technique that allows us to remove the hydrochloric acid in a controlled way so that PVC can be made suitable for chemical recycling if necessary.”
FSE Science Newsroom | Text René Fransen
