Plastic is a light but durable material, these are wonderful properties, as long as you need it. But since plastic contains various additives – dyes, flame retardants, only a small amount of its varieties can be recycled without compromising performance and aesthetic qualities. Even the most recyclable plastic, PET, polyethylene terephthalate, is recycled only by 20–30%. The remaining species are usually sent to incineration plants or to landfills, where the decomposition of carbonaceous material takes centuries.
Researchers from the National Laboratory. Lawrence Berkeley (Lawrence Berkeley National Laboratory), USA, developed a recyclable plastic. Like the Lego constructor, it can be disassembled into components at the molecular level, and then reassembled with a different shape, texture, color, but without loss of performance. A new material, polydiketoenamine (PDK), is reported in the journal Nature Chemistry.
“Most plastics have never been recycled,” says lead researcher Peter Christensen, “But we discovered a new way to create plastics that allows for recycling at the molecular level.”
All plastics, from those of which water bottles are made to those used to manufacture car cases, consist of large molecules called polymers, which, in turn, consist of repeating units of shorter carbon-containing compounds, monomers.
According to researchers, the problem with many plastics is that chemicals added for greater functionality, such as fillers that make plastics more rigid, or plasticizers that are added for flexibility, are strongly associated with monomers and remain in the plastic after processing.
During processing at the plant, plastics with different chemical composition – both hard, and elastic, and transparent, and colored – are mixed and crushed. When this mixture of crushed plastics is melted to produce a new material, it is difficult to predict what properties this material will inherit from the original plastics.
The fact that properties are inherited unpredictably prevents plastic from becoming a fully recyclable material, so that the initial monomers can be restored for reuse or to obtain a better product.
When reusable packaging made from recycled plastic wears out, it cannot be recycled again. When the service life comes to an end, such packaging is either incinerated or sent to landfill.
“Complete processing of plastics is an important task,” said Brett Helms, a researcher at the National Laboratory for them. Lawrence Berkeley, – We are already seeing the results of the spread of plastic waste in aquatic ecosystems. This trend is likely to be exacerbated by the growing volume of plastics production. ”
Researchers want plastics to disappear from landfills and from the oceans, they want to encourage recycling of plastics, which is possible with polymers formed from MACs.
“When MPCs are used, the unchangeable bonds of conventional plastics are replaced by reversible bonds, this allows plastic to be processed more efficiently,” Helms says.
Unlike conventional plastics, monomers in MPC can be reduced and freed from any additives by simply immersing the material in a high acid solution. The acid helps break the bonds between the monomers and separate them from the additives that form the appearance of the plastic.
“We are interested in how to make plastic recycling from a linear cycle,” says Helms. “We see an opportunity to make a difference for the better when there are no recycling options.” This applies to adhesives, phone cases, watch straps, shoes, computer cables and solid thermo-active elements made of hot plastic.
Researchers first discovered a property that allows recycling of MPC-based plastics when Christensen applied various acids to glassware used to make MPC adhesives. He noticed that the composition of the glue had changed. Surprised that the glue had been transformed, Christensen analyzed the molecular structure of the sample using NMR spectroscopy. “To our surprise, we saw the starting monomers,” says Helms.
After testing various compounds in the Molecular Foundry, the researchers found that acid not only splits MPC-polymers into monomers, but also allows the separation of monomers from additives.
Then they proved that the reduced MPC monomers can be collected into polymers, and the processed polymers can form new plastic materials without inheriting color or other features of the starting material. A strap that has fallen into the trash can gain new life in a computer keyboard if it is made of MPC-plastic. It will also be possible to recycle plastic, giving it additional qualities, such as flexibility.
Researchers believe that new recyclable plastic may be an alternative to many non-recyclable plastics that are currently in use.
“We are in crisis and we need to think about the infrastructure for the modernization of processing plants in order to further sort and process the new plastic,” Helms says. “If these installations were intended for processing MPCs and related plastics, we could more effectively avoid plastic from landfills and landfills, as well as oceans. It’s time to design materials and processing plants to make it possible to manufacture recyclable plastics. ”
The plans of the researchers are the development of MPC-plastics with a wide range of thermal and mechanical properties for various applications, such as textiles, 3D printing and foams. In addition, they want to expand the composition due to the inclusion of plant materials.