By Stephen Beech via SWNS
A radical new process “vaporizes” plastic bags and bottles to help make recycled materials.
The innovative chemical procedure turns the ubiquitous waste items into hydrocarbon “building blocks” for new plastics, say American scientists.
They explained that the process works “equally well” with the two dominant types of consumer plastic waste: polyethylene, the component of most single-use plastic bags; and polypropylene, the stuff of hard plastics, from microwavable dishes to luggage.
It also efficiently degrades a mix of the two types of plastics, according to the findings published in the journal Science.
The research team say the process, if scaled up, could help bring about a “circular economy” for many throwaway plastics – with the plastic waste converted back into the monomers used to make polymers, thereby reducing the fossil fuels used to make new plastics.
Clear plastic water bottles made of polyethylene tetraphthalate (PET), a polyester, were designed in the 1980s to be recycled that way.
But now the volume of polyester plastics is “minuscule” compared to that of polyethylene and polypropylene plastics, referred to as polyolefins.
Research leader Dr. John Hartwig, of University of California, Berkeley, said: “We have an enormous amount of polyethylene and polypropylene in everyday objects, from lunch bags to laundry soap bottles to milk jugs – so much of what’s around us is made of these polyolefins.
“What we can now do, in principle, is take those objects and bring them back to the starting monomer by chemical reactions we’ve devised that cleave the typically stable carbon-carbon bonds.
“By doing so, we’ve come closer than anyone to give the same kind of circularity to polyethylene and polypropylene that you have for polyesters in water bottles.”
He explained that polyethylene and polypropylene plastics make up about two-thirds of consumer plastic waste worldwide.
About 80% ends up in landfills, is incinerated or simply dumped in the street, often ending up as microplastics in streams and the ocean.
The rest is recycled as low-value plastic such as decking materials and flowerpots.
To reduce waste, scientists have been looking for ways to turn the plastics into something more valuable, such as the monomers that help to produce new plastics.
Dr. Hartwig noted that while many researchers are hoping to redesign plastics from “the ground up” to be easily reused, today’s hard-to-recycle plastics will be a problem for decades.
He said: “One can argue that we should do away with all polyethylene and polypropylene and use only new circular materials.
“But the world’s not going to do that for decades and decades.
“Polyolefins are cheap, and they have good properties, so everybody uses them.”
Dr. Hartwig added: “People say if we could figure out a way to make them circular, it would be a big deal, and that’s what we’ve done.
“One can begin to imagine a commercial plant that would do this.”
