New polymer could create win-win scenario in war against plastic waste
Getting rid of plastic waste remains a Sisyphean task despite our efforts to tackle it by employing PET-eating bacteria and turning it into footwear, liquid fuel, and even the foundations for an entire village. The material that ends up being recovered and reused is just a drop in a non-stop growing mountain of garbage. But what if there was a way to create a super-durable alloy out of two of the biggest sources of packaging waste while using less oil at the same time?
Bringing this potential win-win scenario a step closer to reality is a team of scientists from Cornell University and the University of Minnesota, who recently announced the creation of a polymer additive that can create such an alloy out of polyethylene (PE) and polypropylene (PP). The idea, according to researcher Geoffrey Coates, a professor of chemistry and chemical biology at Cornell University, is two-fold: to make a better material from the world's most used polymers and also help recycle them more efficiently.
"If you could either make their properties better, you can use less of them, or if you can recycle these polymers, we would have a huge impact on sustainability in a way that we don't currently have," says Coates. "The dream is: could you take all the world's polyethylene and polypropylene and just throw it together, melt it down and get a material that has good or even better properties than either one of the materials alone?"
Though PE and PP are individually tough as standalone plastics and have a similar hydrocarbon makeup, they are immiscible with one another. Common grades of the polymers become brittle and unusable when blended together, thus limiting what companies can do to recycle these materials.
To get around this problem, the research team developed a multiblock copolymer that can weld common grades of commercial PE and isotactic polypropylene (iPP) together, depending on the molecular weights and architecture of the block copolymers, by creating molecular stitches between the two materials. This makes the resulting blend as tough as iPP and PE themselves.
In their tests, the researchers welded together two strips of iPP and PE plastic using different multi-block polymers as adhesives, and then pulled them apart. In most cases, the polymers are easily separated due to their incompatibility, as was demonstrated when the researchers carried out the tests with di-block polymers. However, in the case of the tetrablock additive, the plastic strips held together so well that it ripped the polymer apart, a sign that it is "a very good material" to glue polyethylene and polypropylene together, says Coates.
"People have done things like this before but they'll typically put 10 percent of a soft material, so you don't get the nice plastic properties, you get something that's not quite as good as the original material," he explains.
According to the researchers, what makes the results all the more encouraging is that they were able to create the alloy with just one percent of the additive, giving rise to the possibility that it could improve recycling and also lead to the creation of a whole new class of mechanically tough polymer blends.
For Ernie Simpson, global vice-president of research and development at TerraCycle, the New Jersey-based company that specializes in upcycling consumer waste, what makes this a potential game changer is the cost savings it could bring to a company's bottom line compared to the current compatibilizers on the market.
"If the claims are true that a one percent addition is as efficient at 10 percent of other compatibilizers, on a cost-basis, this would be a serious game changer," Simpson tells New Atlas. "It would essentially reduce the overall cost of modifying polyolefins and significantly increase the amount of polypropylene and polyethylene that gets recycled because the formulations can be made at a lower cost."
Of course, this depends on factors such as the amount of compatibilizers being used and their original cost. Assuming this new material comes in at roughly the same cost and requires just one percent instead of 10, the savings would encourage people to make new formulations based on the tetrablock and use them in various applications, he points out.
Fixing a broken system
At present, the recycling industry is broken. In the United States, falling commodity prices, coupled with a fragmented recovery system made up of local systems with different and often incompatible agendas, have made recycling a costly and labor-intensive process, the results of which do not always justify the man-hours spent salvaging the materials. And despite endless reports on how plastic waste is harming the environment and wildlife, little progress has been made.
According to a report by the Ellen MacArthur Foundation, only 14 percent of plastic packaging is collected for recycling globally. The rest of it, valued at US$80-120 billion each year, ends up leaking into the environment in one form or another. The same report also predicts that at the rate things are going, there will be more plastics than fish (in terms of weight) in the world's oceans by 2050.
Given that it is still early days for this study, it remains to be seen exactly how sustainable this new plastic alloy is and how effectively it would lend itself to cradle-to cradle applications. In the case of the latter, improvements would certainly have to be made to current packaging supply chains to ensure that materials are designed and produced with long-term sustainability in mind. If all goes well, however, this could be the kind of innovation to impact the recycling market at scale.
"If you could make a milk jug with 30 percent less material because it's mechanically better, think of the sustainability of that. You're using less plastic, less oil, you have less stuff to recycle, you have a lighter product that uses less fossil fuel to move it," concludes lead author James Eagan.
The study was published in Science.
Source: Cornell University