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We must change how we think to solve the plastic waste crisis

The world has a plastic waste problem. Most single-use plastics, which represent about 50 percent of all plastic production and include everyday items like straws and shampoo bottles, wind up in landfills, incinerated, or leaked into the environment. In the U.S. alone, we discard 40 million tons of single-use plastics every single year —  the visual equivalent of throwing away 100 Empire State buildings. By 2050, we are estimated to have more plastic in our oceans than fish.

Yet despite this grim situation, we now have more reason to fundamentally change the way we think about plastic waste — not just as a burden, but as an opportunity to harvest valuable resources and energy. 

Single-use plastics like HDPE, LDPE, and PP, labeled numbers 2, 4, and 5, respectively, on our everyday products, are made from chemicals sourced from oil and gas that require high levels of energy to produce, consuming 0.3 percent of our total energy consumption alone. Chemically, these plastics have the same components as the gas resources that we use to power our cars and homes. But instead of utilizing this resource, it flows through our systems only to sit in the landfill. By changing the way we think about recycling or re-using single-use plastics, we can create a more sustainable use for these often discarded resources and build a more robust energy economy.

It’s true that recycling exists. However, only 10 percent of plastics are even collected for recycling in the U.S, and even when single-use plastics are collected, they are not recycled in a circular process, the way glass and aluminum are.  

This is because the process of mechanical recycling breaks down the performance of plastics. Imagine the polymers that make up plastics, the cap on your yogurt container or your child’s favorite toy duck, as a long stack of blocks, superglued together. In this scenario, each block represents a molecule that is connected to make the polymer of the plastic. Instead of pulling apart each block to break it down individually so that it can be built back up correctly, our current recycling process of grinding, heating, and molding the stack at very high temperatures randomly cracks the stack of blocks into far less useful materials that can’t be rebuilt.

So, why then do we rely on mechanical recycling? Well, it comes down to a chemistry problem. The same properties that make polyethylene and polypropylene the durable cornerstone of so many plastics make them incredibly difficult to break down. With no straightforward way to controllably break down the superglued stack of blocks, we just do whatever we can manage with mechanical tools. 

Fortunately, there is an increasingly viable alternative, called chemical recycling, that can help us make the shift from thinking of plastic waste from purely a burden to a stream of resources waiting to be harvested, and motivate us to reduce the amount of plastics that end up in our landfills and our oceans. 

While the concept of chemical recycling has been around for a few years, it has struggled to take off in part because of its large energy requirements of the first technological approach. Motivated by bringing down the currently prohibitive energy cost of chemical recycling, my lab at Colorado School of Mines has discovered an earth-abundant material that can efficiently break down the polyethylene and polypropylene polymers at the heart of most plastics near 200 degree Celsius. Excitingly, this is 500 degrees lower than the current processes for chemical recycling and just above the melting point of the relevant plastics. This suggests that we can develop low-energy tools to address our plastic crisis, enabling a more circular recycling process that facilitates greater capture of the oil- and gas-based polymers used in plastics. 

While further research is needed to build a sustainable and scalable version of this process, this is one of the stepping stones we need to pursue our plastic challenge wholeheartedly. 
We do not need to let an enormous store of plastics — essentially, oil and gas — sit in a landfill. We can change how we think about plastic waste, effectively mining that plastic to keep energy and resources flowing through our economy and waste out of our oceans. 

C. Michael McGuirk is an assistant professor of chemistry at Colorado School of Mines, where he runs The McGuirk Lab focused on the interdisciplinary research of synthetic chemistry and materials science. 

Tags Plastic waste single-use plastics

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