The Plastics Recycling Conundrum: Technology, Economics And Human Behavior

The recent announcement by the industry group Alliance to End Plastic Waste that it will commit over $1 billion to eliminate plastic waste has focused scientific and commercial attention on creating a sustainable path for the use of plastics.

Since the mid-1950s, when commercial plastics production began in earnest, over 8 billion metric tons of primary plastics have been produced, principally from hydrocarbon feedstock. Almost one-third of these plastics remain in use, mostly in infrastructure, buildings, transportation vehicles and industrial machinery. Only 500 million tons or about 6% of the produced plastics have been recycled; the majority has been discarded (55%) or incinerated (8%).

The very qualities that make plastics attractive – their durability and stability – also make it difficult to dispose of them when their usefulness comes to an end.

About 2% of that plastic waste, or 8 million tons – predominantly from China, Indonesia, Philippines, Sri Lanka and Vietnam – ends up in the oceans and other marine ecosystems each year. It gets there in a variety of ways, in both visible and microscopic form, through accidental spills, airborne and water borne microplastics and microfibers, careless dumping and runoff from landfills, among other routes.

The challenge is clear. Reducing the amount of plastic waste would mean less plastic makes it to the world’s waterways. There are several ways to address that:

 

• Increased recycling; with less material discarded as intact plastics, there is less opportunity for synthetic plastics to make it into the marine ecosystem.
• Switching to bio-based materials that can degrade in the ecosystem.
• Incorporating sustainability into polymer manufacturing.

All three are needed, but that last idea offers perhaps the most exciting promise, even offering the potential to convert plastic waste from a problem to a solution.

At the least, we clearly should do better than recycling only 10% of all discarded one-time use plastics, but that will require meeting challenges and opportunities that are technological, economic and most importantly, behavioral.

Technologically, in most cases reusing plastics leads to a degradation of the material properties, resulting in downcycling the materials to lower value products.

That downcycling through traditional recycling routes, along with the intrinsic costs of collecting, cleaning and sorting prior to remanufacturing of the plastic materials, makes plastics recycling cost-prohibitive and an unattractive proposition. One potential solution is finding ways to use the embedded energy in those discarded plastics without the challenges of downcycling, while managing the costs of handling the plastics from consumer to recycled material.

Currently, such upcycling technologies are in their infancy and are largely exploratory.

Economically, the most significant challenge is the collection, sorting and cleaning of plastic waste for recycling.  Recently, I wrote about demonstrations of improvements in last-mile technologies, and those technologies have raised significant excitement in the public. Advances in the last-mile solutions that incorporate digital technologies are hard to scale up, and they intrinsically are site-specific. Nevertheless, these last-mile solutions are becoming more and more important as each community grapples with the challenge of increasing plastic recycling rates.

Solving the technical and economic issues will require that we understand human behavior and attitudes about plastic waste, and the cultural and societal nuances that come into play. For instance, increased recycling efforts have made people feel freer to use more plastics and therefore, have led to significant increases in the consumption of single-use plastics. Similarly, the development of bio-based plastics – made from renewable biological resources including plant waste – has resulted in increased use of plastics. These non-intuitive responses indicate that we ought to pay close attention to human behavior and how people respond to proposed changes.

Plant- or bio-based plastics that could replace those produced from fossil fuels is often touted as a sustainable solution. Many bio-based materials are seen as drop-in replacements for fossil-based materials by replacing at the molecular building block level a fossil fuel derived material with a bio-derived material; while reducing our dependence on fossil energy, however, this solution does not address the environmental and especially the marine impacts of plastics.

Beyond that, bio-based plastics that perform comparably to the synthetic plastics they aim to replace, composed of building blocks which degrade naturally at their end of use, are still a long way off.

Even if high-performance bio-based plastics do become a reality, they won’t automatically solve the problem of plastic pollution in the marine ecosystem. The challenges of large objects and single-use plastics, as well as finely dispersed plastics accidentally being delivered directly or indirectly to waterways, such bio-based plastics do not address the environmental issues resulting from the physical characteristics of the plastic objects.

The direct discarding of waste, while visually upsetting and the most often discussed issue, is only a small part of the challenge we face in protecting the marine ecosystem. The proliferation of microplastics and other plastic waste that we cannot easily discern is perhaps the bigger challenge.  While most research to date suggests that microplastics have not been proven to cause toxicological issues, the smaller fragments are nevertheless more easily absorbed by both humans and wildlife.

Amid all these challenges, we do, however, have opportunities. The most attractive involves designing sustainability and inherent recyclability directly into the plastics manufacturing process.

Today a rubber tire or wind turbine blade has to be incinerated or degraded all the way to their fundamental building blocks through the use of energy-intensive depolymerization. Vulcanization or irreversible chemical cross-linking confers these materials with outstanding properties such as strength and resilience, but these materials can’t be recycled by simple mechanical means. What if we were instead to design and develop a rubber or epoxy material in such a way that the links between molecules can be easily unlocked by either heating or exposure to a chemical or microwave radiation, allowing the material to be easily reprocessed?  These technologies are rapidly developing and moving from the realm of science fiction to everyday applications.

For such a process to work, we would need to redouble our efforts to recycle plastic waste, perhaps by focusing on it as a product supply chain rather than a waste disposal paradigm. Then last-mile solutions might indeed become the first-mile opportunities. This would fundamentally revolutionize the world of plastics and their impact on our environment.

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Dr. Ramanan Krishnamoorti is the chief energy officer at the University of Houston. Prior to his current position, Krishnamoorti served as interim vice president for research and technology transfer for UH and the UHSystem. During his tenure at the university, he has served as chair of the UH Cullen College of Engineering’s chemical and biomolecular engineering department, associate dean of research for engineering, professor of chemical and biomolecular engineering with affiliated appointments as professor of petroleum engineering and professor of chemistry.

 

Dr. Krishnamoorti obtained his bachelor’s degree in chemical engineering from the Indian Institute of Technology Madras and doctoral degree in chemical engineering from Princeton University in 1994.