A group of materials now known collectively as plastics has played a definitive role in delivering much of the socio-economic advantages of modern life, and their production has outpaced that of almost every other material since the 1950s.
But what are plastics? Today nearly everyone, everywhere, every day comes into contact with them. They have become the workhorse material of the modern economy due to several reasons: availability, versatility, but above all they are virtually unrivalled in terms of great performance at low cost.
Sometimes too much performance.
The word plastic, now the tag of fame and shame for this group of materials, emerged from the key physical property defining how versatile they are: plasticity. Largely through heat, they enter a range in which they can be processed and, through modern-day sculpting, turned into fibres, films or shapes of amazing complexity. And this can (at least theoretically) be done multiple times, making these materials a good candidate for recycling – but more on that later.
Plasticity as a property is exhibited by a wide range of materials, including metals, human tissue or natural yarns. But it’s through the emergence of industrial polymer chemistry that possibilities increase at scale. As it turns out, many polymers display plasticity. And we can make them in huge quantities cheaply, reliably and with an amazing ability to obtain almost any physical property desired through their composition and processing.
Polythis, polythat. What are polymers?
Many polymers (Latin for “many units”) display plasticity – but they are not the same. Nature from the very first has been assembling large chains of individual units (life itself is encoded in polymers) through processes that are deeply linked to our evolution. Scientists learned how to make them at industrial levels using chemical reactions in ways that allow us to use not only the same building blocks but a greatly expanded set. The terms poly-this or poly-that tell us what they are, their composition.
Plastics became a household name as they found their way to a myriad of everyday items. The synthetic polymers in our lives are also described based on the properties they display: plastic, rigid, elastic are the most common, but the list extends to electroluminescent (think OLED television displays), hydrophobic and oleophobic at once (think non-stick cookware), insulating (for wiring) or biocompatible (artificial skin). They’re all polymers, most show plasticity… some don’t.
Our understanding of how to build large molecules, and especially which small units to stitch together, has developed symbiotically with the modern petrochemical industry. And while various sources can be tapped for these building blocks, over 90% of synthetic polymers are made from fossil sources. Their production involves a series of reactions that have been optimized for yield, selectivity, robustness – but above all scale.
One basic petrochemical product is the king of versatility through engineering: ethylene. Plentiful ethylene is at the origin of most synthetic polymers known today, and can be obtained from petroleum, natural gas or sugar cane. The economics and reliability of producing modern materials is highly dependent on scale. Without the scale we have achieved in the conversion of petroleum or gas, most alternative sources remain irrelevant. And since the properties of polymers are determined by their composition and structure, not by their source, the same polymer (e.g. a particular grade of polyethylene) will behave the same whether made from oil or a renewable source like sugar cane. Both source materials have the same properties when it comes to being recycled. And both may result in polymers that show bio-degradability or bio-compatibility.
The most commonly used polymers under the consumer-friendly word plastics are: polyethylene terephthalate (PET), polyethylene of various densities (PE: LDPE, LLDPE, HDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyamides (PA), polycarbonate (PC), and polyurethanes (PU). The first five families, accounting for about 75% of all uses, are thermoplastic and can be, in principle, mechanically recycled.
To give the final boost to the performance of these seemingly homogeneous materials, a few often ignored but absolutely critical transformations take place at or right before parts are fabricated. They include the incorporation of additives (colour, tactile enhancers, stiffeners, antimicrobials), layering (to combine the properties of different films) and metallization or surface modification (to allow coating).
By the time they are deployed to applications, compositions have increased in complexity quite significantly. After these modifications, plastics exhibit various performance characteristics (e.g. a bag of chips is light, flexible, almost impenetrable by moisture, air or bacteria; it’s also chemically inert, thermally sealable and very inexpensive). These characteristics are also interrelated (for example, reducing chemical inertness to allow for degradation compromises the integrity of the product). It is here, at this interplay of properties, where many technical challenges to improve materials lie.
Thanks to plastics, countless lives are saved through their applications in healthcare – from sophisticated medical devices or artificial organs through tubing and syringes to anti-malarial mosquito nets. The growth of clean energy from wind turbines and solar panels has been greatly facilitated by plastics, and lightweight materials have made transport more energy-efficient.
But the cheapness of plastic, which makes it so convenient in our day-to-day lives, also makes it ubiquitous, resulting in one of our planet’s greatest environmental challenges.
Too good, too much, too fast, too cheap?
When the weight of packaging matters, when shapes mean brand recognition, when good seals are needed to preserve the integrity of food and beverages, consumer industries turned to polymers for packaging. And through this widespread incorporation we have come to face important trade-offs:
- Polymers are often too durable in comparison to their expected service life. This difference is quite dramatic in food and consumer goods packaging, where we have materials with ‘usable’ lives of tens or hundreds of years for ‘in-use’ lives of months or even days.
- Polymers with decreased performance in certain dimensions (e.g. shorter lives) are often more expensive to make, formulate and fabricate into products.
- Polymers are generally produced and utilized at much higher rates than our ability to deal with post-use material. In comparison, the investments made in infrastructure (collection, separation, processing), and above all the absence of business models that make economic sense to justify the investments needed, continue to hamper our ability to manage post-use material.
- Polymers live too many and too different lives in comparison with their discrete sources.
- Reused material often doesn’t meet the performance of virgin material.
- Reused material is often more expensive than virgin material.
Packaging is the dominant generator of plastic waste, accounting for almost half of the global total.
Due to the trade-offs above, polymers underperform as they accumulate in the environment and cause adverse change.
Can’t we simply replace with better materials?
There is no universal consensus on better or worse materials. A comparison using only one environmental performance criterion is insufficient, as materials have different relative impacts across different environmental performance criteria. In order to comprehensively understand the multiple ways in which using these materials impacts the natural environment, comprehensive life-cycle analyses (LCAs) are needed. These account for resource utilization and emissions across the various stages of a product’s life, from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, as well as disposal or recycling.
Waste happens when we can’t extract value from materials that have served their purpose. In the case of polymers, we have been unable to work fast enough, which is why we’re seeing overflows (literally, leakages) across the entire life of synthetic polymers. These materials are creating a serious burden for the environment, with around 3% of global annual plastic waste entering the oceans each year through multiple routes.
In our oceans, waste plastic comes from both land-based and marine sources: mainly fishing nets, lines, ropes or vessel parts. These marine sources contribute an estimated 20-30% of ocean plastic waste, with land-based input being the dominant source at an estimated 70-80%.
Due to such complexity, many responses have been formulated to address plastics pollution, ranging from immediate remediation tactics to longer-term strategies. These include the proposed basis of the New Plastics Economy Global Commitment, the culmination of a four-year endeavour led by the Ellen MacArthur Foundation: Eliminate-Innovate-Circulate.
Governments are now taking steps towards the elimination of problematic or unnecessary plastic packaging through regulatory and other policy actions. Municipal, national and perhaps soon global directives from policy-making bodies rely on banning the use of plastics in shopping bags, straws and other applications with single and/or short uses.
There is little debate about the need for more innovation. Research is greatly needed in product development, where challenges include untangling performance criteria in materials, developing novel compositions or formulations, and deepening our understanding of decomposition chemistry. Research in process technology is needed to further develop the mechanical, biological and especially chemical processes that will turn post-use materials into valuable resources.
Arguably, most of the attention today lies on circulation, as we aim to increase the number of waste-to-feed processes and re-establish the value of plastic waste whether as a high-energy carbon source or as feedstock for new materials. Globally, 18% of plastic is recycled, up from nearly zero in 1980. Prior to 1980, recycling and incineration of plastic was negligible; 100% was therefore discarded. From 1980 for incineration, and 1990 for recycling, rates increased on average by about 0.7% per year.
These average figures, however, don’t tell the full story. While recyclability rates can be as high at 70% in the case of PET (e.g. beverage bottles) through mechanical and chemical routes, PVC and PS remain challenging, with rates in the low digits. Format matters – certain sizes or shapes are still too difficult to recover (think small food wrappers, chewing gum) without dedicated collection.
Why should we transition to a new plastics economy?
Putting the concept of a circular economy into concrete action, though, will require the buy-in of stakeholders from all sides. Only through collaborative action in the design, deployment, monitoring and assessment of systemic interventions will we achieve the impact needed at regional and global scale. The Global Plastic Action Partnership, forged from a collaboration between public and private sector leaders and hosted at the World Economic Forum, was founded last year to achieve this purpose. It is bringing governments, industry and civil society together to transform goals and commitments into policy and implementation; starting with Indonesia, which has pledged to reduce marine plastic debris by 70%.
Other initiatives include Loop, which promotes reusable consumer packaging, and the Alliance to End Plastic Waste, a grouping of of nearly 30 companies worldwide seeking to reduce and eliminate plastic waste in the environment, especially the ocean.
This requires a view of the global economy through multiple lenses: materials; policies (financial and fiscal, labour, environmental, and energy); a strong commitment to innovation and infrastructure development; public awareness and engagement; and especially a re-thinking of the set of economic incentives behind decision-making. And interventions, in this complex system, need to not only be multiple but, more importantly, coordinated.