Welcome to this module on plastic waste management. Did you know that we only started with mass production of plastics in the 1950's? And that all plastics produced until now are still around in stocks, landfills or the environment, unless they were burnt? Plastics are a very important share of the waste we produce, and represent one of the waste fractions with the smallest recycling rate. Most of the unmanaged plastics ends up ultimately in the oceans, where it is fragmented into smaller particles, creating an incredible negative impact in marine life. Microplastics are now global. Plastic particles have been detected in all of the world's oceans, in the ice of the Arctic, and even in several commercial salts and bottled water. So it's time to start taking action on this issue. In this module, you will learn current world plastic flows, including some basics on the sources of marine litter, and what plastics are. We will introduce two important features: The source of plastics, whether they are fossil-based or bio-based; and the biodegradability of the material. Here we see how global production of plastic materials has drastically increased since the 50's. We are currently producing more than 340 million tons of plastics per year, which is around half of the global wheat production. Since the 1950's, we have produced around 6300 million tons of plastics. Only 9 percent of this has been recycled, while 12 percent has been incinerated. The remaining 79 percent has been discarded, and, therefore, it is accumulated in stocks, landfills, and in the environment. Current estimates say that around 8 million tons of plastics end up in the ocean every year. This is equivalent to a waste truck full of plastics discharging into the ocean every minute. But where is all this marine litter coming from? 20 percent of the world's marine pollution originates from dumping activities on the water, including vessels, offshore platforms as well as fishing piers. The remaining 80 percent originate from land-based sources, 60 to 95 percent of which is plastic debris. This is clearly caused by unsound waste management practices. OK. But plastic is an organic material after all. Won't it ever degrade completely? This is a great question. But in order to answer it, we first need to get some background understanding on what plastics exactly are. Plastic is a synthetic material made from organic polymers. A polymer is a large molecule composed of many repeated sub-units, called monomers. Here, for instance, we see a PET polymer chain composed of its corresponding monomers. Plastics are usually classified by the chemical structure of the polymer's backbone and side chains, leading to this classification. You might recognise some of these codes in your food packaging. All plastics are then classified into two main groups, based on their thermal processing behaviour: thermoplastics and thermosets. Thermoplastics can be melted and solidified over and over again, which allows recycling the material, whereas thermosets can only be melted and solidified once. Luckily, thermoplastics represent 80 percent of all plastics produced. There are two important and often confused features of plastics. On the first hand, we have nature of polymers, whether they are fossil-based or bio-based, and on the second hand we have the biodegradability of the plastics. Let's talk about the nature of the polymers first. Petrochemical or fossil-based plastics are made of fossil feedstocks, like petroleum and natural gas, which have taken millions of years to form. The Petro-chemical industry has been optimizing the synthesis of these plastics since the 1950's. It relies on an efficient production chain and a well-developed distribution system. Comparatively, bio-based plastics are those that are entirely or partially derived from biomass, such as plants, trees or micro-organisms. Their advantage is that they avoid the use of fossil fuels to use biomass instead, reducing the product's carbon footprint. The manufacturing industry and logistics chain for these plastics, however, are relatively new
compared to that of conventional plastics. Currently, around 1 to 2 percent of the plastics are bio-based. But it is a fast growing sector. The second property to mention is the degradability. Pay attention, because this is where the answer to our question comes. The biodegradability of plastics does <i>not</i> depend on whether the polymers are bio-based or fossil-based. It mainly depends on its chemical structure, but also on the thickness of the material as well as the environmental conditions, such as temperature, moisture and presence of oxygen. But I am still not really telling you what biodegradable plastics are, right!? Biodegradable plastics are those that can be broken down into their constituent monomers and metabolized into
microbial biomass: water and carbon dioxide, through the action of naturally occurring micro-organisms, such as bacteria and fungi, over a short period of time; say, from a few weeks to several years. One of the main advantages of biodegradable plastics is that they offer an additional recovery option. Besides the material recovery and energy recovery options, which are also practiced with conventional plastics, biodegradable plastics are also suitable for organic recycling. Let's clarify one thing: Compostable plastics are an example of biodegradable plastics. But they can only be biodegraded under industrial composting conditions. Namely: elevated temperatures, high relative humidity and the presence of oxygen. They won't degrade in the natural environment, such as on the soil surface or in the oceans. Finally, a few words on oxo-degradable plastics or rather fragmentible plastics. Oxo-degradable plastics are made from conventional plastics and supplemented with specific additives
in order to mimic bio-degradation. In truth, however, these additives only facilitate the fragmentation of the materials, breaking them down into smaller fragments, which are most of the times not biodegradable, and therefore remain in the environment. The website of the European Bioplastics Association contains numerous resources on bioplastics as well as
on oxo-degradable plastics. I just mentioned the term "bioplastics". And this is a confusing term, since it is often used to refer to plastics that are bio-based, or bio-degradable, or both. So it could be everything that is covered now with the green ovals. Therefore, it is better to specify which of the two aspects apply to the given material. That's it for now about plastics. In this module, we learned about the current world plastic flows, including some of the basics on the sources of marine litter, and what plastics are. We talked about the nature of the polymers, whether they are bio-based or fossil-based, and the biodegradability potential. For further information, please have a look at this key literature.
