By Ian Mallov, Ph.D., Research Chemist at inkbox Tattoos
You might have seen news of the young sperm whale who died on a beach in Scotland two weeks ago. A necropsy of the animal found more than 100 kilograms of plastic in its stomach. Fishing nets, plastic cups, bags and rope were among the debris. It’s as yet undetermined whether the plastic contributed to the animal’s death.
Perhaps we’ve become immune to this type of news lately – a dull reminder of the accumulating impact humans have on the planet’s other inhabitants. But, disturbingly, this is not the end of these plastics’ life cycle: the recovered plastic will likely go to a landfill and await a degradation process in the tens or hundreds of years. Assuming sufficient light and oxygen, gradual oxidation of the polymers will occur until brittle enough that physical breakage into smaller and smaller pieces allows microbes to metabolize them. Perhaps, before this happens, they will be swept out to sea again.
Essentially, the end-of-life issues are a problem of chemical kinetics. I work on the other end of the life cycle. Each day the company I work for, like so many others, rolls out products packaged in plastic to ship throughout the United States, Canada and overseas. To paraphrase the first principle of green chemistry, it’s better to prevent waste than to clean it up later. But how do manufacturers prevent waste when plastics are often the cheapest and most efficient protective packaging?
We are all familiar with the excellent barrier properties and light weight of plastics. But since the first synthetic plastic, Bakelite, was patented in 1909, a century of manufacturing optimization has resulted in formidably cheap, widely customizable materials composed of one or more of several common polymers: low- and high-density polyethylene (LDPE and HDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and silicones, among others. The efficiency of manufacture of most traditional plastics, including material and energy inputs, makes it difficult for other materials to compete, and indeed this optimization contributes positively to minimizing the environmental impact of their early life cycle.
But it is the end-of-life problem that is increasingly urgent. Most plastics in North America still end up in the landfill. Alternatives to landfills such as recycling, pyrolysis to hydrocarbon fuels, and incineration are available, but fillers, stabilizers, plasticizers and colorants complicate these processes, as does food, adhesives, and other contamination from mixed solid waste streams, particularly when trying to recycle plastics. As of 2017, only 8% of U.S.-generated plastics were recycled, 16% incinerated, and the rest went to landfill. This is especially challenging in other parts of the world, especially in Southeast Asia, where a lack of waste management practices result in far less recycling, incineration or landfilling.
So what functions do we need from plastics? Their ubiquity makes this seem almost a rhetorical question, and depending on the application, there will be different functions. After all, the functions we need from plastics that go into building, automobile, marine, packaging or other applications vary tremendously and represents a formidable challenge in designing new plastics. For example, as a manufacturer of any good with a limited shelf life, you need a few key benefits from packaging: protection from physical damage, protection from dirt, and reduced exposure to water vapor and oxygen, to name just a few.
Measuring the effectiveness of packaging can be quantified by measuring hardness, density, tensile strength, heat resistance and glass transition temperatures. Just as importantly, moisture vapor transmission rate (MVTR) and oxygen transmission rate (OTR), often measured in grams per square inch per twenty-four hour period, give an indication of how packaging will slow spoilage of food, goods and chemicals from oxidative processes.
Having a rudimentary idea of what to measure, and which metrics are key for your product, allows you to begin the process of evaluating options beyond traditional polymer materials. In the case of plastic packaging, one of the desirable functions that has been suggested is the ability for the plastic to be biodegradable and compostable. A few resources have been developed to help chemists answer the question of whether or not the plastic will be biodegradable and compostable. One such resource is the New York-based Biodegradable Products Institute (BPI), founded in 1999. The BPI has developed a scientifically-based certification system for products to be considered industrially compostable, that is, degrading under typical conditions of industrial compost facilities on a timescale of weeks. The BPI requests physical samples of materials to test for certification.
Another venerable resource is ISO 17088: Specifications for Compostable Plastics, published in 2008. While not free, the availability of an ISO standard for over a decade is testament to the slow progress industries have made on this problem.
More recently, a myriad of small companies offer bio-based and renewable alternatives to traditional plastics in the form of industrially compostable polymers such as the class of polyhydroxyalkanoates (PHA) including the most recognizable, polylactide (PLA), or paper or cellulose-based materials that mimic the properties of traditional plastics. Companies such as Australia-based Grounded Packaging offer a range of products that are certified compostable under even the milder conditions of home compost piles, mitigating the problem of access to municipal composting facilities.
Recent articles in this newsletter have highlighted other approaches to plastics production such as using the pyrolysis of sugar or other biomass to produce monomers through a Fischer-Tropsch process for use in more than just hydrocarbon fuels. The most notable example of this approach is the “Plant Bottle”, developed by Coca-Cola, and now used by a number of drinks manufacturers.
Legislation is beginning to catch up with growing consumer demand for more sustainable alternatives to traditional plastics. The parliament of the European Union passed a single-use plastics ban in March of 2019, while Canada followed suit in June. Both are to come into effect in 2021. Countries such as Bangladesh, South Korea, Rwanda and Colombia have announced more limited bans on plastic items. Many cities and municipalities have single-use plastic bans or taxes.
With legislation gaining momentum, it is up to chemists to help ensure that laws are informed and effective, and to continue to push the boundaries of their creativity, to think beyond the consumer to a systemic solution for plastics use in modern society. This responsibility includes influencing decisions made in the production and manufacturing of chemicals and consumer goods. After all, the functions plastics impart are essential. It is imperative that we learn how to design and manage them in a way that does not adversely affect human health or the environment. After all, it’s a problem of kinetics.