The legendary terminator of plastic pollution may cause more serious pollution

As global demand for plastics continues to surge, humans are increasingly calling for more sustainable plastic solutions. Bio-based plastics are one of the potential alternatives to ordinary plastics, but can current technology support bio-based plastics to meet the needs of building a sustainable circular economy?

Written by Zhu Yehua

The entry of bio-based plastics

If civilizations are remembered for their legacy, our current era might be labeled the “Age of Plastics.” The first peer-reviewed paper documenting plastic pollution in nature was published in 1971[1]. Since then, a vast body of work on plastic pollution has accumulated. We now know that the ubiquity of plastic in the environment is unquestionable. Since the early 1950s, humans have produced 8.3 billion tons of plastic products, of which approximately 6.3 billion tons have become plastic waste. Of this 6.3 billion tons, 9% has been recycled, 12% has been incinerated, and 79% has gone to landfill or been dumped into the natural environment. If current production and waste management patterns continue, it is estimated that 12 billion tons of plastic waste will be produced by 2050[2]. The onslaught of plastic waste has prompted the development of numerous potential solutions, and bio-based plastics are one of them.

First of all, we need to clarify two concepts. Bio-based plastics and bioplastics are not the same thing. In fact, bioplastics are a general term for bio-based plastics and biodegradable plastics. This article focuses on "bio-based plastics", which are made from carbon extracted from crops such as corn or sugarcane and other chemicals such as plasticizers used in traditional plastics. This is different from the traditional plastics whose skeleton is mainly carbon chains from fossil fuels.

PLA tableware丨Source: Internet

The two most commonly used bio-based plastics are PHA (polyhydroxyalkanoate) and PLA (polylactic acid), the former is usually made from algae, and the latter is made from crops such as corn and sugarcane as raw materials. PLA costs one-tenth of PHA, so it is more widely used in disposable tableware and various packaging. PHA is used as an internal coating for paper cups and medical applications.

However, neither of these two bio-based plastics has been widely used because their strength and other properties are simply not comparable to traditional plastics, and the cost is much higher. On the other hand, although both of the bioplastics currently in use can be decomposed by microorganisms, they need to be collected and composted in high-temperature industrial composting facilities, and there are not many such facilities in municipal waste treatment plants, especially in developing countries where plastic pollution is the most serious. In addition, compared with traditional plastics, the production of bio-based plastics also needs to compete with food crops for land, and there is also considerable controversy over whether the raw material crops of bio-based plastics are environmentally friendly.

Competition for land and continued pollution

Growing crops for PLA bioplastics requires a lot of land. A 2020 study estimated how much land would be needed to completely replace conventional plastics with bioplastics. The results showed that the area of ​​land required to achieve this goal is larger than the land area of ​​France, and the amount of water required is 60% more than the annual freshwater withdrawal of the European Union[3].

So the conclusion of the article is: It seems unfeasible to replace all petrochemical plastic packaging with bio-based plastics at present, because this will inevitably lead to a significant increase in land and water use. Unless ways to reduce the demand for plastics are found, most efforts to stop plastic pollution may be temporary and insufficient. In addition, land competition will affect natural biodiversity, because land use change has been one of the main drivers of biodiversity loss.

On the other hand, the environmental pollution problem of bio-based plastics still exists. A study by the University of Pittsburgh compared the pollution of 7 traditional plastics, 4 bio-based plastics and 1 plastic made from fossil fuels and renewable energy. After comparative analysis, it was found that the fertilizers and pesticides used in growing crops, as well as the chemical processing required to convert organic materials into plastics, have led to a large amount of pollutants in the production process of bio-based plastics.

Compared to traditional plastics, bio-based plastics have a greater impact on ozone depletion and require a lot of land. After combining the negative impacts of agriculture and chemical processing, it was found that mixed plastics have the greatest potential toxic impact on ecosystems, the most carcinogens, and the lowest score in life cycle analysis [4].

But if you look at it from a carbon emissions perspective, bio-based plastics produce far less greenhouse gas emissions over their lifespan than conventional plastics. When they decompose, there is no net increase in carbon dioxide, because the plants that make bio-based plastics absorb an equal amount of carbon dioxide during their growth.

Is technological advancement bringing hope?

Although it is still controversial whether bio-based plastics can completely replace traditional plastics, some researchers are still working hard to improve the properties of bio-based plastics to make them more suitable for consumer products and more environmentally friendly.

Image source: Unsplash

First, the issue of competition for land with food production seems to be gradually being resolved. As technology continues to improve, the land used to produce bioplastics today only accounts for 0.3% of the total agricultural land area. In addition, the proportion of land use can be further reduced by developing second- and third-generation bioplastics, whose raw materials are not food but agricultural residues, bacteria, fungi or microalgae. This development helps to minimize the pressure on agricultural land and reduce potential conflicts with food production.

New manufacturing methods have also made researchers more "confident" about bio-based plastics. In 2021, a research team led by the Yale School of the Environment created a lignocellulosic bioplastic, which they claim can not only replace petroleum plastics, but also replace existing bio-based plastic materials. The researchers used a cheap wood processing residue - wood powder - as a raw material for bio-based plastics. They used a biodegradable and recyclable deep eutectic solvent (DES) to decompose the loosely structured wood powder composed of cellulose, hemicellulose and lignin. The paper explains that DES has two functions: dissolving lignin and breaking down cellulose in wood cell walls into micro/nanofibers. Lignin is then regenerated or "deposited" by adding water and combined with a network of micro/nanofibers to produce a lignin-cellulose "slurry", and finally a bio-based plastic is formed from the slurry through a simple casting process. In these processes, the modification of lignin is key. In the past, it was very expensive to separate lignin and cellulose, but the regeneration of in situ lignin does not require the separation of the two, thus greatly reducing the production cost of bio-based plastics. In addition, the in situ lignin regeneration process can also be applied to various types of materials. In addition to wood, grass, wheat straw or sugarcane bagasse can be used to produce in situ lignin[5].

In addition to PHA and PLA, cellulose diacetate (CDA), which is primarily derived from wood pulp, is another common bio-based plastic that is widely used in cigarette filters, textiles, coatings, films, food packaging, and other items such as eyeglass frames and tool handles. According to a study published in Environmental Science & Technology Letters, it breaks down and degrades much faster in the ocean than previously assumed. The researchers cultured nearly 350 CDA and control samples in customized seawater and equipped the experimental system with a continuous flow of seawater. As seawater flowed through the samples, the researchers used a variety of techniques to monitor the degradation of these samples. Time-lapse photos and mass loss measurements showed that the CDA material disintegrated in seawater on a timescale of several months, which is significantly shorter than the previously assumed degradation time [6].

It is worth mentioning that bio-based plastics are an initiative aimed at achieving sustainable utilization goals by leveraging their environmental benefits. Although some research teams have achieved certain results in the research and development of new materials, most improved and promising bio-based plastics are still in the research stage and it will take a long time before they can be promoted on a large scale.

According to the Institute for Bioplastics and Biocomposites (IfBB) at the University of Hannover in Germany, 2.61 million tons of bio-based plastics were produced worldwide in 2018, but this is less than 1% of global plastic production. As the demand for plastics continues to grow, the demand for more sustainable plastic solutions is also growing. By 2021, statistics show that the share of bio-based plastics has risen to 1.5% of the world's plastic production and 2.3% of Europe's plastic production [7]. Therefore, bio-based plastics cannot become an effective way to end global plastic pollution in the short term.

References

[1] Buchanan JB. Pollution by synthetic fibers. Marine Pollution Bulletin. 1971; 23.

[2] https://www.mdpi.com/2071-1050/14/8/4855.

[3]https://www.sciencedirect.com/science/article/pii/S2590332220303055.

[4] Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers (pitt.edu).

[5] Yale study introduces breakthrough bio-based plastic - Yale Daily News.

[6] Michael G. Mazzotta et al, Rapid Degradation of Cellulose Diacetate by Marine Microbes, Environmental Science & Technology Letters (2021). DOI: 10.1021/acs.estlett.1c00843.

[7] https://www.ifbb-hannover.de/files/IfBB/downloads/faltblaetter_broschueren/f+s/Biopolymers-Facts-Statistics-2019.pdf.

This article is supported by the Science Popularization China Starry Sky Project

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

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