L22. Bio-plastics

plastic straw Are plastics good or bad? What about bioplastics? Neither question is simple.

Plastic pollution (e.g. plastic cups, bottles, and straws in the oceans and rivers) is a problem, but is that a problem with plastic or with plastic management?

Plastic is used in variety of different applications. Plastic bottles, cups, straws, and other packaging materials are most common, but plastic is also used for automobile parts, seat cushions, medical devices, computers and so much more. Each use requires a different type of plastic and has a different cradle-to-grave life cycle. That means when we ask the question "good or bad" we have to think of what alternatives we have for each application and then compare plastic to those alternatives. Bioplastics - plastics derived from renewable biomass sources, like the plastic made from corn mentioned in the video in Lesson 18 - are a possible alternative.

What is Plastic?

The materials we call plastics are synthetic organic polymers of high molecular mass. The phrase “synthetic organic polymer” means it is a man-made compound, which is composed of long hydrocarbon chains. Hydrocarbon refers to a chain made up primarily of hydrogen and carbon atoms. The illustration below is a representation of a polymer. In this case, it is a linking of several ethylene molecules (2 carbon and 4 hydrogen) together resulting in a polymer called polyethylene (PE). Each paper clip represents an ethylene molecule. The chain of paperclips represent the plastic polyethylene.

Typically, the hydrocarbons used to create the plastic polymers come from fossil fuels like crude oil and natural gas, but these hydrocarbons can also be produced from biorenewable resources. It is estimated that over 90% of the feedstock for the plastics industry is furnished by oil and gas. Plastic manufacture accounts for around 6% of the world's output of oil. About half of that used as chemical feedstocks, e.g. ethylene, and half is used to to provide energy required to extract the feedstock and make the plastic.

Types of Plastic and Their Uses

In 2015, about 407 million metric tons (Mt) of plastic was produced¹. Note: a Mt refers to metric ton which is equal to one million kilograms. 407 Mt = 407,000,000 kg. Compared to the mass of cement and steel produced globally each year this mass of plastic is relatively small. However, this amount of plastic is significant for a variety of reasons we will be discussing.

Material	Mass Produced Globally in 2015 (Mt)
Plastic¹	407
Steel⁴	1,620
Cement⁵	4,100

There are many types of plastics. Each plastic has a unique chemistry and is designed for specific characteristics. The plastic used in plastic bags is much different than the plastics used in computers or pipes for plumbing.

Plastics are generally categorized according to the form of the polymer "backbone". For instance, polyethylene is one category of plastic that is made up of "ethylene" backbone. The composition of the backbone can be only carbon and hydrogen, like polyethylene, or can include other elements such as oxygen or nitrogen, or a variety of other chemicals. The main types of plastics manufactured are referred to as resins (e.g. polyethylene, polypropylene). Figure 2 shows the global production of all plastics, including types of resins, fibers, and additives. In total, about 407 Mt of plastics are produced.

Figure 2. Types of plastics and their estimated global annual supply¹.

The table below summarizes some of the most common plastic resins, what they are used for, and their resin ID. This resin ID code is stamped on the finished plastic product. Most of us are familiar with these resin IDs because of the recycling instructions and restrictions. Note codes 1, 2 and 4 are all from a polyethylene backbone.

resin code 2

Most plastics are used for packaging purposes. Polyethylene—the most widely used plastic for packaging—makes up 34% of the plastics market¹.

Plastics used for packaging are generally single use, with an estimated lifetime from production to disposal of less than one year. Plastics used in other applications have longer lifetime usages; for instance, plastics used in building and construction have an estimated lifetime of 35 years, in transportation it's 13 years, and clothing is 5 years.

Plastic Generated and Plastics Discarded

Widespread adoption of the use of plastics began in the 1950's. With each subsequent year more types of plastics were developed and the application and use of plastics has grown. Cumulatively, about 6.3 billion tons of plastic waste has been produced since 1950, with projections that we will far exceed that amount in the coming years¹.

Why is Plastic Use a Problem?

Plastics are very stable and durable, which is part of the reason they have had such wide-spread adoption. Plastics are really good at what they are designed for!

"Plastics are a cheap, moldable, and corrosion resistant material, making them easily manufactured into a wide range of products. As a result, this material has become a dependable staple in our everyday lives, supplying items ranging from grocery bags to take-out containers to straws. With the amazing properties plastics provide, we contend that plastics should be celebrated for their unique capabilities and the life-changing applications they enable." (The good, the bad, the plastic Links to an external site., Northwestern University)

However, these same qualities mean that if plastics are not discarded properly they can remain in the natural environment for a very long time. For instance, an estimate for the time it takes for some common plastic items to decompose include: 400 years for a plastic drinking cup, 450 years for a disposable diaper, and 600 years for fishing line.¹⁰

Other concerns about plastic are related to specific chemicals and toxicity in the environment. For instance, BPA (Bisphenol A) has been used in the production of some polycarbonates for over 50 years, and is used in products with direct contact to food and liquids, such as some food storage containers, water bottles, baby bottles, and as an epoxy resin lining of cans. BPA can leach from these products, especially when they are exposed to heat. Recent research suggests that BPA may have negative health effects on development of fetuses, infants, and children (effects on the brain, behavior, and prostate gland)⁹ and can be carcinogenic (Seacrest 2015 Links to an external site.). There are additional additives to plastic with other potential toxic effects.

A large fraction of plastic that is produced (about 40%) is used only once, then discarded. Though many plastics can be recycled, research shows that since 1950, only around 9% of the plastic produced in the US was recycled, about 12% was incinerated (burned for energy), and about 79% discarded to landfills¹. The filling up of our landfills with plastic can also be a concern.

It is unclear what percent of the plastic in the US ends up in the natural environment, but we have all seen plastic bags or bottles along the roadside, in waterways, and in the ocean. Since plastics don’t degrade, any plastics that are not discarded properly remain in the environment for a long time. Plastic pollution is particularly a concern in the ocean, and there is increasing awareness of its potential problems in freshwater systems as well. Efforts are underway to reduce plastic pollution, both through cleanup efforts and in new thinking about plastics called the "Circular Plastic Economy." This concept focuses on decoupling plastic production from fossil fuels, increasing plastics recycling, and utilizing more biodegradable plastics for packaging⁶.

Bioplastics

bioplastic As is the theme of this course since the beginning, the human population is consuming too many resources. Plastics from fossil fuels are no exception. The obvious first step is to reduce plastic consumption. But could we also replace some of the plastic with plastic made from biorenewable sources? Might this be better?

Bio-based plastics or bioplastics are general terms used to describe plastics made from biorenewable resources. But just like plastics from fossil fuels, there are different types of bioplastics. The two big categories are relate to how they break down in the environment - non-biodegradable or biodegradable.

Non-biodegradable: Bioplastic does NOT mean that the plastic is biodegradable or compostable. It only means that the plastic is made from plant material. Ethylene, used for the plastic polyethyelene, is typically made from fossil fuels, but can be produced from plants through fermentation and subsequent processing. The end product is a plastic that is chemically identical to a polyethylene plastic from fossil fuel. These plastics are sometimes call "drop-ins" because they can be used seamlessly in the existing markets and deliver the same level of performance as fossil-based plastics. This means packaging companies do not need to change their equipment or processes to handle the drop-ins; distributors and retailers get the same performance; and drop-ins can be collected and recycled alongside their fossil-based counterparts, in the same systems. These plastics are often denoted using the prefix "bio;" examples would be bio-PET, bio-PE, etc.

The use of non-biodegradable plastics derived from plant sources has become a push for some companies in their sustainability efforts. For example, Coca-Cola has made a push to increase the amount of plastic in its bottles coming from plant sources. If you have ever picked up Dasani bottled water, you may have noticed labeling indicating that the bottle was made partly from plants. The end product cannot be differentiated from the 100% fossil fuel based product.

Biodegradable: There are also plastics made from plant biomass that are able will degrade under the correct environmental conditions. These plastics are biodegradable, meaning that they can undergo microbial-facilitated decomposition in the environment. Examples of these include polylactic acid (PLA), polyhydroxyalkanoates (PHA), thermoplastic starch, and cellulose acetate. Biodegradable plastics differ structurally from non-biodegradable plastics in that their chemical bonds (think linkages in the paper clip chain) can be broken down easier. PLA and PHA can theoretically be recycled though they lose some physical properties after several cycles.

The following table summarizes some common types of bioplastics, the raw material used to synthesize them, and some examples of applications. We've also included information on how they are produced if you are interested, but you will not be quizzed on these processes.

bioplastics

In 2014 only about 1.7 Mt of biobased plastics were produced or about 0.6% of total plastics⁶. Of this about 50% were non-biodegradable plastics. Growth is expected in the bioplastics industry, but it is being limited by the fact that bioplastics cost 30-100% more than traditional plastics. Much of this cost is in feedstocks production.

Are Bioplastics Better?

Since most of the concern over plastics is related to the environment (e.g. pollution, landfill space, toxicity) the real question is "Are bioplastics better for the environment?"

Using an LCA analysis for BioPET, a 2016 report from the University of Minnesota suggest that "better" depends on the source of the biomass used for the plastic.

"Researchers from the University’s Institute on the Environment compared the environmental impacts of 12 types of bottles with varying proportions of PET made from fossil fuels, row crops and forest residues . . . . They found that BioPET made from row-crop feedstocks such as corn grain and stover, wheat and switchgrass performed worse than traditional fossil-fuel-based PET in almost every environmental impact category assessed, including smog and particulate production, acidification and fossil resource depletion.

However, BioPET made from forest residues was found to require 22 percent less fossil fuel inputs and produce 21 percent fewer greenhouse gases than traditional PET." (University of Minnesota)

This type of mixed results are common. A summary of LCAs on the biodegradable plastic PHA found some studies showing benefits, others showing no benefit⁸. This is understandable given the many assumptions that need to be made in an LCA analysis. Remember, in a cradle to grave analysis of bioplastics there are several steps to include. Corn production is energy intensive as is the fermentation and further processing to make the plastic. Forest residue has different inputs to consider for harvesting and material processing. There are also land use considerations. For example, should we be using land to grow corn for bioplastics or for food or forests for lumber?

Two items are clear with LCA studies. New research is making the growing of biomass and the processing into bioplastics more efficient. This will lead to more consistently favorable LCA results for bioplastics. In addition, the "end of use" phase for plastics is a critical component of these LCA analysis. Incineration of bioplastics offsets the use of fossil fuels and subsequent GHG emissions. Some suggest that landfilling of non-biodegradable bioplastics results in some carbon sequestration. Plants are removing carbon from the atmosphere and storing it in the plastic for 100s of years. Proper accounting for this is important. If "end of use" results in plastic pollution of our oceans and waters, or release of toxic substances, then there may be benefits to biodegradable plastics that are not considered in traditional LCA analysis.

Another issue with biodegradable plastics is the contamination of the plastics recycling wastes stream. Biodegradable plastics in that recycling waste stream would cause problems with any products produced.

Summary

Plastics can be made from biorenewable resources and can be used to replace plastics from fossil fuels. These bioplastics can be identical to plastics from fossil fuels or can be chemically different and used as substitutes for fossil fuel based plastics. The current use of biobased plastics is limited primarily because of cost.

References

Geyer, R., Jambeck, J. R., & Law, K. L. (2017). Production, use, and fate of all plastics ever made. Science advances, 3(7), e1700782.
Hillmyer, M.A. (2017). The promise of plastics from plants. Science 358(6365):868-870
Albertsson, A. C., & Hakkarainen, M. (2017). Designed to degrade. Science, 358(6365), 872-873.
World Steel Association (WSA), “Steel Statistical Yearbooks 1978 to 2017” https://www.worldsteel.org/steel-by-topic/statistics/steel-statistical-yearbook-. Links to an external site.html Links to an external site.
U.S. Geological Survey (USGS), “Cement Statistics and Information" https://minerals.usgs.gov/minerals/pubs/commodity/cement/ Links to an external site.
World Economic Forum, Ellen MacArthur Foundation and McKinsey & Company. (2016) The New Plastics Economy — Rethinking the future of plastics. http://www.ellenmacarthurfoundation.org/publications Links to an external site.
Spierling, S., Knüpffer, E., Behnsen, H., Mudersbach, M., Krieg, H., Springer, S., Albrecht, S., Herrmann, C. and Endres, H.J., 2018. Bio-based plastics-A review of environmental, social and economic impact assessments. Journal of Cleaner Production, 185, pp.476-491.
Narodoslawsky, M. et al. 2015. LCA of PHA Production- Identifying the Ecological Potential of Bio-plastic. Chem. Biochem. Eng 29(2) 299-305
NIH National Toxicology Program https://www.niehs.nih.gov/health/materials/bisphenol_a_bpa_508.pdf
Wilcox, C., Van Sebille, E. and Hardesty, B.D., 2015. Threat of plastic pollution to seabirds is global, pervasive, and increasing. Proceedings of the National Academy of Sciences, 112(38), pp.11899-11904.

Other Reading