Materials series part II : what’s the deal with Bioplastics?
Updated: Jan 29, 2020
I would like to start this article with a personal story. A few weeks ago, I got myself caught in an argument in an Italian supermarket. Since Jan 1st, 2018, the plastic bags at the fruit and vegetable department in all Italian supermarkets and shops need to be biodegradable and they charge you 1cent for them. Since I am far from perfect and have not found and bought the perfect re-usable produce bags yet (it is on my to-get-list for sure) I still take some bags once in a while, however, try to keep them to the bare minimum. I do this by putting different fruits and veg together in 1 bag and putting the different price labels on the bag. An employee sees me doing this, walks up to me and tells me that I need to use separate bags for different products. So I tell him that I don't want to do that because I don't want all these plastic bags. After some discussion, he walked away saying he would do it for me at the register. An older couple makes a comment that they only cost 1 cent so I should just do what the man asks and "follow the rules" or go back to Switzerland (I'm not even Swiss!!!) and that the bags are biodegradable and that you can simply compost them, so there was no issue according to them. I tried to explain that these bags are not actually compostable and do not break down completely, but they didn't even want to listen and walked off.
To be honest, I was quite upset by this event. After giving it some thought, I do understand the confusion. The word biodegradable is very misleading and that's the reason why I wanted to write this piece to shed some light on the stories behind bioplastics, biodegradable, compostable and conventional plastics.
Plastics are divided in 7 different categories of which we will discuss a few. You will be able to recognise them better now when you examine an item simply looking the little triangle with a number in it (the category) and the abbreviations below. Want to learn more? Click here.
#1 Polyethylene terephthalate (PET or PETE or polyester)
#2 High density polyethylene (HDPE)
#3 Polyvinyl chloride (V or Vinyl or PVC)
#4 Low density polyethylene (LDPE)
#5 Polypropylene (PP)
#6 Polystyrene (PS)
#7 Other (O) - all other plastics
Common petroleum-based plastics
#1 PET (polyethylene terephthalate) is probably the best known. It is commonly used in items such as plastic drinking bottles. It is petroleum-based and there is a large focus on recycling for re-use towards different purposes such bottles for non-food items, clothing such as fleece, carpets,…
#2 HDPE (high-density polyethylene) is the plastic used to make milk bottles, ice-cream tubs, bottles for toiletries and cleaning products. It can be recycled into recycling and compost bins, pipes, crates, flower pots and outdoor furniture.
#3 PVC (polyvinyl chloride): Soft PVC (softened with plasticizers) used in toys, clear food (e.g., take-out) and non-food packaging (e.g., blister wrap, cling wrap), squeeze bottles, shampoo bottles, mouthwash bottles, cooking oil and peanut butter jars, detergent and window cleaner bottles, loose-leaf binders, shower curtains, blood bags and medical tubing, "pleather" clothing, wire and cable insulation, carpet backing and flooring. Rigid PVC is used for blister packs and clamshell packaging, credit cards, piping (e.g., for plumbing), vinyl siding, window frames, fencing, decking, and other construction materials. PVC is widely considered the most toxic and hazardous plastic that is still - unbelievably so - commonly used to make numerous consumer products. It may contain and/or leach a variety of toxic chemicals including, but not limited to: bisphenol A (BPA), phthalates, lead, dioxins, mercury, and cadmium.
#4 LDPE (low-density polyethylene) is used to make cling-film, most squeezy bottles, food bags and plastic carrier (shopping) bags. This is not commonly recycled but can be used for outdoor furniture, fence posts, tubing.
#5 PP (polypropylene) is the plastic used to make dairy food containers such as yoghurt pots and cheese containers, butter containers, Tupperware and other plastic food storage boxes, and medicine bottles. Most plastic bottle tops are made out of this. Recycling efforts of PP have been increasing and a cool example is a product such as Wasteboards’ skateboards.
#6 PS (polystyrene) includes colourless, transparent polystyrene and expanded polystyrene, which is more commonly known as styrofoam. This is used for takeaway food containers, hot beverage containers, food produce boxes and deli packaging. The transparent polystyrene is also used to plastic cutlery.
This is not commonly recycled and predominantly makes two products, insulation and plastic ‘timber’. To recycle it has to be mixed in with new ‘virgin’ polystyrene.
Petroleum plastics may degrade into smaller and smaller pieces, but most won’t decompose or be absorbed by the surrounding environment.
OK, this was the more common and known part, let’s get into the newer and possibly more confusing part.
Bioplastics are commonly believed as being a better alternative to the petroleum-based plastics however there is more than meets the eye at first sight. Bioplastics are made from plants. Usually, the base is corn, sugarcane or potato starch. Bioplastics may or may not be biodegradable, compostable or toxic depending on the chemicals used during manufacturing.
One of the more common bioplastics is PLA (polylactic acid) which is biodegradable and compostable, but we will talk about what that really means later. As with other plastics, bioplastics still require additives to infer specific properties, and these additives may not be biodegradable or tested for safety. Natureworks, the largest manufacturer of PLA in the world, state on their website "Although PLA has an excellent balance of physical and rheological properties, many additives have been combined with it to further extend the range of properties achievable and thus optimize the material for specific end-use applications." For bottles made with their PLA ‘Ingeo’ plastic, Natureworks suggest these “basic” additives are used:
Toner and colourant: without additives ‘Ingeo’ is slightly yellow, and adding a toner can make the plastic colourless and more appealing to customers. Alternatively, they may be used to make the plastic a different colour.
A reheat additive can be used to make the heating process more efficient whilst moulding the bottles.
A UV Blocker will be required if the product is sensitive to UV light, or in order to prolong shelf life.
Oxygen absorbers can be added to protect products sensitive to oxygen.
A slip or process aid can be added to help prevent bottles scuffing and scratching during manufacture, packing and transport.
PLA can be recycled however also here there are some restrictions since it is part of category #7, so it might end up in landfill anyway because there is no specific recycling system, unlike PET.
Another question we can ask here is if it is the best and most responsible choice to use large areas of land suitable for agriculture to grow crops to make plastic rather than for food production?
Biodegradable vs compostable
Biodegradable means capable of being broken down by bacteria or other living organisms and returning to compounds found in nature. However, biodegradable doesn't really say anything about the timeframe, for example, wood is biodegradable, but a log cabin can stand for generations.
Degradable means capable of being broken down into smaller pieces. This is not the same as biodegradable. Plastic generally breaks down into microplastics that do not break down further and get into the soil or the oceans. Most plastics are therefore degradable, but not biodegradable.
Compostable means capable of breaking down in a compost pile. Compostable plastic [as defined by the plastics industry] is “that which is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with known compostable materials”. ‘Carbon dioxide, water, inorganic compounds and biomass’ technically includes every substance in the known universe and this definition allows compostable plastic to leave toxic residues whilst still being classified as compostable.
A plastic may be biodegradable but not compostable, meaning it will break down more slowly than would be expected in a compost pile, and may not disintegrate.
Commercial Composting vs Home Composting
Compostable bioplastics often require industrial composting facilities to break down. This means an active composting phase of a minimum of 21 days, with temperatures remaining above 60ºC for at least 7 days, and regular turning. Industrial composting works much faster and better than home composting systems, which generally do not reach the same high temperatures and are not regulated.
Often compostable plastics can only be composted in industrial facilities and are not suitable for home composting. This does mean that the recycling of biowaste and compostable plastics needs to be done properly otherwise it might still end up in a landfill or get incinerated. Depending on the country you live in, this might mean different things.
The pictures below show what happens when you home compost corn-based plastic cups
Photo credit: Zane Selvans via Flickr. These Caltech cups are made from corn-based plastic. Caltech doesn't compost these themselves (so most will be sent to landfill). To see how compostable they were, Zane put six of the cups in his very active compost pile at home (which reached 70°C a couple of times) and left them for two years. After two years, this is what they looked like.
Using either conventional plastics or bioplastics for mere minutes is simply not green or sustainable. Whilst bioplastics may have the potential to be composted and decrease the landfill burden, it still requires specific circumstances to so and they still contain undeclared additives that may leach into our food or our soils. The reality is that most of these bioplastics don't end up in composting facilities, but head to straight to landfill, or worse, end up as litter.
My personal point of view is just to avoid as much as possible any type of single-use plastic!
This chart was created by Less Plastics and can help you to start reducing your plastic impact 1 step at a time! Be bold and challenge yourself as well as people around you to use fewer plastics!