The post about disposable cups’ materials and their (bio)degradability
I saw a disposable coffee cup just left there on a bench, just like that. Of course, I took it and through away into a nearest garbage container. As a chain reaction in my mind, the idea about today’s post has arisen.
Why I clean plastic trash when I see it in Nature plots?, – Because it is my Planet.
Why I am writing about it to you now?, – Because it is my Planet.
Lots of people work hard to buy just tiny or bigger plot of land, to have it as “theirs”.
I take it for free. I clean it – I take it. In my mind the whole world is mine:) Any Nature plot I have cleaned – now it is mine. It is mine means I am responsible for it, it is mine means I love it, it is mine means I take care of it.
1. What does it mean (bio)degradable?
The term (bio)degradability. How do disposable coffee cups degrade in Nature?
(Bio)degradability means that (bio)degradable substance decomposes to its simpler components. But it does not disappear in a space, right?!
In the case of disposable coffee/tea cups it means, that “building blocks” of the thermoplastics, bio plastics or paperboard cups with plastic coating remains in Nature, even after slow partial decomposition.
Plastics could be decomposed only if properly collected and degraded under the specific conditions of industrial composting.
That is why it is crucial to bring it back to a producer. The next, higher level is, of course, to use your own multiply use coffee/tea mugs:)
Chemical decomposition of plastics
Degradable substances could be decomposed by chemical reactions only, such as hydrolysis, oxidation (sorry, guys, for the chemical terms included, but anyway, there is no need to remember those).
Biological decomposition of plastics
Biodegradable substances could be decomposed by natural biological processes, such as soil bacteria or UV light.
2. What are disposable cups made of?
Disposable cups are made of petro-plastics, bio plastic or paperboard lined with plastic coating (1).
|Petro-plastics||HIPS = high impact polystyrene|
EPS = expanded polystyrene
PP = poly propylene
PET = poly ethylene terephthalate
RPET = recycled PET
|Bio plastic||PLA = polylactic acid|
|Paperboard lined with plastics or wax||PE = poly ethylene |
PLA = polylactic acid
Polyethylene (PE), Polypropylene (PP), Polystyrene (PS) and poly ethylene terephthalate (PET), as well as recycled PET are thermoplastics, which means they could be heated and cooled.
That is why these materials are used to produce disposable coffee/tea cups (hot beverage). Thermoplastics (heat resistant plastics) are considered as non-biodegradable plastics (2).
The term “bio” is used because polylactic acid (PLA) was initially made from plants instead of petroleum, extracting lactic acid (a building block of PLA) from fermented starchy vegetables and crops.
These days, lactic acid and other building blocks, necessary for synthesis of PLA could be synthesized in laboratory, and it is much cheaper to produce.
Therefore, the term “bio plastic” in many cases remains as a historical reminder about the origin, but not as a source of the factual materials used.
Polylactic acid (PLA) is thermoplastic too and is not biodegradable in Nature under normal conditions. PLA could be safely degraded only under the specific conditions of industrial composting (for example, so-called thermal decomposition at elevated temperatures – pyrolysis).
Author’s note: chemical composition of plastic materials (so-called thermal depolymerization) changes dramatically during thermal treatment at high temperatures and is accompanied with an emission of toxic fumes and by-products. The process requires special equipment, filters, etc.
PLA in medicine
In medicine, PLA is called biomaterial and is widely used to produce temporary implants, orthopedic devices, sutures, etc. However, the same prefix “bio” in medicine refers to the materials (both natural and synthetic) suitable to introduce into a body tissue as an implant or medical device. So, in medicine also the prefix “bio” does not necessarily indicate the biological or natural origin of it.
To be precise, PLA could be degraded by some bacteria, such as Amycolatopsis and Saccharothrix and sunlight (UV radiation, so-called photodegradation). However, these bacteria and even direct prolonged sunlight are not enough to deal with the enormous amount of plastic garbage worldwide.
PLA is made of lactic acid “blocks”, probably it is OK?…
P. S. Lactic acid (a building block of PLA) is widely used in food industry because “it naturally occurs in a body”.
However, an excess of lactic acid (because it is an acid) rises acidity of body fluids (lowers its pH level) and could cause acidosis, inflammations and other health concerns.
There are so much to say about lactic acid, its negative impact on muscles (specific pain after physical exercises or alcohol consumption) and about correlation between lactic acid and gout, but lets make it in another post, later.
Paperboard lined with plastics
Although the paperboard on the coffee/tea cups is recyclable, the plastic coating (PE, PLA) can greatly limit their recyclability, sometimes making it even harder to recycle on the industrial scale.
Disposable coffee cup, left by someone just like that – on a bench
If not properly recycled by industry, paperboard cups create huge amount of microplastic pollution. This happens because when paper (cellulose fiber) naturally biodegrades in Nature – a thin layer of thermoplastics remains and cause the pollution for water, animals, earth and air (3).
Degradable materials could degrade in Nature for some extent, but that only means that their unnatural to the natural environment “building blocks” would stay in soil, water, air, poisoning it.
After some time they would be consumed by animals, birds and marine creatures, and a bit later, yes, would come back into a plate of an average civilized consumer.
Pardon, not “would”, they are already there.
Are you ready to change your plate content?
- Van der Harst E, Potting J. A critical comparison of ten disposable cup LCAs. Environ Impact Assess Rev. 2013;43:86-96
- Raziyafathima M, Praseetha P, Rimal I. Microbial degradation of plastic waste: a review. Chemical and Biological Sciences. 2016;4:231-42
- Yuhui M. Problems and resolutions in dealing with waste disposable paper cups. Sci Prog. 2018;101(1):1-7