I have to admit that writing these lessons is super fun but also quite difficult at times...
Recycling is such a fascinating topic because it allows one to read into the chemical details of polymers while tying it to economical realities. It therefore is never easy to keep these lessons short. Therefore, be assured that if you want to know more, checking out the links included will not disappoint you. At least, if you ask me :D
Today's Lesson: How Plastics Are Recycled #3
Exploring the different Types of Recycling
Number Of The Day
A publication estimated that in 2017 approximately 180000 tons of European Polyethylene waste ended up in oceans. They used data from 30 European countries to 50 major receiving countries.If you remember last lesson, at the end of 2017 China banned most waste imports, so the past 2017 data will be interesting to look at.
180558 tons
What You Need To Know
A New Member For Research
South Korea is now the first Asian country to join the Horizon Europe program that is funding research in e.g., climate change & health
Literally Laboratory Sustainability by I2SL
If you like to learn about sustainability in laboratory design, construction and operations have a look at these resources.
Convincing With Green Chemistry
An online event on the 2nd of May on the benefits of green chemistry with case studies of employees successfully initiated change.
Types Of Plastic Recycling
If plastic is not recycled it A) ends up on a landfill where it rots and light plastics are blown away… B) is incinerated and companies can talk about “energy recovery” or C) it ends up in nature.
There are different types of recycling. Primary recycling involves processing plastics to produce the same product as the original while secondary recycling results in the creation of a different product, often of lower quality than the original one.
Also, there are different recycling processes. Mechanical recycling is by far the most common. It (mostly) does not change the chemical structure of the material, it simply “cuts” it into smaller pieces, which are then re-shaped under higher temperatures.
For mechanical recycling, extrusion is widely used as a method to transform waste plastics into regranulated material. This process involves to partially melt the plastics by heating while applying mechanical force. Then the granulate is melted and shaped into a desired form.
To some extent, thermal conduction and viscous shearing applied to polymers within an extruder leads to thermo-oxidative and shear-induced chain scission, chain branching or crosslinking of the material. This unwanted chain degradation reduces the polymer chain length and in turn lowers its mechanical properties and processability. Free radical reactions can promote these processes. Thus, one adds both thermal and light stabilizers. - Read More -
Chemical Recycling (Tertiary Recycling)
This process breaks down chemical bonds to dissolve plastics into their basic components. One example is pyrolysis, where plastics are subjected to high temperatures in the presence of a catalyst. While a promising method, it requires significant energy inputs and difficult to implemented on an industrial scale. - Read More -
Biodegradation
While biodegradable can be somehow similar to landfill degradation, (realsing methane and other gases) this type involves enzymes that break down the polymer chains into simpler compounds, facilitating faster degradation compared to conventional plastics. - Read More - One notable example is Polylactic Acid (PLA), which is derived from organic sources. So why then don’t we use more of these plastics?
Biodegradable plastics are great, but there are two major challenges:
1) A big proportion of plastics will be contaminated and thus, often must be incinerated.
2) Plastics such as PLA have partially undesired properties. PLA is less heat resistant (which obviously can be an issue in the laboratory), is more vulnerable to sunlight and is thought to have higher permeability (i.e., leaking potential) than other plastics. Moisture and oxygen are more likely to diffuse through PLA.
But why don’t we use traditional plastics that are recycled then?
Mechanical recycling processes will shorten polymer chain lengths, leading to a reduction in overall quality. This is why these are more often downcycled since they would result in products that are more likely to leak, are less resistant to tensile forces and less transparent.
Yes, indeed, I could not fiind another picture but this one that portrays an opaque and transparent item ... you can find the article by Henkel that saved me - here -
Of note, greyish plastics is not transparent because of micro-irregularities (e.g., scratches). In pipette tips this can result in a higher surface area and thus will lead to higher adhesion – resulting in imprecisions when pipetting.
Also, many plastics are not 100% pure they contain additives that optimize their properties (e.g., for UV or heat resistance). During mechanical recycling they would spread into the other items and together with the shorter polymer chains more likely to leak after recycling – contaminating our solutions.
Recycled items could become a reality if labs decide to have one high and one lower quality stock. Otherwise, we need to wait until chemical recycling becomes the standard.
But let us close on an optimistic mark: There is one company (Eppendorf) was so far able to produce high quality tubes with 90% plant oils from waste streams called Bio-Based Tubes!
Take Away
Mechanical Recycling is the most common approach. It shreds plastic waste under tension and heat into smaller pieces. Then, those are shaped into new products. Since this process is damaging the polymer chains to some extend, these plastics are often downcycled i.e., made into products of lower quality.
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