Tuesday, 28 January 2020

Microplastics: What Should We Know About Them and How Are They Impacting Our Life?


The environmental impact of plastics is an actual concern and a reoccurring topic in the media. In this context, the term microplastics is often referred to (Figure 1).

Google trend search on "Microplastics"

Figure 1: Google trend search “Microplastics” (2018-2019).


In this blog post, we approach microplastics in a general way:
-What is it?
-How can we define it?
-Where does it come from?


In addition, we look at some specific topics such as microplastics in humans, cosmetics, oceans and associated health concerns.


Microplastics definition


Mircoplastics are solid particles which are insoluble in water and were synthetically generated. We can distinguish between primary and secondary microplastic particles:


- Primary microplastics are all primary manufactured particles, i.e. (liquid) prepolymers, plastic pellets and powders;
- Secondary microplastics are fragments of larger plastic parts. For example, fragments of plastic bottles, bags and so on.


What are the sizes of microplastics?


In general, microplastics have a size smaller than 5mm. However, the term “microplastics” covers different sizes [1]:
- Milli range from 1-5 mm
- Micro range from 1-999 µm
- Nano range from 1-999 nm


Where do microplastics found in our environment come from?


There are seven major release sources of microplastics which contribute to environmental pollution, especially in our oceans.



According to Figure 2, the major release source is the washing of synthetic clothes (35%). Microfibers of polyester and polyamide end up into the wastewater stream and then into the ocean. Main regions affected by this are India and South Asia. Following, are microplastics generated through wheel erosion during driving (28%). We have currently over 1 billion cars and the wheel debris is made up out of elastomeric particles. The third major generator of microplastics is city dust (24%). Smaller release sources are road markers (7%), marine coatings (4%), personal care products (2%) and plastic pellets (0.3%). The latter is mainly generated by resin manufacturers and/or resin processers.

Figure 2: Overview of major microplastic release sources [7].


Microplastics in humans


As shown before, we are all exposed to many sources of microplastics and interesting is now to understand their impact on our body.


Investigations have shown that we take up 2.000 microplastic particles when eating table salt. Altogether, it should be 32.000 particles which every one of us takes up per year [6]. The studied published by South Korean researches sampled salt from 21 countries all over the world, including Europe, North and South America, Africa, and Asia. The study found that the amount of microplastics varies strong among the different brands and regions. Asian brands contain much higher amounts of microplastics. Salt from Indonesia has the highest amount of microplastics and this region is known to have the second-worst level of plastic pollution in the world.


Comparing the different geographical sources of salt, microplastics levels were highest in sea salt, followed by lake salt and rock salt.
In 2018, the Medical University of Vienna, Austria found microplastic particles in the human feces of eight out of eight tested people. They tested five women and three men form different countries, the Netherlands, United Kingdom, Italy, Poland, Russia, Japan, and Austria. For one week, all people wrote down what they consumed daily and delivered a stool sample at the end of the week. Researchers found 20 microplastic particles per 10 grams stool. Nine different plastics could be identified in the size of 50 to 500 microns. Most materials found were PP (polypropylene) and PET (Polyethylenterephthalate) [3].


The World Health Organization (WHO) is looking intensely into the impact of microplastic in humans and started several investigations [5]. The concern of WHO is that microplastics can enter the human body over drinking water and harm body functions. However, this concern has so far no scientific back up. The report from WHO states that there is insufficient information to draw firm conclusions on the toxicity of microplastics. The investigations are still ongoing. Mr. Gordon, who is the WHO coordinator of water, sanitation and hygiene, stated that as a consumer who is drinking bottled or taped water you should not be necessarily concerned to be exposed to health risks.


My wrap-up on microplastics


In various areas in our life we are exposed to microplastics and studies have shown that PE and PP are the most found type of microplastics. In general, large Mw polymers such as polyolefins are harmless materials when eaten due to their macromolecule size. On the other hand, plastics usually contain additives (small molecules), which can be easily released out of the compound into the environment. For instances, due to human safety regulations, food and beverage packaging plastics comply with strict standards concerning allowed additives and respective amounts.


However, with city dust this is not the case. As described above, microplastic from rubber car wheels is a major cause of air pollution, together with car brake dust. In major cities, millions of cars impact in this way our air quality. People all around the world already realized that and work on concepts to change and improve it. Smart city concepts are on the raise. For instances, these enable transportation of multiple people by e.g. autonomous electric people movers, which have the potential to reduce allover amount of wheels in a city by reducing the allover amount of cars. Furthermore, braking in electric cars does not release brake dust due to regenerative braking (converting the kinetic energy for immediately use or storage in battery).


At the moment, it is difficult to avoid intake of microplastics and we will have them around since cars and clothes will not disappear. However, public awareness increased in the past years and organizations like the WHO and research organizations initiated several studies on their impact on our health. It is important to understand the cause-effect relationships in this context and find solutions which consider environmental, as well as economic-social aspects.


Thank you for reading and till next time!
Best regards,
Herwig Juster

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Literature:
[1] H.A. Leslie: Review of Microplastics in Cosmetics, 2014
[2] https://www.addendum.org/plastik/besser-als-sein-ruf/
[3] https://www.meduniwien.ac.at/web/ueber-uns/news/detailseite/2018/news-im-oktober-2018/erstmals-mikroplastik-im-menschen-nachgewiesen/
[4] https://www.sciencehistory.org/case-study-plastics-and-the-human-body
[5] Susan Freinkel, Plastic: A Toxic Love Story (New York: Henry Holt, 2011), p. 89
[6] https://www.nationalgeographic.com/environment/2018/10/microplastics-found-90-percent-table-salt-sea-salt/
[7] https://phantomplastics.com/plastics-the-environment/

Sunday, 26 January 2020

High Performance Polymers: Suitable for Low Temperatures?






At this time of the year winter is all over our places and temperatures can get really frosty. In this post, we discuss the suitability of high performance polymers (polymers with continuous use temperature above 150°C) for lower temperature applications.


When writing down the requirements for your application during the material selection phase, most applications have a temperature range which needs to be fulfilled in order to ensure proper end use. In the automotive industry, for example internal combustion engines (ICE), have a temperature requirements ranging from -30°C to 140°C.


When screening the datasheet values of most plastics, room temperature properties such as mechanical, electrical and chemical properties indicate good resistance against environmental stress cracking. However, decreasing temperatures can lead to a brittle behavior with low values in failure stresses. Therefore, a material’s low temperature behavior also needs to be carefully taken into account during your material selection.


How to test the brittleness temperature of plastics and elastomers?


The brittleness temperature provides us information about the temperature at which brittle fracture is the dominant failure mechanism.


The test method ASTM D746-04 is usually utilized for measuring the brittleness temperature. The obtained temperature is usually found in the onset region of the glassy phase. It is rather difficult to obtain an exact temperature point. Accordingly, a brittleness temperature is estimated. This indicates a 50% probability of a brittle fracture to occur at this temperature.


ISO 974-2000 is another standard test method, which can be also be utilized. It is technically equivalent to ASTM D746-04 though. In case you want to test rubbers for impact brittleness, ASTM D 2137 is the preferred method.


Low temperature properties considerations


Application of rapid loads at room temperature can lead to the same effect of failure than having a higher load at lower temperature. This shows that apart of temperature, time and fatigue play an important role in the brittleness behavior of plastics.


Glassy vs. brittle


In general, polymers with a Tg above room temperature have a glassy state at room temperature. Examples are for instances PS, PMMA, and PET. These are easier to break since they are inherently more brittle. On the other hand, polymers which have a Tg below room temperature have a rubbery state at room temperature. These are, for example, PP and PE (LD, HD, LLDE), which are rather flexible and difficult to break at room temperature.


Fluoropolymers show a different behavior. PTFE has a Tg of 115°C. At room temperature as well as below room temperature one may think PTFE should be brittle. However, this is not the case due to its unique carbon-fluoro bond, which results also in a high melting point of 400°C. As a result, PTFE has good strength at higher as well as lower temperatures, below its Tg.


Service temperatures


The majority of applications have a service temperature range of -20°C up to 60°C and many commodity plastics are available to fulfill those ranges. There are low-temperature applications such as aircraft parts, oil rigs, industrial refrigeration, superconducting magnets, and liquid-helium devices, which are exposed to temperatures down to -270°C. Material selection becomes critical to prevent any part failure at such low service temperatures. At temperatures below -40°C, the choice for plastic materials becomes limited. In this temperature range, resistance to Liquid Oxygen (LOX) also becomes an extremely important application requirement.


LOX compatibility


Among different polymer families, high performance polymers such as fluoropolymers show good to excellent Liquid Oxygen compatibility. PTFE, FEP, and PCTFE show the best in class suitability, followed by PVDF. Altogether, fluoropolymers are good candidates for low temperature applications, since they are excellent insulators and have high chemical resistance.


Most important property of fluoropolymers at low temperatures is their ductility: when reaching the absolute zero temperature point (-269°C), the ductility of these polymers holds at approximately 1%. All in all, fluoropolymers are a good material choice for static seals at low temperatures.


Minimum service temperature of different high performance polymers


As we have already discussed, low temperatures are as challenging as high temperatures. This due to polymers showing brittle behavior, which can lead to fracture and crack formation in the final part. Besides fluoropolymers, other high performance polymers can be used at temperatures down to -50°C. For cryogenic temperature applications where high loads are involved, PAI and PI can also be used.


The graph below shows the minimum service temperature of different high performance polymers.

Summary
For most materials including plastics, low temperatures are a difficult environment. However, polymers such as PAI, PI and fluoropolymers can be a solution. In particular fluoropolymers, with their stable carbon-fluoro bonds, are suitable at extreme low temperatures. This in turn, supports designers to solve low temperature material problems in an efficient manner.


If you want to know more about fluoropolymers and why they are important in the future, you can find an article I wrote already here.



Thanks for reading & till next time!
Greetings, Herwig Juster

If you liked this post, share and like!
Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section
Check out also my personal webpage.



Literature:
[1] http://www.tangram.co.uk/TI-Polymer-Low_temperature_plastics.html