Thursday, 27 August 2020

Design Properties for Engineers: Transition Temperatures (Tg, Tm, CUT) of High Performance Polymers

Today we discuss the major thermal transition temperatures of high performance polymers. Details on alpha, beta, gamma and delta transitions are explained in this blog post. Amorphous thermoplastics show a linear behavior up to the glass transition temperature. Semi-crystalline polymers have a two-step behavior: the first drop in mechanical values can be observed at the Tg, followed by the second drop at the crystal melt temperature. The structural crystal elements can resist much more the temperature increases. 

In the graph below, the glass transition and crystal melt temperature of different high performance polymers are shown. It can be seen that polyimides (PI, PAI, PBI) outperform other polymers. Checking the glass transition temperature is important during the material selection when you decide on the suitability of the polymer to fulfill the application service temperature. Thermoplastics show already a drop in mechanical performance at the glass transition area. 

Transition Temperatures of High Performance Polymers

PTFE, PAI, PBI, and PI are not melting when the glass transition or crystal melt temperature is reached. These polymers show a particular molecular structure (thermoset-like). Nevertheless, using such polymers above their continuous use temperature is not good since thermal-oxidative degradation starts.

Thank you for reading and #findoutaboutplastics

Greetings, 
Herwig Juster

If you liked this post, please share and like!

New to my Find Out About Plastics Blog – check out the start here section



Title of the document Enroll Now!

Wednesday, 12 August 2020

Design Properties for Engineers: Thermal Conductivity of High Performance Polymers

 In this blog post we discuss the thermal conductivity of filled and unfilled high performance polymers.

Thermal conductivity is a key figure to show the thermal transfer of different materials. Polymers have compared to metals (45 W/mK average value) a very low thermal conductivity. Semi-crystalline polymers have a higher thermal conductivity compared to amorphous polymers since the crystalline regions allow a better heat transfer. In amorphous polymers, polymer chains are unstructured and this leads to a lower thermal conductivity. Furthermore, thermal conductivity is higher in processing (= orientation) direction than perpendicular to it. This can be observed in injection moulding parts with thin wall thickness.

Unfilled high performance polymers behave similar in their thermal conductivity and not many differences can be observed (Table 1). Thermal conductivity can be immediately increased by adding carbon fiber or graphite (Table 2). Improved thermal conductive plays an important role in high temperature applications, where an improved heat transfer between metal housing and plastic part leads to better mechanical part endurance. Therefore it is important to consider such a requirement during the polymer material selection process.

Table 1: Thermal conductivity of unfilled high performance polymers

Table 2: Thermal conductivity of filled high performance polymers

Thank you for your attention and #findoutaboutplastics
Best regards, 
Herwig 

If you liked this post, please share and like!

🔥 Check out my new online course "Polymer Material Selection incl. free preview"

New to my Find Out About Plastics Blog – check out the start here section

Friday, 7 August 2020

What is the Difference Between an Industrial Designer and a Design Engineer? incl. Polymer Part Design Checklist [Guest Post]



Our guest author and polymer design engineer Vatsal Kapadia presents in this post the difference between an industrial designer and design engineer. This post reflects his personal experiences in this area and he wants to share them with us. 
As an engineering tool for your next plastics part project, we worked on a Polymer Part Design Checklist which can be found in the end of this post.

What is the difference between an Industrial Designer and a Design Engineer? 

An Industrial Designer creates the concept for a part with major emphasis on aesthetics and innovation. A Design Engineer designs a part considering functionality. Thus, dimensions, tolerances and limits are established according to the technical requirements of the envisaged product. 

A refined part is the one which satisfies all expectations including performance and appearance and is commercially economical to produce. Different other factors contribute to the dimensions and properties of a part, i.e. utilized machines, processes and skill level of workers. 

Dimensions and tolerances are fundamental for manufacturing any polymer-based part. This leads us to the following question: How do you choose a tolerance? You should start by consulting the tolerance chart available for the materials you want to produce your part with and review these together with the manufacturing team. Resulting manufactured prototypes shall subsequently be inspected for obtained dimensions. In the final drawing sheet, all the tolerances along with the dimensions in an orthographic view are necessary. Such process is crucial for concept to completion or design to manufacture. Concepts of GD&T (Geometric Dimensioning and Tolerance system) have allowed designers to work more precisely with datum points facilitating efficient exchange of part’s design data between involved parties as well. 

A foolproof design engineer and/or tool designer shall also be thorough when it comes to material selection as the choice of the right material is crucial for part design and manufacturing. Important material properties influencing part’s design include e.g. mechanical, thermal, electrical and chemical properties, shrinkage factor, surface finish and material recyclability. Selection of a suitable processing technique accordingly completes the whole part design process. 

Finally, I would like to share a non-technical experience: Cooperation and communication between industrial designers, design engineers and tool designers can save time by ensuring that the product is not only accurately designed to accomplish its functionality, but also that it can be molded and assembled. 

The following Polymer Part Design Checklist will allow you to gather all necessary information about the part. Having such a checklist not only allows the present job work to be systematic, but it should also help in the future when a part failure occurs in any real life application.

Thank you and #Findoutabouplastics!
Vatsal & Herwig 



If you liked this post, please share and like!

🔥 Check out my new online course "Polymer Material Selection incl. free preview"

New to my Find Out About Plastics Blog – check out the start here section



Tuesday, 28 July 2020

Holiday Experiences: How Plastics Protect Everyday Life in Mexico’s Yucatán Peninsula

Holbox, Mexico - bottle collection box in the shape of a fish

Before the Covid-19 pandemic stroke in Europe, especially in Italy, Spain, France and Germany, we were far away on holiday in Mexico. It was end of February 2020 when our holiday started and two weeks later, Italy and Germany announced the restriction of going out to flatten the infection curve. The Covid crises spread all over Europe causing the healthcare systems to be highly exhausted.

During our holiday, I made several observations on how plastic-based products facilitate the life of people in areas where jungle dominates and infrastructure is limited. We visited the island of Holbox, located in the north east of Yucatan surrounded by the Gulf of Mexico. It is connected to the mainland over a fair, starting from Chiquila.

Holbox, located in the north east of Yucatan surrounded by the Gulf of Mexico

As you can imagine, things in a well-established system on the mainland, can work on an island completely different. Drinking water supply is a major challenge on islands. Here, plastics packaging plays a major role to ensure fresh drinking water supply. In the example of Holbox island, drinking water supply is ensured by a daily truck loaded with 10, 18 up to 20 liter water bottles coming from Chiquila. Once arrived on the island, the truck drives to the major square and people all over the island come to pick up such bottles to be used in their homes. They also bring their used bottles back for recycling purposes. Most of the bottles are made out of Polyethylenterephthalate (PET). The wall thickness is increased compared to a standard 1 liter PET bottle, since more mechanical strength needs to be provided considering transportation as well as hot climate aspects. One time we saw a boy who just had picked up such an 18 liter bottle and was carrying it home on his bicycle.

Drinking water supply is ensured by a daily truck loaded with 10, 18 up to 20 liter PET water bottles

There are also creative ways on how to collect the PET bottles. One example is the collection box in the shape of a fish which is made of a metal net, similar to a fence. It should remind that littering is harming the sea and its animals. A picture of the collection box with myself is at the beginning of this post.

Rain water tanks
Apart of PET bottles filled with fresh water, one can also see on most houses allover Mexico, rain water collection tanks. Those are mainly provided by a company called Rotoplas. However, rain water collection is not the only reason to have such plastic tanks. Most water pipes are gravity fed or very low pressure fed for the distribution of water to and within the house. Therefore, most homes pump additional water into roof tanks as well. This allows having a good pressure for showering and doing the laundry, as well as other activities. The tanks are made by rotational moulding and in most cases Polyethylene (PE) powder is used. Rotational moulding allows you to make hollow plastic parts. The moulding tool represents the outer wall of your final product. The tool is loaded with the PE powder and closed. The tool starts rotating and will be heated at the same time. The PE melts and distributes along the tool walls to form the outer layer of the product. After cooling down, the tool is opened and the product which is in this case a rain water collection tank can be used. The big advantage is to make hollow parts.
Water collection tank on the rooftop of houses.

In both cases, plastic products provide access to fresh water for many people in an efficient, durable, save and thus cost effective way. This is valid if you think of utilizing other materials such as glass, metal or wood for the described purposes.

On our returning trip from Mexico to Germany, Coronavirus was already spreading. The north of Italy was heavily affected, as well as Germany, followed by France, Spain and the UK. However, plastics are playing a crucial role in fighting the Coronavirus.

Following are a few examples how plastics are protecting us during the pandemic and beyond:
 - Packaging of food: especially vegetables and fruits are exposed to liquids released when sneezing and blowing your nose.
 - Single-use plastic bags: the one time use prevents to spread germs and viruses. - Medical devices protecting equipment: face shields, masks, ventilator components, intubation boxes are examples where plastics play a crucial role.
 - 3D printing filaments: all over the economy, companies provide their additive manufacturing resources to produce e.g. the face shield holding frame.

Although there are several plastic bans on the way such as the single-use plastics ban directive of the European Union [1], it could be demonstrated in several life cycle assessment studies that plastics are the greenest solution [2-4]. In these studies, e.g. single-use plastic bags are the best and cotton based bags are the worst due to a very energy-intensive life cycle. 

My food for thought: we do not have a waste problem but a littering problem. This means that people are to blame for throwing away the plastics into the nature and not the materials itself. 

Thank you for reading and till next time! 

Best regards,
Herwig

If you liked this post, please share and like!

🔥 Check out my new online course "Polymer Material Selection incl. free preview"

New to my Find Out About Plastics Blog – check out the start here section

Literature: 
[1] https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=LEGISSUM:4393034&rid=1
[2] https://phantomplastics.com/plastics-the-environment/ https://belu.org/when-the-answer-to-your-anti-plastics-challenge-is-in-fact-plastic/
[3] Civancik-Uslu, et.al.: Life cycle assessment of carrier bags and development of a littering indicator, Science of the Total Environment 685 (2019) 621–630
[4] Our World in Data, Danish Environmental Protection Agency, 2018