Dimensional Stability of Polymer Based Parts after Processing: 3 Considerations

 Hello and welcome back to a new blog post. Today we discuss three considerations for optimal dimensional stability of plastics parts after processing.

Polymer based parts have a dimensional stability which is not equal to that of metals. It can vary with several factors which we discuss in the following in more detail. If it is a critical part, this needs to be considered during the polymer material selection.

Definition dimensional stability

In short, dimensional stability means that the required dimensions are kept after processing and when the application is in use. Three considerations help to keep the dimensional stability of your part: moisture, mechanics, and thermal stability (Figure 1). 

Figure 1: Plastic part design - three considerations help to keep the dimensional stability of your part.

Consideration 1: Residual moisture and moisture uptake during use

General rule of thumb is that when materials are exposed to moisture, dimensional changes are likely to occur. In case your application has tight tolerance requirements, polymers with low moisture absorption should be taken. For example, an aliphatic Polyamide was specified for an application with tight tolerances. Due to the moisture uptake, part performance decreased and a replacement material is needed. In such a case, a semi-aromatic Polyarylamide (PARA) can be an alternative, since it has the lowest moisture uptake of Polyamides. There are also other polymers such as PEI, PPS, and PEEK, which have excellent mechanical, and moisture performance. PPS, PPA, and PEI can be used for applications, which are exposed to high temperature and moisture during the use of the application (water pumps in cars for example). Also during processing, keeping a maximum allowed moisture level is essential to not harm the polymer during processing. In this post, different maximum moisture levels after resin drying to ensure proper processing are shown.

Consideration 2: Mechanical strength

In case of structural applications, loading strength of the selected polymer is important and can influence the dimensional stability. For complete evaluation, short-term property data such as tensile and compression strength, together with long-term data such as tensile creep should be considered. Examples of high performance polymers which show high dimensional stability are PPS, PAI, and PEEK.

Consideration 3: Thermal stability

Temperature load can have a severe impact on the plastic part dimensions. Therefore, it is critical to evaluate the maximum use temperature and the continuous use temperature, together with the environment (air, water-glycol) of your application. For evaluation of the temperature impact, dynamic mechanical analysis (DMA) data, as well as head deflection data (HDT) of the selected polymers are helpful.

Overall, there are some factors, which influence the polymer part performance. In this post, I show you additional factors to consider for your plastic part design.

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

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

My YouTube channel

Literature: 

[1] https://apex-intl.com/2017/02/24/engineering-plastics-understanding-dimensional-stability-in-material-selection/

Decision Making in the Plastics Industry – Avoid the Survivorship Bias Trap

Hello and welcome to a new post. Today we have a look at a well-known cognitive bias that psychologists refer to as “survivorship bias” and how to use this information for better decision making in our daily plastics operation.

The focus on people, companies, or products that have themselves successfully established and forgetting about other important factors such as failure is referred to as survivorship bias.

Let us put this bias in relation to some examples

Analyzing of World War II bomber airplanes

Most famous example is the US Air Force dilemma of lost airplanes during World War II. They investigated the returning airplanes and found out that the wing tips, body and tail had the most holes. Their plan was to reinforce those areas for better protection. Luckily they had Mr. Abraham Wald as part of the Statistical Research Group (SRG) on their team. He explained to the military leader that this would be a terrible mistake since they did not look at the airplanes, which were shot down. The weakest parts are not the wing, tail or body. It is the engine and once you get a hit there, the airplane will hit the ground quite fast.

Example plastics industry

Looking at the engineering polymer Polyamide, it is a well-established and successful material, which is used in lots of applications. Material manufacturers, which have their focus on other polymer resins, may want to add such Polyamide resin and compounds to their portfolio to gain a share of the cake. However, it is better to look at companies which failed to enter the market place with their new Polyamide resin or compounds, followed by companies which have mediocre sales and profit numbers when they entered with their new Polyamides. Tendency is to look at the market leaders and established companies. 

In conclusion, it pays off to look at not successful launches of products too and not only the successful ones. It is harder to find the stories of failing products, however it is worth taking the extra step and fighting the survivorship bias. 

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

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

My YouTube channel

Literature

[1] http://blog.idonethis.com/7-lessons-survivorship-bias-will-help-make-better-decisions/

Engineering Biopolymers - Using the 3P-Triangle to Select Them

Hello and welcome to a new post. Today I show you how you can use the 3P (price, performance, and processing)-triangle to select engineering biopolymers.

An overall summary on bio-based polymers can be found in this three part bio-based polyamide series.

Motivation of Engineering Biopolymer Usage

Engineering polymers represent much lower volumes compared to commodity plastics and bio-derived engineering polymers represent a niche within this engineering plastics segment. Packaging materials are much more visible to consumers on a daily basis compared to for example under the hood automotive applications. Therefore, research focus was more directed towards replacing high volume single use polymers with recycled and bio-based materials solutions. However, consumer perspective is shifting towards all different polymer applications to have recycled content or be bio-based. In addition, more and more OEMs demand recycling and bio-based content in their plastic parts. Material suppliers work on drop-in bio-based solutions for traditional polymer applications. One way are hybrid materials out of a 100% bio based polymer blended with a traditional engineering polymer such as PC (Table 1). Often biopolymers show a brittle behaviour. Blending a bio-copolyester such as Polybutylene adipate terephthalate (PBAT) with a Polylactic acid (PLA) will result in a ductile (derived from PBAT) and stiff (derived from PLA) material. Polyamides are among the most used engineering polymers and there are already several short- and long chain bio-based Polyamides available, where one or both monomers are derived from bio sources (Table 2).

Table 1: hybrid materials out of a 100% bio based polymer blended with a traditional engineering polymer

Table 2: overview bio-based Polyamides

Material Selection – Visual approach using the 3P-triangle

The price, processing and performance triangle allows to compare similar plastics and how well they measure up against each other in a visual way. Incorporation of environmental sustainability values is done over “processing” where the nature of feedstock is included and over “performance” which takes the materials impact during use-life and recycling phase.

With bio-based engineering polymers, the balance between fulfillment of rigorous property requirements of the target application and life-cycle impact need to be found during material selection. I developed three steps to achieve such a balance.  

1. Step: We define the maximum allowed environmental impact of the material which can be provided by the customer (numerical value – example: GWP)

2. Step: Incorporate this value into the semi-quantitative polymer comparison triangle together with price, processing and performance.

3. Compare different polymers to each other and make a decision which to investigate further

Example: injection / blow moulded water bottle

In the following, an example helps to better understand the 3P-triangle approach. For an injection moulded water bottle, the incumbent material is most of the times PET and can be placed more towards the price vertex due to its low costs. As a next alternative, bio-based PET can be used  which improves towards the processing vertex. PLA, on the other hand will improve processing, however will increase material costs. This may change in the future too, due to more availability of bio-based materials. Altogether, the 3P-triangle is a tool which can be put into your polymer material selection tool box and supports selecting bio-based polymers.

I made also a short training video on this topic: 

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

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

My YouTube channel

Literature: 

[1] Plastics and Sustainability: Towards a Peaceful Coexistence between Bio-based and Fossil Fuel-based Plastics, Michael Tolinski

Polymer Material Selection - My New Book is Coming Soon!

 

Polymer Material Selection - my new book

Hello and welcome to this project reveal post. 

My latest project is a book called *Polymer Material Selection*.

Currently I'm previewing it and I can tell you it looks already promising.

In the book I will show you how to select polymers in a systematic way using my polymer selection funnel method.

We will go over the entire selection process, from how to establish part requirements, gather material data, rank different polymers all the way to how to select a vendor after selecting the polymer.

After reading the book, you know everything you need to select the optimal polymer material for your project, save thousands of dollars by preventing part failure, and have fun in the process.

Leave your email on my site to be the first to be informed as soon as the book launches. 

Sign up here to be informed about the book launch

I'll exclusively send you my product requirement checklist which is part of the polymer material selection funnel.

Thank you and stay tuned.

Greetings and #findoutaboutplastics

Herwig 

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

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

My YouTube channel

Bio-Based Polyamides – Part 3: Sustainability Facets (Bio Sourcing, LCA, Certifications) and Example Polyamide 6.10

 Hello and welcome to part 3 of our bio-based Polyamide series. 

Check out part 1: PA 5.6 and 5T (Chemical Structure, Production, Properties, Applications, Value Proposition) here and part 2: Short and Long Chain Aliphatic Polyamides (PA 6, PA 11, PA 6.10, PA 10.10) here. 

In this post, I focus on three topics under the sustainability umbrella: bio sourcing, LCA, and certifications

Bio sourcing for polyamides

Materials based partially or complete on renewable biomass fall into this definition. Castor beans, trees, and crops are major examples of this category. Fossil based or biomass based materials have all carbon atoms in their back. This allows a distinction of bio-based polyamides in terms of their bio content. For functional groups and inorganic groups, this is not possible and a mass-based approach is used.

ASTM D6866 and EN 16640 are used for the determination of bio-based carbon content in polyamides and other polymers. Base working principle is the radiocarbon analysis which allows to determine the carbon fraction (C14 measurement) [1].

Life Cycle Assessments

Life Cycle Assessments (LCAs) are used to identify the environmental impact of a certain material or produced good thorough their life cycle and currently two major standards are used for LCAs: ISO 14040:2006 (Environmental management — Life cycle assessment — Principles and framework) and ISO 14044:2006 (Environmental management — Life cycle assessment — Requirements and guidelines).

The structure of a LCA contains a scope section and the impact categories. Within the scope section distinctions between three variations is done: gate-to-gate, cradle-to-gate, and cradle-to-grave. For polymers the preferred scope is cradle-to-gate and this scope covers all processes as well as environmental impacts (buying feedstock and making the polymer). Often high performance bio-polyamides are tailored to the specific customer requirements by compounding selected additives into the base polymer. End-of-life disposal is more complex and harder to access for the polymer manufacturer. Environmental impact can be estimated using following metrics:

-greenhouse gas emissions,

-ozone depletion,

-human toxicity (cancer effects),

-human toxicity (non-cancer effects),

-photochemical ozone formation,

-ionizing radiation, particulate matter,

-terrestrial acidification,

-terrestrial eutrophication,

-marine eutrophication,

-ecosystem toxicity,

-resource depletion (fossil),

-resource depletion (abiotic),

- and water resource depletion.

For customers and polymer manufacturers, the global warming potential (GWP expressed over CO2 equivalent) is the most interesting value as well as the most frequently requested value within the LCA report.

Example Polyamide 6.10

Manufacturing of a long chain Polyamide PA 6.10 is made as shown in Table 1 by sebacic acid (C10H18O4) and HMDA (C6H16N2). For bio-based Polyamide 6.10, the sebacic acid is bio-sourced. In general, bio-sourced products have a lower carbon footprint since they contain locked atmospheric (biogenic) carbon in the product. In case of combustion or degradation of sebacic acid (based on castor oil) at the end-of-life, this would result in approximately 1.5 kg of CO2 equivalent release. The whole Polyamide 6.10 would lead to a release of 2.2 kg of CO2 equivalent. The total carbon footprint (from raw material, polycondensation of Polyamide minus the biogenic carbon of sebacic acid) of Polyamide 6.10 is 4.6 kg Co2/kg. In case Polyamide 6.10 is made 100% out of petrochemicals, the carbon footprint would be 7.3 kg CO2/kg. The aforementioned 2.2 kg of CO2 equivalent are most probably released before 100 years since end-of-life is reached before 100 years (GWP calculations use a 100 year time frame).

Table 1: overview of bio based Polyamides

Certifications

As already mentioned under the section “Bio-sourcing”, radiocarbon dating is a good method to distinguish between fossil based carbon and bio based carbon. The C14 isotopes for fossil based material display a different set compared to bio based ones. Standard is DIN ISO 10694. Other certifications are ISCC PLUS and REDcert². Both are leading sustainability certification systems for bio-based and recycled materials. Certifications and proper labeling get more and more important since the end customers are demanding such distinctions more and more.

What are some trends in 2022?

We see more and more the use of recycled plant based oils and fats to produce Polyamides which reach a carbon footprint of only 0.5 kg Co2/kg [2]. Also, 100% bio-based carbon content is possible with Polyamides. PA 11 uses only 11-aminoundecanoic acid which can be won from castor oil. This enables a 100% bio-based carbon content. Also PA 5.10 can be produced in a 100% bio based carbon way using pentamethylene diamine and sebacic acid out of corn and castor oil.

Thanks for reading and #findoutaboutplastics

Greetings, 

Herwig 

Interested to talk with me about your plastic selection, sustainability, and part design needs - here you can contact me 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

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

My YouTube channel

Literature: 

[1] https://www.findoutaboutplastics.com/2021/07/biopolymers-difference-between-bio.html

[2] https://akro-plastic.com/compound-overview/akromid-next/

[3] Stephan Kabasci: Bio-Based Plastics: Materials and Applications