Tuesday, 1 April 2025

Nature is built on 5 Polymers. Modern life is built on over 200 different Polymers - How to select the right one?

Hello and welcome to a new post. Today I would like to start with a quote of mine: 

"Nature is built on 5 polymers. Modern life is built on over 200 different polymers. Therefore, optimal polymer selection is key for successful applications and to prevent plastic art failure in the long run." 

"Nature works with 5 polymers," is a statement from Mrs. Janine Benyus and reflects a key concept in her advocacy for biomimicry. It highlights the efficiency and elegance of natural systems compared to human industrial processes. Here's a breakdown of what she means:

Polymers in Nature:

Polymers are large molecules made up of repeating smaller units. They are the building blocks of many materials. Nature primarily uses a limited set of these polymers to create a vast array of structures and functions.

These "five polymers" generally refer to:

  • Cellulose: Found in plant cell walls, providing structural support. Cellulose was used in the past to create one of the first human made plastics: Celluloid. It is made by mixing nitrocellulose and camphor.
  • Chitin: Forms the exoskeletons of insects and crustaceans, as well as fungal cell walls.
  • Lignin: A complex polymer that provides rigidity to plant cell walls, particularly in wood.
  • Proteins: Versatile polymers that perform a wide range of functions, from structural support to enzymatic activity.
  • Nucleic acids (DNA and RNA): Carry genetic information.
5 Natural Polymers: Cellulose, Chitin, Lignin, Proteins and Nucleic Acids [1].

Biomimicry Application:

Benyus's statement encourages us to look to nature for inspiration in materials science.

By mimicking the way nature uses these polymers, we can create materials that are:

  • Stronger
  • More durable
  • More sustainable
  • Easier to recycle.

In essence, "Nature works with five polymers" is a powerful reminder of nature's ingenuity and a call to action for us to learn from its wisdom.

Modern life is built on over 200 different polymers - How to select the right one? 

An important step in the selection journey are the mastering of the what i refer to as the 6 Polymer Material Selection skills (6 POMS skills; Figure 1): 
P- Properties: Understanding key polymer properties
P - Part Design: Defining Application Requirements for Plastic Part Design
P - Polymer material values: Translating application requirements to qualitative and quantitative material values
P - Process: Polymer material selection process
P - Performance: Evaluation of material and part performance
P - Plastic supplier: Selection of material and supplier

Figure 1: Overview of the 6 Polymer Material Selection skills. 

Check out the detailed description of the 6 POMS here

In order for you to assess where you are currently ranking at the 6 POMS skills, I created a simple scorecard consisting out of 26 Yes / No questions and after completing the questionnaire, you receive an overall POMS score and detailed scores for each of the six critical elements of polymer material selection.

Also, you get a customised report with actionable steps to immediately start improving your POMS score and your impact in the field of polymer material selection.

A quick 5-step selection guide
Selecting the optimal thermoplastic material can be challenging and my aim is to provide you with a practical guide which leads you fast through the selection journey. 
Improper selection of plastics for the application is the leading cause for plastic part failure and since most parts fail along weld lines or knit lines, optimal mould design including filling and processing of the part are crucial too. 

Apart from the 200 polymers,  there are almost 100 generic “families” of plastics and additionally blending, alloying, and modifying with additives results in 1,000 sub-generic plastic types. Also, selecting the wrong polymer for your product may result in additional financial resources, since the selection process needs to be repeated (including making new tools) or even worse, product failure leads to claims and recalls. The following guide will help you to prevent the major mistakes and if you want to be sure, you can always reach out to a plastic expert to review your selection or help you to select the optimal grade.

What are the 5-steps (download here the guide): 

1. Define Application Requirements: In the first step we lay out all the application requirements and focus on Function, Loading Conditions, Environmental Factors, Regulatory Requirements, and Processing Considerations. A suitable acronym for this step is called FLERP:  F- Function; L- Loading conditions; E - Environmental Factors; R- Regulatory requirements; P- Processing requirements.

2. Identify Candidate Materials: Based on your application requirements, research potential engineering plastics that possess the necessary properties. Material selection charts and dashboards, supplier websites, and technical data sheets can be helpful resources. Consider factors like: Mechanical properties (short- and long-term; as a function of time and different temperature levels), thermal properties, chemical resistance, electrical properties, processing characteristics, and cost. 

3. Evaluate Material Performance: 
Carefully review technical data sheets from potential suppliers to understand the specific properties of different plastic grades within a material family. Most of the time only a single temperature is covered (room temperature). This is useful for comparing different material data sheets to each other, however for part design it has its limitations. Also, consider Multipoint Design Data which helps to think in time-dependency and temperature-dependency behaviors. Graphically such behaviors can be better accessed. Utilizing CAE software to simulate the filling of your part as well as the performance of your design using different material options.

4. Additional Considerations: Consider processing methods and cost. Evaluate environmental and regulatory factors.
Consider the material availability in order to ensure the chosen material is readily available from reliable suppliers. Additionally, evaluation of the environmental impact of the material, including its recyclability or biodegradability, if applicable can be done. Long-term performance check is needed to check the  material's resistance to degradation and expected lifespan in your application. 

5. Testing and validation. 
In the last step, prototyping is done. You can start by obtaining samples from material suppliers for simple analysis.
Next is to create prototypes using the previous identified candidate materials to test performance under real-world conditions. After concluding the final tests, final material selection can be done and a suitable supplier of the material chosen. 

6. Bonus Consult with Plastic Experts and Material Suppliers:
Discuss your application requirements with experienced polymer engineers and material suppliers. Seek recommendations based on their expertise and access to the latest materials.

My Polymer Selection Funnel Method

For a more detailed selection approach, as mentioned before,  I created the Polymer Selection Funnel methodology (POMS-Funnel).  Figure 2 presents the four different stages of the material selection funnel as well as the tools we can use to facilitate the selection. We can use this as a guideline throughout the selection journey.

Figure 2: Overview of the Polymer Selection Funnel method. 

Funnel stage 1: Material selection factors
In this first stage we map out the true part functions and material requirements. After this we translate the requirements into material selection factors.

Funnel stage 2: Decision on thermoplastic or thermoset
After translating the requirements into material selection factors, the first decision is made:
Which is the most suitable polymer chemistry to fulfill the listed requirements and selection factors? Thermoplastics or thermosets?

Funnel stage 3: Selection discussion with worksheet (qualitative matrix analysis)
The third funnel stage represents a core element in the whole material selection funnel. It is a detailed selection discussion with a worksheet. I call it the decision matrix analysis and it ranks all of the pre-selected polymers. The decision matrix analysis consists of five steps. The base calculation principle is a scoring of each of the pre-selected materials for each of the material selection factors. In the end we add up all weighted scores for each material. The material with the highest score is most suitable for selection and further investigation in the fourth stage.

Funnel stage 4: Testing, selection of material and vendor
In the last funnel stage, we would like to know in detail how the materials with the highest scores perform as a final part in a system of plastic parts or as a single plastic part alone. After all the tests are done and the material has passed all tests, commercial conditions with the material supplier can be finalized and first small serial production can start. 

I created a dedicated page for Polymer Material Selection which contains all you need for your material selection, from taking the scorecard test, online selection tools, and examples which have used the POMS funnel method. 

If you want to see the POMS funnel method in action, check out this example: Base plate of a filter coffee machine.

Conclusion

In material selection, there is no "one-size-fits-all" solution. The optimal material will depend on the unique needs of your specific application. A balance between performance, cost, and processing is often necessary. By following a five step guide or the POMS funnel method, leading to a thorough evaluation, you can make an informed decision and select the optimal engineering plastic for your project!

Literature: 
[1] https://www.amazon.de/-/en/Janine-M-Benyus/dp/1094025003
[3] https://www.polymermaterialselection.com/

Saturday, 15 March 2025

Metal Replacement with Plastics: A 5-Step Roadmap


Hello and welcome to a new blog post. Today I present to you a metal replacement roadmap which contains five major steps and when all steps are followed, success in metal replacement will be secured. 

Why Change from Metal to Plastic?

There are many reasons to consider changing from metal to plastic. Some of the most important benefits include:

  • Part consolidation and function integration: Plastic parts can be designed to integrate multiple functions into a single part, which can save on manufacturing and assembly costs.
  • Weight saving: Polymer have a lower density compared to metals, so switching to plastic can help to reduce the weight of products.
  • Lower processing costs: Plastic parts can be manufactured using a variety of processes, such as injection moulding, which can be less expensive than metal forming processes.
  • Fewer or no secondary operations: Plastic parts often do not require secondary operations, such as painting or finishing, which can save on manufacturing costs.
  • Freedom and flexibility of design: Plastic can be molded into a variety of shapes and sizes, which gives designers more freedom to create innovative products.
  • Corrosion resistance: Plastic is resistant to corrosion, so it is a good choice for products that will be used in harsh environments.
  • Surface aesthetics, color aspects, markability: Plastic can be easily colored and marked, which makes it a good choice for products where aesthetics are important.
  • NVH reduction: Plastic can help to reduce noise, vibration, and harshness (NVH) in products.
  • Possibility to reduce the product carbon footprint; lead free material solutions

Metal to plastic conversion roadmap

As outlined before, replacing metal components with plastic ones offers several benefits, including reduced weight, lower costs, and improved design flexibility. However, the process requires careful planning and execution to ensure optimal results. This roadmap (Figure 1) outlines the key steps involved in efficient metal replacement:

1. Metal Part Identification

2. Polymer Material Selection

3. Design and Engineering

4. Prototyping

5. Production

Figure 1: 5 Step Metal to Plastic Conversion Roadmap.

What are the 5 steps leading to successful metal to plastic replacement?

1. Metal Part Identification

  • Identify the specific metal components targeted for replacement.
  • Define the objectives and required outcomes for the replacement.
  • Outline the preliminary requirements and boundary conditions for the new plastic component.

2. Polymer Material Selection

  • Choose the most suitable polymer material based on the application requirements.
  • Consider factors such as mechanical properties, chemical resistance, and thermal stability.

3. Design and Engineering

  • Develop a detailed CAD design for the plastic component.
  • Conduct CAE virtual testing and simulations to evaluate the design's performance.
  • Refine the design based on the simulation results.

4. Prototyping

  • Create a prototype tool for the plastic component.
  • Produce molded parts using the selected polymer material.
  • Perform thorough testing on the parts to ensure they meet the required specifications.

5. Production

  • Release the final part design for serial production.
  • Manufacture the plastic components at scale.

By following this roadmap, you can ensure a smooth and successful transition from metal to plastic components.


How a metal replacement project can look like

Example Medical Device Metal replacement  

The following example explains the replacement of surgical retractors (Figure 2), used in total hip replacement replacement (THR) surgeries as a case study for metal-to-plastic conversion. In general, replacing metal with plastic can improve performance and reduce costs in medical devices. High-performance polymers such as PEEK, Polysulfones, and PARA offer similar strength and stiffness to metals, with added benefits.

Figure 2: Surgical hip retractor as an example of metal-to-plastics conversion [1].

1. Metal Part Identification
Orthopedic surgery retractors are traditionally made from metal due to the high strength and stiffness required. The document provides a comprehensive account of converting both single-use and reusable retractors to polymer-based designs using polyarylamide (PARA) and polyaryletherketone (PAEK), respectively.

2. Polymer Material Selection
For medical devices, essential performance requirements include chemical resistance and the ability to withstand sterilization processes, such as steam autoclaving or gamma radiation.
Material selection for both single-use and reusable retractors involves aligning with boundary conditions related to sterilization requirements and usage cycles. 

PARA (Ixef GS-1022), reinforced with 50% glass fiber, is selected for single-use retractors due to its exceptional strength, compatibility with gamma radiation sterilization, and superior surface finish. It delivers performance levels comparable to stainless steel (in this case 17-4 steel)  and can be injection molded, eliminating machining processes and reducing costs.

For reusable retractors, PAEK (AvaSpire AV-651 GF30) is the material of choice, offering a high stiffness-to-weight ratio, hydrolytic stability at elevated temperatures, chemical resistance, and durability even after repeated exposure to disinfectants and steam sterilization. Its ease of processing through injection molding and design versatility further highlight its suitability.

3. Design and Engineering
To replicate the stiffness of metal counterparts in plastics, adjusting the area moment of inertia through design modifications, such as using rectangular geometries or adding ribs was needed. Advanced design using computer-aided engineering (CAE) leverages plastic’s inherent advantages to enhance aesthetics and ergonomics, improving the overall device performance and user experience. A notable design modification for the hip retractor includes optimizing the handle for improved grip and stiffness.

4. Prototyping
Prototyping is crucial in evaluating the feel and functionality of new designs, with 3D printing techniques like selective laser sintering (SLS) employed to create initial prototypes. Validation processes for single-use and reusable plastic retractors involve testing to ensure performance metrics match or surpass those of the original steel retractors. Both plastic versions offer significant weight reduction, decreasing the overall weight of surgical equipment. Additionally, transitioning to plastic reduces the cost of reusable retractors by half and enables economically viable single-use designs.

5. Production
Manufacturing decisions favor injection molding for its cost-effectiveness in large volumes, design flexibility, and quick production turnaround, particularly given the estimated demand for hip retractors over three years.

Metal replacements with high-performance polymers in the medical industry are expanding. Plastic material suppliers, manufacturers, and designers are increasingly focusing their efforts on integrating plastics into medical device designs. Through this transition, the industry aims to meet the dual objectives of enhancing device performance and reducing costs in response to the evolving landscape of healthcare and technology.

Conclusion

Replacing metal components with plastic ones offers several benefits, including reduced weight, lower costs, and improved design flexibility. However, the process requires careful planning and execution to ensure optimal results. The discussed 5-step roadmap outlines the key steps involved in efficient metal replacement.

Interested in assessing the feasibility of metal replacement in one of your components?
Please reach out to me here.

Check out my other metal replacement articles: 

Literature: 
[1] https://www.meddeviceonline.com/doc/medical-device-metal-to-plastic-conversion-in-steps-0001
[2] https://www.findoutaboutplastics.com/2020/02/metal-replacement-with-polyarylamide.html
[3] https://www.syensqo.com/en/product/ixef-gs-1022-wh01




Friday, 14 March 2025

Polycaprolactone (PCL): A Versatile Polymer for Prototyping and Small-Scale Modeling

Hello and welcome to a new post. As a polymer engineer, you'll encounter a vast array of materials, each with unique properties suited for specific applications and systematic polymer material selection is key to success. Polycaprolactone (PCL) stands out as a particularly interesting and useful thermoplastic polyester, especially in the realm of prototyping and small-scale modeling. Let's delve into its key characteristics and advantages.  

Polycaprolactone: Low-cost, biodegradable, and incredibly versatile: PCL is a hidden gem in polymer engineering.

What is Polycaprolactone (PCL)?

PCL is a biodegradable, semi-crystalline polymer with a low melting point (around 60°C). This low melting point is a defining feature, making it incredibly easy to process and manipulate using simple techniques. It's synthesized through ring-opening polymerization of ε-caprolactone.   

Key Characteristics:

  • Low Melting Point: This is perhaps PCL's most significant advantage. It allows for shaping and molding using hot water, heat guns, or even just hand pressure.
  • Biodegradability: PCL degrades through hydrolysis of its ester linkages, making it environmentally friendly compared to many other thermoplastics. The degradation rate can be controlled by varying the molecular weight and crystallinity.   
  • Biocompatibility: PCL is non-toxic and biocompatible, making it suitable for medical applications, including drug delivery and tissue engineering.   
  • Flexibility and Toughness: While relatively soft, PCL exhibits good flexibility and toughness, allowing for the creation of durable prototypes.
  • Ease of Processing: PCL can be processed using various techniques, including melt extrusion, injection molding, and 3D printing (specifically Fused Deposition Modeling - FDM).
  • Solubility: PCL is soluble in hot water and in various organic solvents, such as chloroform, dichloromethane, and toluene, which can be useful for solution processing and surface modifications.   

Advantages for Prototyping and Small-Scale Modeling:

1. Rapid Prototyping:

Due to its low melting point, PCL allows for quick and easy modifications. You can rapidly iterate designs by simply reheating and reshaping the material.   

This makes it ideal for early-stage prototyping where speed and flexibility are crucial.

2. Low-Cost Modeling:

PCL is relatively inexpensive compared to many engineering plastics, making it a cost-effective option for hobbyists, students, and small businesses.

The simple processing requirements also reduce the need for expensive equipment.

3. "Hand-Formable" Properties:

The ability to shape PCL by hand using hot water or a heat gun makes it incredibly versatile.

This is particularly useful for creating complex shapes or intricate details that may be challenging with other materials.

4. Educational Tool:

PCL is an excellent material for educational purposes, allowing students to experiment with thermoplastic processing and learn about polymer properties.

It's safe and easy to use, making it suitable for classroom demonstrations and hands-on projects.

5. 3D Printing Applications:

PCL can be used in FDM 3D printing, enabling the creation of complex geometries and functional prototypes.   

It is often used in biomedical 3d printing applications.   

6. Mould Creation:

Because of its low melting point, it can be used to create moulds for other materials that have a lower melting point.

Applications in Prototyping and Modeling:

  • Conceptual Models: Quickly creating tangible representations of design ideas.
  • Fit Testing: Verifying the fit and functionality of components.
  • Ergonomic Studies: Assessing the comfort and usability of products.
  • Custom Tooling: Creating custom tools and fixtures for specific tasks.
  • Art and Sculpture: Sculpting and molding intricate designs.
  • Medical Models: Creating anatomical models for educational or surgical planning purposes.

Considerations:

PCL's low melting point can also be a limitation in high-temperature applications. It is relatively soft, so it may not be suitable for applications requiring high rigidity or strength. Long term creep can also be a factor to consider.

Conclusion:

Polycaprolactone, the polymer behind products such as Polydoh, Polymorph,  Re-Form,  Plastimake, and NiftyFix is a valuable material for prototyping and small-scale modeling, offering a unique combination of ease of processing, biodegradability, and biocompatibility. Its low melting point and "hand-formable" properties make it an excellent choice for rapid prototyping, educational purposes, and various creative applications. As a polymer engineer and student, exploring the properties and applications of PCL can significantly expand your materials knowledge and practical skills.   

Thanks for reading and #findoutaboutplastics

Greetings

Literature: 
[1] https://www.researchgate.net/publication/366581952_POLYCAPROLACTONE_THE_FORGOTTON_POLYMER
[2] https://www.atamanchemicals.com/pcl-solid_u30611/
[3] https://taylorandfrancis.com/knowledge/Engineering_and_technology/Chemical_engineering/Polycaprolactone/
[4] https://materialdistrict.com/material/polymorph/

Wednesday, 5 March 2025

Polyarylamide (PARA; MXD-6) and Recycling: How much regrind is possible?

Hello and welcome to a new post in which we discuss the usage of regrind when processing the high-performance Polyarylamide (PARA; MXD-6).


Recycling Process:

Polyarylamide regrind (sprues, runners, etc.), containing reinforcements such as glass fibers, can be recycled with virgin PARA compound. Important is to exclude any contamination such as oil, release agents, and other additives.

Impact on Mechanical Properties and Color Variation:

Several studies and experiments have shown [1] that a split of 70/30 (70 wt% virgin PARA / 30 wt% regrind) is preferred. The compound used in each cycle was 70% virgin compound (containing 50 wt% glass fibers) mixed with 30% regrind from the preceding cycle. Very little change was observed in the mechanical properties (tensile strength, elongation at break) after recycling. Successive recycling may cause a slight change in color. 

Recommendations:

Important is to confirm the recycling rate experimentally to ensure the finished part meets specifications. Also, drying the regrind prior to injection unless directly grinded and reinjected at the moulding machine. Mark parts to facilitate after-use recycling (check out the part marking codes here).

Thanks for reading and #findoutaboutplastics

Greetings

Literature: 
[1] https://content.solvay.com/ixef-para-processing-guide