Hello and welcome to a new blog post. In this post we are comparing glass-fiber filled PET vs. PBT, especially heat distortion properties (HDT). We dive into why PET's higher stiffness, heat resistance, and lower water uptake can be a game-changer for E&E and metal replacement applications. It can help you to elevate your material selection process - let us get started!
PET compounds vs PBT compounds
When it comes to high-performance engineering plastics, glass-fiber reinforced compounds of PET (Polyethylene Terephthalate) and PBT (Polybutylene Terephthalate) are often top contenders. While both offer enhanced strength and rigidity, their distinct properties can make one a clear winner over the other for specific demands.
One of PET's significant advantages lies in its higher stiffness, which directly translates to reduced creep under sustained loads. This superior mechanical integrity ensures long-term performance where dimensional stability is critical. Furthermore, PET compounds boast a notably higher heat distortion temperature (HDT). Specifically, when measured with HDT/B, PET can exhibit a delta of up to 20°C higher than PBT, making it more resilient in high-heat environments (Figure 1).
Figure 1: Comparison of HDT/A and HDT/B of PET-GF30 and PBT-GF30
Another crucial differentiator is PET's lower water uptake. This property directly contributes to better dimensional stability, as the material is less prone to swelling or warping in humid conditions. In the realm of electrical and electronic (E&E) applications, glass-fiber filled PET truly shines due to its good dielectric properties and the potential for achieving high UL RTI (Relative Thermal Index) values. These characteristics ensure reliable insulation and performance at elevated temperatures.
These combined attributes—superior stiffness, higher heat resistance, better dimensional stability, and excellent electrical properties—make glass-fiber filled PET compounds particularly compelling for demanding applications in the E&E industry. They are also an excellent choice for metal replacement, offering a lighter, often more cost-effective, and corrosion-resistant alternative without compromising on critical performance metrics. When designing your next component, understanding these nuances can lead to superior product design and longevity.
Hello and welcome to a new post. For many of us, LEGO® bricks are synonymous with durability and endless creative possibilities. They withstand countless builds, deconstructions, and even the occasional barefoot step. So, when a childhood treasure, carefully preserved for decades, suddenly crumbles in your hands, it's a stark reminder that even the most robust plastics have a lifespan. This is precisely the experience my friend Dirk Moses recently encountered with his 1986 LEGO® "Mobile Recovery Vehicle" set, and it offers a fascinating case study into the world of plastic part failure, particularly in ABS.
Dirk's story is a familiar one: a nostalgic journey with his son, building a cherished set from his own youth, only to be met with the disheartening sound of "crack!" as original, seemingly well-preserved parts disintegrated. No sunlight, no moisture exposure – just the relentless march of time. This isn't just a frustrating experience; it's a prime example of how polymers, even when seemingly inert, undergo subtle changes that can lead to catastrophic failure over extended periods.
Figure 1: Broken ABS bricks of the LEGO® "Mobile Recovery Vehicle" set from 1987 [1].
The Material Culprit: ABS and Its Vulnerabilities
The iconic LEGO® bricks are predominantly made from Acrylonitrile Butadiene Styrene, or ABS. ABS is a terpolymer, meaning it's made from three different monomers (check my detailed review on ABS here):
Acrylonitrile (A): Provides chemical resistance, rigidity, and hardness.
Butadiene (B): A rubbery component that contributes toughness and impact strength.
Styrene (S): Offers rigidity, processing ease, and gloss.
This combination gives ABS its desirable balance of properties – stiffness, impact resistance, and a good surface finish – making it an ideal choice for durable toys like LEGO®. However, it's the "Butadiene" component that often holds the key to its long-term degradation.
The Invisible Enemy: Thermal Oxidation of Butadiene
While Dirk meticulously stored his LEGO® set away from sunlight and moisture, he couldn't escape the effects of thermal oxidation. This is a common degradation mechanism in polymers, where oxygen from the air reacts with the polymer chains, often accelerated by even ambient temperatures over extended periods.
The butadiene component in ABS, with its unsaturated double bonds, is particularly susceptible to oxidation. Here's a simplified breakdown of what happens:
Initiation: Heat and oxygen initiate the formation of free radicals on the butadiene backbone. These free radicals are highly reactive.
Propagation: These free radicals react with more oxygen and then abstract hydrogen atoms from adjacent polymer chains, creating new free radicals. This forms a chain reaction, leading to the formation of hydroperoxides and other oxidized species.
Chain Scission and Cross-linking: The hydroperoxides are unstable and can decompose, leading to further free radical formation. This ongoing process results in two primary detrimental effects:
Chain Scission: The polymer chains break down into smaller fragments. This leads to a reduction in molecular weight and a loss of mechanical strength, making the material brittle and prone to cracking.
Cross-linking: In some cases, the free radicals can also react with each other to form new covalent bonds between polymer chains, leading to excessive cross-linking. While some cross-linking can increase stiffness, excessive cross-linking makes the material extremely rigid and brittle, also reducing its ability to absorb impact.
In the case of Dirk's 40-year-old LEGO® bricks, it's highly probable that the butadiene in the ABS underwent significant oxidation. This would have caused the once tough and resilient material to become brittle, explaining why parts that felt solid suddenly "cracked" under minimal stress. The internal structure of the plastic had been fundamentally altered at a molecular level, even without external stressors like UV light or repeated use.
The Takeaway for Polymer Engineers and Consumers Alike
Dirk's experience is a valuable lesson for polymer engineers and consumers alike. For engineers, it underscores the critical importance of understanding long-term material degradation mechanisms, even in seemingly stable polymers. Accelerated aging tests are crucial, but real-world shelf-life data, like Dirk's, provides invaluable insights. Developing new additives that can better inhibit thermal oxidation in ABS and other polymers is an ongoing area of research.
For consumers, it's a gentle reminder that even our most cherished plastic possessions have a finite lifespan. While storing items in their original packaging and away from harsh conditions can certainly extend their life, it cannot stop the slow, inexorable march of molecular degradation. During material selection, understanding all the requirements and transforming them into proper part specifications is key to prevent part failure at a later stage.
Dirk's spontaneous shift to a new LEGO® Dreamzzz set for his son, and the "priceless" joy it brought, highlights a beautiful truth: while the physical bricks may crumble, the spirit of play and connection that LEGO® fosters endures, bridging generations even when the plastic sometimes falls apart. And perhaps, for Dirk, his new mission to "quality control" his "Wrinkle Knights" castle will offer further valuable data in the ongoing saga of plastic longevity!
Many thanks to Dirk for sharing with us his experiences!
Hello and welcome to a new rule of thumb post. Today we discuss how to select the optimal PET grade (fiber vs sheet vs bottle grade) for your application.
Figure 1: Selecting the optimal PET grade
PET Intrinsic Viscosity (IV; dL/g) as a Key Indicator for selection and quality
Polyethylene terephthalate, or PET, is a ubiquitous polymer in our daily lives, from clothing to packaging. John Rex Whinfield and James Tennant Dickson, British chemists, are credited with inventing polyethylene terephthalate (PET) in 1941. They patented the material while working at the Calico Printers' Association of Manchester, building upon early research by Wallace Carothers. By using an aromatic diacid, properties of the resulting Polyester could be improved. This was the major start of PET which became the foundation for synthetic fibers like polyester, Dacron, and Terylene, as well as bottles, and sheets.
But not all PET is created equal. The key to its diverse applications lies in its Intrinsic Viscosity (IV), a crucial measure of its molecular weight and, consequently, its strength and processing characteristics. This is especially vital when utilizing recycled PET. Figure 2 shows the different process steps in PET production, including the IV obtained at every stage and the resulting potential applications.
Figure 2: PET process technology and the importance of Intrinsic Viscosity (IV) [4].
Application-Specific IV Ranges
For yarn and fiber applications, where flexibility and drape are paramount, PET with an IV between 0.6 and 0.7 dL/g is preferred. Moving up the scale, 0.7 to 0.8 dL/g PET is ideal for sheet applications, offering the necessary rigidity for thermoforming.
The familiar PET bottles we see daily, typically created through injection moulding into preforms, require an IV of 0.8 to 0.85 dL/g to ensure robust performance. For demanding uses like water jerry cans, where extreme durability is essential, PET with an IV greater than 0.85 dL/g is selected.
Summary of the PET IV ranges:
Yarn & Fiber (0.6-0.7 dL/g)
Sheet (0.7-0.8 dL/g)
Bottle (0.8-0.85 dL/g)
Jerry Cans (> 0.85 dL/g)
Choosing the correct IV grade is fundamental for achieving optimal product performance and ensuring efficient processing, highlighting why precise PET grade selection is critical for quality and sustainability across industries.
Hello and welcome to a new blog post in which we discuss the benefits of incorporating Life Cycle Assessment (also referred to as Life Cycle Analysis; LCA) into your plastic product design.
What is a LCA and why is it important?
LCAs are part of the holistic Life Cycle Engineering (LCE) approach and quantify the environmental impacts of plastic products across all stages of their life cycle, including raw material extraction, manufacturing, transportation, use, and disposal or recycling. One can analyze "cradle-to-cradle", where the end of a lifecycle is taken as the end of the recovery process or focus only on "cradle-to-grave", where the end of lifecycle is the disposal of post-consumer plastic waste. In addition, there is also "cradle-to-gate", where the end of lifecycle is taken to be delivery of the product at your factory gate (Figure 1). Altogether, a LCA provides a comprehensive picture of the overall environmental burden associated with a plastic part, allowing designers to identify areas where improvements can be made.
There are two major standards helping to bring a LCA to reality:
ISO 14040: providing the principles and framework.
ISO 14044: provides the roadmap on how to make the LCA. It provides information on the four steps a LCA should contain in order to systematically be able to quantify the environmental impact.
Figure 1: Overview of Polymer Life Cycle Engineering (LCE) and Life Cycle Assessment (LCA).
What are the four stages of a LCA?
Following is a brief description of the four stages of a Life Cycle Assessment (LCA), which should help you understand the process (Figure 1):
1. Goal and Scope Definition: This initial stage defines the purpose and breadth of the LCA study. It clarifies the product system being assessed, its functions, the intended application of the results, and the audience. This step also outlines the system boundaries, functional unit, and data quality requirements.
2. Life Cycle Inventory (LCI): This stage involves collecting data on all inputs and outputs associated with the product system. This includes raw material acquisition, energy consumption, manufacturing processes, transportation, use phase, and end-of-life treatment. The LCI aims to quantify all relevant environmental exchanges, such as resource use and emissions.
3. Life Cycle Impact Assessment (LCIA): In this stage, the environmental impacts associated with the inventory data are evaluated. The LCIA aims to translate the LCI results into environmental impact categories, such as climate change, ozone depletion, acidification, eutrophication, and resource depletion. Different LCIA methods are available, each with its own set of impact categories and characterization factors.
4. Interpretation: The final and crucial stage involves analyzing the LCI and LCIA results to draw conclusions and make recommendations. This stage assesses the significance of the results, identifies key environmental issues, and evaluates the consistency and completeness of the study. The interpretation should provide clear and transparent conclusions that address the defined goal and scope of the LCA.
The single stages can be supported by software solutions such as GaBi (Sphera) or Echochain.
What are the benefits of incorporating LCA into your plastic product design?
Currently, over 80% of the product's environmental impact is determined at the design stage. Integrating Life Cycle Assessment right from the design phase of plastic products can unlock some really significant advantages. Here are five key benefits for you to keep in mind:
1. Reduced Environmental Impact: LCA allows you to identify environmental hotspots and by considering the entire life cycle – from raw material extraction to end-of-life disposal – during design, you can actively choose materials and processes that minimize environmental burdens. This includes lower greenhouse gas emissions, reduced water and energy consumption, and decreased waste generation. For example, opting for recycled plastics or designing for easier recyclability can significantly lessen the environmental footprint.
2. Enhanced Resource Efficiency: LCA encourages designers to think critically about material usage and optimize product design for longevity and repairability. This can lead to using less material overall, extending the product's lifespan, and facilitating component reuse or remanufacturing. Think about modular designs that allow for easy replacement of worn-out parts rather than discarding the entire product.
3. Cost Optimization: While the initial LCA might involve some investment, it can lead to significant cost savings in the long run. By identifying resource-intensive stages or materials with high price volatility, designers can explore more cost-effective alternatives. This could involve using less expensive but equally functional materials, replacing metal by high performance polymers, streamlining manufacturing processes, or designing for efficient logistics and waste management.
4. Improved Product Performance and Innovation: The insights gained from an LCA can actually spark innovation and lead to better-performing products. Understanding the environmental constraints and material properties throughout the life cycle can drive the development of novel polymeric materials, innovative designs for durability and functionality, and even new business models like product-as-a-service.
5. Stronger Brand Reputation and Stakeholder Engagement: In today's environmentally conscious world, companies that demonstrate a commitment to sustainability through practices like LCA often build stronger brand loyalty and attract environmentally aware consumers. Transparently communicating the environmental performance of products based on LCA findings can also enhance engagement with stakeholders, including investors, regulators, and the wider community.
6. Informed Decision-Making: By providing a quantitative assessment of environmental impacts, LCAs help designers make more informed choices about polymer material selection, design features, and end-of-life strategies. This can lead to the development of more sustainable plastic parts with a reduced environmental footprint.
7. Comparing Alternatives: LCAs can be used to compare the environmental impacts of different plastic types, manufacturing processes, and end-of-life management options, helping designers choose the most sustainable approach. This can lead to the development of plastic parts that are not only functional but also environmentally responsible. As an example, Figure 1 compares the Global Warming Potential (GWP) and density of different plastics.
8. Supporting Circular Economy and Waste Reduction: LCAs are valuable tools for promoting a circular economy for plastics by helping to identify opportunities for reuse, recycling, and remanufacturing. By understanding the full life cycle of a plastic part, designers can create products that are more easily recycled or repurposed, reducing waste and promoting a more circular approach to plastic production.
Example of a LCA: Packaging
A LCA was done on 10,000 units of 12oz packages produced in different materials in the United States [10]. In the stage four, (interpretation), a contribution analysis was done, in order to understand the Global Warming Potential (GWP) of the different packaging materials. This in turn allows for better decision making, when the aim is to reduce the product carbon footprint of the packaging material.
Figure 2 presents the comparison of the GWP of aluminum can, glass bottle and PET bottle. By switching from glass bottle to PET-bottle, a 50% reduction in GWP can be achieved.
Figure 2: Comparison of GWP of a 12oz bottle made out of glass, aluminum and PET [10].
Conclusion
In conclusion, LCAs are essential tools for promoting sustainable plastic part design by providing a comprehensive and quantitative understanding of the environmental impacts associated with plastic products throughout their life cycle. By using LCAs, designers can identify hotspots, make informed decisions, and develop more sustainable and eco-friendly plastic parts that contribute to a circular economy and a healthier planet.
Often, a full LCA is not needed, it is better to make a simplified one and focus on one or two key outputs, than to have no LCA done at all.
Want to deep-dive into designing a sustainable future with polymers? Check out my talk on this topic:
Curious about how Life Cycle Assessment can revolutionize your plastic product design process? Do you have questions about its implementation or the benefits it can unlock? I'd love to hear from you. Contact me here to start a conversation and discover the possibilities.
