Hello and welcome to a new blog post. Let me start today with the following question: How do you ensure the long-term performance of polyolefin materials in demanding applications?
Understanding and measuring oxidative stability is key. The following post explores why oxidative stability matters for polyolefins like polypropylene, and how Differential Scanning Calorimetry (DSC) provides valuable insights into material durability, processing effects, antioxidant performance, and ultimately prevent plastic part failure. Dive in to learn how this classic yet often overlooked test method can help you make informed decisions about material selection and process optimization.
DSC Testing for Oxidative Stability
DSC measures the heat absorbed or released by a material as temperature or time changes. While commonly used for phase transitions (melting, recrystallization, glass transition), it is also effective for detecting exothermic events like oxidation.
How does a typical test procedure for oxidative stability look like?
A sample (raw material or molded part) is placed in the DSC.
The sample is heated in a nitrogen atmosphere to a set temperature (commonly 200°C/392°F, which melts PE or PP).
After reaching the target temperature, air or oxygen is introduced.
The antioxidant in the polymer protects it until it is depleted; then, oxidation occurs, shown by a sharp increase in the DSC baseline.
The time from oxygen introduction to oxidation onset is called the Oxidation Induction Time (OIT).
Also, the test can be used to access the oxidation onset temperature (OOT).
Example PP raw material with standard antioxidant package vs. PP raw material with improved antioxidant package
Figure 1 shows the result for a tested polypropylene (PP) raw material and the OIT was measured at 2.29 minutes. A second PP raw material, which contains an improved antioxidant package, showed a higher OIT (6.42 minutes), indicating better resistance to oxidation under the same test conditions [1].
Figure 1: Using DSC to estimate the anti-oxidant level in Polyolefins - Example PP [1].
Interpreting OIT Results
The OIT value alone is not meaningful, but comparing OITs of materials with similar antioxidant chemistries provides a relative measure of oxidative stability. AS a rule of thumb, higher OIT indicates better oxidative stability and, typically, higher antioxidant content.
DSC offers a quick and practical way to assess oxidative stability compared to more complex antioxidant quantification methods.
Applications of OIT measurements
Raw Material vs. Molded Part:
Processing (molding) consumes some antioxidants, so molded parts usually have a lower OIT than raw materials.
Changes in processing conditions (temperature, screw speed, backpressure) affect OIT and thus the remaining antioxidant content.
Post-Processing and Environmental Effects:
Sterilization (gamma or E-beam) can significantly reduce OIT, leading to loss of material toughness.
Long-term heat aging also reduces OIT over time.
Conclusion
DSC-based OIT testing, despite its limitations in perfectly simulating real-world conditions, remains a valuable and practical method for comparing the oxidative stability of polyolefins. It is particularly useful for evaluating the impact of processing and post-processing on antioxidant depletion and for comparing materials with similar stabilizer chemistries.
Hello and welcome to a new blog post. Today we are diving into a powerful technique for polymer identification: Differential Scanning Calorimetry (DSC). Specifically, we will explore how DSC can help you distinguish between two common polyamides, Polyamide 6.6 (PA 6.6) and Polyamide 6 (PA 6).
What is DSC?
Differential Scanning Calorimetry (DSC) is a thermal analysis technique used to observe thermal transitions in polymers. This includes identifying key characteristics such as:
Glass Transition Temperature (Tg): The temperature at which an amorphous polymer transitions from a rigid, glassy state to a more flexible, rubbery state.
Melting Points (Tm): The temperature at which crystalline regions of a semi-crystalline polymer melt.
Crystallization and Crystallization Rate: For semi-crystalline polymers, DSC can also reveal information about how they crystallize upon cooling.
The Polyamide Puzzle: PA 6.6 vs. PA 6
Imagine you have a failed injection molded part made of polyamide, but you are unsure if it is PA 6.6 or PA 6. As part of your failure analysis you need to identify the polyamide type. This is where DSC becomes incredibly handy. You can take a small piece of the part, perform a DSC analysis, and the results will provide a clear answer.
Looking at a typical DSC diagram, which plots heat flow over temperature, we can observe distinct differences between PA 6.6 and PA 6 (Figure 1):
Polyamide 6.6 (PA 6.6): This polymer typically exhibits a melting point around 268°C (approximately 270 °C). On the DSC curve, this appears as a clear, sharp peak in the higher temperature range.
Polyamide 6 (PA 6): In contrast, Polyamide 6 has a lower melting point, typically around 220 °C. Its peak will appear distinctly at this lower temperature on the DSC curve.
While both PA 6.6 and PA 6 have similar glass transition temperatures (around 50°C to 70 °C), making them less ideal for differentiation, their melting points provide a robust and clear identification.
Figure 1: Material identification using DSC - Example PA 6.6 vs PA6.
Conclusion
Using DSC to identify PA 6.6 and PA 6 by their distinct melting points is a very practical and effective method. While it requires a laboratory equipped with a DSC instrument, the clarity it provides in material identification can be invaluable for quality control, material verification, and troubleshooting in the plastics industry.
Hello and welcome to a new Rule of Thumb post with focus on the Lindy Effect.
What is the Lindy Effect?
The Lindy Effect, when applied to polymers, suggests that the longer a polymer material or its application has been in use, the longer it is likely to continue to be used in the future. This effect highlights the idea that longevity in the face of time and competition implies robustness and adaptability, making older technologies or materials potentially more durable and relevant than newer, less tested alternatives.
Examples - Polymers and the Lindy Effect
1. Established Polymer Applications: Consider the long-standing use of polyethylene (PE) in packaging or polyvinyl chloride (PVC) in construction as flame retardant flooring material as well as window frame polymer. The Lindy Effect would imply that these established uses are likely to continue for many years to come, as they have already demonstrated their longevity and reliability (Figure 1).
Figure 1: Polymers and the Lindy Effect - Examples PVC and PE.
2. Mature Polymer Materials: Similarly, materials like natural rubber or certain types of thermosetting plastics, which have been used for a considerable time, are likely to remain relevant due to their proven track record.
In essence, the Lindy Effect in the context of polymers suggests that the longer a polymer or its application has been around, the more likely it is to persist into the future. This is because its longevity indicates a degree of robustness and adaptability that makes it a reliable choice in the face of new innovations and changing needs. This brings me to one of my top 10 rules for plastic part design and selection (Rule Nr. 10): Past performance can be guarantee of future results. It can pay of to revisit past application designs to understand what worked in the past (materials selection and design).
Check out more Rules of Thumb in the "Start Here" section.
Hello and welcome to the Part 2C of our High Performance Thermoplastics selection blog series. Today we discuss Polyphenylene Ether (PPE) and PPE blends, their chemistry and production processes, their main properties, processing methods, and applications.
Overview - 6 major high performance thermoplastics families (“the magnificent six”)
In this blog post series we discuss six major high performance thermoplastics families (“the magnificent six”) which are outlined in the following enumeration
Polyphenylene Ether (PPE) and its Blends with Polystyrene (PS) and Polyamide (PA)
Polyphenylene ether (PPE), also known as polyphenylene oxide (PPO), is a high-performance thermoplastic polymer renowned for its excellent thermal, mechanical, and electrical properties. While pure PPE exhibits some processing challenges due to its high melt viscosity, blending it with polystyrene (PS) significantly improves its processability while retaining many of its desirable characteristics. These PPE/PS blends have become commercially significant engineering thermoplastics.
Jack Welch's team at General Electric faced a challenge with Polyphenylene Oxide (PPO): its extremely high glass transition temperature (208°C) made it difficult to process without degrading the material (the methyl groups of PPE are expected to undergo autoxidation). An important key to future success was the research team around Dan Fox, Allan S. Hay, and E. M. Boldebuck, who found out the miscibility of PPO with PS first. To overcome this, they decided to blend PPO with polystyrene (PS). This clever solution allowed them to maintain many of PPO's desirable properties, lower the glass transition temperature, while also making the material easier to process at lower temperatures and more cost-effective.
Chemistry and Production Process
1. Chemistry of Polyphenylene Ether (PPE)
The base polymer, PPE, is typically synthesized through an oxidative coupling polymerization of substituted phenols, most commonly 2,6-dimethylphenol (also known as 2,6-xylenol). This reaction is catalyzed by a copper-amine complex in the presence of oxygen. The general chemical structure of PPE can be represented as (Figure 1):
Figure 1: Chemical structure of the polymer Polyphenylene Ether (PPE) [1].
The ether linkages (-O-) in the polymer backbone, along with the aromatic rings and the methyl substituents, contribute to PPE's stiffness, thermal stability, and chemical resistance.
2. Production of PPE/PS Blends
The production of PPE/PS blends primarily involves melt blending the two polymers. This process is typically carried out in extruders or other intensive mixing equipment. The key steps include:
Raw Material Preparation: PPE and PS resins are typically received in pellet form. They may be dried to remove any moisture before blending.
Melt Blending: The PPE and PS pellets are fed into an extruder, where they are heated and mechanically mixed. The screw design and processing conditions (temperature, screw speed) are crucial for achieving a homogeneous blend. Compatibilizers, such as styrene-butadiene-styrene (SBS) or styrene-ethylene/butylene-styrene (SEBS) block copolymers, are often added to improve the compatibility between the relatively non-polar PS and the more polar PPE. These compatibilizers help to reduce interfacial tension and prevent phase separation, leading to enhanced mechanical properties.
Pelletizing: The molten blend exiting the extruder is then cooled and cut into pellets, which are the final product form for subsequent processing by manufacturers.
The ratio of PPE to PS in the blend can be varied to tailor the properties of the final material to specific application requirements. Higher PPE content generally leads to better thermal and mechanical performance, while higher PS content improves processability and reduces cost (Figure 2).
Figure 2: Changing the glass transition temperature of PPE by changing the ratio of PPE and PS [1].
Main Properties of PPE/PS Blends
PPE/PS blends exhibit a combination of properties derived from both constituent polymers, often enhanced by the presence of compatibilizers.
Key properties include:
Excellent Thermal Stability: PPE inherently possesses high glass transition temperatures (Tg ) and heat deflection temperatures (HDT). Blending with PS can reduce these values compared to pure PPE, however the blends still offer good high-temperature performance compared to many other engineering thermoplastics.
Figure 3 shows the DMA of PPE+PS blend in comparison to High Impact Polystyrene (HIPS) and Polycarbonate (PC). PS has a glass transition temperature of about 100°C and up to this temperature PPE+PS can match PC in thermal performance (PC drops sharply at Tg of 147°C). There is no sharp drop in modulus observed with PPE+PS.
Figure 3: Dynamic Mechanical Analysis (DMA) of PPE+PS vs HIPS vs PC.
Good Mechanical Strength and Stiffness: PPE contributes to the blend's rigidity and strength. The impact strength can be tailored depending on the blend ratio and the use of impact modifiers.
Excellent Electrical Insulation Properties: PPE is an excellent electrical insulator with a low dielectric constant and high dielectric strength, which are largely retained in the blends.
Good Chemical Resistance: PPE offers good resistance to many chemicals, including acids, bases, and detergents. The chemical resistance of the blend is generally good but can be influenced by the PS content, which is more susceptible to certain solvents.
High Stability towards Hydrolysis: hydrolysis resistance of PPE is superior when compared to other engineering plastics such as PBT and PA.
Improved Processability: The addition of PS significantly lowers the melt viscosity of PPE, making the blends easier to process using conventional methods like injection molding and extrusion.
Dimensional Stability: PPE contributes to low water absorption and excellent dimensional stability, which is important for applications requiring tight tolerances.
Flame Retardancy: PPE is inherently flame retardant. Blends often exhibit good flame retardant properties, especially when combined with flame retardant additives.
Apart from blending PPE with PS; blends out of PPE with PA are possible too. PPE/PA blends have the following advantages:
Combines Key Strengths: Blends the excellent dimensional stability, low water absorption, and heat resistance of PPE with the superior chemical resistance and flow of PA.
Enhanced Performance: The resulting material is exceptionally chemically resistant and boasts the stiffness, impact resistance, and heat performance needed for demanding applications like on-line painting.
Significant Weight Savings: Unfilled PPE/PA blends can offer part-weight reductions of up to 25% compared to glass or mineral-filled resins, thanks to their low density.
Outperforming properties of PPE/PS blends:
Low specific gravity: 1.1 g/cm3. Most engineering polymers such as PC, PBT, and POM have a specific density of 1.2 g/cm3 and more.
High self-extinguishing property: PPE has a high oxygen index (27-29) and it is easy to add flame resistancy.
Excellent dielectric properties: PPE has a dielectric constant of 2.8 and a dielectric tangent of 6x1E-3. The dielectric breakdown strength (110 MV/m @ 0.5 mm thickness) is the highest among engineering plastics.
High dimensional accuracy: PPE has one of the lowest coefficient of linear thermal expansion among engineering polymers (5.8 x 10E-5 1/°C).
Processing Methods
PPE/PS blends can be processed using various thermoplastic processing techniques, including:
Injection Moulding: This is the most common method for producing complex shaped parts from PPE/PS blends, leveraging their improved flow properties compared to pure PPE.
Extrusion: These blends can be extruded into profiles, sheets, and films for various applications.
Blow Moulding: Certain grades of PPE/PS blends can be blow molded to produce hollow parts.
Thermoforming: Sheets extruded from PPE/PS blends can be thermoformed into various shapes.
Applications of PPE/PS Blends
The unique combination of properties makes PPE/PS blends suitable for a wide range of applications across various industries:
Construction and Plumbing: Applications include pump housings, impellers, and other components requiring good mechanical and chemical resistance.
Automotive Industry: Interior and exterior components such as instrument panels, door panels, wheel covers, and electrical connectors benefit from the blends' thermal stability, dimensional stability, and impact resistance.
Electrical and Electronics: Housings for electrical connectors, circuit breakers, switchgear, and other electrical components utilize the excellent electrical insulation properties and flame retardancy of PPE/PS blends.
Household Appliances: Components for washing machines, dishwashers, microwave ovens, and other appliances benefit from the blends' heat resistance, chemical resistance, and good mechanical properties.
Business Equipment: Housings and internal components for computers, printers, and other office equipment utilize the blends' dimensional stability, electrical properties, and aesthetic appeal.
Healthcare: Certain grades of PPE/PS blends can be used in medical devices and equipment due to their sterilizability and chemical resistance.
Trade Names
Several companies market PPE/PS blends under various trade names. Some well-known examples include:
Noryl™: Formerly a trademark of GE Plastics, now owned by SABIC Innovative Plastics. This is one of the most widely recognized families of PPE-based resins, including various PPE/PS blends and other modifications.
XYRON™ from Japanese chemical company Asahi Kasei.
Various manufacturers such as Global Acetal (Lemalloy PPE) produce generic PPE/PS blends with specific property profiles.
Economic Aspects
The market for PPE/PS blends is significant within the broader engineering thermoplastics market. The demand is driven by the increasing need for high-performance materials in automotive, electronics, plumbing and appliance industries.
Cost Factors: The cost of PPE/PS blends is influenced by the price of the base polymers (PPE and PS), the concentration of PPE in the blend, the type and amount of compatibilizers and additives used, and the manufacturing process. Generally, higher PPE content leads to higher costs.
Market Trends: The trend towards lightweighting in the automotive industry and miniaturization in electronics continues to drive the demand for materials like PPE/PS blends that offer a balance of performance and processability. Growing environmental concerns are also pushing for more sustainable material solutions, which may influence the development of new PPE-based blends with recycled content or improved recyclability.
Regional Variations: The demand and market dynamics for PPE/PS blends can vary across different geographical regions based on industrial activity and specific application needs.
In conclusion, polyphenylene ether (PPE) and its blends with polystyrene and polyamide represent a versatile class of engineering thermoplastics offering a compelling combination of high-performance properties and improved processability. Their wide range of applications across various industries underscores their economic and technological significance in the world of polymer engineering. As a polymer engineering student, understanding the nuances of these materials will undoubtedly be valuable in your future endeavors.
In the upcoming Part 2C we will continue to discuss the Polyether high performance polymers such as PAEK, PEEK, and PEKK.
Hello and welcome to todays post focusing on gluing plastics. Ever tried to glue two pieces of plastic together, only for the bond to fail miserably? You're not alone! Gluing plastics can be surprisingly tricky, and a key factor often overlooked is something called surface energy. Think of surface energy as how "eager" a material's surface is to bond with something else. And when it comes to adhesives, eagerness is a good thing!
The Rule of Thumb: High Surface Energy = Stronger Bonds
Here's the golden rule for gluing: the higher the surface energy of a material, the greater the strength of the adhesion you can achieve.
Imagine a tiny water droplet on a surface. On a highly energetic surface, the water spreads out, trying to maximize its contact. On a low energy surface, it beads up, shrinking away. Adhesives behave similarly. They want to spread out and "wet" the surface completely to form a strong bond.
Diving Deeper: High vs. Low Surface Energy Plastics
Plastics are generally categorized into two main groups when it comes to surface energy:
High Surface Energy (HSE) Plastics: These plastics are generally easier to bond. Their surfaces are more receptive to adhesives, allowing for better "wetting" and stronger molecular interactions.
Low Surface Energy (LSE) Plastics: These are the notorious "difficult-to-glue" plastics. Their surfaces are less receptive, causing many common adhesives to bead up and struggle to form a lasting bond.
A Quick Look at Surface Energy Values (mJ/m²)
To give you a better idea, below is a small table (Table 1) with approximate surface energy values for some common plastics and other materials. Remember, these values are guides, and specific formulations can impact them.
Table 1: Overview of surface energy values of plastics [1].
As you can see, materials like PTFE (often known as Teflon) have very low surface energy, making them incredibly challenging to bond without specialized adhesives or surface treatments. Another example is the high performance polymer PPS. The surface energy of untreated polyphenylene sulfide (PPS) is typically around 38 mJ/m2. This relatively low surface energy makes PPS challenging to bond to other materials without surface treatment. However, PPS can be treated to increase its surface energy, such as through plasma treatments, which can raise the surface energy to 38 mJ/m2 or higher, depending on the treatment method. In contrast, materials like Polyimide are much more accommodating.
What Does This Mean for Your Next Plastics Gluing Project?
When you're facing a plastic gluing challenge, keep this rule of thumb in mind:
Identify the Plastic: If you know the type of plastic, you can often infer its surface energy.
Opt for HSE Plastics When Possible: If you have a choice of materials, pick higher surface energy plastics for easier and more reliable bonds.
Specialized Adhesives for LSE Plastics: For low surface energy plastics, don't reach for your all-purpose super glue. You'll likely need specialized adhesives designed for LSE materials, or consider surface preparation techniques (like primers or plasma treatment) to temporarily increase the surface energy.
Conclusiones
Understanding surface energy is a game-changer for anyone working with adhesives and plastics. By keeping this simple principle in mind, you'll significantly improve your chances of achieving strong, long-lasting bonds and avoid those frustrating gluing failures. Happy gluing!
More Rule of Thumbs can be found in the section "Start here".
Hello and welcome to today’s blog post on thermal aging of PPS compounds. During material selection, focus on gathering and understanding all the requirements of the application is essential. Key questions to answer are: What is the service environment of your part? And also: What types of load at which service temperature and time need to be fulfilled?
Thermal aging of Polyphenylene sulfide (PPS) compounds (glass; glass/mineral filled)
High performance polymers such as Polyphenylene sulfide (PPS) offer excellent performance during high heat exposure. PPS mouldings, both filled and unfilled, maintain inherent flame resistance and excellent chemical resistance due to the base resin.
Long-term heat aging results align with the polymer's thermal stability. PPS has a UL 746B continuous use temperature (CUT) of 220°C. It is in a similar range with PPSU which has a CUT of 210°C and PTFE is even above 230°C.
Figure 1 highlights the good retention of tensile properties in glass and glass/mineral-filled compounds over long-term exposure. An aging test was performed at two temperatures (175°C and 230°C) for a maximum duration of 10,000 hours [2].
Figure 1: Thermal aging of PPS compounds (175°C and 230°C; 10,000 hours).
Due to the curing characteristics of cross-linked PPS, aging at temperatures above those in Figure 1 can enhance property retention, attributed to a "case hardening" effect from high-temperature air exposure.
At elevated temperatures, PPS compounds show classical deterioration beyond their glass transition temperature (Tg). Despite crystallinity effects, strength loss is gradual, with significant integrity retained even at 200°C. PPS compounds filled with glass and mineral can retain the tensile properties at both temperatures at a higher level (80% retention rate) compared to glass fiber reinforced PPS compounds (60% retention rate).
Generally, 40% glass-filled mouldings retain about 80% of their original strength at 100°C, 60% at 160°C, and 40% at 200°C.
Conclusion
In conclusion, Polyphenylene sulfide (PPS) compounds demonstrate exceptional performance under high heat exposure, making them a reliable choice for applications requiring thermal stability. Both filled and unfilled PPS moldings exhibit inherent flame resistance and chemical resistance, aligning with the polymer's robust thermal properties. The long-term heat aging results confirm PPS's ability to retain tensile properties, even at elevated temperatures. With a continuous use temperature of 220°C, PPS stands out among high-performance polymers, maintaining significant strength and integrity over time. This makes PPS an excellent candidate for applications demanding durability and reliability in challenging thermal environments. When selecting materials, it is crucial to thoroughly understand the application's requirements, including service environment, load types, and service temperatures, to ensure optimal performance and longevity.
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.
