Introduction
Dynamic Mechanical Analysis (DMA) is a powerful tool for understanding the viscoelastic properties of materials.
However, its application in the sub-ambient region has historically been limited by the constraints of traditional cooling systems.
At EXPERTA | TESTING, our partner overcomes these limitations using the TA Instruments DMA with the ACS-3 Refrigerated Cooling System, enabling continuous isothermal measurements from -100°C.
This breakthrough allows for TTS - Time-Temperature Superposition to be applied effectively, even through the glass transition of materials like ABS (Acrylonitrile Butadiene Styrene) and other elastomers.
In this post, we explore how this approach unlocks new possibilities for material characterization, with a focus on the benefits for ABS and other polymers.
The Challenge: Sub-Ambient DMA Limitations
Traditionally, performing TTS in the sub-ambient region was nearly impossible.
As TTS requires isothermal measurements at multiple temperatures, each subjected to a spectrum of frequencies to deform the sample at a fixed strain.
However, liquid nitrogen cooling systems (the previous standard) had a finite supply, making continuous, stepwise measurements unfeasible.
This limitation was particularly problematic for materials like ABS and other elastomers, where understanding behavior through the Tg - Glass Transition is critical.
Without the ability to perform TTS in this region, researchers and engineers missed out on valuable insights into how these materials behave at low temperatures and high frequencies.
The Solution: Unlimited Cooling with ACS-3
Our premium partner adopted the TA Instruments DMA with the ACS-3 Refrigerated Cooling System.
Unlike liquid nitrogen, the ACS-3 provides an unlimited supply of chilled air, enabling:
- Continuous isothermal measurements from -100°C upwards
- Dynamic programming across a wide temperature range
- Precise control for TTS analysis, even in the sub-ambient region
This setup allows us to perform isothermal steps as close as 1°C apart, applying a broad frequency spectrum (e.g., 0.1, 0.3, 1, 3, and 10 Hz) to capture the full viscoelastic response of the material.
Case Study: TTS for ABS in the Sub-Ambient Region
To demonstrate the power of this approach, we performed a TTS evaluation for ABS, focusing on the butadiene transition in the sub-ambient region.
Measurements were taken between -100°C and -20°C, with data shifted to a reference temperature of -60°C.
Key Findings:
1. Glass Transition Insights: At -60°C, the TTS analysis revealed that ABS does not reach a glassy state until a deformation frequency of 10^8 Hz is applied. This is a critical insight for applications where ABS is subjected to high-frequency stresses at low temperatures.
2. Tan Delta Shifting: The shifting process was performed using the Tan Delta signal, which is highly sensitive to transitions in the material’s viscoelastic properties. This allowed us to accurately construct the master curve for ABS, providing a comprehensive view of its behavior across temperatures and frequencies.
3. Master Curve Construction: By shifting the data, we created a master curve that predicts the material’s response at frequencies and temperatures beyond the original test conditions. This is invaluable for designers and engineers who need to understand how ABS will perform in real-world applications.
DMA Setup and TTS Data for ABS
Overcoming these Problems: Using The (unlimited) ACS-3 Air chiller
- With our TA Instruments DMA, it is now possible to run stepwise isothermal measurements continuously from -100°C using a broad frequency spectrum. We use the ACS-3 Refrigerated cooling system which gives unlimited supply of coolant (chilled air) enabling isothermal or dynamic programming from -100°C upwards.
- The measurement below shows the TTS evaluation for ABS in the sub-ambient region (butadiene transition). Isothermal steps were 1°C apart and the frequency range applied was 0.1, 0.3, 1, 3 & 10 Hz. Measurements were made between -100 to -20°C. The data was shifted using TTS at a reference temperature of -60°C. At this temperature the TTS indicates that the material does not reach a glassy state until a deformation frequency of 108 Hz is reached. Shifting was performed using the Tan Delta signal.
- We have used this approach successfully to identify where Epoxy adhesives become Glassy in nature by performing TTS on Beta relaxations from data gathered in the Sub-ambient region. We have also used this set up to evaluate elastomers with TTS from data gathered through the main glass transition.
Why DMA and TTS Matter for ABS
ABS is a widely used thermoplastic known for its toughness, impact resistance, and dimensional stability.
However, its performance at low temperatures and high frequencies has always been a challenge to characterize.
Here’s why DMA and TTS are game-changers for ABS:
1. Predicting High-Frequency Behavior
TTS allows us to extend the frequency range of DMA data, predicting how ABS will respond to high-frequency stresses (e.g., vibrations, impacts) at low temperatures. This is crucial for applications in automotive, aerospace, and consumer electronics, where ABS components may experience dynamic loading.
2. Understanding Glass Transition
The butadiene phase in ABS undergoes a glass transition at low temperatures. By performing TTS through this transition, we can identify the exact conditions under which ABS shifts from a rubbery to a glassy state. This helps in designing materials for low-temperature applications without compromising performance.
3. Material Optimization
With TTS, we can compare different grades of ABS or evaluate the impact of additives and fillers on its viscoelastic properties. This enables manufacturers to fine-tune formulations for specific applications, ensuring optimal performance across a range of temperatures and frequencies.
4. Accelerated Testing
TTS reduces the need for lengthy, expensive tests at every possible temperature and frequency. By shifting data to a reference temperature, we can predict long-term behavior from short-term tests, saving time and resources.
Beyond ABS: Applications for Elastomers and Epoxy Adhesives
The benefits of this approach extend beyond ABS.
At EXPERTA | TESTING, we’ve also have experience with applying DMA and TTS to:
- Elastomers: Evaluating TTS through the main glass transition to understand their behavior in sub-ambient conditions. This is particularly useful for seals, gaskets, and flexible components in cold environments.
- Epoxy Adhesives: Identifying where these materials become glassy by performing TTS on beta relaxations in the sub-ambient region. This helps in selecting adhesives for applications requiring high strength at low temperatures.
Takeaways
1. DMA + ACS-3 = Sub-Ambient TTS: The combination of TA Instruments DMA and the ACS-3 Refrigerated Cooling System removes the limitations of traditional cooling methods, enabling continuous TTS analysis from -100°C.
2. ABS Insights: For ABS, TTS reveals critical information about its glass transition and high-frequency behavior, helping engineers design for low-temperature and dynamic applications.
3. Broader Material Applications: This approach is not limited to ABS. It can be applied to elastomers, epoxy adhesives, and other polymers to unlock new insights into their viscoelastic properties.
4. Efficiency and Accuracy: TTS allows for faster, more cost-effective testing by predicting material behavior across a wide range of conditions from a single set of isothermal measurements.
Conclusion
The ability to perform TTS in the sub-ambient region is a game-changer for material characterization.
At EXPERTA | TESTING, our premium partner leveraging the TA Instruments DMA with ACS-3 cooling to push the boundaries of what’s possible, providing our clients with unprecedented insights into the behavior of ABS, elastomers, and other critical materials.
If you’re interested in exploring how DMA and TTS can benefit your projects, just contact in via email, to discuss your needs or Book a meeting