By Hitoshi Taniguchi, Application Scientist
While interpreting a DSC thermogram from a pure material is relatively straightforward, understanding measurement data from a multi-component system can be challenging. In food packaging, for example, polymer films are often stacked to enhance the material’s properties such as barrier protection, strength, and saleability. Interactions between each layer can become difficult to interpret during analysis, especially in cases where novel materials are used for R&D formulations.
In such applications, having real-time footage of the sample as it undergoes thermophysical transitions would be greatly beneficial in understanding your materials’ behavior. In this blog post, a multilayer polymer film sample from Copol International Ltd. was investigated with Rigaku’s Sample Observation DSCvesta to demonstrate the expanded thermal analysis capability offered by the sample observation DSC.
The sample has a layer structure as shown in Figure 2 below. The innermost layer with material C is sandwiched by layers with material B and is sandwiched again by layers with material A.
To first investigate the sample’s thermal behavior, the sheet was cut into a smaller size and was inserted into the aluminum pan. The sample was then loaded into Rigaku DSCvesta with the Sample Observation Feature, and the measurement footage was recorded along with the DSC thermogram.
Using the reporting feature, the visuals of the sample at each transition state can be attached along with the DSC thermogram. From the sample observation footage, we can confirm that the film curls up as the intermediate layer melts, causing the thermal contact to be non-optimal.
To obtain DSC data with higher resolution, several films were stacked into the sample pan, and the pan was crimped with an aluminum lid to prevent the sample from curling away from the bottom of the pan. The crimped sample pan is shown below.
This sample setup significantly improved the resolution of the DSC data, as shown below. The following temperature profile was used for this measurement:
- Heating from room temperature to 225°C at 10°C/min.
- Cooling from 225°C to -50°C at 2°C/min.
- Heating from -50°C to 225°C at 10°C/min.
The cooling rate of 2°C/min was chosen to facilitate slow re-crystallization of the polymer melts, such that the degree of crystallinity is maximized. The sample is then reheated to 225°C at the same heating rate of 10°C/min.
From Figure 6 above, the first and second heating ramps, along with the cooling ramp, can be isolated for separate analyses.
Upon a close inspection of the first heating ramp in Figure 7, a minor perturbation in the baseline can be observed in the region marked by a red dotted circle. A tiny fluctuation such as this one can be mistaken for a noise in the baseline, but the sample observation footage confirms that this is indeed a phase transition of some kind. By magnifying the DSC curve in Figure 7, this behavior can be attributed to the glass transition of the intermediate layer, and the magnified curve is shown in Figure 10.
From Figure 9, it can be observed that the endothermic peaks for major melt behaviors have greater areas under the peaks due to increased crystallinity. It can also be seen that the initial transition of the middle layer is virtually undiscernible after the initial heating ramp, possibly due to the layer integrity being lost through the melting of all three layers.
Table 1: Summary of Thermal Analysis Results
| Heating/Cooling Ramp | Layer Material | Enthalpy Change (J/g) | Onset Temp. | Midpoint Temp. | End Temp. |
| First Heating (25 – 225°C, 10°C/min) | A | 40.2 | 137°C | 146°C | 153°C |
| B | – | 86.4°C | 88.4°C | 90.0°C | |
| C | 5.04 | 172°C | 181°C | 185°C | |
| Cooling (225 – -50°C, 10°C/min) | A | -60.2 | 108°C | 111°C | 114°C |
| B | – | – | – | – | |
| C | -4.53 | 158°C | 160°C | 162°C | |
| Second Heating (-50 – 225°C, 10°C/min) | A | 57.2 | 140°C | 146°C | 151°C |
| B | – | – | – | – | |
| C | 4.39 | 178°C | 182°C | 185°C |
These procedures are quite routine for thermal analysis using DSC instruments, but the correlation between these data and the actual thermal events would have been challenging without a visual confirmation of those transitions. Rigaku’s Sample Observation DSC offers a unique capability to capture thermophysical events in real-time, providing unequivocal insights into your material’s thermal profile.
Interested in Learning about the Thermal Analysis of Your Materials?
C-Therm’s Thermal Analysis Labs offer advanced testing services to help you better understand the thermal behavior of complex materials, like multilayer polymer films. Whether you’re working in R&D, quality control, or product development, our team can support your testing needs with expert insights and fast turnaround.
Request a Quote or Schedule a Consultation to explore how our lab services can accelerate your materials innovation.
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About the Author
Hitoshi Taniguchi is a Technical Specialist at C-Therm Technologies Ltd.. Hitoshi recently received his Bachelor of Science in Chemical Engineering from the University of New Brunswick and has swiftly made the transition from academia to industry. He is a certified Installation Technician for various pieces of thermal analysis equipment distributed by C-Therm and has played a significant role in developing new technologies and testing protocols at the company. With a strong interest in R&D, his daily tasks such as data acquisition, analysis, and technical presentations directly contribute to the development of new products. His previous experiences as a tutor for chemical engineering and mathematics courses show his passion in helping students succeed in academics.
Frequently Asked Questions (FAQ)
1. What is differential scanning calorimetry (DSC) used for in food packaging?
DSC is used to analyze the thermal properties of polymer films in food packaging, such as melting points, glass transitions, and crystallization behavior. This helps in optimizing material performance for barrier protection, strength, and shelf stability.
2. How does Rigaku’s Sample Observation DSC improve thermal analysis?
Rigaku’s Sample Observation DSCvesta provides real-time visual footage of the sample during thermal transitions, allowing researchers to correlate DSC data with physical changes like melting, curling, or phase transitions.
3. Why is thermal analysis of multilayer polymer films challenging?
Multilayer films contain different polymers with unique thermal behaviors. Their interactions during heating and cooling can complicate interpretation of DSC thermograms, especially when novel materials are used.
4. What are the benefits of using crimped pans in DSC testing?
Crimping the DSC pan improves thermal contact between the sample and the pan, reducing heat loss and enhancing the resolution of thermal events in the DSC data.
5. Can DSC detect subtle transitions like glass transitions in polymer layers?
Yes, DSC can detect subtle transitions such as glass transitions, especially when paired with sample observation footage that confirms physical changes during the transition.
6. What temperature profile was used in this study?
The sample was heated from room temperature to 225°C at 10°C/min, cooled to -50°C at 2°C/min to promote crystallization, and reheated to 225°C at 10°C/min.