Introduction
If you work in the blown film extrusion industry, you must have heard the name of the “DSC test.” The full form of DSC is differential scanning calorimetry, but what is this test? How is it actually used in the production process? And how does it impact your film quality? We will explain the answers to all these questions in this article in simple and clear language. DSC is a thermal testing method that reveals important properties of polymer materials such as melting, crystallization, and glass transition — which directly affect your extrusion process and film quality. Let’s understand step-by-step the role of DSC in blown film extrusion.
Table of Contents
What is DSC test?
- DSC is differential scanning calorimetry. This is a thermal analysis technique that studies the heat flow behavior of materials like polymers, specifically when the material is heated or cooled.
- In simple words, when a polymer like LDPE, LLDPE, HDPE, etc. is heated, the material starts melting and changes its physical state at certain temperature points. After that, with the help of DSC, we check at what temperature and with what energy these changes are taking place in the material.
Which properties do we check with the help of DSC?
Let us understand which key properties we check with the help of DSC:
1. Melting Temperature (Tm)
- With the help of DSC, we check the melting temperature of the polymer. With its help, we come to know which polymer will melt at which temperature. This data is very useful for setting the temperature of the barrel and die in blown film extrusion. If the melting temperature of the polymer is not known accurately, then the polymer will either overheat or under-melt, due to which troubleshooting starts in the quality of the film.
2. Crystallization Temperature (Tc)
- When a polymer is cooled, then at what temperature it cools down and converts into a crystalline phase is known from the crystallization temperature. If you know about TC, then with its help, you can help in designing a cooling air system in blown film extrusion and optimizing film clarity.
3. Glass Transition Temperature (Tg)
- Tg is the temperature where the polymer changes from a rigid formation to a rubbery state. Glass transition temperature plays an important role in the multilayer blown film extrusion process because, with the help of Tg, it becomes easy to decide the flexibility and toughness of the multilayer film.
4. Crystallinity
- With the help of the DSC curve, you can calculate the crystallinity by calculating the area under the melting peak. This property tells how much the polymer is ordered (crystalline) and how much is disordered (amorphous).
- High crystallinity = More stiffness and better barrier
- Low crystallinity = more sealability and flexibility
Note: Read more about blown film extrusion
How is a DSC test done?
The DSC test is a scientific but simple procedure performed in a standard lab setup. During this test, you are provided with a clear graph of the thermal behavior of the polymer that helps you accurately understand changes such as melting, crystallization, and glass transition.
Step-by-Step Procedure:
1. Sample Preparation
- A small piece (2–10 mg) of polymer is taken.
- It is placed in a lightweight aluminum pan.
- The sample is tightly sealed to prevent moisture loss or contamination.
2. DSC Machine Setup
- The DSC instrument has two pans: one contains the polymer sample, and the other is a reference pan, which is empty.
- The machine heats/cools both pans at the same rate.
3. Heating/Cooling Cycle Start
- The sample is heated/cooled to a predefined temperature range (e.g., -50°C to 300°C).
- The machine then records how much heat is flowing into the sample and how much heat is flowing into the reference pan.
4. Graph Output (DSC Curve)
The result is obtained in the form of a DSC thermogram:
- X-axis: Temperature
- Y-axis: Heat flow
You will see endothermic peaks (melting) and exothermic peaks (crystallization) on the curve.
5. Data Analysis
By measuring the start, end, and area of the peaks, you can derive the following properties:
- Tm (Melting Temp)
- Tc (Crystallization Temp)
- Tg (Glass Transition)
- ΔHf (Enthalpy of Fusion) → to calculate crystallinity
Note: Read more about DSC test
FAQ About DSC Test
Why is DSC Test Blown Film Extrusion Important?
DSC (differential scanning calorimetry) is a thermal analysis technique that measures the melting point, crystallization temperature, and glass transition (Tg) of a polymer. In blown film extrusion, it helps ensure material quality, process optimization and consistent film properties.
What problems of blown film are detected by DSC test?
Irregular melting → Due to irregular melting, weak spots, gel particles, and burning particles can form in the film.
Low crystallization → Due to low crystallization, the film can become softer or more transparent.
Polymer degradation → Due to polymer degradation, the strength of the film decreases.
Impurities → With the help of DSC, impurities can be checked because if there is impurity in the film, then stains or bubbles can appear on the film.
Mechanical properties can be predicted from % crystallinity.
With the help of the DSC curve, an accurate percentage of crystallinity is determined, which helps in film design and performance.
Mechanical properties can be predicted from % crystallinity.
- More crystallinity = Higher strength and stiffness
- low crystallinity = high flexibility and better sealability
