Figure 1: A scientist places the sample compartment cap on a DSC instrument
Designing novel polymers and composites is full of challenges. Processes for products which use these materials will need detailed material data for proper design. Differential Scanning Calorimetry (DSC) is a workhorse technique of thermal analysis which is used to characterize the response of these materials to temperature. So what are the top 5 things Differential Scanning Calorimetry (DSC) testing can help you understand about your polymers and composites?
1. Specific Heat Capacity
Theoretical estimates of thermal properties – particularly for composites and blends – may vary by over 50%. DSC test methods, by contrast, can determine the heat capacity with an accuracy of better than 7%. Knowledge of material heat capacity is necessary to engineer thermal management systems in devices and processes – and DSC is the best way to quickly get an accurate determination of this process-critical property.
2. Glass Transition
The glass transition temperature (Tg) of a material is the key property which determines if a thermoplastic polymer will behave as a brittle material or as a rubbery material. Understanding at what temperature this physical transition occurs is key to verifying the suitability of the polymer for a given application.
Figure 2: The assignment of the glass transition temperature
A glass transition is evident on the heat flow vs temperature plot as an S-shaped kink in the baseline of the plot that is associated with the sharp change in the heat capacity of the polymer as it passes through the glass transition point. The glass transition is usually determined as the midpoint temperature of the S-shaped transition.
3. Crystallization Behavior
After the glass transition temperature, semi-crystalline and crystalline polymers may exhibit additional transitions: the cold crystallization (or, in some literature a “post crystallization”) and the melt. An amorphous polymer will only become progressively softer as temperature increases. For a crystalline or semi-crystalline material, the molecules gain more mobility within the matrix and eventually, gain enough to rearrange into a more ordered structure.
As seen in the above plot, the cold crystallization is an exothermic event. The peak may be integrated to determine the heat of crystallization, which is important to understanding process thermal management needs. The temperature at the peak maximum is reported as the crystallization temperature for a polymer material. The extent of crystallization during the process affects optical, mechanical, thermal, and chemical properties of the material, and it may be controlled by adjusting process conditions like pressure and cooling rate. Understanding the cold crystallization of the material is key to tuning the process conditions to produce a product with the desired properties.
4. Melting Behavior
Above the cold crystallization, crystalline and semicrystalline polymers will exhibit a melt, as well. The melt occurs when the material has gained enough energy to become flowable.
As seen above, the melt is an endothermic event. The temperature of the peak of the thermal event is typically reported as the melt temperature for a polymer. The heat of the melt can be determined by integrating the area under the curve.
The melt temperature is key to determining processing conditions for polymers and composites, as the temperature for plastic and composite forming processes like injection molding and extrusion is typically chosen to be above the melt, but below the thermal degradation temperature.
5. Thermal History Effects
Thermal history effects may be understood on the polymers by looking at the shift of onset temperatures for thermal events – like glass transition, melt and crystallization – as a function of thermal history. These effects are associated with changes in the mechanical and chemical properties of the material. Studying these changes is needed in determining projected lifespan and weathering of polymer materials as well as suitability of polymers and composite productsfor different applications.
TAL: DSC Expertise for Polymers and Composites Testing
Thermal Analysis Labs (TAL) offers a full range of contract testing and expertise in DSC and other techniques such as TGA, TMA, DMA, DTA, and thermal conductivity measurement. For a full overview of our services, consult our 2023 contract testing catalog. Have a question? Reach out to one of our thermal analysis experts to start the discussion.
About the Author
|Sarah manages the contract testing laboratory, Thermal Analysis Labs, at C-Therm Technologies, and has over ten years of experience in thermal analysis. She holds a Master of Science in Chemistry from the University of New Brunswick.|