When to Use Thermomechanical Analysis to Characterize Your Polymers and Polymer Composites

Introduction

Thermomechanical Analysis, or TMA, is a sensitive tool for measuring and analyzing thermal behavior in polymers and polymer composites. TMA measures thermal expansion anisotropy directly and precisely; thus, it is the ideal tool to characterize the properties of materials. This method can also be utilized to determine the softening point of polymers and composites under different loads and measure the glass transition temperature of thermoplastics. Further to understanding thermal history, TMA may also assess and measure the mechanical properties of polymers and composites. This is essential during design and development processes with products employing these materials.

Scope

TMA testing can inform mechanical designs, revealing information on a material’s processing conditions. Furthermore, TMA has an advantage over other thermal expansion techniques since it employs a vertical expansion measuring configuration, which removes inaccuracies brought on by bending or sagging of the equipment. This makes it possible to use incredibly low forces, improving and increasing measurement accuracy on rubbery and soft materials. TMA is accessible to low-budget researchers as it does not require an expensive optical table or sound cancellation. In a nutshell, TMA is a powerful tool used to characterize polymers and polymer composites, providing valuable insight into the thermal and mechanical properties of material. 

Procedure

The TMA working procedure measures the dimensional changes of a sample when exposed to controlled variations in temperature, time, and mechanical force. The preparation of samples starts with meeting the specified dimensions and surface quality. The prepared sample is placed on a sample holder within the TMA instrument, and a probe—selected based on the analysis type (e.g., expansion, penetration, or tension)—is positioned in contact with the sample. The instrument is programmed with a temperature profile (heating, cooling, or isothermal) and force application mode (static or dynamic). During the test, measurements are made continuously on probe dimensions of changes in the dimensions, which are captured as a function of the condition. Data was obtained and analyzed to get features like the coefficient of thermal expansion, glass transition temperature, and behavior due to material softening.

Sample size

The following are the technical specifications of ASTM C848:

Result

TMA results provide critical insights into the thermal and mechanical properties of polymers and composites:

1. Coefficient of Thermal Expansion (CTE)
2. Glass Transition Temperature (Tg)
3. Softening and Decomposition
4. Creep and Stress Relaxation
5. Composite Behavior

Factors Affecting Thermomechanical Analysis (TMA)

• Thermal conductivity: Materials composites or polymers with low thermal conductivity may exhibit a delayed or unbalanced response to heating or cooling.
• Viscoelasticity: Material exhibiting time-dependent deformation: The analysis becomes difficult for static dimensional modifications.
• Moisture Content: Hygroscopic materials can absorb or release moisture during the test, affecting their dimensions and thermal properties.
• Temperature Range and Rate: The heating or cooling rate usually affects the resolution of transitions such as Tg. Faster rates might miss subtle transitions, whereas slower rates give more detailed data.

Conclusion

Thermomechanical Analysis (TMA) is an essential tool for polymer and polymer composite characterization regarding thermal and mechanical behavior. These insights are crucial for material selection, product design, quality control, and failure analysis in the automotive and aerospace industries. However, this test method provides precise and reliable data by preparing the sample, calibrating the instrument, and using experimental conditions to ensure the accuracy of results. Thus, researchers and engineers can integrate TMA into their material characterization workflows to ensure optimal performance and reliability in various applications of polymer-based materials.

FAQ’s