How to improve thermal stability in use (mechanical aging over time)?

When polymers degrade due to heat, a series of chemical reactions occur that break down the long chains that make up the polymer.

1. Loss of mechanical strength:

• Chain scission: The primary culprit is chain scission, where the polymer's backbone (the long chains) breaks into smaller segments. This significantly reduces the material's ability to withstand stress and strain, making it more brittle and prone to cracking or breaking.

2. Changes in appearance:

• Discoloration: Heat can cause chemical changes in the polymer structure, leading to discoloration. This may appear as yellowing, browning, or even charring depending on the severity of the degradation.
• Surface Roughness: As the polymer chains break down, the surface can become rougher and lose its original smoothness.

3. Loss of performance:

• Reduced flexibility: Polymers often rely on their flexibility for various functions. Heat degradation can make them stiffer and less flexible, hindering their intended use.
• Deformation: In some cases, the polymer might soften or melt excessively under high heat, losing its shape and compromising its functionality.
• Changes in electrical properties: For polymers used in electrical applications, heat degradation can alter their conductivity or insulative properties, leading to malfunctions.

4. Release of volatile compounds:

• Off-gassing: As the polymer degrades, it may release volatile compounds as byproducts. These can have unpleasant odors or even be harmful depending on the specific polymer.

Amongst various methods to check degradation in polymers, following can be used to check for effect of heat:

• Thermogravimetry (TGA)
• Differential Scanning Calorimetry (DSC)
• Dynamic Mechanical Analysis (DMA)

Thermal degradation of Nylon 6,6 (Image credits: TA Instruments²)