Degradation of Fatty Acid Phase-Change Materials (PCM): New Approach for Its Characterization

Area of Science:

• Materials Science
• Chemical Engineering
• Building Science

Background:

• Thermal energy storage (TES) systems enhance building thermal comfort and reduce energy demands.
• Phase change materials (PCMs) are effective for TES, but their long-term stability is crucial.
• Fatty acids are studied as potential PCMs for TES applications.

Purpose of the Study:

• To evaluate the thermal degradation and stability of capric and myristic acids under various thermal stresses.
• To determine if their thermophysical properties change over time during service.
• To identify potential degradation mechanisms affecting PCM performance.

Main Methods:

• Two fatty acids, capric and myristic acids, were subjected to thermal stability tests at a constant temperature (60°C for 100h and 500h).
• Thermal cycling stability was assessed by heating and cooling between 15°C and 70°C (0.5°C/min ramp) for 500 and 1000 cycles.
• Changes in thermophysical properties, particularly melting enthalpy, were measured.

Main Results:

• Myristic acid exhibited no significant changes in thermophysical properties after thermal treatments.
• Capric acid showed a 6.6% decrease in melting enthalpy after 500 hours of constant temperature treatment.
• Evidence of chemical degradation was observed in capric acid, correlating with the reduction in its thermophysical properties.

Conclusions:

• Capric acid demonstrates potential degradation issues over extended service periods, impacting its effectiveness as a PCM.
• Myristic acid appears to be a more stable option for TES applications compared to capric acid.
• Further research into the chemical degradation pathways of capric acid is needed to mitigate performance loss in TES systems.