Location: Plant Polymer ResearchTitle: Accelerated long-term assessment of thermal and chemical stability of bio-based phase change materials
|PATEL, JIGNESH - Us Army Research|
|GAO, ELIZABETH - Us Army Research|
|STEPHENSON, LARRY - Us Army Research|
|KUMAR, ASHOK - Us Army Research|
Submitted to: Journal of Building Physics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2015
Publication Date: 2/1/2016
Citation: Patel, J.S., Gao, E., Boddu, V.M., Stephenson, L.D., Kumar, A. 2016. Accelerated long-term assessment of thermal and chemical stability of bio-based phase change materials. Journal of Building Physics. doi: 10.1177/1744259115624178.
Interpretive Summary: Reduction in the use of fossil fuels and energy consumption are driven mainly by energy costs and climate change. Energy requirements for environmental control inside buildings and other residential structures are huge. For example, home heating, cooling, and ventilation costs are about 60-70% of the total energy in a typical home in the U.S. Innovative technologies to reduce the net heating and cooling energy requirements are very much needed. Phase change material (PCM) (e.g., butter and paraffin wax melt and solidify with small ambient temperature changes) absorb or release thermal energy in the form of latent energy near room temperatures. The use of PCM allows the storage of thermal energy over a range of temperatures; for example, absorbing solar thermal energy during the day and releasing it at night, providing significant energy savings. A relatively new bio-based commercial PCM shows large latent heat and flame retardant properties, making it suitable for incorporating into home construction. This bio-based PCM contains a form of fatty acid ester made from palm oil and soy oil (POSO), which are relatively inexpensive and can be derived from renewable agricultural sources. However, the thermal and long-term stability of these bio- PCMs need to be evaluated for wider commercial adaptation. The simulated aging studies presented in this research suggest that these materials are thermally and chemically stable for up to 20 years. The information generated in this study will benefit all parties in the value chain involved with the production of soybeans or palm fruit, from the grower through the processor and the developer. Ultimate consumers will benefit from the reduction in energy costs expended to heat or cool their home or place of business.
Technical Abstract: Thermal energy storage (TES) systems incorporated with phase change materials (PCMs) have potential applications to control energy use by building envelopes. However, it is essential to evaluate long term performance of the PCMs and cost effectiveness prior to full scale implementation. For this reason, we have used the accelerated long term approach for studying the thermal performance and chemical stability of a commercially available bio-based PCM during thermal cycling over a simulated period of 20 years. The PCM was subjected to accelerated thermal aging under controlled environmental conditions. Small samples of the PCM were periodically removed to measure its latent heat, thermal decomposition, and chemical stability using various analytical methods such as differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and infrared (IR) spectroscopy. The topographic changes in the PCM due to the aging process were observed using scanning electron microscopy (SEM). The DSC data indicate a significant reduction of 12% in the latent heat during heating and cooling cycles during the initial 6.2 years, remaining nearly constant thereafter. The TGA results showed that the PCM has excellent thermal stability within the working temperature range and also shows long term decomposition temperature stability. The FTIR spectra of the PCM indicate absorption of moisture but the PCM was chemically stable over the duration of the accelerated aging cycles. After several aging cycles, the baseline surface morphology appeared to be changed from a uniform mix of PCM materials with microstructures to segregated microstructures as evidenced by the observation of the SEM micrographs.