UBC Theses and Dissertations
Cellulose nanofibrils aerogel with enhanced thermal management performance Song, Mingyao
This study aimed to improve the thermal management and mechanical performance of cellulose nanofibrils (CNF) aerogels. We expected that closed-pore structure of CNF aerogel can be gained by Pickering emulsion templating and solvent exchange method, and that paraffin can be encapsulated by CNF to fabricate CNF/Phase change material (PCM) aerogel with excellent stability, super thermal regulation performance, and flexibility. It was also expected that the addition of CNF to prepared emulsion can enhance the structure to further improve the thermal management and mechanical performance. First, CNF aerogels with closed internal pores were successfully fabricated by Pickering emulsion templating and solvent exchange techniques. CNF stabilized oil-in-water Pickering emulsion can be converted into closed pores by sequential solvent exchanging to acetone and tert-butanol, followed by freeze drying from tert-butanol to suppress the formation of large ice crystals. The closed pore was verified by both confocal microscopy and scanning electron microscopy images, and was confirmed to reduce thermal conductivity for aerogel. In addition to the ultra-low thermal conductivity, the CNF/emulsion composite aerogel also demonstrates high performance in properties such as low density, high mechanical properties, superb flexibility, and infrared shielding properties. In addition, robust CNF/PCM aerogels were successfully fabricated with CNF stabilized paraffin by Pickering emulsion templating technique. The CNF/PCM aerogels were ultralight with impressive mechanical properties, which were significantly enhanced by the addition of CNF to the as-formed PCM emulsion. The freeze-dried CNF/PCM aerogels were flexible, and the shape of CNF/PCM aerogel can be well maintained even loaded with a weight of over thousands of times its own weight. The exceptional thermal regulation performance was demonstrated by a series of heating and cooling tests. The CNF/PCM aerogels exhibited excellent shape stability with no leakage after 51 heating-cooling thermal cycles. The latent heat of CNF/PCM aerogel (4:6) can reach approximately 84.4% of that of pure paraffin. In brief, this work fabricated sustainable CNF aerogel with closed-pore structure for the first time, and also obtained CNF/PCM aerogel with high shape stability and energy density. The thermal management and mechanical performance of CNF aerogel were significantly improved.
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