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UBC Theses and Dissertations

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UBC Theses and Dissertations

Pickering emulsion of cellulose nanofibrils stabilized phase change materials for thermal management applications Zheng, Yi

Abstract

Phase change materials (PCM) has been increasingly used over the past decades to combat the large amount of energy needed for thermal comfort of human beings. Organic PCM is desired in temperature control, but it suffers from thermal leaking and unstable form during phase transition. This study aimed to develop cellulose nanofibrils (CNF) – phase change mamterials based functional materials for thermal management applications. PCM, using paraffin as an example, is encapsulated into micron-sized emulsions using CNF as interfacial stabilizer. We expected that microencapsulation using CNF can improve the flexibility and thermal stability of PCM, and such emulsion can be used in various applications such as spray coating and 3D printing. Firstly, CNF/PCM Pickering emulsion can be stabilized due to the amphiphilic nature and strong network of CNF with optimized sonication conditions, including sonication time and amplitude, ratio of CNF and PCM, and CNF concentrations. Results indicated uniform PCM emulsion particles of 4.2 ± 2.1 μm could be obtained using 0.8 wt.% CNF suspension sonicated at 100%A and 7 mins with 2:8 paraffin to CNF ratio. The CNF-stabilized paraffin emulsion showed excellent long-term stability with unchanged particle size when stored at 45 °C for 28 days. In addition, differential scanning calorimetry (DSC) results showed high thermal stability after 51 heating-cooling cycles. The CNF-stabilized paraffin Pickering emulsion demonstrated improved thermal stability and versatility for spray-coating application, which can coat a regular polyester-cotton fabric to improve its thermal shielding performance, without sacrificing its flexibility. Secondly, the CNF-stabilized paraffin Pickering emulsion can serve as a gradient to prepare CNF/paraffin printable ink for direct-ink-writing 3D printing. The rheological properties of the inks were characterized in details to demonstrate their printability. Lightweight 3D printed scaffold (35.0 mg/cm³ for pure CNF matrix) endowed the composite monolith with high PCM loading (up to 82% with respect to the composite) and high thermal storage capacity (up to 153 J/g).

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Attribution-NonCommercial-NoDerivatives 4.0 International