Biocompatible and Smart Composites from Cellulose, Wool, and Phase-Change Materials Encapsulated in Natural Sporopollenin Microcapsules

摘要

Natural pollen grains were cleaned to remove all external and internal cytoplastic materials to produce sporopollenin exine capsules (SECs). SECs are empty microcapsules with extensive networks of holes that are similar to 200 nm in diameter, which remain intact. Various substances including phase-change materials (PCMs) such as n-octadecane (C18), n-eicosane (C20, EIS), n-docosane (C22), or a mixture of them (C18 + C22) can be encapsulated into the cavity of SECs. [EIS (or PCMs)@SEC] was obtained with an encapsulation efficiency of at least 76 wt %. SECs are robust and very stable. They protect encapsulated EIS during phase transitions, so they retain their phase change property and guard them against corrosive environments and elevated temperatures. [EIS@SEC] can therefore be incorporated into cellulose (CEL) and keratin (KER, from wool) composites using butylmethylimmidazolium chloride [BMIM+Cl-], a simple ionic liquid, as a sole solvent to synthesize [CEL + KER + EIS@SEC] composites. EIS in the [CEL + KER + EIS@SEC] composites behaves similarly to EIS alone. It will melt when heated and crystallize when cooled. Energy resulting from these phase transitions allows [CEL + KER + EIS@SEC] composites, like other PCMs, to warm their surroundings by releasing energy and, conversely, to cool their surroundings as they heat up by absorbing energy. The latent heat storage and release efficiency of the [CEL + KER + EIS@SEC] composites is estimated to be about 80%. After going through the heating-melting cycle 200 times, the DSC curves of the [CEL + KER + EIS@SEC] composites remained the same. This indicates that SECs are in fact fully and effectively retaining the encapsulated EIS and protecting it from leaking out. The [CEL + KER + EIS@SEC] composites are robust, have strong mechanical properties, and possess antibacterial activity. This makes them superior to other microencapsulated PCMs that are currently available. Furthermore, the composites are sustainable and biocompatible as they are synthesized from naturally abundant materials (cellulose, wool, natural pollen grains, and wax) using a green and recyclable synthesis. More importantly, the fact is that not only individual PCM such as EIS but also a mixture of two different PCMs such as a mixture of (C22 + C18) can be simultaneously encapsulated into the SEC. These features enable the [CEL + KER + EIS@SEC] composites to be uniquely suited as high-performance materials for such uses as dressings to treat infected burn wounds, smart textiles for clothing, smart building materials, and energy storage at any given temperature.