No abstract

New levulinate ionic liquids (ILs) were able to dissolve cellulose in high amounts. The ecotoxicity profiles of these new ILs were also assessed.

Sporopollenin exine capsules (SECs) are empty microcapsules that are 25 μm in diameter and have extensive networks of ∼200 nm diameter holes obtained by chemically removing all external and internal cytoplastic materials from the natural pollen grains. We have demonstrated that a phase change material (PCM) such as n-eicosane (EIS), a natural paraffin wax, can be successfully encapsulated in the SECs to produce [EIS@SEC]. The high stability and robust nature of SECs retain EIS in the microcavity even during phase transitions, enabling EIS to fully maintain its phase change property while also protecting the EIS from elevated temperatures and corrosive environments. [EIS@SEC] can, therefore, be incorporated into cellulose (CEL) composites with a synthetic process that uses the simple ionic liquid butylmethylimmidazolium chloride to produce [CEL+EIS@SEC] composites. Similar to EIS alone, EIS in the [CEL+EIS@SEC] composites melts when heated and crystallizes when cooled. The energies associated with the crystallization and melting processes enable the [CEL+EIS@SEC] composites to fully exhibit the properties expected of PCMs, i.e., heating the surroundings when they cool and absorbing energy from the surroundings when they warm. The efficiency of latent heat storage and release of [CEL+EIS@SEC] composites was estimated to be around 57% relative to pure EIS. The fact that the DSC curves of the [CEL+EIS@SEC] composites remain the same after going through the heating-melting cycle 220 times clearly indicates that SEC effectively retains EIS in its cavity and protects it from leaking and that the [CEL+EIS@SEC] composites are highly stable and reliable as a phase change material. The [CEL+EIS@SEC] composites are superior to any other available materials based on encapsulated PCM because they are not only robust, reliable, and stable and have strong mechanical properties. They are also are sustainable and biocompatible because as they are synthesized from all naturally abundant materials using a green and recyclable synthesis. These features enable the [CEL+EIS@SEC] composites to be uniquely suited as high performance materials for such uses as dressings to treat burnt wounds, smart textiles for clothing, smart building materials, and energy storage.

Levulinate protic ionic liquids allow for the dissolution and the levulination of their parent polysaccharide.

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 ∼200 nm in diameter, which remain intact. Various substances including phase-change materials (PCMs) such as noctadecane (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.