Shape-stabilization of polyethylene glycol phase change materials with chitin nanofibers for applications in "smart" windows

Green, recyclable and high latent heat form-stable phase change composites supported by cellulose nanofibers for thermal energy management

Efficiently addressing the challenge of leakage is crucial in the advancement of solid-liquid phase change thermal storage composite materials; however, numerous existing preparation methods often entail complexity and high energy consumption. Herein, a straightforward blending approach was adopted to fabricate stable phase change nanocomposites capitalizing on the interaction between TEMPO-oxidized cellulose nanofibers (TOCNF) and polyethylene glycol (PEG) molecules. By adjusting the ratio of TOCNF to PEG and the molecular weights of PEG, TOCNF/PEG phase change composites (TPCC) with customizable phase transition temperature (40.3-59.1 °C) and high phase transition latent heat (126.3-172.1 J/g) were obtained. The TPCC of high-loaded PEG (80-95 wt%) ensured a leakage rate of less than 1.7 wt% after 100 heating-cooling cycles. Moreover, TPCC exhibits excellent optical properties with a transmittance of over 90 % at room temperature and up to 96 % after heating. The thermal response analysis of TPCC demonstrates exceptional thermal-induced flexibility and good thermal stability, as well as recyclability and reshaping ability. This study may inspire others to design bio-based phase change composites with potential applications in thermal energy storage and management of smart-energy buildings, photothermal response devices, and waste heat-generating electronics.

Keratin protein nanofibers from merino wool yarn: a top-down approach for the disintegration of hierarchical wool architecture to extract α-keratin protein nanofibers

We report the extraction of keratin nanofibers from the medulla of a parent yarn after denaturing the cuticle and cortex microstructures of a merino wool yarn. Controlled alkaline hydrolysis, followed by high-speed blending in acetic acid, allowed for the extraction of keratin protein nanofibers with an average diameter of 25 nm and a length of less than 3 μm. SEM and AFM analyses showed the removal of cuticle cells from the yarn. FT-IR and DSC analyses confirmed the hydrolysis and denaturation of the sheet protein matrix of cuticle cells. XPS analysis provided strong evidence for the gradual removal of the epicuticle, cuticle cells, and cortex of the hierarchical wool structure with an increase in alkaline hydrolysis conditions. It was confirmed that the merino wool yarn subjected to hydrolysis under alkaline conditions exposed its internal fibrillar surface. In an acetic acid medium, these fibrillar surfaces obtained a surface charge, which further supported the defibrillation of the structure into its individual nanofibrils during high-speed blending. The extracted nanostructures constitute mainly α-helical proteins. The morphology of the nanofibers is composed of a uniform circular cross-section based on the images obtained using AFM, TEM, and SEM. The extracted nanofibers were successfully fabricated into transparent sheets that can be used in several applications.

Bio-Based Polymers for Environmentally Friendly Phase Change Materials

Phase change materials (PCMs) have received increasing attention in recent years as they enable the storage of thermal energy in the form of sensible and latent heat, and they are used in advanced technical solutions for the conservation of sustainable and waste energy. Importantly, most of the currently applied PCMs are produced from non-renewable sources and their carbon footprint is associated with some environmental impact. However, novel PCMs can also be designed and fabricated using green materials without or with a slight impact on the environment. In this work, the current state of knowledge on the bio-based polymers in PCM applications is described. Bio-based polymers can be applied as phase-change materials, as well as for PCMs encapsulation and shape stabilization, such as cellulose and its derivatives, chitosan, lignin, gelatin, and starch. Vast attention has been paid to evaluation of properties of the final PCMs and their application potential in various sectors. Novel strategies for improving their thermal energy storage characteristics, as well as to impart multifunctional features, have been presented. It is also discussed how bio-based polymers can extend in future the potential of new environmentally-safe PCMs in various industrial fields.

Microencapsulated phase change material via Pickering emulsion based on xylan nanocrystal for thermoregulating application

Phase change materials (PCM) are promising for thermal regulation and energy storage, but suffer from the deformation and leakage of capsules. Herein, inspired by cellulose nanocrystal (CNC), xylan nanocrystal (XNC) with a dimension of 25-60 nm was successfully prepared through oxalic acid hydrolysis of high-crystalline xylan as raw materials via a top-down approach. With the introduction of hydrophobic groups, compared to XNC, succinylated XNC showed more remarkable emulsifying property over 7 days of storage at room temperature. Microencapsulated PCM composite consisting of sodium alginate (SA) as "matrix" and succinylated xylan nanocrystal (XNC) stabilized paraffin-based Pickering capsule (PCM beads) as "core" was facilely fabricated. PCM composite with the latent heat of 105.59 J·g^-1 showed excellent thermoregulating performance. Our work suggests a new pathway toward sustainability of hemicelluloses in the application of food emulsion and thermal energy management.

Fibrous form-stable phase change materials with high thermal conductivity fabricated by interfacial polyelectrolyte complex spinning

Polyethylene glycol (PEG)-based composite phase change materials (PCMs) containing hydroxylated boron nitride (BN-OH), cellulose nanofiber (CNF), and chitosan (CS) were prepared by the method of interfacial polyelectrolyte complex spinning, based on in-situ ionic cross-linking between CNF and CS. The wrapping effect of cross-linked CNF/CS networks and the strong interfacial interactions contributed to superior shape-stability throughout the phase change process. Furthermore, the homogeneously dispersed BN-OHs was beneficial to the construction of the continuous thermal conductive paths, and the excellent interfacial interactions between BN-OH and the matrix would lower the heat loss caused by phonon scattering in the interface. As a result, the thermal conductivity of the PCMs containing 47.5 wt% BN-OH reached 4.005 W/mK, which was 22.56 times higher than that of the pure PEG. Combined with the excellent thermal reliability and thermal stability, the form-stable PCMs showed a promising application potential in the fields of electronic cooling or temperature-adaptable textiles.