Magnetic cellulose nanocrystals hybrids reinforced phase change fiber composites with highly thermal energy storage efficiencies

Intrinsically Flexible Phase Change Fibers for Intelligent Thermal Regulation

Owing to the significant latent heat generated at constant temperatures, phase change fibers (PCFs) have recently received much attention in the field of wearable thermal management. However, the phase change materials involved in the existing PCFs still experience a solid-liquid transition process, severely restricting their practicality as wearable thermal management materials. Herein, we, for the first time, developed intrinsically flexible PCFs (polyethylene glycol/4,4'-methylenebis(cyclohexyl isocyanate) fibers, PMFs) through polycondensation and wet-spinning process, exhibiting an inherent solid-solid phase transition property, adjustable phase transition behaviors, and outstanding knittability. The PMFs also present superior mechanical strength (28 MPa), washability (>100 cycles), thermal cycling stability (>2000 cycles), facile dyeability, and heat-induced recoverability, all of which are highly significant for practical wearable applications. Additionally, the PMFs can be easily recycled by directly dissolving them in solvents for reprocessing, revealing promising applications as sustainable materials for thermal management. Most importantly, the applicability of the PMFs was demonstrated by knitting them into permeable fabrics, which exhibit considerably improved thermal management performance compared with the cotton fabric. The PMFs offer great potential for intelligent thermal regulation in smart textiles and wearable electronics.

Eco-friendly synthesis of chemically cross-linked chitosan/cellulose nanocrystal/CMK-3 aerogel based shape-stable phase change material with enhanced energy conversion and storage

Phase change materials (PCMs) have attracted numerous attention owing to their high energy storage density, cost-effective and operationally simple, however, the "solid-liquid" leakage and limited solar absorbance seriously hinder their widespread applications. Herein, an innovative chitosan/cellulose nanocrystal/CMK-3 (CS/CNC/CMK-3) aerogel based shape-stable PCM (SSPCM) was successfully synthesized, in which chemically cross-linked CS and CNC acted as three-dimensional supporting skeleton, CMK-3 endowed solar-to-thermal energy conversion ability and the impregnating polyethylene glycol (PEG) acted as the latent heat storage unit. The as-synthesized CS/CNC/CMK-3 aerogel/PEG (CCCA/PEG) showed ultrahigh melting/crystallization enthalpy of 178.5/171.1 J g-1 and excellent shape stability. The PEG was effectively embedded into the hierarchical porous architecture and the composite PCM could preserve its original shape without any leakage even compressed above the melting point of PEG. Meanwhile, the CCCA/PEG exhibited robust thermal reliability with an ultralow enthalpy fading rate of 0.030 ± 0.012 % per cycle over 100 thermal cycles. Intriguingly, the introduction of CMK-3 also significantly improved the solar-to-thermal energy conversion performance of CCCA/PEG, and a high solar-to-thermal conversion efficiency of 93.1 % could be realized. This work provided a potential strategy to design and synthesize high-performance sustainable SSPCM, which showed tremendous potential in the practical solar energy harvesting, conversion and storage applications.

Preparation and Analysis of Sheath-Core Intelligent Thermo-Regulating Fiber

In this work, a skin-core composite intelligent temperature-adjusting fiber was prepared using the composite melt spinning method, with polypropylene as the skin layer and T28-type paraffin as the core layer, in order to obtain clothing fibers with a bidirectional temperature adjustment function. A differential scanning calorimeter was used to test the phase-change latent heat of fibers with different amounts of paraffin injections, and an infrared thermal imager was used to monitor the skin-core composite intelligent temperature-adjusting fiber bundles and ordinary polypropylene fiber bundles under the same heating and cooling conditions. The temperature of the fiber bundle was considered to be a function of time. The results showed that with the increase in the amount of the paraffin injections, the proportion of the paraffin component in the fiber and the latent heat of the fiber phase transition also increased. When the paraffin injection amount was 1.5 mL/min, the melting enthalpy and the crystallization enthalpy reached 65.93 J/g and 66.15 J/g, respectively. Under the same conditions, the heating speed of the intelligent temperature-adjusting fiber bundle was found to be slower than that of the ordinary polypropylene fibers, and the maximum temperature difference between the two reached 8.0 °C. Further, the cooling speed of the former was also observed to be slower than that of the latter, and the maximum temperature difference between the two reached 6.7 °C.

Form-stable phase change composites based on nanofibrillated cellulose/polydopamine hybrid aerogels with extremely high energy storage density and improved photothermal conversion efficiency

The development of form-stable phase change materials (PCMs) with superior photothermal conversion efficiency and high phase change enthalpy is critical for the utilization of solar energy. In this work, nanofibrillated cellulose (NFC)/polydopamine (PDA) hybrid aerogels (NPAs) were synthesized by cation-induced gelation of NFC/PDA suspension. Then, novel form-stable PCMs with superior energy storage density and improved photothermal conversion efficiency were successfully synthesized by impregnating n-octacosane into NPAs. Differential scanning calorimetry (DSC) analysis showed that the composite PCMs exhibited extremely high phase transition enthalpy (>248 J g-1) and excellent thermal reliability. Thermogravimetric analysis (TG) showed that the composite PCMs exhibited excellent thermal stability. In photothermal experiments, PDA acted as a photon trap and effectively improved the photothermal conversion efficiency (up to 86.7%) of the composite PCMs. In conclusion, the synthesized composite PCMs displayed high phase change enthalpy and superior photothermal conversion efficiency, suggesting their promising characteristics for solar energy utilization applications.