Abstract:

Objective Latent heat energy storage materials absorb and release the latent heat during phase change, which could provide a kind of efficient and clean energy storage method. Electrospun fibrous membranes have potential application prospects in various latent heat energy storage materials. However, challenges remain in the development of eco-friendly phase change materials (PCMs) with high thermal conductivity and no leakage. Hence, the study of efficient latent heat energy storage materials as green energy carrier has essential scientific significance and potential application prospects.

Method Polycaprolactone (PCL) has been widely used as a medical biodegradable material and drug release system because of its good biodegradability and biocompatibility. However, few studies of the PCM composite based on PCL matrix were carried out. In order to explore polycaprolactone (PCL) as a kind of eco-friendly polymer in the application of phase change energy storage fibers, this paper proposes a new type of composite phase change fibers consisting of PCL as sheaths, polyethylene glycol (PEG) and hydroxylated multiwall carbon nanotubes (MWCNTs-OH) as cores by coaxial electrospinning.

Results The obtained PCL/PEG/MWCNTs-OH phase change composite fibers have smooth surface and core-shell structure, and the introduction of MWCNTs-OH did not affect the core-sheath structure of the fiber (Fig.3), and the thermal conductivity of the fiber is greatly improved. When the mass fraction of MWCNTs-OH reaches 4%, the thermal conductivity of PCL/PEG/C4 fiber membrane increases to 0.121 8 W/(m·K) (Fig.4). Compared with PCL/PEG membrane without MWCNTs-OH, the thermal conductivity of PCL/PEG/C4 fiber membrane increases by 9.53%. Meanwhile, the thermal stability of PCL/PEG/MWCNTs-OH enhance remarkably because of the addition of MWCNTs-OH in the core layer. Moreover, the PCM composites display the desirable thermal reliability as well as the effective temperature regulation capacity. It is almost no change of latent heat for the PCL/PEG/C4 after 100 thermal cycles (Fig.7). It is clear that PCL sample presents much faster temperatare rise and decrease rates than PCL/PEG/C4 PCM composite (Fig.8). The thermal energy storage and release time of PCL/PEG /C4 are 33.3% and 48.8% longer than that of PCL, suggesting the existence of PEG in the PCM composite could realize the effective thermal energy regulation. Derived from the excellent mechanical properties of PCL and MWCNTs-OH, composite phase change fibrous membranes exhibit higher tensile strength and elongation at break, and the composite phase change fibrous membrane containing 4% MWCNTs-OH has a tensile strength of 7.43 MPa and elongation at break of 132.2%. Compared with PCL/PEG, the tensile strength and elongation at break of the composite phase change fibrous membranes with MWCNTs-OH are significantly improved, showing excellent mechanical properties that are conducive to its repeated use in practical applications.

Conclusion In summary, a series of PCL/PEG/MWCNTs-OH composite phase change fibrous membranes have been prepared by coaxial electrospun in this research, exhibiting perfect thermal conductivity and thermal stability by virtue of the addition of MWCNTs-OH. Since the components of composite phase change fiber are physically mixed, the phase change characteristics of PEG remain unchanged, and the melting temperatures of composite phase change fibrous membranes have no obvious change, ranging between 38.85 ℃ and 39.35 ℃, slightly higher than the normal temperature of human body. Therefore, the composite phase change fibrous membranes are promising for the biomedical materials with temperature regulation. The proposed method provides a new avenue for degradable phase change fibrous membrane to simultaneously achieve robust mechanical properties and leakage-free.

Key words: polycaprolactone, polyethylene glycol, hydroxylated multiwalled carbon nanotubes, coaxial electrospinning, composite phase change fibrous membrane, phase change material