Abstract:

Objective Polyester fiber has the advantages of high strength, high elasticity, good conformability and low cost, which occupies an important position in the modern textile industry. Especially, polyester nanofiber membranes prepared by electro-spinning have a three-dimensional porous structure, excellent air permeability and high production efficiency, and received extensive attention. However, polyester nanofiber membranes have high hydrophilicity, high thermal conductivity and poor thermal stability, which are regarded as disadvantages. Therefore, it is of great importance to develop thermal insulating polyester membranes with low thermal conductivity, superhydrophobicity and flexibility for the thermal protection of workers in extreme hot and humid environments.

Method Superhydrophobic thermal insulating polyester nanofiber/silica (PETS) aerogel composite membranes were prepared by in-situ condensation of silica aerogel in the polyester nanofiber, followed by hydrophobic treatment, solvent exchange and ambient pressure drying. The structural and mechanical properties of PETS aerogel composite membrane were characterized and analyzed by scanning electron microscopy, and a universal tensile testing machine. Thermal insulating properties of PETS aerogel composite membranes were characterized by infrared thermal imager and hot disk thermal analyzer in humid environments.

Results PET and PETS aerogel composite membranes were shown to have the construction of silica aerogels in the polyester nanofibers created by in-situ condensation (Fig. 2). Within the polyester nanofiber membrane, the silica aerogel gradually developed a continuous three-dimensional porous structure as the molar ratio of ethanol to tetraethyl orthosilicate increase to 10∶1 (Fig. 4). As the content of silica aerogel increased, the tensile break strength of PETS aerogel composite membrane demonstrated a gradually decrease. Notably, the PETS₁₀ aerogel composite membrane had a stable structure in high temperature environment because the silica aerogel was tightly bound to the surface of PET nanofibers as an inorganic protective layer, which effectively inhibited the structural collapse of polyester nanofibers. Furthermore, the thermal conductivity of PETS₁₀ aerogel composite membrane was only 66.5 mW/(m·K) at 150 ℃, while the pure polyester nanofiber membrane was seriously deformed and its thermal conductivity was as high as 135.6 mW/(m·K) (Fig. 7). This was attributed to the three-dimensional nanopore structure of silica aerogel, which effectively inhibited heat transfer and endued the PETS aerogel composite membrane excellent thermal insulating properties. Benefiting from the replacement of hydrophilic Si—OH by hydrophobic Si—CH₃ in silica wet gels, the PETS aerogel composite membrane exhibited superhydrophobi-city (water contact angle of 153°) compared to the polyester nanofiber membrane (water contact angle of 17°) (Fig. 8). Therefore, the superhydrophobic PETS could effectively prevent the adsorption of water molecules, and its thermal conductivity was 74.5 mW/(m·K) at 50 ℃ and 100% high humidity, while the thermal conductivity of pure polyester nanofiber membrane was as high as 170.6 mW/(m·K) (Fig. 9). Compared with silica aerogel composites previously reported, PETS aerogel composite membrane showed a lower thermal conductivity, indicating its great potential for thermal insulation in high-temperature and humid environments.

Conclusion The PETS aerogel composite membrane is found to exhibit excellent temperature resistance, superhydrophobicity, and thermal insulation capabilities. The interfacial bonding between SiO₂ aerogel and PET nanofiber can be optimized by controlling the functional groups of the silica wet gel, thus further optimizing the mechanical properties of the PETS aerogel composite membrane. Furthermore, this strategy can also be used for modifing other nanofiber membranes with good generalizability.

Key words: polyester, nanofiber, silica aerogel, superhydrophobic composite membrane, thermal insulating material, electro-spinning