Large-Scale Nanofiber Manufacturing| Facile fabrication of environmentally friendly and mechanically robusttransparent, waterproof, and breathable fibrous membranes

Prof. Huang Gang & Assoc. Prof. Zhao Jing et al. from Wuyi University: Facile Fabrication of Environmentally Friendly and Mechanically Robust Transparent, Waterproof, and Breathable Fibrous Membranes

Functional fibrous membranes combining optical transparency, waterproofness and breathability are in high demand for various applications. However, these materials remain underdeveloped due to significant technical manufacturing challenges. Moreover, current processes using hazardous solvents raise environmental and health concerns.

Researchers from Wuyi University - Prof. Huang Gang, Assoc. Prof. Zhao Jing, Prof. Wang Xianfeng and Assoc. Prof. Feng Qi - developed a safe, simple and efficient method to fabricate transparent, waterproof and breathable membranes (TWBMs) using an eco-friendly process combining electrospinning with ethanol as green solvent and thermal curing of fluorine-free paraffin emulsion coating.

The electrospinning process employed ethanol-soluble polyamide/waterborne polymer isocyanate fibers. The wax coating provided excellent waterproofness while enhancing mechanical strength. An optimized thermal curing process precisely controlled porous structure and membrane thickness, achieving high transparency while preserving micropores essential for breathability.

The resulting membranes demonstrated:

• 90% transmittance

• 111.4 kPa water resistance

• 5.3 kg m-2 d-1 water vapor permeability
  Outperforming commercial transparent materials. Published in Chemical Engineering Journal as "Facile fabrication of environmentally friendly and mechanically robust transparent, waterproof, and breathable fibrous membranes."

Figure 1. Preparation of high-performance and environmentally friendly transparent, waterproof and breathable membranes (TWBMs) using ethanol-soluble polyamide (EPA) and waterborne polymer isocyanate (API) electrospun materials coated with paraffin wax emulsion (PWE) (EPA/API@PWE): (a) Schematic diagram of preparation process; (b) Images demonstrating waterproof and breathable properties of prepared TWBMs; (c) Schematic illustration showing transition from opaque to transparent in fiber membranes after thermal curing treatment; (d) Images displaying transparency and haze effects of EPA/API@PWE TWBMs, with length scale indicating distance between membrane and flower below.

Fabrication Process:

1. EPA/API Fiber Electrospinning:

   • Dissolved EPA chips in anhydrous ethanol

   • Slowly added API emulsion under mechanical stirring

   • Electrospun homogeneous EPA/API solution into fibers

2. PWE Emulsion Immersion:

   • Immersed EPA/API fibers in aqueous fluorine-free PWE emulsion

   • Coated fiber surfaces with PWE

   • Enhanced hydrophobicity, reduced pore size, improved bonding structure

3. Thermal Curing:

   • Dried PWE-coated membranes

   • Cured EPA/API@PWE-3 membrane at various temperatures

   • Precisely controlled porosity and thickness

   • Maintained breathable micropores while achieving transparency

   • Significantly enhanced mechanical strength

Figure 2. Characterization of PWE-coated EPA/API nanofiber membranes (NFMs) with different PWE concentrations (0, 1, 3, and 5 wt%).

Figure 3. Scanning electron microscopy (SEM) images of EPA/API@PWE-3 nanofiber membranes (NFMs) obtained at different curing temperatures: (a) 120°C, (b) 150°C, (c) 180°C, and (d) 210°C. Characterization of EPA/API@PWE-3 nanofiber membrane samples obtained at different curing temperatures: (e) Thickness, (f) Porosity and dmax, (g) Water contact angle (WCA). (h) Optical image demonstrating the flexibility of nanofiber membrane sample obtained at 150°C curing temperature.

Figure 4. Optical properties of EPA/API@PWE-3 nanofiber membranes (NFMs) obtained at different curing temperatures: (a) Total light transmittance and (b) haze; (c) Light transmittance and haze at 550nm incident wavelength. (d) Comparison of light transmittance at 550nm incident wavelength between EPA/API@PWE-3 nanofiber membrane and other commercial transparent materials. Optical images of EPA/API@PWE-3 nanofiber membranes obtained at different curing temperatures: (e) Demonstration of tunable optical properties; (f) Demonstration of light scattering effects. (g) Potential application demonstration of EPA/API@PWE-3 nanofiber membrane as industrial equipment cover.

Figure 5. Schematic diagrams of mechanisms affecting waterproof and breathable performance of EPA/API@PWE-3 nanofiber membranes (NFMs): (a) Waterproofness; (b) Breathability. Characterization of EPA/API@PWE-3 nanofiber membrane samples obtained at different curing temperatures: (c) Hydrostatic pressure and water vapor transmission rate (WVT); (d) Breathability; (e) Tensile strength and elongation. Comparison of EPA/API@PWE-3 nanofiber membrane prepared at 150°C curing temperature with other commercially available transparent membranes: (f) Hydrostatic pressure and WVT; (g) Tensile strength and elongation; (h) Breathability.

This study addresses the lack of functional membranes combining transparency, waterproofness and breathability by developing high-performance eco-friendly TWBMs. The method integrates:

• Green electrospinning (ethanol solvent with EPA/API materials)

• Fluorine-free PWE coating (reduces pores, enhances bonding, provides hydrophobicity)

• Optimized thermal curing (controls porosity/thickness)

The EPA/API@PWE-3 membrane cured at 150°C showed outstanding properties:

• Hydrostatic pressure: 111.4 kPa

• Moisture permeability: 5.3 kg·m⁻²·d⁻¹

• Light transmittance: 90%

• Tensile strength: 21.2 MPa

• Elongation: 568%

The random fiber network maintained inherent breathability while minimizing light transmission loss for optical transparency. This work provides valuable insights for next-generation TWBMs and enables new applications in various fields requiring simultaneous transparency, waterproofing and breathability.