Abstract:

Objective Driven by strong market growth in functional textiles and rising demand for waterproofness and moisture permeability, current fabrication of waterproof and moisture permeable materials face key certain challenges, in that single-polymer systems cannot simultaneously achieve water resistance and moisture permeability, that multi-step post-treatments to fabric substrates are complex and costly, and that the mechanistic insights into composites remain limited. In order to address these issues, a SEBS/FPI composite was developed by a one-step electrospinning process to produce high-performance waterproof and moisture permeable fibrous membranes. Elucidating the relationships between structure and property in the composite provides theoretical guidance and technical support for next-generation functional textile design.

Method Styrene-ethylene-butene-styrene (SEBS) was selected for its excellent flexibility and hydrophobicity, and fluorinated polyimide (FPI) for its ultra-low surface energy and superior chemical stability. Using tetrahydrofuran (THF) as the solvent, SEBS/FPI membranes were fabricated by a single-step electrospinning process. The influence of SEBS/FPI ratio on the membranes' microstructure, pore morphology, waterproof and moistave permeable properties and mechanical properties was systematically investigated, and the synergistic mechanisms arising from the interactions between the two polymer components were analyzed.

Results With FPI fixed at 1%, SEBS was varied at 10%, 12%, 14%, and 16%, it was found that as SEBS content increased, the solution viscosity rose, causing the average fiber diameter to increase from 739 nm to 1 269 nm. Concurrently, fiber fusion intensified, leading to the reduction of membrane porosity from 75.47% to 63.18%, maximum pore size from 4.3 μm to 2.8 μm, and mean pore size from 1.8 μm to 0.6 μm. The decrease in relative FPI content also led to a reduction in water contact angle from 134.7° to 108.4°. Smaller pores and lower porosity resulted in a drop in air permeability from 13.12 mm/s to 6.24 mm/s and a decrease in water vapor transmission rate from 15.55 kg/(m²·d) to 12.42 kg/(m²·d), while hydrostatic pressure increased from 18.1 kPa to 27.0 kPa. The optimal balance of waterproofness and moistnre permeability was achieved at 12% SEBS, where the membrane exhibited a water contact angle of 132.5°, hydrostatic pressure of 21.8 kPa, and a water vapor transmission of 14.53 kg/(m²·d). Next, with SEBS fixed at 12%, FPI content was varied at 2%, 5%, 8%, and 11%, increasing FPI content reduced solution viscosity and average fiber diameter from 636 nm to 460 nm. While fiber fusion decreased, membrane porosity was increased from 57% to 72%, maximum pore size from 1.8 μm to 3.2 μm, and mean pore size from 0.61 μm to 1.3 μm. Higher fluorine content raised the water contact angle from 132.2° to 138°. The enlarged pore structure enhanced air permeability from 2.59 mm/s to 7.31 mm/s, and water vapor transmission rate from 9.08 kg/(m²·d) to 18.08 kg/(m²·d), but reduced hydrostatic pressure from 53.8 kPa to 11.0 kPa. The composite membrane reached its best overall performance at 5% FPI, exhibiting a water contact angle of 132.9°, hydrostatic pressure of 53.4 kPa, water vapor transmission rate of 9.71 kg/(m²·d), tensile strength of 4.6 MPa, and elongation at break of 90.6%.

Conclusion A high-performance waterproof and moisture permeable fibrous membrane was fabricated by a one-step electrospinning process using a SEBS/FPI composite system. Single-factor optimization identified the optimal formulation as 12% SEBS and 5% FPI. The resulting composite membrane exhibited outstanding performance, with a hydrostatic pressure of 53.4 kPa, a water vapor transmission rate of 9.71 kg/(m²·d), a tensile strength of 4.6 MPa, and an elongation at break of 90.6%. Mechanism analysis indicated that the introduction of fluorine-containing groups into the FPI molecular chain endows it with low surface energy characteristics, thereby reducing the overall surface energy of the composite fiber membrane. Additionally, the rigid chain structure of FPI reduces the viscosity of the spinning solution, improves the stability of the jet, and promotes the formation of fine fibers and optimized the membrane's micro-porous structure. This is the first attempt to apply a SEBS/FPI composite system for waterproof and moisture permeable membranes, which expands the range of electrospun raw materials and establishes a clear composition-structure-property relationship. As a polymeric material, FPI is not prone to migration or accumulation in the environment. Moreover, fluorine atoms are stably incorporated into the polymer backbone in the form of C—F covalent bonds, preventing the release of free fluoride ions. The fabricated fibrous membranes show great promise for medical protective clothing, everyday protective gear, and other applications, providing a new technical pathway and theoretical foundation for the industrialization of high-performance waterproof and moisture permeable materials.

Key words: functional material, electrospinning, waterproof and moisture permeable, styrene-ethylene-butene-styrene, fluorinated polyimide, nanofibrous membrane