Electrospinning of Ultrafine Poly(1-trimethylsilyl-1-propyne) [PTMSP] Fibers: Highly Porous Fibrous Membranes for Volatile Organic Compound Removal

Poly­(1-trimethylsilyl-1-propyne) [PTMSP] possesses a rigid backbone chain with bulky trimethylsilyl side groups which limit the rotational freedom and provide packing-inefficiency that leads extremely high free volume. PTMSP is a hydrophobic polymer showing solubility in common organic solvents such as chloroform and tetrahydrofuran. Therefore, it can be formed as self-standing dense membrane (film). Hence, PTMSP is widely studied for separation applications owing to these outstanding properties. The aim of this research is to produce self-standing poly­(1-trimethylsilyl-1-propyne) [PTMSP] fibrous membrane via electrospinning method to further enhance the application area of PTMSP. Electrospinning was achieved using tetrahydrofuran/tetrachloroethane (1:2 v/v) solvent mixture. Extensive optimization studies were performed to obtain bead-free and uniform ultrafine fibers which were obtained at 3.5% (w/v) polymer concentration with respect to solvent, and beads-on-string morphology was obtained below this concentration as confirmed by SEM imaging. Random and aligned fibers were produced using a stationary and a rotating collector, respectively. The optimized sample (P6), which was produced using 12 kV voltage and 20 cm tip-to-collector distance, possesses an average fiber diameter of 1.4 ± 0.4 μm. Additionally, PTMSP dense membrane was fabricated by solvent evaporation method to compare the properties with fibrous membrane. Structural characterization and elemental composition of PTMSP samples were conducted using FT-IR and 1H NMR and XPS spectroscopies. Hydrophobicity of the samples was compared using their water contact angle measurements. While PTMSP dense membrane shows 90 ± 2°, the electrospun PTMSP fibrous membranes possess hydrophobic nature having 145 ± 5° and 152 ± 2° water contact angles for fibers having aligned and random morphology, respectively. In addition, fibrous membrane possesses high surface area that is the same as powder form showing ∼850 m2/g BET surface area which is slightly higher than that of dense membrane (780 m2/g). Consequently, the high surface area electrospun PTMSP fibrous membrane was tested for volatile organic compounds (VOCs) removal as it can accommodate a significant amount of organic molecules in its porous structure. Furthermore, the VOC entrapment capacity of dense and fibrous membrane was compared using aniline, benzene, and toluene as model compounds. PTMSP membranes have shown the highest uptake for aniline where the uniform fiber morphology was maintained after sorption for fibrous membrane. In addition, lower boiling point VOCs, benzene and toluene, were trapped in fibrous membrane higher that the dense membrane since they cause swelling in fiber morphology