The Effect of the Fiber Diameter, Epoxy-to-Amine Ratio, and Degree of PVA Saponification on CO2 Adsorption Properties of Amine-Epoxy/PVA Nanofibers

Abstract

Achieving carbon neutrality requires not only reducing CO₂ emissions but also capturing atmospheric CO₂. Direct air capture (DAC) using amine-based adsorbents has emerged as a promising approach. In this study, we developed amine-epoxy/poly(vinyl alcohol) (AE/PVA) nanofibers via electrospinning and in situ thermal polymerization. PVA was incorporated to enhance spinnability, and B-staging of AE enabled fiber formation without inline heating. We systematically investigated the effects of electrospinning parameters, epoxy-to-amine ratios (E/A), and the degree of PVA saponification on CO₂ adsorption performance. Thinner fibers, obtained by adjusting spinning conditions, exhibited faster adsorption kinetics due to increased surface area. Varying the E/A revealed a trade-off between adsorption capacity and low-temperature desorption efficiency, with secondary amines offering a balanced performance. Additionally, highly saponified PVA improved thermal durability by minimizing side reactions with amines. These findings highlight the importance of optimizing fiber morphology, chemical composition, and polymer properties to enhance the performance and stability of AE/PVA nanofibers for DAC applications.

Keywords: amine-epoxy nanofibers; carbon capture; electrospinning; nanofiber; poly(vinyl alcohol).

Figure 1

Chemical structural formula of (a) 1,7-octadiene diepoxide (ODE), (b) ethylene glycol diglycidyl ether (EDE), (c) 1,3-bis (N,N-diglycidyl aminomethyl) cyclohexane (T-C), (d) N,N,N′,N′,-tetraglycidyl-m-xylenediamine (T-X), (e) triethylenetetramine (TETA), (f) polyethyleneimine (PEI), and (g) poly(vinyl alcohol) (PVA).

Figure 2

A schematic illustration of the electrospinning apparatus. A heat gun is positioned between the syringe and the collector, angled at 45°, to direct heat toward the fiber formation zone. Fibers are collected on a cylindrical collector.

Figure 3

A schematic diagram of the CO₂ adsorption test apparatus. Gas cylinders containing 10% CO₂/N₂ and pure N₂ are connected to mass flow controllers (MFCs). The gases are bubbled and mixed in a mixing chamber to produce a humidified gas stream at 20 °C and 50% relative humidity (RH), with a CO₂ concentration of 400 ppm. This gas is delivered to a sample placed in a water bath maintained at 20 °C, 50 °C, 65 °C, or 80 °C. CO₂ concentrations are monitored before and after the sample using CO₂ analyzers.

Figure 4

(a) Time-dependent CO₂ adsorption profiles of three web samples with distinct fiber diameters. Measurements were conducted for samples with mean fiber diameters of 383 nm, 420 nm, and 454 nm. (b) Correlation between fiber diameter and CO₂ adsorption half-time.

Figure 5

(a) Theoretical and experimental values of specific surface area as a function of fiber diameter. The blue curve represents the theoretical values calculated assuming a material density of 1.1 g/cm³. Red points indicate experimentally measured values. (b) Correlation between the mean fiber diameter and CO₂ adsorption half-time.

Figure 6

CO₂ adsorption and desorption profiles of fiber samples prepared with different epoxy-to-amine ratios (E/A). The adsorption amount is plotted as a function of time for E/A of 0.3 (red), 0.4 (green), 0.5 (black), and 0.55 (blue). The temperature is varied at 20 °C for 990 min for adsorption, and at 50 °C, 65 °C, and 80 °C for desorption for 90 min each (For E/A = 0.3, 110 min at 50 °C).

Figure 7

(a) CO₂ adsorption profiles of AE/PVA–117 before and after heat treatment. The solid blue line represents the original AE/PVA–117 sample, while the dashed blue line corresponds to the sample after heat treatment at 85 °C for 200 h. (b) CO₂ adsorption profiles of AE/PVA–217 before and after heat treatment. The solid red line represents the original AE/PVA–217 sample, while the dashed red line corresponds to the sample after heat treatment at 85 °C for 200 h.

Figure 8

FT-IR spectra of AE/PVA–117 (blue) and AE/PVA–217 (red) before and after heat treatment. Solid lines represent the original samples, and dashed lines correspond to samples after heat treatment at 85 °C for 200 h. Enlarged FT-IR spectra of AE/PVA–117 and AE/PVA–217 in the range of 1800–1000 cm⁻¹ are inserted to highlight characteristic absorption bands. Peaks corresponding to C=O (~1700 cm⁻¹), NC=O (~1500 cm⁻¹), and –O– (~1200 cm⁻¹) are annotated.

Figure 9

The proposed reaction mechanism between the acetate groups in the PVA-based polymer and the amine groups in the curing agent. The reaction leads to the formation of amide bonds, R–C(=O) –N(–R’)–R”, as suggested by FT-IR spectral changes observed after heat treatment.