Abstract:

Objective In order to overcome the dual constraints of inefficient resource recovery and persistent ecological impacts from polyethylene textile waste, this study explores the recycling of polyethylene (PE) fabric waste, a low-cost and widely used polymer, into high-conductivity carbon fiber fabrics via a simple sulfonation-induced crosslinking reaction and high-temperature charring process. The resulting carbon fiber fabrics are designed to achieve enhanced EMI shielding performance, providing an eco-friendly solution that simultaneously addresses plastic waste reduction and EMI shielding.

Method Polyethylene (molecular weight of 1 500 000) woven fabric was used as the carbon precursor. The sulfonation reaction was conducted using sulfuric acid at 130 ℃ for 3-9 h. After sulfonation, the fabric was thoroughly washed with deionized water and acetone, then vacuum-dried at 80 ℃. Charring was carried out in an argon atmosphere by heating the fabric at a rate of 10 ℃/min to 400 ℃, followed by further heating to 800-1 000 ℃. The morphology and structure of polyethylene-derived carbon fiber fabrics were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The electrical conductivity was measured using a four-point probe method, while the EMI performance was evaluated through vector network analysis in the 8.2-12.4 GHz frequency range.

Results The study revealed that sulfonation time significantly impacted the structural integrity of the fabric. An optimal duration of 6 h was identified, while prolonged sulfonation (up to 9 h) progressively loosened the woven structure and caused fiber breakage. This was attributed to the incorporation of sulfonic acid groups and subsequent fiber swelling. SEM observations showed that fibers treated for 3 h exhibited hollow interiors due to insufficient crosslinking, whereas 6-h sulfonated samples maintained their structural integrity. The prolonged sulfonation for 9 h caused deformation of the fabric structure, indicating excessive cross-linking. EDS mapping confirmed sulfur enrichment within the fabric, validating the successful sulfonation process. XRD analysis revealed a gradual attenuation of the characteristic PE crystalline peak at 2θ=21.5°, indicating the dissociation of the crystal structure due to molecular chain irregularity and solvent penetration. The charring process demonstrated strong dependencies on sulfonation duration and temperature. The carbon yield at 900 ℃ increased from 17% for the 3-h sulfonated fabric to 38% for the 9-h sulfonated fabric. However, a higher charring temperature of 1 000 ℃ led to reduced mass retention, likely due to the collapse of the carbon skeleton. Charring temperature significantly influenced the electrical conductivity, with the 1 000 ℃ charred sample achieving 321.8 S/m, compared to 36.2 S/m at 800 ℃. The EMI shielding effectiveness in the X-band also increased with higher carbonization temperatures. A 1 mm-thick sample exhibited a shielding effectiveness of 34 dB, while a 3 mm-thick sample reached 87 dB, demonstrating the material's enhanced electromagnetic wave attenuation capability. The improvement was attributed to the improved graphitic microcrystallites of the carbon fibers and the formation of robust conductive networks maintained by the well-preserved textile structure. The charred fabric exhibited excellent EMI shielding performance, effectively reducing electromagnetic wave transmission, making it a promising candidate for lightweight and flexible EMI shielding applications.

Conclusion This study successfully demonstrated that polyethylene woven fabric can be transformed into high-performance carbon fiber fabric for EMI shielding through sulfonation-induced crosslinking and charring. The results highlight carbonization temperature, sulfonation time, and fabric thickness as key factors influencing electrical conductivity and shielding effectiveness. The excellent EMI shielding performance of the carbonized fabric is primarily attributed to the formation of highly conductive carbon fiber networks, which enhance the reflection and attenuation of electromagnetic waves. These findings present a sustainable and cost-effective approach for recycling polyethylene fabric waste into efficient EMI shielding materials. Future research could explore the mechanical property optimization and scalable fabrication of polyolefin-derived carbon fabrics to meet the growing demand for low-cost, high-performance, and flexible EMI shielding materials in modern society.

Key words: polyethylene, woven fabric, charring, sulfonation, electromagnetic interference shielding, electromagnetic protective material