Study of Hemp Fiber Properties Modified via Long-Duration Low-Pressure Argon and Oxygen Plasma Treatments

Hemp is a lignocellulosic fiber used in fiber-reinforced composites, technical textiles, and clothing with surface properties that can be modified by plasma to improve processability. In contrast to previous studies reporting the effects of short-duration plasma treatment (<10 min), this paper investigates the effects of extended (30 min-4 h), low-pressure (∼0.4 mbar) argon and oxygen plasma treatments on dew retted hemp fibers at varying power levels (40 and 80 Hz). Scanning electron microscopy (SEM) revealed marked surface fiber etching after prolonged treatment, with argon plasma inducing fibrillation and heterogeneous motifs, while oxygen plasma yielded irregular morphologies. Atomic force microscopy (AFM) confirmed a near 4-fold rise in surface roughness (70 to 270 nm) after 4 h of plasma treatment. All plasma-treated fibers exhibited complete wetting (water contact angle θ = 0°) versus θ = 62° for untreated controls, based on drop-shape analysis and tensiometry. Fourier transform infrared spectroscopy (FT-IR) revealed no major chemical shifts, although sharper -OH and -CO peaks suggested a subtle physicochemical change. X-ray diffraction indicated slightly enhanced crystallinity without crystallite size alteration. Fiber tensile strength remained unaffected across treatments. Fluorescence microscopy suggested a degree of lignin removal, evidenced by reduced surface fluorescence after 4 h of argon plasma treatment. Thus, long-duration argon and oxygen plasma treatments distinctly modify hemp fiber surfaces, without substantially altering internal chemistry or crystallinity. These findings highlight plasma treatment as an alternative to wet chemical methods for surficial hemp fiber modification, offering potential for precise surface engineering in textile applications.