Effect of fiber length and treatments on the hygroscopic properties of milkweed fibers for superabsorbent applications

Abstract

This study investigated the influence of pre-treatment methods and size distribution on the hygroscopic properties of milkweed fibers (MW). Pre-treatment methods included hydrothermal treatment and hybrid treatment, which involves the hydrothermal treatment followed by the alkaline treatment. Scanning electron microscope (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) were used to investigate the effect of pre-treatments on morphology, chemical composition, and crystallinity of milkweed fibers, respectively. Brunauer–Emmett–Teller (BET) surface area analysis was also used to measure the surface area of milkweed fibers after each pre-treatment. The results revealed that only after 5 min of stirring, hydrothermal treatment and hybrid treatment enhanced the water absorption capacity of non-treated MW fibers from 18 ± 4 g/g to 54 ± 4 g/g and 50 ± 1 g/g, respectively. The SEM and FTIR confirmed the removal of waxes from the surface of milkweed fibers after applying hydrothermal treatment without causing any changes to the hollow structure of fibers. Hydrothermal treatment improved hydrophilicity and hence better hygroscopic characteristics of MW fibers, as evidenced by increased absorption capacity and better water retention property. The hybrid treatment, on the other hand, caused the hollow structure of MW fibers to collapse completely, and left holes on the surface. As confirmed by FTIR and XRD, this occurred because of the dissolution of lignin and hemicellulose. As a result of these severe morphological alterations, the hybrid treated MW fibers showed inferior water retention properties compared to the hydrothermally treated sample. Further, it was observed that MW fibers with larger size distribution exhibited higher water absorption capacity and better water retention properties compared to the smaller fibers. Therefore, it can be concluded that hydrothermal treatment can improve the hydrophilicity of MW fibers and pave the way for their application as superabsorbent materials in a simple and cost-effective manner. • The effect of treatment methods on hygroscopic properties of MW fibers were studied. • MW fibers offer a promising potential for application as sustainable superabsorbent. • Hydrothermal treatment improves MW fibers hygroscopic properties by removing waxes. • Hybrid treatment diminished water retention property due to morphological defects. • Longer MW fibers showed better water retention only after hydrothermal treatment.