Effect of alkali surface treatments on mechanical and morphology of natural galangal fibers

Abstract

This study addresses the value-addition to agricultural residues by investigating the effects of alkali treatment on the physical and mechanical properties of Alpinia galanga (L.) Willd (AG) and Alpinia siamensis K. Schum (AS) pseudo-stem fibers. The fibers were extracted from pseudo-stem segments with an initial length of 25-30 cm. The untreated fiber diameters were 131.96 ± 38.42 µm for AG and 172.50 ± 42.94 µm for AS. To evaluate treatment efficiency, both a thermal-assisted at low concentration route and a conventional room-temperature process were compared. Morphological and surface roughness analyses (  and ) revealed that alkali treatments effectively dissolved surface impurities, reduced fiber diameters (reaching minimums of 107.99 ± 20.90 µm for AG at 10% wt. NaOH and 62.75 ± 11.77 µm for AS at 15% wt. NaOH), and induced distinct fibrillation. Regarding mechanical performance, the treated fibers showed enhanced tensile strength and elongation. The maximum tensile strength for AG was 147.67 ± 53.47 MPa (at 5% wt. NaOH), while AS peaked at 215.64 ± 95.57 MPa (at 0.5% wt. NaOH). Although extreme concentrations (15% wt. NaOH) yielded maximum elongation for both AG (7.25 ± 1.74%) and AS (5.93 ± 1.30%), they triggered cellulose degradation and reduced tensile strength. These findings highlight that optimized, low-chemical alkali treatments can successfully tailor galangal fibers into sustainable reinforcing materials, advancing circular economy principles in composite engineering.