Influence of alkali treatment on internal microstructure and tensile properties of abaca fibers

The objective of this study is to investigate the effect of alkali treatment on the internal microstructure and tensile properties of abaca fibers. The abaca fibers were immersed in aqueous solutions of NaOH (5, 10, or 15 wt%) for 30 min, rinsed and dried. The fibers were subsequently characterized by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and tensile strength tests. The lumen is a hollow region in each elementary fiber of the abaca fiber bundles. It was found that the lumen of the abaca fibers completely collapsed after 10 and 15 wt% NaOH treatment, due to swelling of the fibers. The fibers also became twisted after these alkali treatments. It was found that cellulose I in abaca fibers was partially transformed to cellulose II after 15 wt% NaOH treatment, as evidenced by XRD measurements. FT-IR analysis indicated that the alkali treatment led to a gradual removal of binding materials; such as hemicelluloses and lignin, from the abaca fibers, resulting in the separation of abaca fiber bundles into individual elementary fibers. The tensile strength of alkali-treated abaca fibers did not vary with alkali concentration. The Young's modulus of the abaca fibers treated with 5 wt% NaOH solution increased by 41%, whereas those treated with 10 and 15 wt% NaOH solution decreased by 24 and 29%, respectively. A non-linear behavior was observed in the stress-strain curves of the abaca fibers after 10 and 15 wt% alkali treatment, which could be attributable to the twisting of the fibers.