Effect of alkali treatment on microstructure and mechanical properties of individual bamboo fibers

The aim of this study was to study the microstructure and mechanical properties of individual bamboo fibers after alkali treatment. The individual bamboo fibers were treated by sodium hydroxide (NaOH) solution with varying concentration (6, 8, 10, 15 and 25%) followed by rinsing and freeze-drying treatments. The alkali treated individual bamboo fibers were subsequently characterized by scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, confocal laser scanning microscopy and tensile strength tests. The results indicated that the alkali treatment resulted in more wrinkles and pores on the surface of bamboo fibers. Microfibril aggregates treated by 15 and 25% NaOH solution changed from a randomly interwoven structure to a granular structure. Cellulose I was transformed to cellulose II after 15 and 25% NaOH solution treatment. The alkali treatment reduced the diameter, lumen and cross sectional area of fiber, leading to the cracks in cell wall. The tensile strength and modulus of elasticity (MOE) of individual bamboo fibers decreased with alkali treatment. NaOH concentration almost did not affect the tensile strength but influenced the MOE significantly. The elongation at break of treated individual fiber increased significantly. When compared to untreated individual fibers, the elongation at break of the fiber was increased by 232 and 221% after 15 and 25% NaOH treatments, respectively. Besides, increasing alkali concentration caused the change of the fibers from brittleness to ductility, indicating that alkali treated bamboo fibers have a promising application in textile.