Combination of ultrasonication/mechanical refining with alkali treatment to improve the accessibility and porosity of bamboo cellulose fibers for the preparation of magnetic bionanocomposite cellulose beads

Ultrasonication and mechanical refining pretreatments were carried out to enhance alkali swelling of bamboo fibers to improve accessibility and porosity. Cellulose-based magnetic beads were synthesized with the alkali swollen bamboo fibers and Fe₃O₄ nanoparticles. Compared to the fibers treated with alkali alone, the water retention value (WRV) increased by 33.87% for the fibers treated by sonication and alkali, and by 94.58% for those treated by mechanical refining and alkali. The increased WRV was attributed to disruption of the crystalline region of fibers in the combined treatments which resulted in decreased crystallinity and degree of polymerization of cellulose. Furthermore, compared with the control sample which was treated by alkali alone, the specific surface area and pore volume of the samples treated by the combined processes increased markedly, which favored the adsorption of Fe₃O₄ nanoparticles in the synthesis of functional magnetic cellulose beads for the applications of protein immobilization, drug carrier and wastewater treatment.