Preparation of millimeter-long cellulose I nanofibers with diameters of 30–80 nm from bamboo fibers

Ultralong and highly uniform cellulose I nanofibers (CNFs) with lengths >1 mm, diameters of 30–80 nm, and aspect ratios >10,000 were successfully prepared from bamboo fibers, by using chemical pretreatment combined with high intensity ultrasonication to purify and defibrillate bamboo fibers into parallel arrays cellulose nanofibrils (1–5 nm width and several microns long), and then assembling the nanofibrils into ultralong CNFs by simple freeze-drying; Similar findings were also observed from the micrographs of CNFs fabricated from wheat straw and softwood fibers. The chemical composition of the fabricated CNFs is mainly cellulose because hemicelluloses and lignin were appreciably removed during the chemical process. With the removal of the matrix materials, the cellulose I crystal structure was maintained, whereas the crystallinity and thermal stability of the fibers increased. The crystallinity and thermal degradation temperature of the CNFs reached 61.25% and over 309 °C, respectively. Ultralong CNFs could serve as unique building blocks for green nanocomposites and are expected to open up new opportunities for application in tissue engineering scaffolds.