Investigation of the structure of ramie fibers by enzymatic peeling

Ramie offers excellent wearability compared to other fibrous material; however, since the inner structure of the fibers remains largely unexplored, this excellent wearability lacks a reasonable explanation. In this study, enzymatic peeling, using xylanase and laccase coupled with PM, FLSM, and SEM, was confirmed to be an effective and efficient method to characterize the inner structure of ramie fibers. The surface of bio-degummed ramie fibers is smooth, has a fibrillar structure and contains dislocations including kinks, nodes, and scales. The transverse structure is multilayered (designated as L1, L2, and L3 layers) and has a big compressed lumen. The L1 layer is the outermost layer, which shows bright indigo fluorescent signals that indicate xylan. After removal of the L1 layer via enzymatic treatment, fibers become twisted and cracked, and the fibrillar and buckled secondary cell wall structure clarifies. Under laccase treatment, visible pores can be exposed on the secondary wall, including pit-like pores on the bulk of the cell walls and irregular pores lined at the dislocation region. L3 was identified as the innermost layer. Almost the complete L3 layer was separated from the secondary wall, using an enzymatic peeling method, and showed a closed, round, and blunt tube end and a honeycomb-like inner structure. The mesopores were filled with pectin and the surface of the tube emitted a blue fluorescent signal. The honeycomb-like innermost layer together with the pore structure of the secondary wall forms a physical basis for the cause of special wearabilities such as the shrinkage, absorbency, and scratchiness of ramie fibers.