Hot-Water Extraction and Multi-Stage Refining of Tobacco Stems Balance Bulkiness and Strength in Reconstituted Tobacco Sheets

Abstract Balancing bulkiness and mechanical strength is critical for preparing high-quality reconstituted tobacco sheets from tobacco stem fibers. Herein, mild hot-water extraction combined with multi-stage refining was used to regulate fiber morphology and porous network structure. Micro-CT showed that hot-water extraction loosened the compact internal structure of tobacco stems, facilitating fiber separation and fibrillation during refining. As the refining pass increased, the beating degree increased from 22 °SR to 31 °SR, and the fine pulp yield increased from 5.33% to 12.23%. Two-stage refining produced the most favorable fiber morphology, with sufficient fibrillation and limited fiber damage. Consequently, the tensile strength and elongation reached maximum values of 0.371 kN·m⁻¹ and 1.030% at 28 °SR, while maintaining a relatively high bulk of 11.560 cm³·g⁻¹. Further refining compacted the fiber network and reduced bulk to 10.155 cm³·g⁻¹. SEM and micro-CT analyses confirmed that moderate refining formed a uniform and interconnected porous network, enabling an improved bulkiness-strength balance. These findings clarify how controlled fiber fibrillation and pore-network regulation jointly govern the bulkiness-strength balance of reconstituted tobacco sheets.