Stevia byproducts as biomass-derived pore-forming additives for porous Hanji composites: Microstructure and property relationships

This study investigated the structural, mechanical, air permeability, and thermal properties of porous traditional Korean paper (Hanji) composite sheets containing stevia byproducts. Stevia byproducts were incorporated into Hanji fiber networks as biomass-derived additives, and their effects on thickness, bulk, tensile properties, Gurley air resistance, morphology, elemental composition, and thermal degradation behavior were evaluated. Increasing stevia content increased sheet thickness and bulk, indicating the formation of a more porous fiber network. Gurley air resistance decreased with stevia incorporation, demonstrating enhanced air permeability. However, dry and wet tensile strengths decreased because stevia particles reduced fiber–fiber bonding within the cellulose network. SEM observations revealed that the cellulose fiber network was maintained, while stevia-derived particulate regions were distributed between fibers. EDS analysis confirmed that carbon and oxygen were the dominant elements in all samples. TGA and DTG analyses showed typical cellulose-based thermal degradation behavior, whereas stevia-containing sheets exhibited slightly increased residual mass after decomposition. These results indicate that stevia byproducts act as pore-forming and structure-modifying biomass additives in Hanji composites, improving air permeability while reducing mechanical strength. The findings highlight the structure–property trade-off governing porous cellulose-based composite sheets.