Plant‐based natural colorants for leather footwear: Dyeing performance, antibacterial activity and color fastness

Abstract Lining leather is a critical component in footwear requiring adequate mechanical performance, hygiene and durability. This study explores an eco‐friendly dyeing approach for sheepskin leather using plant‐based colorants derived from Calligonum aphyllum , oak bark and Rubia tinctorum . In response to the environmental impact of synthetic dyes in leather colorisation, natural alternatives were evaluated in terms of colorimetric, mechanical and antibacterial properties. The results showed that both individual and combined extracts produced a wide range of color shades while enhancing functional performance. Notably, the combination of Rubia tinctorum and oak bark exhibited superior tensile strength (29.4 MPa) and the highest color intensity ( K/S = 1.464). Whole dyed leathers demonstrated antibacterial activity, with Rubia tinctorum yielding the largest inhibition zone (up to 4 mm). The microscopic analysis of the cross‐sectional morphology of the dyed leather demonstrated that the penetration depth of the natural dyes ranged from 12% to 65% of the leather thickness. The dyed leather samples exhibited good dry rubbing fastness, with color fastness ratings ranging from 3/4 to 4/5 according to the grey scale, indicating satisfactory fixation of the natural colorants. This variation reflects differences in the diffusion behaviour and affinity of the plant‐based colorants towards the collagen matrix. These findings indicate that plant‐based dyes can improve both the structural integrity and hygienic performance of leather, highlighting their potential as sustainable alternatives in footwear lining applications.