Natural dyeing of bacterial cellulose membranes with cochineal insect–derived pigment

Abstract

The growing demand for sustainable textile materials has increased interest in bacterial cellulose (BC) as a renewable alternative to conventional cellulosic fibres. However, the coloration of BC with animal‐derived natural dyes remains insufficiently explored. In this study, Kombucha‐derived BC membranes were dyed with cochineal ( Dactylopius coccus ) pigment after mordanting with potassium aluminium sulphate, iron(II) sulphate or copper sulphate. The membranes were characterised by “SEM‐EDX”, FTIR spectroscopy, CIELab colour measurements, UV transmittance, tensile testing, water contact angle and apparent surface free energy analyses. SEM observations confirmed that the nanofibrillar BC structure was preserved after pretreatment, mordanting and dyeing, while EDX verified the incorporation of Al, Fe and Cu ions into the cellulose matrix. FTIR spectra indicated that the cellulose backbone remained intact following all treatments. The alum‐mordanted membrane showed the highest colour strength (K/S = 21.87), whereas iron and copper mordants produced darker, brownish shades. Mordanting markedly enhanced UV shielding, with the copper‐mordanted membrane exhibiting the lowest UVA (0.05%) and UVB (0.07%) transmittance. Although oxidative pretreatment reduced tensile strength from 20.55 to 14.51 MPa, iron mordanting partially restored it to 19.60 MPa. H ₂ O ₂ pretreatment increased surface wettability by reducing the water contact angle from 56.7° to 51.8°, whereas glycerol treatment substantially increased apparent hydrophobicity. The iron‐mordanted membrane displayed the highest contact angle (118.9°) and lowest surface free energy (11.8 mJ m ⁻² ). Overall, cochineal dyeing combined with appropriate mordant selection offers a promising route for producing sustainable, coloured and multifunctional BC membranes with improved optical, mechanical and surface properties for textile applications.