Table 2 Values that are important for the indigo demand for a large-scale denim dyeing unit. These parameters are later used to assess the required plant capacities that could enable a commercially attractive biological indigo platform
Values important for indigo demand for a conventional large-scale denim dyeing unit | ||
|---|---|---|
Amount of annually dyed yarn | 36 million metres | A value reported for an industrial Pakistani dyeing unit (Meraj et al. 2016) |
Liquid indigo consumption for yarn dyeing | 35Â g per metre yarn | A value sourced from indigo rope dyeing methodology (Meraj et al. 2016). It is estimated that 95% of denim fabric is produced by this technique, or slasher dyeing (Textiletuts 2021) Within the dyeing industry, indigo may be used to dye the cotton thread, and the established dyeing are rope- and slasher-dyeing and loop dyeing being the third option. Alternatively, finished garments it could be directly applied to dyed formed garments; however, this is not as common. The following text assumes that the indigo produced with the biological platform is used for rope dyeing of the cotton yarn, as this is a well-established established processing option (Paul et al. 2021) |
% of indigo in liquid indigo solution | 40% | Concentrates contain 10–50% indigo pigment (Graham Keegan 2021). An exemplary commercially available product is, a pre-reduced liquid indigo, that contains: 40% indigo, < 2% sodium hydroxide (caustic soda), < 3% potassium hydroxide, and ~ 35% water (DyStar 2009, 2021a) |
Annual indigo supply needed by a large-scale plant | 504 t which would dye 200,000 pairs of adult jeans | Equation: (dyed yarn metres/year) × (liquid indigo consumption/metre yarn) × (indigo % in liquid solution) |