| Conventional exhaust dyeing |
Commonly pH 3–6, 80–100 °C, 45–60 min and LR 1 : 20–1 : 50; selected systems at 1 : 10 |
Protonation, adsorption and internal diffusion |
Broad applicability; K/S usually increases with acidity and temperature until equilibrium or degradation |
Established equipment and process control |
High water, heating, rinsing and soaping demand |
Industrially established |
20, 40, 59, 76, 77, 96, 115 and 132
|
| Mordant-free dyeing |
Usually pH 3–5 and 70–100 °C; alkaline for indigo and cationic dyes |
Ionic attraction, hydrogen bonding, hydrophobic association or in situ pigment formation |
K/S = 18.60 for olive leaf and 21.94 for T. catappa; wet fastness up to 4–5, but poor light fastness in some systems |
Avoids metal salts and metal-bearing effluent |
May require strong pH control, reduction, heat and repeated washing |
Laboratory to pilot |
40, 72, 80, 96, 122, 132 and 140
|
| Metallic mordanting |
Commonly 0.2–10% owf or g L−1; pre-, simultaneous/meta- or post-mordanting |
Dye–metal–fiber coordination and metal–tannin complexation |
FeSO4 increased K/S from 10.6 to 15.8 and light fastness from 4 to 7; alum, tin and zinc effects were dye-dependent |
Can improve fixation and reduce unfixed dye |
Toxicity, residual-metal release, sludge and shade alteration |
Technically mature but increasingly restricted |
22, 74, 78, 79, 102, 115, 120, 131, 133, 135, 137, 139, 145 and 150
|
| Biomordanting |
Approximately 1–50% owf; pre-, simultaneous or post-application |
Additional phenolic, cationic, proteinaceous or film-forming sites |
Walnut husk and pinecone gave K/S = 18.77 and 18.62 with washing fastness = 5 and light fastness = 8 |
Renewable or waste-derived alternatives to metals |
High dosage, extraction, variability, COD, curing and washing |
Mainly laboratory or pilot |
22, 33, 42, 57, 70, 88, 90, 102, 117, 118, 120, 130, 137, 140, 143, 158 and 170
|
| Microwave-assisted dyeing |
Generally 1–10 min irradiation; optima frequently 4–6 min |
Volumetric heating and accelerated diffusion |
Exhaustion increased from 63% to 93%; K/S was approximately 8.4 after 4 min in one system |
Major reduction in treatment time |
Non-uniform heating and insufficient specific-energy reporting |
Laboratory |
13, 67, 83, 84, 92, 127 and 170
|
| Ultrasound-assisted dyeing |
Approximately 30–100 °C, 30–120 min and 100–500 W |
Cavitation and boundary-layer disruption |
K/S increased to approximately 6.35–7.21; selected fastness grades improved by about 0.5 grade |
Potential reduction in temperature or duration |
Scale-dependent acoustic distribution and pigment degradation |
Bench or laboratory |
37, 43, 82, 92 and 123
|
| Plasma activation |
Air plasma, DBD or corona; seconds to 15 min |
Surface oxidation, roughening and increased wettability |
Rice-straw K/S increased from 6.6 to 10.7; washing fastness increased from 4 to 5 in a separate study |
Dry and rapid surface activation |
Surface ageing, high voltage and possible over-etching |
Laboratory to semi-industrial |
20, 41, 65 and 93
|
| Laser activation |
Approximately 4–20 W with controlled scanning |
Local thermal or photochemical morphology modification |
K/S increased from 9.7 to 15.1 at 12 W but declined at higher powers |
Dry, localized and patternable |
Fiber melting, adhesion and limited penetration |
Laboratory or pilot patterning |
45
|
| Electron-beam activation |
Up to approximately 300 kGy |
Radical generation and surface functionalization |
Maximum K/S = 18.1 with an 8% breaking-force loss |
Rapid treatment without wet initiators |
Shielding, capital cost and strength loss |
Laboratory |
105
|
| Enzymatic coloration |
HRP/H2O2 at approximately 55 °C for up to 3 h |
Oxidative polymerization of phenolic precursors |
K/S up to 4.5 with ex situ chitosan |
Mild temperature and no metallic mordant |
Enzyme cost, oxidant use and long reaction time |
Proof-of-concept |
32, 33 and 144
|
| Microbial in situ coloration |
Approximately 30 °C for up to 24 h |
Biosynthesis and simultaneous pigment formation or fixation |
Avoids separate pigment synthesis or reduction in selected systems |
Lower processing temperature and fewer isolated stages |
Long reaction, sterility and biological control |
Proof-of-concept |
34, 157 and 160
|
| Nanoformulation |
Aqueous nano-dispersions or biosynthesized nanoparticles |
Improved dispersion, surface area and entrapment |
AgNP-assisted K/S = 3.36, light fastness = 5 and 100% antibacterial reduction |
Can combine coloration and functional finishing |
Nanoparticle release and toxicological uncertainty |
Laboratory |
163, 172 and 174
|
| Deep eutectic solvent |
ChCl/LA 1 : 2, 60 °C and 60 min |
Nonaqueous pigment solubilization and transport |
K/S = 3.33, but washing ΔE = 10.77 |
Eliminates the aqueous dye bath |
High viscosity, solvent recovery and after washing |
Early laboratory |
158
|
| Supercritical CO2
|
Approximately 110–120 °C and 3500–5000 psi |
CO2 plasticization and nonaqueous diffusion |
Water- and mordant-free PA66 coloration |
No conventional dye-bath wastewater |
High pressure, capital cost and restricted natural-dye solubility |
Laboratory or pilot |
68 and 165
|
| Low-liquor or solvent-assisted dyeing |
LR down to 1 : 10–1 : 20; D5 or oil-based carriers |
Increased bath concentration or phase transfer |
LR 20 : 1 gave 72.14% berberine exhaustion; D5 gave K/S = 2.64 |
Reduced water and heated-liquor volume |
Solvent recovery, toxicity and washing requirements |
Laboratory to technically scalable |
66, 76, 164 and 166
|
| Digital inkjet printing |
Approximately 80 pL droplets and 300 dpi in the reported system |
Localized drop-on-demand deposition |
High-resolution curcumin coloration and functionalization |
Low application liquor and suitability for short runs |
Ink stability, nozzle performance, pretreatment and after washing |
Industrial platform; natural-dye inks mainly laboratory-scale |
42
|
