Hemp Reactive Dyeing

Hemp reactive dyeing applies bi-functional or multi-reactive dyes (Sumifix HF, Remazol RGB, Levafix CA series at 1–5% owf) in exhaust dyeing (liquor ratio 1:8–1:15) or pad-batch process, covalently bonding dye triazine or vinyl sulphone groups to cellulose hydroxyl groups under alkaline conditions (Na₂CO₃ 10–20 g/L, NaCl or Na₂SO₄ 30–80 g/L) at 60–80°C for 45–90 minutes. Dye fixation efficiency on scoured hemp is 65–75% versus 75–85% for mercerized cotton due to lower accessibility of hemp cellulose crystalline regions. Mercerization pre-treatment (18–22% NaOH under tension) increases hemp reactive dye fixation to 78–88% and colour depth by 20–30%. Colour fastness to washing (ISO 105-C06) is grade 4–5 and to rubbing (ISO 105-X12) grade 3–4 for optimised dyeing. Unfixed dye hydrolysis (25–35% of applied dye) requires thorough hot washing (80–90°C, 2–3 rinses) consuming 60–80 L water/kg fabric. Low-liquor ratio dyeing (1:5–1:8 with HT jet) reduces water and salt consumption by 40–50% versus conventional exhaust processes.