Hemp Dyeing and Finishing
category
Hemp dyeing and finishing follows similar cellulosic chemistry to cotton and linen but requires additional pretreatment to address hemp-specific challenges: higher lignin content (3–5% versus 0.5–1% cotton) causing yellowish natural colour (CIE L* 75–85, b* 10–18 for scoured hemp versus L* 88–92, b* 2–5 for scoured cotton), wax surface barrier reducing dye uptake, and pectin residues causing unlevel dyeing. Scouring (NaOH 2–5 g/L, non-ionic surfactant 1–2 g/L, 95°C, 45–60 min) removes 85–95% wax and reduces lignin to below 2%. Bleaching with H₂O₂ (4–8 g/L, NaOH 2–4 g/L, stabiliser 1–2 g/L, 90°C, 60 min) achieves whiteness index of 75–85 (Berger) versus cotton 85–92. Reactive dyes (bi-functional, 2–4% owf) provide the best colour yield and wash fastness (grade 4–5, ISO 105-C06) on hemp. Mercerization (18–22% NaOH) increases dye uptake by 20–30% and improves luster. Annual hemp wet processing chemical consumption in China exceeds 15,000 tonnes of dyestuffs.
Role
Hemp wet processing converts naturally coloured, waxy bast fibre into dyeable textile substrate meeting commercial colour fastness and whiteness standards, with each pretreatment step progressively removing non-cellulosic impurities that would otherwise cause unlevel dyeing and poor wash fastness.