Hemp Scouring and Bleaching

Hemp scouring removes wax (0.8–1.5%), pectin residues (0.5–1.5%), and protein (0.5–1.0%) using NaOH (2–5 g/L) and non-ionic surfactant (1–2 g/L) at 95–98°C for 45–60 minutes in jet or beam dyeing machines, achieving weight loss of 4–8% and wax removal >90%. Pre-scouring with enzyme (amylase 0.1–0.3% for sizing removal, pectinase 0.05–0.1% owf for pectin removal at 50°C, 45 min) before alkali scouring reduces NaOH concentration requirement by 30–40% and improves fabric softness. Hydrogen peroxide bleaching (H₂O₂ 4–8 g/L, NaOH 2–4 g/L, sodium silicate stabiliser 2–3 g/L, 90°C, 60 min) achieves CIE whiteness index (WI) of 75–82 for hemp versus 85–92 for cotton due to residual chromophoric lignin structures absorbing at 350–420 nm. Ozone bleaching (O₃ 5–15 mg/L in aqueous phase, 20–30°C, 10–20 min) selectively oxidises lignin chromophores, achieving WI 70–78 at 60% lower chemical cost and 80% lower water consumption versus peroxide bleaching. Chlorite bleaching (NaClO₂ 2–4 g/L, pH 3.5–4.0, 80°C, 45 min) provides WI 80–88 but generates ClO₂ gas requiring sealed vessel processing.