Extraction — Refab — Cellulose Pulp SOP (Version 1.0)

Scope: Lab-scale and scaled-up procedure to convert 100% cotton black textile waste into high-purity cellulose pulp suitable as feedstock for MCC/CNC/pharma/food applications. Includes pre-scour, dithionite reductive decolorization, medium alkaline extraction (80% hemicellulose removal target), peroxide bleaching (TAED and TAED-free options), gentle mechanical pulping, and drying. Optimized for 20 g batches; scale-up table included for 100 g, 500 g, 1 kg, 5 kg.

Notes about your equipment & chemicals

• Heating method: hot plate + beaker
• Suggested blender for pulping: 500–750 W mixer grinder (Philips HL7505/HL7600 recommended)
• Hydrogen peroxide available: 50%
• Reducing agent: Sodium dithionite (Na₂S₂O₄)
• pH meter known to read ~+0.5–1.0 high: targets are given in meter reading and real pH.

Safety & PPE

Work in a well-ventilated area or fume hood. Dithionite can release SO₂; peroxide is an oxidizer. Wear nitrile gloves, eye protection, lab coat. Use face shield if handling bulk peroxide. Prepare sodium hydroxide solutions with care (add NaOH to water, not vice versa). Have baking soda (sodium bicarbonate) and vinegar available for emergency neutralization of small spills; follow institutional hazardous waste disposal rules for spent baths (sulfite-containing wastes, peroxide wastes).

Overview (sequence)

1. Pre-scour (detergent) — removes oils/waxes/finishing agents
2. Reductive decolorization (Na₂S₂O₄) — breaks dyes
3. Rinse to neutral
4. Medium alkaline extraction (NaOH 4 g / 600 mL) — removes hemicellulose
5. Rinse to neutral
6. Oxidative bleaching (50% H₂O₂; TAED preferred) — final whiteness
7. Rinse and neutralize
8. Mechanical pulping (gentle blending in water)
9. Dewatering, pressing, drying
10. QC: brightness, alpha-cellulose, DP (CED viscometry), ash

SOP — Detailed step-by-step (20 g batch)

Materials (per 20 g fabric, 600 mL baths unless noted)

• Textile waste (100% cotton): 20 g
• Distilled water: 600 mL per bath (adjust with scale)
• Non-ionic detergent (lab detergent): 1% w/v (6 g per 600 mL)
• Sodium dithionite (Na₂S₂O₄): 15 g (reductive bath)
• Sodium hydroxide (NaOH): dosing solution 0.5 M (2 g NaOH in 100 mL water); extraction: 4 g per 600 mL; TAED bleach: 12 g per 600 mL if TAED used
• TAED (preferred): 6 g per 600 mL
• EDTA (chelating agent): 0.3–0.5 g per 600 mL (recommended)
• Hydrogen peroxide 50%: primary bleach dose equivalent to 24 mL of 30% → 14.4 mL 50% for TAED-enabled bleaching
• Optional sodium carbonate (washing soda) for scouring: 0.5–1 g

Note about pH meter offset: All pH target values are given as two numbers: (meter reading ≈ X — real pH ≈ Y). Your meter reads high (~+0.5–1.0).

1) Pre-scouring (Detergent wash)

1. Cut fabric into ~1–2 cm pieces.
2. Prepare a 600 mL bath: water + 1% detergent (6 g) + optional 0.5 g Na₂CO₃.
3. Heat to 60–70°C on hot plate, stir gently for 30 minutes.
4. Filter and rinse hot → cold until rinse water runs clear.
5. Check pH of rinsed fabric: pH 6–7 (meter). If not, rinse more.

Note: Do not use strong NaOH in this step unless heavy waxes are present. Scouring improves subsequent dye removal and prevents foam in peroxide stage.

2) Reductive decolorization (Sodium dithionite)

Goal: Cleave chromophores of reactive/sulfur/vat dyes with minimal DP loss.

Bath prep (600 mL):

1. Fill beaker with 600 mL distilled water (room temp).
2. Adjust pH to meter ≈ 10.0 (real pH ≈ 9.0) using dosing solution (0.5 M NaOH). Add 1 mL steps, stir, measure frequently.
3. Add Na₂S₂O₄ 15 g in 3 portions (5 g each) with 1–2 min between portions; stir gently.
4. After dithionite dissolves and pH stabilizes at meter ~10, add fabric (20 g).
5. Heat slowly to 85–90°C over ~10–15 min. Maintain 85–90°C and pH meter ≈ 9.8–10.2 (real ~9.0) for 60 minutes. Top up NaOH in 0.5–1 mL increments if meter pH dips below 9.5.
6. After reaction time, remove fabric and rinse hot → cold until rinse pH neutral (meter ~7–8).

Safety: Keep ventilation on; faint SO₂ is expected. If strong SO₂ or brown sludge appears, abort and restart with fresh bath.

3) Medium Alkaline Extraction (Option B)

Goal: Remove hemicellulose (target 80–90% removal) using moderate alkali.

1. Ensure fabric is rinsed to neutral before continuing.
2. Prepare 600 mL distilled water. Add NaOH 4 g (solid) and stir to dissolve.
3. Add the rinsed fabric to the NaOH extraction bath.
4. Heat to 80°C and hold for 60 minutes with gentle stirring.
5. After extraction, remove fabric and hot rinse thoroughly until rinse pH neutral (meter ~7–8). Collect extraction liquor for waste handling.

4) Oxidative Bleaching

Two paths provided:

A — Preferred TAED-activated bleaching (Bath: NaOH 12 g, TAED 6 g, EDTA 0.3 g, H₂O₂ 14.4 mL (50% equiv). Heat 70°C for 60–90 min.)

B — TAED-free conservative bleaching (NaOH 1 g, EDTA 0.3 g, H₂O₂ 50%: 5 mL; heat 75–80°C for 45 min; may require second mild pass).

5) Mechanical pulping (gentle)

1. Place bleached rinse-neutral fibers into 400–600 mL distilled water (pulp:water ≈ 1:20–1:30).
2. Use a low-speed mixer grinder; run in short bursts (3 × 8–12s) with 60–90s rests.
3. Check fibers: opened, not mushy; lengths ~0.5–3 mm.
4. Screen through 200–100 mesh to remove fines.

6) Dewatering, pressing & drying

1. Drain slurry on mesh. Press gently to ~50–60% moisture.
2. Dry in hot air oven at 50–60°C to constant weight. Do not exceed 70°C.

7) QC & Analytics

• Brightness (ISO) – target > 85 for high-quality pulp
• Alpha-cellulose – target ≥ 92–94%
• Ash – target < 0.3–0.5%
• DP (CED viscosity) – recommended target DP 500–900
• pH of final pulp – neutral
• Visual – uniform white, no yellowing, long fibers, no powder

8) Waste handling

Collect extraction liquors; neutralize if required and follow local disposal. Dithionite baths contain sulfite/sulfate — treat per regulations. Peroxide can be deactivated by dilution and sodium sulfite if required.

Scale-up Table

Batch	Fabric (g)	Bath vol (mL)	Na₂S₂O₄ (g)	NaOH (extraction) g	H₂O₂ 50% mL	TAED (g)
20 g	20	600 mL	15 g	4 g	14.4 mL	6 g
100 g	100	3.0 L	75 g	20 g	72 mL	30 g
500 g	500	15 L	375 g	100 g	360 mL	150 g
1 kg	1000	30 L	750 g	200 g	720 mL	300 g
5 kg	5000	150 L	3750 g	1000 g	3600 mL	1500 g
              

Troubleshooting

• Strong SO₂ smell: ventilate, pause, check pH; abort if severe.
• Yellowing during bleach: stop heating, rinse, run mild rescue bleach.
• Excess fines: reduce blending time/speed and increase water ratio.
• pH meter unreliable: calibrate daily with buffers.

QC sample COA template

Batch ID, Date, Raw material, Yield (%), Moisture (%), Alpha-cellulose (%), Brightness (ISO), Ash (%), DP (CED), Remarks

Document prepared for: Refab - Chemical Recycling. Version 1.0.