# unturf.

### grow food not lawn

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## Hemp Bioplastic: Process

A step-by-step recipe for turning hemp stalks into bioplastic. Three approaches exist — from full cellulose extraction (most chemistry) to citric acid crosslinking (least chemistry). This page covers all three with exact quantities, temperatures, times, & safety notes.

Start with a 50g test batch. Expect 2-3 days from stalk to finished object. Expect to fail the first time. Expect to learn why.

STEP 1

### Which Parts of Hemp We Harvest

Hemp bioplastic comes from stalks only — specifically bast fiber, the outer bark layer of the main stem. Not leaves. Not seeds. Not roots. Each part serves a different purpose.

bioplastic comes from stalk bast fiber. everything else serves other purposes.

Plant Part | Use for Bioplastic? | What It Does Instead
--- | --- | ---
Stalk — bast fiber | Yes — primary source | 77% cellulose, highest quality
Stalk — hurd (core) | Yes — lower grade | 44% cellulose, or use for hempcrete, animal bedding, garden mulch
Leaves | No | Compost, mulch, animal feed
Seeds | No | Food (hemp hearts), oil, or save for next crop
Roots | No | Stay in ground — improve soil structure, break compaction, add organic matter
Flowers | No | Fiber varieties produce minimal flower; if present, compost or dry

Harvest stalks when they reach full height (2-4 meters, ~120 days). Cut at ground level. Leave roots in soil — they decompose & feed next season's crop. Strip leaves & set aside for compost. Collect seeds if needed for replanting.

STEP 2

### Three Approaches

No single canonical recipe exists. Research reveals three distinct paths, each with different tradeoffs between chemistry complexity & material quality.[1]

pick your path based on equipment, chemistry comfort, & desired result.

Approach | Chemistry | Time | Strength | Best For
--- | --- | --- | --- | ---
A: Cellulose extraction | NaOH + acid + bleach | 2-3 days | 2-7 MPa | Pure bioplastic objects
B: Fiber + bioresin | Seaweed + starch (no NaOH) | 1 day | Moderate | Panels, flat sheets
C: Citric acid crosslink | Citric acid + glycerol (no NaOH) | 1 day | Up to 70 MPa | Strongest result, safest chemistry

Recommendation for first attempt: Approach C (citric acid crosslinking) avoids all NaOH, all acid work, & all bleaching while producing material up to 70 MPa tensile strength.[5] If you want to understand full cellulose extraction, try Approach A on a second batch.
STEP 3

### Equipment

total equipment cost: $500-2,000 for basic workshop setup.

#### Chemistry (Approach A only)

- Stainless steel pot, 2-5 liter — NOT aluminum (reacts with NaOH)
- Hot plate capable of 80-100°C
- Digital thermometer, 0-200°C range
- pH strips, range 1-14
- Vacuum filtration: Buchner funnel + vacuum flask + water aspirator
- Kitchen scale, 0.1g precision
- Mortar & pestle or coffee grinder for fiber size reduction
- Metal sieve, 1.5mm mesh
- Multiple large buckets for washing

#### Pressing (all approaches)

- Metal mold — aluminum soap mold works for test batches
- Oven capable of 140-200°C, or a rosin press ($200-500)
- Bench vise, hydraulic press, or heavy C-clamps for pressure
- Heat-resistant gloves rated 200°C+

#### Safety (non-negotiable)

- Chemical splash goggles — not just safety glasses
- Nitrile gloves, elbow length
- Ventilated workspace — fume hood or work outdoors
- Bottle of 2% vinegar nearby for NaOH spill neutralization
- Running water within arm's reach

STEP 4

### Retting (Preparing Stalks)

Before separating fiber from stalk, retting partially breaks down the pectin that binds bast fiber to hurd. Skip this & decortication becomes very difficult.[12]

dew retting takes 3-45 days depending on temperature. three tests confirm readiness.

#### Dew Retting (simplest)

1. Lay harvested stalks on grass, exposed to rain & dew
2. Turn stalks every few days for even breakdown
3. Maintain ~30% moisture — sprinkle with water if dry
4. Duration depends on temperature:
   - 37°C → 3 days
   - 20°C → 7-8 days
   - 12°C → 15-17 days
   - 7°C → 30-45 days
   - Below 5°C → retting stops

#### Water Retting (faster)

1. Submerge stalks in warm water for ~10 days
2. Change water periodically — it will smell
3. Bacteria in water accelerate pectin breakdown

#### Three Tests for Readiness

Bend test: Bend dried stalks back & forth. Hurd should crack & fall free. Fiber should NOT break when shaken.
Peel test: Peel fiber at base of stem. Should separate easily for several inches. If fiber breaks after a few inches, retting needs more time.
Color test: Fiber bundles turning white signals readiness.
Over-retting weakens fiber. Under-retting makes separation very difficult. Test every 2-3 days. When in doubt, under-ret — you can always ret longer but cannot un-ret.
STEP 5

### Decortication (Separating Fiber)

After retting, separate bast fiber from hurd by hand.[9] Target: 95% clean bast fiber with 5% or less hurd contamination.

1. Break: Bend & snap dried retted stalks repeatedly. Woody hurd should crack & fall away from flexible bast fiber.
2. Shake: Shake vigorously to dislodge hurd fragments.
3. Scutch: Beat fibers against a hard surface to remove remaining hurd.
4. Hackle: Pull fibers through coarse wire brushes or metal combs to remove short fibers & debris.

For fresh (un-retted) stalks: use a knife at the base to separate the green outer fiber layer from the woody core. Peel bast fiber upward toward the tip. Slower but works without retting.

STEP 6

### Approach A: Cellulose Extraction

Full chemical extraction produces the purest cellulose. Three protocols exist — start with Protocol 2 (gentlest) for a first attempt.[1]

50g hemp powder yields ~25g pure cellulose through 4 stages.

#### Size Reduction

1. Dry separated bast fibers at 50°C until constant weight
2. Cut to 2-3 cm lengths
3. Grind using blender, coffee grinder, or mortar & pestle
4. Pass through 1.5mm metal sieve
5. Weigh 50g of powder (test batch)

#### Protocol 1: Full Extraction (highest purity)

Alkali treatment:[2]
50g hemp powder + 750 mL of 12% NaOH solution (= 90g NaOH pellets dissolved in 750 mL water). Solid/liquid ratio 1:15. Heat to 80°C with continuous stirring at 500 rpm. Hold for 3 hours. Vacuum filter. Wash with deionized water 4-5 times until wash water reaches neutral pH. Dry at 60°C overnight.
Bleaching (optional but recommended):[3]
8% hydrogen peroxide solution, pH adjusted to 12 with NaOH. 40°C, solution/solid ratio 30:1. 1 hour per cycle, repeat 4 cycles. Wash until neutral. Safer than sodium chlorite for workshop use.
Hemicellulose removal:
Treat bleached product with 17.5% NaOH solution. Room temperature. 5 hours with continuous stirring at 500 rpm. Vacuum filter. Wash 3 times with deionized water. Dry at 60°C overnight.

#### Protocol 2: Gentle Extraction (best for beginners)

Alkali treatment:[6]
5% NaOH solution (= 50g NaOH per liter of water). Soak hemp fibers at room temperature (23°C) for 4 hours. No heating required. Wash with tap water until pH ~7. Oven dry at 80°C until constant weight.
This protocol found 5% NaOH for 1 hour nearly as effective as 4 hours. Start with 1 hour, check results, extend if needed.
NaOH safety. ALWAYS add NaOH pellets to water, NEVER water to NaOH. Dissolution generates heat & can spatter violently. At 12-17.5% concentration, NaOH solution dissolves skin on contact. Wear splash goggles & elbow-length nitrile gloves. Keep running water within arm's reach. If skin contact occurs, flush with water for 15+ minutes. Store NaOH pellets in airtight containers — they absorb moisture from air.
STEP 7

### Approach B: Fiber + Bioresin Composite

Robert Murray-Smith's method skips all chemical extraction.[4] Instead, hemp fiber acts as reinforcement inside a bioresin matrix made from seaweed & corn starch.

Bioresin recipe:
25g dried seaweed (carrageenan or agar) + 50g corn starch + 1 liter water. Heat & stir until dissolved into a viscous liquid.
Process:
1. Prepare a hemp fiber mat (loose fiber spread into a flat layer)
2. Pour bioresin over fiber mat
3. Roll with a roller until resin penetrates fully through the mat
4. Dry in oven at 150-200°C for 20 minutes
5. Result: a rigid composite panel
Variant: Replace seaweed/starch with casein (milk protein) + tannin (from strong tea or chestnut extract) for a harder result. Murray-Smith describes this as "quite hard, quite plastic."

This produces a composite — not pure bioplastic. Hemp fiber (30-50% by weight) reinforces a starch or protein matrix. Simpler chemistry, fewer hazards, one-day process. Tradeoff: less versatile shapes, works best for flat panels & sheets.

STEP 8

### Approach C: Citric Acid Crosslinking

Developed by Beluns et al. at Riga Technical University (2023).[5] No NaOH. No acid baths. No bleach. Produces material up to 70 MPa tensile strength — comparable to commodity petroleum plastics. The safest & strongest approach.

Process:
1. Chop hemp stalks (bast + hurd together works) & soak in water
2. Spread fibers on a screen, press flat, dry — making a rough hemp paper
3. Prepare impregnation solution: 2g glycerol + 1g citric acid + small amount of PEG (polyethylene glycol), dissolved in minimal water
4. Soak hemp paper in solution until saturated
5. Place on a metal sheet, cover with another sheet
6. Cure at 140°C in oven for 30-60 minutes under weight (a brick or cast iron pan on top)
7. Wash in water for 24-48 hours to remove unreacted material
8. Dry at room temperature

Tradeoff: requires xylan (hemicellulose powder) & PEG (polyethylene glycol) — specialty chemicals, but non-hazardous & available from lab suppliers online. The citric acid crosslinks cellulose chains, creating thermal bonds that reduce water uptake 7-fold versus untreated hemp paper. These bonds reverse at high temperature, making the material theoretically recyclable by re-heating.

STEP 9

### Mixing & Hot Pressing (Approach A)

After extracting cellulose via Approach A, mix with plasticizer & press into shapes.

the material MUST be completely dry before pressing. this is the most common failure point.
Mixing:
1. Weigh dried cellulose
2. Add glycerol: 15% by weight for rigid, 30% for flexible
3. Add water to make a workable slurry
4. Stir at 80°C for 60 minutes until homogeneous
5. Optional: add 5% citric acid by weight for water resistance
Drying (critical):
6. Spread mixture on a tray
7. Dry at 60°C overnight — or until weight stabilizes
8. Grind to a breadcrumb/sawdust consistency
Pressing:[11]
9. Coat mold interior with thin layer of vegetable oil
10. Fill mold with dry material, compress lightly by hand, add lid
11. Heat to 150°C (oven or heat press)
12. Once at temperature, apply maximum pressure — bench vise, hydraulic press, or C-clamps
13. Hold at temperature & pressure for 10-30 minutes (30 min gave best strength in testing)
14. Release pressure
15. Cool slowly in mold — do not rush, rapid cooling causes cracking
16. Demold
If material stays wet when pressed: Steam creates voids. Result becomes spongy & porous. This represents the most common failure mode. Murray-Smith emphasizes: "if it's wet and you heat it and press it, you'll press off a lot of steam and it won't form properly."[4] Dry overnight. Verify weight has stopped changing. Then press.
STEP 10

### Troubleshooting

every failure teaches something. expect the first batch to teach more than it produces.

#### Quality Indicators

Check | Good | Bad
--- | --- | ---
Color after extraction | White to off-white | Brown/yellow (lignin remains)
Texture when dry | Fibrous, fluffy, crumbly | Stiff hard chunks (hurd contamination)
Weight loss from original | 40-50% for bast (normal) | >70% (over-treated) or <30% (under-treated)
Surface after pressing | Smooth, glossy | Rough, porous, bubbled (wet)
Sound when tapped | Solid "click" | Hollow "thud" (voids inside)
Water drop test | Water beads or absorbs slowly | Instantly absorbs & softens (needs crosslinking)

STEP 11

### Scaling Up

Scale | Input | Yield | Time | Notes
--- | --- | --- | --- | ---
Test batch | 50g bast fiber | ~25g cellulose | 2-3 days | One soap-mold-sized object. $5-10 in chemicals.
Useful batch | 2 kg bast fiber | ~1 kg cellulose | 3-5 days | 10-20 liter reaction vessel needed. ~100+ liters wash water.
Community batch | 20 kg bast fiber | ~10 kg cellulose | 5-7 days | Needs mechanical stirring, larger press, waste handling plan.

Scaling NaOH: Dissolution stays exothermic. At larger volumes, add pellets slowly & monitor temperature. A 20-liter NaOH batch generates significant heat. Never dump all pellets at once.

Approach C (citric acid crosslinking) scales most easily — no chemical extraction means no waste liquor management. Just make more hemp paper, apply more solution, cure in a larger oven. A community could run this with minimal training.

### Honest Summary

Making hemp bioplastic at home stays possible but labor-intensive. A 50g test batch costs $5-10 in chemicals & takes 2-3 days. Results will vary. First batches teach more than they produce. Approach C (citric acid) offers the safest entry point with the strongest results. Approach A (full extraction) teaches the most about cellulose chemistry. Approach B (bioresin composite) produces useful panels fastest.

None of this replaces buying groceries in glass jars or using cloth bags — those remain easier. But for seed trays, plant pots, serving ware, & packaging where you want a compostable container made from your own land, this process closes a cycle. Grow it. Process it. Use it. Compost it. Grow again.

### Sources

1. Chalannavar et al. (2025), "Industrial Cannabis sativa: Hemp Cellulose Based Bioplastic Production," Magna Scientia. Comprehensive review reproducing Liao protocol with 50g/12% NaOH/1:15 ratio/80°C/3h parameters. ↩
2. Liao (2022), McGill University thesis. Hemp nanocellulose extraction: 49.6% yield from bast fiber at 97% purity. Detailed NaOH protocol with exact quantities. ↩
3. Hydrogen peroxide bleaching protocol from PMC 10611065. Safer alternative to sodium chlorite for workshop-scale cellulose bleaching. ↩
4. Robert Murray-Smith, "A Hemp And Seaweed Bioplastic" (2020) & "Hot Press Molding Hemp Casein Plastic" (2020). Workshop demonstrations with bioresin composite & casein-tannin approaches at 150°C. ↩
5. Beluns et al. (2023), "Sustainable hemp-based bioplastics with tunable properties via reversible thermal crosslinking of cellulose," Int J Biol Macromol. No chemical pretreatment, citric acid crosslinking at 140°C, achieving up to 70 MPa tensile strength & 7-fold water uptake reduction. ↩
6. Dhakal et al. (2022), PMC 9182753. 5% NaOH treatment of hemp at room temperature for 1-4 hours — gentlest effective protocol. ↩
7. PMC 12073554 (2025). Hemp waste cellulose extraction via alternating 2% NaOH & 1M HCl treatments. Milder protocol with 47% yield. ↩
8. PMC 5456901. Abraham et al. (2016), hemp hurd cellulose microfiber extraction via alkaline & acid hydrolysis. ↩
9. Hemp In A Pot, "Manual Decortication of Hemp Stalks By Hand" (2020). Practical video demonstration of hand decortication. ↩
10. Solis Garcia et al. (2025), "Extraction of cellulose fibers from hemp stalk by chemical treatment". Optimal at 10% NaOH / 120 min yielding 75.11% alpha-cellulose. ↩
11. Bio-protocol (2025). Hemp cellulose + glycerol + NaOH, stirred 60 min at 80°C, hot pressed at 240°C for 10 min. ↩
12. Robert A. Nelson, "Hemp Husbandry, Chapter 3: Hemp Fiber". Comprehensive retting reference with temperature/duration data. ↩

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