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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.

Hemp plant anatomy: which parts we use for bioplastic
bioplastic comes from stalk bast fiber. everything else serves other purposes.
Plant PartUse for Bioplastic?What It Does Instead
Stalk — bast fiberYes — primary source77% cellulose, highest quality
Stalk — hurd (core)Yes — lower grade44% cellulose, or use for hempcrete, animal bedding, garden mulch
LeavesNoCompost, mulch, animal feed
SeedsNoFood (hemp hearts), oil, or save for next crop
RootsNoStay in ground — improve soil structure, break compaction, add organic matter
FlowersNoFiber 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]

Three approaches: cellulose extraction, fiber composite, citric acid crosslinking
pick your path based on equipment, chemistry comfort, & desired result.
ApproachChemistryTimeStrengthBest For
A: Cellulose extractionNaOH + acid + bleach2-3 days2-7 MPaPure bioplastic objects
B: Fiber + bioresinSeaweed + starch (no NaOH)1 dayModeratePanels, flat sheets
C: Citric acid crosslinkCitric acid + glycerol (no NaOH)1 dayUp to 70 MPaStrongest 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

Equipment needed for a 50g test batch
total equipment cost: $500-2,000 for basic workshop setup.

Chemistry (Approach A only)

Pressing (all approaches)

Safety (non-negotiable)

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]

Retting process and three tests to check readiness
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]

Cellulose extraction process: prepare, alkali treat, bleach, purify
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.

Mixing cellulose with glycerol and hot pressing into molds
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

Common problems and solutions
every failure teaches something. expect the first batch to teach more than it produces.

Quality Indicators

CheckGoodBad
Color after extractionWhite to off-whiteBrown/yellow (lignin remains)
Texture when dryFibrous, fluffy, crumblyStiff hard chunks (hurd contamination)
Weight loss from original40-50% for bast (normal)>70% (over-treated) or <30% (under-treated)
Surface after pressingSmooth, glossyRough, porous, bubbled (wet)
Sound when tappedSolid "click"Hollow "thud" (voids inside)
Water drop testWater beads or absorbs slowlyInstantly absorbs & softens (needs crosslinking)
STEP 11

Scaling Up

ScaleInputYieldTimeNotes
Test batch50g bast fiber~25g cellulose2-3 daysOne soap-mold-sized object. $5-10 in chemicals.
Useful batch2 kg bast fiber~1 kg cellulose3-5 days10-20 liter reaction vessel needed. ~100+ liters wash water.
Community batch20 kg bast fiber~10 kg cellulose5-7 daysNeeds 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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