Where Hevea trees cannot grow, rubber can come from guayule, a desert shrub with 5-10% rubber by weight of the whole plant, from Russian dandelion, whose roots hold 5-15% rubber, from the rubber fig, which yields less, or from salvaged tires, tubes and hoses. Guayule and dandelion rubber must be extracted from crushed plant material rather than tapped, which means processing a large mass of plant for a small mass of rubber. Salvage is the largest immediate source.
Part of Rubber Processing
Rubber sources for communities outside the tropical belt, and what each costs in effort.
Plants Without A Tapping Season Need Extraction, Not Collection
A Hevea tree is tapped repeatedly. Guayule and Russian dandelion hold their rubber inside the plant and give it up only when the plant is cut, crushed and the rubber separated out. The result is that the mass of plant per kilogram of rubber is large.
| Source | Climate | Rubber content (carrier) | Other corpus figures |
|---|---|---|---|
| Guayule (Parthenium argentatum) | Desert | 5-10% of the whole plant by weight | 8-12% in bark and stems (Natural Rubber Sources) |
| Russian dandelion (Taraxacum kok-saghyz) | Temperate | 5-15% of root | 6-15% by dry root weight (Dandelion Rubber); 6-10% in the sources article |
| Rubber fig (Ficus elastica) | Widely adaptable | Lower yield | |
| Salvage (tires, tubes, gaskets, hoses) | Any | Already rubber | See Reclaimed Rubber |
The figures do not line up exactly across the three articles: the 5-10% is for the whole shrub while 8-12% is for bark and stems only, and the dandelion percentages are quoted on a dry-weight basis in one article and unspecified in the carrier. Do not plan a harvest to the decimal.
What You Need
- Seed or cuttings of the plant you choose, and land to grow it on.
- A way to crush or mill the plant material, and water to separate rubber from fibre.
- Patience: these crops take a season or more before the first harvest.
Method: Choosing
Step 1: Match the plant to the climate. Guayule for dry country, dandelion for temperate, as the sources article says.
Step 2: Prefer salvage first. The carrier names salvaged tires, inner tubes, gaskets and hoses as the largest immediate source; see Devulcanization Methods and Blending with Fresh Rubber.
Step 3: Plan for plant mass. Work out how many kilograms of plant one kilogram of rubber needs.
Worked Example
At 5% rubber, one kilogram of rubber needs 1 ÷ 0.05 = 20 kg of plant. At 15%, it needs 1 ÷ 0.15 ≈ 6.7 kg. For the carrier’s dandelion root range of 5-15% that is 6.7-20 kg of root for each kilogram of rubber. A 100 kg annual rubber need is therefore 100 × 6.7 = 670 kg to 100 × 20 = 2,000 kg of dry root, before counting losses in extraction.
Common Mistakes
- Planning on the highest percentage. The lowest figure in the range is the safe planning number.
- Ignoring the water content. Percentages are by dry weight in one source; fresh roots weigh more.
- Skipping salvage while waiting for a crop.
Safety
Milling and solvent extraction
Crushing roots or shrubs in a mill brings the nip hazard described in Compound Mixing. If a solvent is used to pull the rubber out of crushed plant, its vapour is flammable and harmful; see the solvent warning in Hoses and Tubing.
What’s Next
- Learn next: Reclaimed Rubber — the immediate source
- Combine with: Crepe Rubber Production — washing the extracted rubber