Bioplastics are polymers made from renewable biological sources, and the practical ones for a settlement are casein from milk, shellac from lac insects and animal glues, with cellulose acetate and PLA possible only with more chemistry. Casein hardened with formaldehyde becomes a waterproof plastic usable up to about 80 °C, and shellac melts at 75-80 °C and insulates well. A plastic made from plants is not automatically biodegradable, and a biodegradable one is not automatically strong.
Part of Polymer Engineering
Bioplastics are polymers derived from renewable biological materials such as milk protein, insect resin, plant cellulose and fermented sugars.
The Advanced Materials article Lists Four Routes
- Cellulose acetate. Wood-pulp cellulose reacted with acetic acid, giving a clear, mouldable thermoplastic used historically for photographic film, tool handles and eyeglass frames. The Advanced Materials article states the reaction in simplified form. Real acetylation needs a stronger acetylating agent and an acid catalyst, so this is not a kitchen process.
- Casein plastic, or Galalith. Milk protein hardened with formaldehyde, for buttons, buckles and decorative items. See Casein Plastic.
- PLA (polylactic acid). Ferment sugars to lactic acid, then polymerise. Biodegradable and used for packaging and 3D printing.
- Shellac. A natural thermoplastic from lac insects, dissolving in alcohol and drying to a hard, glossy coating that is also an excellent electrical insulator. See Shellac.
Match The Material To What A Settlement Can Make
| Material | Source | Doable now? | Limit |
|---|---|---|---|
| Shellac | Lac resin | Yes | Melts at 75-80 °C, softens at 65 °C |
| Casein plastic | Milk, vinegar, formaldehyde | Yes | Usable to about 80 °C after hardening; absorbs water if unhardened |
| Horn, hide glue | Animal | Yes | See Alternative Polymers |
| Cellulose acetate | Pulp, acetic acid and more | With effort | Needs controlled chemistry |
| PLA | Fermented sugar | Hard | Needs purification and careful polymerisation |
PLA is worth understanding even if it is out of reach. The fermentation to lactic acid is within reach (see Fermentation Science), but turning that into long chains needs controlled conditions and removal of water, and a low-quality product is a brittle wax. No process is given here because none is sourced.
Bio-Based Does Not Mean Biodegradable
A bioplastic’s source and its fate are separate questions. A plastic made from plants can last for decades, and a fossil-fuel plastic can be designed to rot. Casein hardened with formaldehyde does not break down quickly. PLA breaks down only under warm, wet, controlled composting conditions, not in cool soil. Choose by use: the long-lived part wants a durable plastic and the disposable wrapper may want a degradable one.
Worked Example: Casein Needed For Buttons
Casein Glue gives about 30-35 g of dry casein from 1 litre of skim milk. If each button uses about 4 g (an assumed mass for this example), 100 buttons need 400 g of dry casein, which is 400 / 35 = 11.4 to 400 / 30 = 13.3 litres of skim milk, so about 12-13 litres. Plan for waste from trimming and cracks.
Formaldehyde and flammable solvents
Formaldehyde used to harden casein is toxic as vapour and a skin irritant, so use it dilute, outdoors or with strong ventilation. Alcohol used to dissolve shellac is flammable, so keep it away from flames and sparks. Do not make or use celluloid (nitrated cellulose) without the safety guidance in the plastics-from-scratch article, because it burns violently.
Common Mistakes
- Equating plant-based with safe or weak — judge each material by its properties.
- Skipping the hardening step on casein — it swells in water.
- Drying casein fast — cracks cannot be repaired.
What’s Next
- Learn next: Rubber Compounding — the best-known natural polymer
- Combine with: Plastics from Scratch — casein, celluloid and Bakelite as a group