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High-Pressure Polyethylene
In March 1933 Eric Fawcett and Reginald Gibson at ICI squeezed ethylene gas with benzaldehyde to about 1400 atmospheres and found a white waxy solid in the vessel. It could not be repeated reliably until 1935, when Michael Perrin's team traced the trick to a trace of oxygen that started the chains. The product was polyethylene - light, tough, a superb electrical insulator, and soon the cable insulation of wartime radar.
**US 2,153,553**, "Polymerization of olefins", Fawcett, Gibson and Perrin, assigned to Imperial Chemical Industries, granted 11. April 1939, claims "subjecting ethylene to a pressure above about 500 atmospheres and a temperature above about 100 C"; its example runs at 2000 atmospheres and 170 °C.
**Nobody reproduces 2000 atmospheres at home.** You work the polymer instead: fuse polyethylene bags into a tough sheet with an iron, then measure its density to tell high-pressure (branched, low-density) polyethylene from its later straight-chain sibling.
Beginner
90 minutes
Instructions
1
1
Sort the bags
Sort the bags
Collect clean, dry carrier or produce bags marked LDPE (recycling code 4). Cut off handles and seams; open each into a flat sheet.
Materials for this step:
Plastic Bags8 piecesTools needed:
Scissors2
2
Stack between parchment
Stack between parchment
Stack 6 layers of bag film, printed side inward, between two sheets of baking parchment. The film must never touch the iron.
Materials for this step:
Baking Parchment Paper2 sheets3
3
Fuse with the iron
Fuse with the iron
Iron on a low-medium setting, no steam, moving constantly for 15 seconds. Ventilate. Too hot and it shrivels and smokes - lower the setting.
Tools needed:
Steam Iron
N95 Respirator Mask4
4
Flip, repeat, cool
Flip, repeat, cool
Flip and iron the other side. Peel the parchment once cool. Re-iron any bubbled patches. The layers are now one welded sheet.
Tools needed:
Steam Iron5
5
Pull-test both
Pull-test both
Cut 20 mm strips from the fused sheet and from a single bag layer. Clamp each in the vise and pull with the spring scale. Record the peak force.
Tools needed:
Force Meter (Spring Scale)
Bench ViseScissors6
6
Float test
Float test
Pour 50 ml isopropyl alcohol into a beaker. Drop in a small chip of the sheet - it sinks. Add water 10 ml at a time, stirring, then 1 ml at a time once the chip starts to lift, until it hangs mid-liquid. Note the total water added.
Materials for this step:
Isopropyl Alcohol 99%50 mlTools needed:
Glass Beaker
Graduated Cylinder
Pipette/Dropper Set
Stirring Rod7
7
Pressure, density, siblings
Pressure, density, siblings
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History & Context
History & Context
**What the patent specifies:** ethylene above about 500 atm and 100 °C (preferred 1000+ atm, 150–250 °C). **Modern build (derived):** post-consumer LDPE film, fused well below its decomposition temperature.
Low-pressure routes in the 1950s gave straight-chain, denser HDPE; both are still made in huge volumes because the branches that make LDPE weaker also make it softer and clearer. Limits: it creeps under load, softens around 100 °C, and burns.
Materials
3- 8 piecesPlaceholder
- 2 sheetsPlaceholder
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Tools Required
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- Steam Iron10% commissionPlaceholder
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- Pipette/Dropper Set10% commissionPlaceholder
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