What is the relationship of ethylene in ethylene glycol (antifreeze)
and polyethylene?
If there was a price spike in polyethylene resins would there be a parallel increase in antifreeze? Is this the same as the fruit ripening gas?
Ethylene glycol is a discrete molecule of low molecular weight. Polyethylene is a polymer, a long, string-like molecule with a molecular weights typically on the order of 100,000 times that of ethylene glycol and properties that are totally different.
Polyethylene is made by polymerization of ethylene. Ethylene glycol (antifreeze) is probably made catalytically from ethylene as well (a different process, of course). Ethylene is the “fruit-ripening gas”. If the price spike in polyethylene was due to the cost of the raw feedstock (ethylene), you might see a parallel increase in antifreeze costs.
I would guess, though, that the worldwide annual production of polyethylene is several orders of magnitude larger (on a weight basis) than that of ethylene glycol.
HOCH[sub]2[/sub]CH[sub]2[/sub]OH is ethylene glycol
-(CH[sub]2[/sub]CH[sub]2[/sub])[sub]n[/sub] is polyethylene.
Ethylene oxide is the fruit ripening gas, so it has one of the same starting materials.
It is also used as a fumigant in africulture and in the pharmaceutical industry, although hydrogen peroxide is now gaining popularity over ethylene oxide as a sterilising agent in the pharmaceutical world.
Ethylene is the plant hormone used to ripen fruit, not ethylene oxide.
This is what an ethylene molecule looks like:
H H
\ /
C==C
/ \
H H
It’s two carbon atom joined with a double bond, with hydrogen taking up the remaining two bonding sites on each atom.
To make polyethylene, lots of ethylene molecules and a catalyst are brought together under high pressure and temperature. This causes the double bond to partially open up:
H H
\ /
-C--C-
/ \
H H
Those unbonded ends are very reactive, and join up to form long chains of polyethylene, often over 100,000 units long. Hence Andy’s shorthand.
Incidentally, polyethylene doesn’t form perfectly straight chains; depending on the polymerization process used, it can form very branched chains, forming flexible low density polyethylene (LDPE). Likewise, relatively straight chains with just a few short chains every few hundred units are high density polyethylene (HDPE).
Just to add to the above points - polyethelyene glycol is a very important preciptatating agent in Protein Crystallography (to help proteins form a crystal). Ethylene glycol is also often used as an additive to aide in crystal growth, although not nearly as useful.