Tuesday, November 11, 2008
DIY PLA
Forrest has just reminded me that I should have blogged this ages ago.
Bath undergraduate Nick Grudgings did some experiments on making polylactic acid. Here's his setup:
The flask contains lactic acid, and is resting in a heater. The tube is feeding in dry nitrogen to eliminate moisture. There's a magnetic stirrer flea under the lactic acid that you can't see. We also put in a thermometer. The whole thing was in a fume cupboard, as you don't want to breathe lactic acid vapour...
We warmed it up gradually, with the stirrer turned on. When the lactic acid started to melt we added 1/600 by weight of tin octoate as a polymerisation catalyst. The melt became quite viscous at around 140oC as polymerization started. You can control the mechanical properties of the result by the amount of catalyst: the polymer chains form from each catalyst molecule, so more catalyst means shorter chains.
Here's the result:
At the bottom of the flask is a cool solid clear lump of polylactic acid, with - it turned out - a little residual lactic acid embedded in it.
After a while (weeks) that lactic acid started to absorb atmospheric water vapour and thereby to disrupt the polymer, from which we learned that we needed to cook it for longer (we used about half an hour) to complete polymerisation. Obviously the longer the polymer chains you go for, and thus the less catalyst you use, the longer the polymerisation will take.
Bath undergraduate Nick Grudgings did some experiments on making polylactic acid. Here's his setup:
The flask contains lactic acid, and is resting in a heater. The tube is feeding in dry nitrogen to eliminate moisture. There's a magnetic stirrer flea under the lactic acid that you can't see. We also put in a thermometer. The whole thing was in a fume cupboard, as you don't want to breathe lactic acid vapour...
We warmed it up gradually, with the stirrer turned on. When the lactic acid started to melt we added 1/600 by weight of tin octoate as a polymerisation catalyst. The melt became quite viscous at around 140oC as polymerization started. You can control the mechanical properties of the result by the amount of catalyst: the polymer chains form from each catalyst molecule, so more catalyst means shorter chains.
Here's the result:
At the bottom of the flask is a cool solid clear lump of polylactic acid, with - it turned out - a little residual lactic acid embedded in it.
After a while (weeks) that lactic acid started to absorb atmospheric water vapour and thereby to disrupt the polymer, from which we learned that we needed to cook it for longer (we used about half an hour) to complete polymerisation. Obviously the longer the polymer chains you go for, and thus the less catalyst you use, the longer the polymerisation will take.
Labels: make plastic, pla
