Thursday, December 16, 2010

PLA that acts like ABS

That's what Purac is claiming for a new PLA (polylactic acid). The trick to acheiving this performance leap is not the result of any additive or modification of the monomer by the addition of various moieties, but instead occurs at a more fundamental level: the polymer is a block copolymer of both the D- and L- stereoisomers. There is no mention of the level of blockiness in these polymers (are they di-block, tri-block,...?), but I imagine that the blocks are not able to co-crystallize and will instead phase separate and crystallize separately. I'm also not able to find anything suggesting that the D- monomer will also not be as biodegradable as the L- monomer is, but that should certainly be confirmed.
It's pleasing to see a simple change in monomers that can produce such a large change in a polymer. (And what about those people who thought that chemists couldn't do anything new with C, H, O and N? Heck, this didn't even need the N!)

3 comments:

agiantamongmolecules said...

I would love to know how they are doing this. I like your suggestion of a stereoblock copolymer, but think the blocks may be stereo pure and atactic, like thermoplactic elastomer polypropylene, instead of D-blocks and L-blocks. I would think that a D-block:L-block copolymer would a form stereoblock complexe and be really really crystalline. Which would be strong, but not really resilient like ABS.

John said...

I like your thoughts, and let me add a few more.

PLA is a lot like that other polyester, PET, in that the crystallization can occur slowly and can be controlled by choosing processing conditions appropriately. (PBT and PEN are also like this, but they are more or less variations of PET - they have an aromatic backbone that PLA is lacking.)

This might be another aspect to this new product.

孙尉翔 said...

In reply to againtamongmolecules, tuning the block length statistics may control the polymer's efficiency to form steorocomplex domains, until the extent John suspected in his post -- not able at all. Annealing is a physical trick, whereas block control is real chemistry (playing with C, H, O and N). But I agree with againtamongmolecules on that there is no real way for PLA to act exactly like ABS.