Cellulose Some, and You Win Some

I have a new obsession — microbial cellulose.  I have been meaning to experiment with this stuff ever since I read Fermented Frocks, the New Couture.  Recently, my sister’s room-mate was discarding a kombucha culture, long past its prime, and I knew I had to have it — despite the fact that was about the closest thing to two gallons of pure biohazard that I have ever laid eyes on.  I peeled a few layers from the decrepit SCOBY that was floating in the middle of the rancid kombucha, and dried them into tough, leathery, translucent “paper” (see the photo with the “paper” covering a CD for perspective). After that, I was hooked — smell be damned — and after some research, I was really hooked.

Microbial cellulose is unlike any material I have ever handled, and it has some remarkable properties.  It is almost pure cellulose — no lignin, no hemi-cellulose etc., so, unlike plant-derived cellulose, you can grow it and use it in its raw form with no chemical processing.  The cellulose molecules are unusually long in comparison to plant-derived cellulose, and the fibrils that the Aceteobacter Xylinum bacteria produce are arranged as stacks of microporous, web-like membranes.  As a result, the material has a surprising strength to weight ratio and endures repeated folding without apparent weakening.  It feels like parchment, but it is extremely hydrophylic and can hold 100x its dry weight in water.  The fact that it is a naturally occurring  hydrogel makes it a great raw material for aerogels and the like, and the fact that it is organized as layers of microporous membranes makes it a good candidate for various kinds of semi-permeable barriers.

To me, it seems like the ultimate green material — no fertilizers, no machinery, little or no post-processing, strong, biodegradable and just generally useful for all sorts of interesting of applications.  Plus, it can be made from waste sugar and can ultimately be recycled by inclusion in paper, or by breaking the cellulose down into sugar and making new cellulose.  What’s not to love?

Anyone can make this stuff.  All you need is a kombucha “mother”, some yeast, some sugary medium and a container in which to grow the stuff.  Here’s a picture of a five gallon bucket that I filled with instant iced tea mix, a packet of yeast and five gallons of water.  I tossed in some fragments from a kombucha mother, poured the  whole shootin’-kaboodle into a shallow tray and within a week, I had a  four square foot mat of cellulose that looked like this:

Of, course, the iced tea mix was a mistake — the artificial color made the resulting cellulose incredibly gross looking.  It literally looked like someone had vomited their guts up, with the cellulose gel mat playing the role of “giant expelled stomach”.

As a parallel experiment, I raised some cellulose in a culture of sugar water, vinegar and yeast.  This made almost pure white cellulose that cleaned up nicely.  The yield of this “vinegar and sugar” batch seemed slightly lower than the “instant iced tea” batch, but the improved aesthetics may be worth the reduced yield.

I am planning to use the material in a number of ways — I converted the iced tea cellulose into shredded cellulose gel and then dried it in methanol, with the intent of using the fibers to make strong, biodegradable composites.  I also intend to use the sheets for composites and I plan to make some thick structures in order to see if I can convert them to cellulose aerogel.