Stumbling across the biopolymer zein

It is hard to find time to hare after all of the potential research directions implicit in the Reprap undertaking. As a result of that, I've tried to concentrate on just a few areas dealing with the increase of the printed percentage of Reprap machines. Yesterday, however, I got off-track for a few hours.

For some reason I found myself looking for the Wikipedia entry for bioplastics and serendipitously keyed in biopolymers instead. There, I ran across a reference I hadn't seen before about a biopolymer called zein.  The article referenced an incredibly detailed review of the material concentrating on its extraction written up a few years ago by John W Lawton at the USDA laboratory at Peoria in Illinois.  Apparently, there is a large collection of zein related articles there which served as the basis of Lawton's extensive article.  A few things about zein jumped out at me.

The biggest was that it was a protein, biopolymer which used corn gluten meal, a rather useless byproduct of the corn milling process.  Corn gluten meal is a non-nutritive waste product that is typically used as a bulk agent for cattle fattening.  It also has developed a small reputation as an "organic" herbicide for home gardens.  This last is important because it means that 50 lb sacks of it can be had by ordinary people in one-off quantities at prices of under $1/lb.  What that implies is that corn gluten meal is basically free and that what you are looking at is mostly the packaging, warehousing and transport cost when you purchase it.

The second was that reading over the Lawton article that the most successful extraction methods were achieved with kitchen chemicals {rubbing alcohol with a touch of lye} and chemistry.  As well, zein has a long history of being used as a plastic, coating and, interestingly a fibre.  This last I will talk about a bit later in this blogging.

Zein was used extensively before being displaced by petroleum-based substitutes during the 1950s and 1960s.  Currently, ready-to-use zein is quite expensive {~$10-25/lb} not because of its intrinsic cost but rather because its very limited market, viz, food grade coatings for pills and food products commands such prices due to its highly regulated nature.

I vaguely remember from my childhood a wool substitute fiber called Vicara which emerged in the 1950s before being replaced by synthetic, petroleum-based fibers a decade or so later.  What shool me about the Lawton article was that Vicara was made from zein.  The rather high softening temperature of Vicara {~245 C}.  If the melting temperature of zein is anywhere near this a whole range of products like coffee makers and the like become possible.  Using PEEK instead of PTFE for thermal barriers in extruders, something that we are already beginning to do regularly, ought to let us get by with that.

Oddly, zein's glass transition temperature is very low {~40 C}.  It may be that like PLA, zein has no real warping problem during printing compared to petroleum-based polymers.

Heretofore, our use of plastic filament as feedstock for printing has caused practical problems when mapped against our desire for a recycling scheme for plastic.  With recycling we have to grind the waste plastic, a problem that appears to have been solved recently.  Afterwards, we have to extrude the filament.  The machinery for doing this extrusion is relatively complicated.  Sadly, you can't just extrude filament.  After it is extruded you have to quench, reheat and run it through a series of godet stations before you can spool it.  This videoclip gives you a fair notion of the complexity and scale of the process. It seems to me that scaling down that sort of process is going to be an undertaking much more complicated than the Reprap printer

The notion that zein was made into fiber coupled with the application of electrospinning to zein fibres led me to quite a new idea.  What would stop us from using spun fiber instead of monofilament in our extruders?

Electrospinning can be achieved with very simple apparatus such at this piece of lab equipment made in New Zealand.

Spinning the filament into thread of the proper diameter is an old, old technology easily scaled to our application.  This Indian charkha shows how simple the technology can get.

Filament is useful in our extrusion technology because it is stiff enough to be forced into our extruder barrel under pressure.  Obviously, fibre thread can't.  Keeping in mind, however, that our thread is polymer, we should be able to draw it through a heated die to consolidate the fibres into a single polymer mass.