PLA: The Plastic That Grows

If you’ve ever taken a coast-to-coast car trip across the United States, the one thing that’s sure to impress you is the mind-bogglingly immense amount of corn that we grow here. If you take the northern route — I’ve done it seven times, so I know it by heart — you’ll see almost nothing but corn from Ohio to Montana. The size of the fields is simply staggering, and you’re left wondering, “Do we really eat all this corn?”

The simple answer is no, we don’t. We grow way more corn than we can eat or, once turned into alcohol, drink. We do feed a lot to animals, many of which subsequently end up as burgers or pork chops. But even after all that, and after accounting for exports, we still have a heck of a lot of corn to put to work. There are lots of industrial uses for this surplus corn, though, and chances are pretty good you’ve got an ear or two worth coiled up next to your 3D-printer, in the form of polylactic acid, or PLA.

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Hold the Salt and Butter, This Popcorn Is For a Robot

Popcorn! Light and fluffy, it is a fantastically flexible snack. We can have them plain, create a savory snack with some salt and butter, or cover with caramel if you have a sweet tooth. Now Cornell University showed us one more way to enjoy popcorn: use their popping action as the mechanical force in a robot actuator.

It may be unorthodox at first glance, but it makes a lot of sense. We pop corn by heating its water until it turns into steam triggering a rapid expansion of volume. It is not terribly different from our engines burning an air-fuel mixture to create a rapid expansion of volume. Or using heat energy to boil water and trigger its expansion to steam. So a kernel of popcorn can be used as a small, simple, self-contained engine for turning heat energy into mechanical power.

Obviously it would be a single-use mechanism, but that’s perfectly palatable for the right niche. Single-use is a lot easier to swallow when popcorn is so cheap, and also biodegradable resulting in minimal residue. The research paper demonstrated three recipes to harness popping corn’s mechanical energy, but that is hardly an exhaustive list. There’s an open invitation to brainstorm other creations to add to the menu.

Of course, if you prefer candy over popcorn, you could build a robot actuator out of licorice instead.

Either way, the robot uprising will be delicious.

[via IEEE Spectrum]

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The Metabolizer Turns Trash into Treasure

The amount of stuff we humans throw away is too damn high, and a bunch of it harms the ecosystem. But what are you gonna do? [Sam Smith] thinks we can do better than shoving most of it in a landfill and waiting for it to break down. That’s why he’s building The Metabolizer. It’s a series of systems designed to turn household trash (including plastic!) into useful things like fuel, building materials, and 3D prints.

The idea is to mimic the metabolism of a living organism and design something that can break down garbage into both useful stuff and fuel for itself. [Sam] is confident that since humans figured out how to make plastic, we can figure out a system to metabolize it. His proof-of-concept plan is to break down waste into combustible, gaseous fuel and use that fuel to power a small engine. The engine will power an open-source plastic shredder and turn a generator that powers an open-source plastic pellet printer like the SeeMeCNC Part Daddy.

Shredding plastic for use as a biomass requires condensing out the tar and hydrocarbons. This process leaves carbon monoxide and hydrogen syngas, which is perfect for running a Briggs & Stratton from Craigslist that’s been modified to run on gaseous fuel. Condensation is a nasty process that we don’t advise trying unless you know what you’re doing. Be careful, [Sam], because we’re excited to watch this one progress. You can watch it chew up some plastic after the break.

If [Sam] ever runs out of garbage to feed The Metabolizer, maybe he could build a fleet of trash-collecting robots.

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3D Printing with Mussels and Beets

What do you get when you combine oven-baked mussels and sugar beets in a kitchen blender? No, it isn’t some new smoothie cleanse or fad diet. It’s an experimental new recyclable 3D printing material developed by [Joost Vette], an Industrial Design Engineering student at Delft University of Technology in the Netherlands. While some of the limitations of the material mean it’s fairly unlikely you’ll be passing over PLA for ground-up shellfish anytime soon, it does have a few compelling features worth looking into.

Joost Vette

For one thing, it’s completely biodegradable. PLA is technically biodegradable as it’s usually made primarily of cornstarch, but in reality, it can be rather difficult to break down. Depending on the conditions, PLA could last years exposed to the elements and not degrade to any significant degree. But [Joost] says his creation degrades readily when exposed to moisture; so much so that he theorizes it could have applications as a water-soluble support material when printing with a multiple extruder machine.

What’s more, after the material has been dissolved into the water, it can be reconstituted and put back into the printer. Failed prints could be recycled directly back into fresh printing material without any special hardware. According to [Joost], this process can be repeated indefinitely with no degradation to the material itself, “A lot of materials become weaker when recycled, this one does not.

So how can you play along at home? The first challenge is finding the proper ratio between water, sugar, and the powder created by grinding up mussel shells necessary to create a smooth paste. It needs to be liquid enough to be extruded by the printer, but firm enough to remain structurally sound until it dries out and takes its final ceramic-like form. As for the 3D printer, it looks like [Joost] is using a paste extruder add-on for the Ultimaker 2, though the printer and extruder combo itself isn’t going to be critical as long as it can push out a material of the same viscosity.

We’ve seen a number of DIY paste extruder mods for 3D printers, which is a good starting point if you’re getting sick of boring old plastic. Before long you might find yourself printing with living tissue.

[Thanks to Mynasru for the tip]

Ask Hackaday: Is PLA Biodegradable?

The most popular plastic for 3D printers is PLA – polylactic acid – a plastic that’s either derived from corn starch, inedible plant detritus, or sugar cane, depending where in the world it was manufactured. Being derived from natural materials, PLA is marketed as being biodegradable. You don’t need to worry about low-poly Pokemon and other plastic trinkets filling landfills when you’re printing with PLA, all these plastic baubles will return to the Earth from whence it came.

3D printers have been around for a few years now, and now objects printed in PLA have been around the sun a few times. A few of these objects have been completely forgotten. How’s that claim of being biodegradable holding up? The results are mixed, and as always, more data is needed.

A few weeks ago, [LazyGecko] found one of his first experiments in 3D printing. In 2012, he was experimenting with tie dying PLA prints by putting his prints in a jar filled with water and blue dye. This jar was then placed in the back of his cupboard and quickly forgotten. 3.5 years later, [LazyGecko] remembered his experiment. Absolutely nothing happened, save for a little bit of blue dye turning the print a pastel baby blue. The print looks and feels exactly like the day it came off the printer.

[LazyGecko]’s blog post was noticed by [Bill Waters], and he has one datum that points to PLA being biodegradable. In 2015, [Bill] printed a filter basket for his fish tank. The first filter basket worked well, but made a small design change a week later, printed out another, and put the first print in storage. He now has two nearly identical prints, one in constant use in a biologically interesting environment, the other sitting on a shelf for a year.

[Bill]’s inadvertent experiment is very close to the best possible experimental design to make the case for PLA biodegradability. The 3D printed filter basket in constant use for a year suffered significant breakdown, and the honeycomb walls are starting to crumble. The ‘inert’ printed filter basket looks like it just came off the build plate.

If that’s not confusing enough, [Bill] also has another print that has spent a year in a fish tank. This end cap for a filter spray bar didn’t see any degradation, despite being underwater in a biologically active environment. The environment is a little different from a filter basket, though; an aquarium filter is designed to break down organics.

To answer the question, ‘is PLA biodegradable,’ the most accurate answer is, ‘maybe’. Three data points in uncontrolled environments isn’t enough to draw any conclusions. There are, undoubtedly, more forgotten 3D prints out there, and more data to back up the claim of PLA being biodegradable.

This is where you come in. Do you have some forgotten prints out there? Your input is needed, the fruits of your labors are evidence, your prints might be decaying and we want to know about it below.

Unlocking silk for uses as an optical, digital, biological, or food storage device

[Fiorenzo Omenetto] gave a TED talk early last year to illustrates a lot of intriguing uses for silk. Before watching his presentation we would have been hard pressed to come up with a use for silk other than in clothing. But it turns out that investigating how silk worms create the material has led to a range of other applications. You can see the full talk embedded after the break.

One of the first things he shows off is a transparent film made of silk. The material looks almost like cellulose film, and can function in a similar way. [Fiorenzo] shines a laser through a silk slide that has a micro-dot of words embedded in it. the result is a clearly readable message projected on the wall. The film can also be used for holographic images.

But it’s the biodegradable aspects that are clearly the breakthrough here. A slide of silk can be doped with pharmaceuticals and programmed for a very specific time release. This way the drugs no longer need to be stored under refrigeration, and can be reclaimed using only water. The same properties allow one to manufacture disposable objects that will quickly and completely degrade. But there’s even more, if you dope the material with a conductor like gold it becomes a disposable circuit.

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