[MeganM (OP)]

Stuart has submitted this question to us:

With all the plastic pollution, would it be possible to 3D print housing using waste plastic? If not, why not?

Any ideas?

[alancalverd]

Probably better to use it to make columns and panels that can be shaped and drilled on site or in a factory. Printing a box may be fairly easy with a big enough printer, but you have to fit pipes and wires so conventional siding or prefab construction may turn out to be easier.

Also note that thermoplastics tend to be a bit soft, so the result will be more like an inflatable tent than a rigid house. Printing with thermo- or chem-set resins will be more rigid but much more complicated to do in a field. Then there's the problem of flammability, melting and the release of toxic gases when heated - difficult to imagine a printable plastic structure that would conform to sensible building regulations.

[syhprum]

A lot of prefabricated houses look fine on the factory floor or exhibition hall but over the years the owners rebuild in a conventual manner, the way houses are built has evolved over ten thousand years and no radical new designs are likely to be successful.
As Allen has said waste plastic may be useful to make some components but I think concrete, glass and timber will be around for a long time..
there are some wonderful Chinese brick wall brick wall building machines produced now but they are yet to find their into the British market

[Bored chemist]

One problem with making stuff from "waste plastic" is that the different plastics don't mix properly when melted.

[wolfekeeper]

I mixed up some thermoplastic polymer concrete a year or two ago. To make it I found all you have to do is just heat a thermoplastic, stir in some sharp sand and then let it cool. I tried a few different polymers and they seemed to all more or less work. It seemed to be potentially 3D printable, although it looked like it was going to be quite abrasive on nozzles. Polymer concretes are actually quite strong.

If the waste plastic is cheaper than portland cement, then it could be quite good; normally plastic is relatively expensive. What kind of cost per kg can you get?

The upsides are that polymer concrete is usually waterproof, but the downsides of concrete is that it's a good thermal conductor; in most cases you want poor thermal conductors for structures, and the flammability is an issue, but with the right additives or polymers might not be an issue.

[stuart a]

thanks to all that considered answers for this question, In response are we not clever enough to work out which plastics are compatible with each other, and secondly in relation to the structure not being strong enough can they not be made like for example breeze block sized and cemented together the conventional way i.e. staggered like bricks, and like Wolfekeeper mentioned the right mix of compounds might reduce risk of fires or bad thermals. If plastics in the manufacturing process are so dangerous to the environment why are we allowed to still manufacture plastic at all. Just feels like we are strip mining the only planet we can call home, and for what , so some people can save a buck or two. looks like our children will be a victim to the Fermi paradox

[alancalverd]

Wolfekeeper: Brilliant!

You might improve the compressive strength by using graded aggregate instead of sand, but whatever the outcome you have the potential for a sound-deadening, waterproof and impact-tolerant wall liner for any property. Thermal conductivity isn't really a problem if you use a modern cavity insulator.

Nozzle abrasion isn't a problem if the temperature is high enough. We routinely pump concrete through 6-inch nozzles. The joy of thermoplastic concrete is that you don't have to scrub out the nozzle after use - just switch on the heater the next day, and it all turns back to slurry.

[wolfekeeper]

So far as I can tell, the compressive strength is similarish to normal concrete, but it has one key advantage- it actually has some tensile strength without further reinforcement, so it's quite robust and not brittle, and the other obvious advantage is that unlike normal concrete it sets off very quickly.

There were some caveats I found, you possibly can't just use any thermoplastic, it has to actually stick the aggregate together, so it probably can't be (for example) polyethylene- polyethylene has a really slippery, "low energy" surface. IRC polyamide worked, those 'glue sticks' work really well for obvious reasons. I tried polycaprolactone and that worked OK because it gets sticky when hot. That was fun because you can mold it with your hands.

Although it's probably significantly more expensive than normal concrete, you probably don't need as much of it because you can put it right where you need it, and you can corrugate it and print it with spaces in the middle.

The real problem is whether there's a killer app for it. I mean you could easily print domes and things with it. Is that something people need though?

Oh yeah, and UV is an issue. Mixing in a tonne of carbon black and painting it would help a lot though.

Edit: graded aggregate is a very, very good idea, but perhaps not in the way you'd initially think- it minimises the amount of plastic you need, because you just have to fill in the gaps between the bigger aggregate, but with graded aggregate most of that is filled with smaller aggregate. Plastic is actually one of the more expensive materials in constructions so anything you can do to reduce it is super helpful.

[Hayseed]

We should learn how to make roads out of it.  Roads that move with the earths temperature.

[wolfekeeper]

Tarmac pretty much occupies that space just fine. Plastic roads sound to me like a terrible idea- they would wear and all the ground-up plastic will end up getting washed out to sea. Building plastic into a permanent structure is at least the opposite of single-use plastic.

[vhfpmr]

I'm sceptical that plastic houses would withstand sunlight for a century.

[Bored chemist]

I'm sceptical that plastic houses would withstand sunlight for a century.

Good point, but with a coat of paint, the plastic wouldn't be exposed to sunlight.

[alancalverd]

You can't have it both ways! Either plastic waste is a dangerous pollutant, or it all crumbles to useless inert dust when exposed to sunlight - you don't hear much about "unacceptable sand", after all. I guess the problem is that it doesn't decay as quickly as natural organics or as slowly as construction inorganics, but painted or pickled wooden structures, from churches to airplanes, have been an acceptable and even admirable feature of human endeavour for as long as homo has been regarded as sapiens. Time to rehabilitate the polymer?