Comments on RepRap: Blog: Drink Bottle Feedstock

Correction: Forrest's just reminded me that the we...

2009-03-16T20:14:22.085Z

Correction: Forrest's just reminded me that the weight of the solid Darwin parts is about 1.4 kg.

Interesting lets say we only get 60% of usable HDP...

2009-03-16T12:22:22.203Z

Interesting lets say we only get 60% of usable HDPE from a milk bottle and we use the honeycomb interior.

A full Darwin print run would only need 8 x 6 pint milk bottles or 13 2 pint milk bottles.

From memory, Darwin's RP parts weigh about 1 kg if...

2009-03-16T10:42:52.345Z

From memory, Darwin's RP parts weigh about 1 kg if you build them solid, about one-third that if you build them with a honeycomb interior.

Mendel should be lighter yet.

I don't know how the hydrolysis will affect the usability and strength of the parts, though I can say that the cloudy bit I took out of the nozzle seems pretty tough.

Interesting stuff!This is not just about feedstock...

2009-03-16T07:53:38.628Z

Interesting stuff!

This is not just about feedstock, it's about independence :) It means that people might be able to bootstrap a machine without needing a specific filament.

Maybe the melting point changes because PET absorbs water.
"PET is hygroscopic, meaning that it naturally absorbs water from its surroundings. However, when this 'damp' PET is then heated, the water hydrolyzes the PET, decreasing its resilience."
http://en.wikipedia.org/wiki/Polyethylene_terephthalate#Drying

I guess that hydrolysis would change the chemical and material properties of PET...
Under the #Crystals heading, there are also some details that might explain the clouding.

with coloured lid removed :-2ltr Milk container is...

2009-03-16T00:37:37.276Z

with coloured lid removed :-

2ltr Milk container is 44g
3.4 ltr Mild container 70g

HDPE Reprap parts xxxg

I guess parts like the screw thread for the lid would not be easy to use this would need to be deducted from the above weights.

Great test!Could this same method work using plast...

2009-03-16T00:26:01.211Z

Great test!

Could this same method work using plastic Milk bottles I beleve they are made from Hdpe.
The next qestion would then be if it is possible to recycle.
By extrudeing objects from strips, roughtly how many 2ltr drinks containers would you extimate would be needed to extrude a set of reprap parts?

Thoughts of local reclying in my own street, poping into my head now.

degreed - degrees...

2009-03-15T23:29:54.132Z

degreed - degrees...

Yup - that's what I thought. But it comes out pre...

2009-03-15T23:29:12.300Z

Yup - that's what I thought. But it comes out pretty runny. My temperature measuring is a thermocouple straight into my multimeter K-junction, but it may be a little off centre, and so a few degreed colder than the polymer. But 30 C below seems unlikely.

Of course, the whole idea of a melting point for a polymer is a rather elastic concept (if that's the right metaphor) anyway...

Odd that you can extrude it below its melting poin...

2009-03-15T23:04:41.201Z

Odd that you can extrude it below its melting point!