material conflustration

I was looking for a filament supplier, and came across several suppliers of raw plastic as well. This one caught my interest as they supply recycled material and they are in the same country as I:

[www.alibaba.com]

However, this article on the use of regrind and recycled plastics has me very confused and a little frightened:

[www.ul-asia.com]

I have in mind to use 100% recycled plastic in my machine if possible, but I don't want the parts to suddenly degrade into dust or smell like

In addition, were one to purchase such raw material; which comes in pellets, flakes, or lumps and apparently not nice, neatly drawn out filament; one would need a device to render it into filament. I found such a thing for sale on alibaba as well, but it's bigger than my whole apartment and probably costs four times more than the rent... I've also seen the filament maker in the Builder's Blog and thought about rendering something of the sort for myself, but it needs a great deal more capacity to be effective. OR... one would need an alternate method of feeding plastic into a nozzle..... ideas?

---

David

Yes, recycled plastic is going to be a bit less strong than new, but we should still be able to use it.

It is going to be a bit of a challenge though; I'm concentrating on getting my Darwin running well first, and then recycling later. I've got my own stash of in house regrind available already - I've got a box full of all the rafts from the parts I've built so far, plus all the failed parts. Eventually I'd like to recycle those, and then perhaps other thermoplastics later. www.willitblend.com was previously mentioned on this forum as a possible grinder...

Making Darwins out of old pop bottles would be awesome, but is probably a bit further out in the future. My fleece shirt was made out of pop bottles though; so perhaps it's not that far out.

A good first step would be to try and order up some recycled plastic from a vendor that has the proper equipment; right now our extruders are pretty sensitive to variations in filament diameter.

Wade

dadederakh Wrote:
-------------------------------------------------------
>
>
> In addition, were one to purchase such raw
> material; which comes in pellets, flakes, or lumps
> and apparently not nice, neatly drawn out
> filament; one would need a device to render it
> into filament. I found such a thing for sale on
> alibaba as well, but it's bigger than my whole
> apartment and probably costs four times more than
> the rent...
>
You have a link to that?

>>Wade

Don't give up on this idea! I have the same thing in mind. I have really easy access to PET bottles and other plastics, so if we ever come up with a method of producing filament or an alternate method of feeding plastic I want to recycle whatever I can.

>>Forrest

Yes in fact i do! It's on sale by a company in China, and ships out of Shanghai...

[www.alibaba.com]

It has PP, PE, and PVC pellets listed as materials it could make welding rod from, but it would not surprise me if it could handle a few other kinds of plastics.

Also, the price is not listed and probably requires some negotiation.

---

David

Greetings David,

I spent a few years in a plastics injection molding factory and the general rule was to never exceed 10% regrind mixed with virgin unless you wanted to manufacture brittle junk.

After being used once the material lost plasticizer such that subsequent use caused it to become brittle.

Some plastics are worse than others so best you experiment. I recall that HDPE was the worst.

Regards, Ross

Ross Wrote:
-------------------------------------------------------
> Greetings David,
>
> I spent a few years in a plastics injection
> molding factory and the general rule was to never
> exceed 10% regrind mixed with virgin unless you
> wanted to manufacture brittle junk.
>
> After being used once the material lost
> plasticizer such that subsequent use caused it to
> become brittle.
>
> Some plastics are worse than others so best you
> experiment. I recall that HDPE was the worst.
>

Fascinating information! Thanks!

When and how is the plasticiser lost? If it is during the injection moulding heat cycle when the part was first made then we are already in trouble because the virgin filament has gone through one heat cycle to extrude it and then we put it through a second when we make the object.

---

[www.hydraraptor.blogspot.com]

well back to the pellet extruder then

'sid

Basically, what we need to do is...

Do while (assess printed object quality)
print maybe 10 kg of ABS/PLA/HDPE,
recycle it into new filament
Loop

...and see how many cycles we get before it is unusuable.

This is very important information that we certainly don't have. The results of such testing should also inform how we develop the technology. If we are only looking at one or two cycles with plastic that makes a very different world from what it would be if we could recycle 10-20 times, for instance.



Edited 1 time(s). Last edit at 11/18/2008 10:25AM by Forrest Higgs.

Greetings all,

I recall hearing that only some plastics contain plasticizers, usually brittle plastics. I suspect that HDPE doesn't contain plasticizers, but ABS may well, to address the rather brittle nature of styrene.

-- Larry

You are correct, some materials have plasticisers and others do not. They also used to add pigments such as TiO2, UV stabilisers, blowing agents etc so this may contribute to a 'diluting' effect. Another effect is the cross-linking that occurs on each heat cycle. This will differ for each material.

The worst product I encountered exhibiting this was a personal fluted rubbish bin in HDPE which was in a variety of colours. Best colour was black which meant they could use a higher regrind content and went up to 20%-30% in some cases. The problem with this high a regrind content was that the bins ended up very brittle and would often have the bottom (or sides) shatter when dropping an item (like an apple) into them.

If they wanted to make high quality coloured bins then it was up to 10% (or no) regrind, if they were making black el-cheapo ones then up to 30% regrind (from the high quality ones) was used but you had to be careful how you used them (I broke may of these when testing them in the factory) and even how you handled these as they would often shatter when a stack of them fell over.

My point is that you should consider the resulting quality of using high regrind ratios, while a Reprap extruding process may be kinder to the material (lower temperatures etc) you may find an item made with 100% regrind will be too brittle for your needs. I don't know the answer, just suggesting you be aware of this and make your own evaluations.

Regards, Ross

Regrind needs to be used as a support material. That seems to be becoming obvious.

I have been looking into making a filament extruder while ive been building my repstrap. My current concept extruder would be a large aluminum block with gear pump pressurizer. very much similar to a auto oil pump mechanism. the feed into the gear direct from a largish heated tank and extruded out of a 4mm end hole.
from there the filement would go through several heated/warm rollers of gradualy smaller diameter till 3mm is achieved.

Admitidly i havent got it built yet but wanted to let others know in case they wished to try something similar.

second concept was to use a triple piston pump connected to pneumatics in order to achieve a consistant pressure. but i think the first idea will be more practical.

Another note: i did a test on melting and recycling 2L pop bottles the other day. the end result came out as a very hard brittle substance with lots of air bubbles through it. Of course this was just a test on my stove and i didnt attempt to form it or anything so the air probably got in through the initaly cut and melt process. Another mistake i made was doing it in a pyrex/porcelan dish. when it cooled it had adheared to the bottom of the dish and then began to shrink, removing the inside layer of the dish i was heating it in.