Monday, September 18, 2006


Trimmer line progress (or lack thereof)

Fired up a hotglue gun and a 35watt soldering iron and tested the trimmer line against them;

The trimmer line got a bit sticky after a few seconds, but after 30sec, still not fully liquified. It had the consistency of marshmallow fluff.

With the soldering iron test, the line was basically pressed against the body of the iron. The line immediately turned mushy and melted, however it also started emitting plenty of wierd smoke. After removing the line there was also a bit of black residue on the metal. I'm not sure if this was because the iron was too hot or because of the trimmer line's composition (pvc fumes?).

At any rate, I am definitely liking the idea of using alternative, higher temp materials in an extruder. Soldering iron element can easily break 200degC and can be mounted without too much effort to an extruder barrel. It would give us a bigger variety of source-material, whether CAPA or recycled material.

Here's some possible sources of polymer with unknown melting points and composition. If anyone knows the composition and whether any of these will make viable sources, please respond:
Lawn Trimmer line (still testing)
Styrofoam / Packing peanuts
Plastic shopping bags (lots of them)
Plastic cups / dishware (many varities)
Plastic bottles (water, soft drink)
Melted-down junk? (computer equipment plastics

Maybe it's a pipe-dream, but the idea of being able to recycle 'junk' and turn it into usable parts/products sounds pretty inticing.

Be careful when you start experimenting with heating plastic that has unknown composition.

PVC, when it decomposes creates Chlorine and Hydrogen Cloride gas. When this enters your lungs, it reacts with moisture to create hydrochloric acid. This tends to irritate best case, and destroy, worst case, any lung tissue it encounters. Needless to say, this is not a good situation to be in.

Other plastics can create other compounds that can also affect your health.

Just be careful and make sure if you are going to do experiments like this, that they be in well ventilated areas, preferably, outside.

Oh, and probably goes without saying, avoid breathing any fumes that happen to be created. :)
To answer your other question, you can generally figure out the kind of plastic by looking for the recycling symbol:

1 = PET or PETE (260 C)
2 = HDPE (120-130 C)
3 = PVC (212 C)
4 = LDPE (105-115 C)
5 = PP (165 C)
6 = PS (240 C)
7 = mixed/other

Clear plastic shopping bags (fruit and vegetable bags) tend to be LDPE; regular plastic shopping bags and milk cartons tend to be HDPE. Soda bottles tend to be PET. Packing peanuts tend to be PS (Styrofoam is PS - Polystyrene, and air). I've seen type 5 in some food packaging. Printer parts and other non-food containers tend to be types 3, 5, or 7 (and they usually do not label them with recycling symbols because, I suppose, they don't get recycled as often as food containers.)
make sure if you are going to do experiments like this, that they be in well ventilated areas, preferably, outside.

Dont worry about that. Anyone that intentionally burns plastic indoors without wondering about health effects isnt going to be around long anyway.

Beagle, of those materials you graciously listed, which ones might be viable, safe sources of polymer?
I think if I were to choose, HDPE is probably the easiest target. I'm not sure what the viscosity vs. temperature curve looks like... You'd want to try to keep the temperature somewhere between 120 C and 200 C; any hotter and I think it starts getting too close to it's decomposition temp.
On the reprap blog I mentioned some of my testing.
HDPE seems to oxides before it turns liquid (though some disagree with me) . It is an amazing plastic though and it worth trying to overcome the problems.
LDPE was the easiest as beaglefury's table suggests.
PET is pretty much out because it reacts with water when heated.
PP and PS both discolored slightly and didn't form a uniform solid. PP distorted badly when cooled.
Didn't do PVC.
My interest is HDPE. It could be possible to make filament at lower temps using higher pressure or keeping the O2 away.
Extrusion aside - I'd like to make blocks of the stuff for machining.
HDPE seems to oxides before it turns liquid (though some disagree with me)

Perhaps there are dyes/inks that are breaking down?
I suspect it is decomposing - question for Eddie.M would be - what was the temperature at the point of contact between your heat transfer unit and the HDPE plastic? I suspect it was probably ~235 C or higher (This is where HDPE starts to decompose in air). It will begin thermally decomposing at ~290 C. It will start burning at ~340 C.

If you can maintain a temperature of 180 C on a metalic container filled with HDPE, I suspect you will not see see much (if any) oxidation.
Be really careful with plastic bags. A lot of them are made of PVC.
Not disagreeing with you, Forrest, but what is the source of the PVC plastic bag warning? In my experience, the grocery stores in our area use HDPE for the semi-opaque grocery bags, and LDPE for the clear vegetable bags. The garbage bags you can buy tend to be LDPE or LLDPE. This seems to be in line with what indicates for common plastics used for bags.

Is there a particular type of bag that is made of PVC (Those more commonly used in craft/gift stores, maybe?) I seem to recall food packaging being possibly PVC based?

In any case, as long as you tune the temperature for HDPE, PVC shouldn't decompose too quickly (It starts decomposing ~200 C, melts at ~210 C, and rapidly decomposes at 250 C)
The more heavily coloured, shinier shopping bags that you get from clothing and book stores tend to be PVC in my experience.
Yes, PVC is the shinier stuff. Also if your better half buys a shiny black kitten outfit don't try to melt it. ;-)

Herr Beagle, about spray on nylon, apparently it is not easy to get the ratio of diamine and a dicarboxylic acid. Well, that's what Wikipedia says anyway. ;-) In the same article they mention a prepared correct ratio "paste" approach, now that could be interesting.

Now this link to a "Nylon in the Comfort of Your Own Home". Sounds like fun.
Oops, well it seems blogger has a very poor implementation for pasting urls into messages. For some reason it truncated the "html" bit at the end...

A quick look through their help files didn't help me much. Does anyone know a good way of pasting an url into a reply?

In any case, for those wanting to click the link to making nylon at home I found it at the bottom of the Wikipedia article on nylon.
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