cheap plastic, where art thou ?!

13 Aug 2006 I've been trying to melt plastic for a while now. The first attempt was not a success because my oven couldn't get hot enough to melt PET (260+ degrees C)

The second attempt was on my barbecue, which did get the PET to melt, but when it cooled down, the plastic became more fragile than I thought. It was more or less like suplho plastics, just a bit harder.

Anyway, so far nothing good came from this project.

A fellow amateur researcher like me came to the same conclusion. He believes it's more trouble than it's worth.

So... what do I do next ?

I was wondering how carmodel builders make their parts. It appears a lot of them are lazy bastards who just buy parts in the store. But some of them do build chassis and things from scratch. It's called scratch building. Unfortunately, it doesn't answer the question of how to make your own plastic.

After digging a little deeper, I found this page on digg.com which showed me that I'm not the only one trying to make plastic stuff on the cheap.

The page mentioned something called Shapelock, but it seems to be very expensive (500 grams for 30 dollars ?!)

Another thing called "Friendly plastic" is also mentioned. After some research, it seems the company that made this material quit somewhere in the 80s.

In any case, both shapelock and friendly plastic melt in hot water. Sure, it's nice to play with, but practically unusable as a construction material.

And then there is this:

For my fellow cheapskates - ...

(That's me)

...I know you are out there - I will share my 
ghetto-fabulous method for molding scavenged plastic. 
ABS plastic dissolves in acetone! Get a good thick 
piece (television/CRT housing, motorcycle fairing, 
etc.), and make a pile of shavings by repeatedly 
drilling holes in it. When you get a good amount, dump 
them into a small disposable container with a bit of 
acetone. Stir until gooey. Remove the blob and mold. It 
will take at least 24 hours to fully cure, so be 
patient. Also, air bubbles inevitably get into the mix, 
making this recycled ABS weaker than original. But it 
won’t melt at 160 degrees, either.
This stuff gets really sticky when molding! It is 
manageable though, if you keep your fingertips wet with 
acetone.
This method can be used to repair cracks in a 
motorcycle fairing!

This sounds reasonable. ABS plastic and acetone. If only now I could find out what's made of ABS and where to get large quantities of it.

here is a PDF with some properties of all kinds of plastics.

[A couple hours later]

The ABS recycling symbol looks like this:


I looked around and found that the remote control of my TV is made from ABS, aswell as the cassette holder of the cassette deck that was in my car.

Furthermore, I found lots more information about solving ABS in acetone here:
http://www.mp3car.com/vbulletin/showthread.php?t=45050

I will quote it here in case the site goes down or internet explodes:

1:


I have been planning my carputer for a LOOOOOOOOOOONG time now and have just been to lazy to get started... well, tonight I started my fabrication and was wondering why more people don't use solvents and solvent adhesives instead of the usual bondo, fiberglass and whatnot...

Basically, I took my Xenarc front housing, gutted it, sanded the paint off it, cut my dash so the housing fit nicely in place, sanded the paint and finish off of it... then I mixed chunks of ABS plastic in a condiment bottle with Acetone (MEK works too) to make an ABS sludge. I slipped the housing into place, used masking tape to close off the holes in the rear where the housing and dash meet together, and then squirted my ABS sludge into the gaps and space. I expect the plastic will cure by tomorrow afternoon at which time I can do a prelimiary grinding and sanding and then put more of the sludge in the low spots. It should only take a couple apps and it will be done.

With the solvent adhesives, you are chemically bonding the two parts together so there is no chance of it cracking apart whereas over time, bondo will eventually crack (I have experienced this plenty!)... so I'm wondering why more people don't use these solvents instead of bondo. IMO, its even less of a mess as well as a more permanent solution. And don't get my wrong, I'm not hacking on the many people who choose fiberglass and bondo as their medium... just curious.

BTW, I'll post picture in the next day or two of my dash work...

TTYL!


2:


Unfortunately, I didn't take pictures of the steps I've taken so far... can't find the ole digital camera! The steps are pretty easy to do by following directions though... as I mentioned previously, I used Acetone but the better chemical for this process is MEK (Methyl Ethyl Ketone)... unfortunately, my local Lowe's didn't have that so I went with Acetone.

To make the ABS paste, you need to mix ABS shavings or chunks in a condiment squirt bottle. I purchased my condiment bottles at Walmart in a three bottle set for about $1... came with one yellow, one red, and one clear (mustard, ketsup, and oil/vinegar I guess)... the type of pastic they are made of is stable with Acetone and MEK so all is good. The smaller your ABS shavings are the better but I didn't want to trash my garage or house, so I just broke some ABS into small chunks (1/4" x 1/4")... but for better/easier work on the mix, either use a drill to make shavings or run the ABS through a router... the router works the best. Now put your shavings into the condiment bottle... lots and lots of shavings... once you add a little solvent, the plastic will condense down quite a bit... you will most likely have to add shavings several times... once you have a decent amount (full bottle), make sure your cap is on tight and shake it up... there you have it... ABS paste...

As long as you have the bottle capped off good, the solvent can't evaporate out so it will remain as a paste... leave the cap off, the solvent evaporates and you then have a chunk of ABS...

The preparation of the plastics to be mated together is the most important part of the process. You MUST sand through all paints on the plastic so that you are working with exposed, virgin plastic. The solvents and paste will pretty much melt the plastic of your monitor housing and your dash panel to create one piece. If you still have paint on the plastic, you aren't doing anything worthwhile. The Acetone might penetrate the paint or finish but it could easy come apart later on. My suggestion is the be sure to sand down to bare plastic... no less!

If you've ever used PVC and PVC glue, you know how quickly this bond takes place. The thinner the paste is put on, the quicker it bonds. In the case of PVC pipe and couplings, you have a tight fit as it is... when you put the glue on the pieces and slip them together, they almost instantly stick. In the case of my dash, I poured the paste on pretty heavy so it is taking a little longer to set up... but rest assured, it will be solid soon. About half of my area that was glued was just a touch of glue... it is already hard as a rock... the other half, I poured the paste on about 1/2" thick so it takes longer to solidify... the thicker areas will also shrink up more as it hardens... but I expect to make one if not two more apps before done.

I have found my digital camera but am charging batteries as we speak. I'll take some pictures late tonight and post them. I apologize for not taking pictures of the steps up until now though. I can find something else to mock up possibly to show the process... or maybe just find some scrap plastic to glue together to show the strength and abilities.

Check back later tonight... I'll post back ASAP. Later!

Randy


3:


BTW, I started writing my reply this morning and finished it once I got home from work a bit ago... I just read the replies and questions and will do my best to answer the questions...

First off, the Acetone (or MEK) isn't being used to glue anything together... it is merely melting the plastic to a liquid. When you squeeze the paste onto or into parts, it will both form to fill the voids and ALSO the solvent within the paste will soften the parts that it touches and cause them to basically melt together.

Yes, this is similar to plumbing glues... I think if you read the ingredients on a can of ABS or PVC glue, you will find that it has either acetone and/or MEK... along with other solvents. There are different solvents that work better with different kinds of plastics. Another solvent that I have used before is THF (Tetrahydrofuran)... it works well with PVC, ABS, and Sintra (another plastic I have used... poly vinyl material I think)... but the latter costs about $40-$50 per gallon and is hard to come by... MEK from what I recall is about half that price... around $25 per gallon... and acetone isn't the absolute ideal solvent (but works well) is about half again of MEK at around $12 or so per gallon.

Anyway, your paste will be the color of the material you disolve in the solvent... so if you have panels that are molded in color, you can use scraps of it to make matching paste... unfortunately, most manufacturers mold parts in black and then add a paint or other finish to that... I think this keeps their cost down because it costs more money for plastics to be ordered in specific colors... I know this because I used to deal with some vacuum forming of ABS and it was gonna cost me an arm and a leg to get the right color ABS sheets to make my parts match the interior of the vehicles I was working with... so it came down to the manufacturers deal... mold in black... custom paint to match.

Someone metioned using Acetone to remove adhesives from plastic surfaces without any trouble... be careful... it will most definitely mess things up... if you don't believe me, take a drop of acetone, put it in an unobscure place on the surface and let it sit for a minute or so... then wipe it dry and feel how tacky the surface feels for a moment... you may not notice it at first touch, but the plastic is softened... and if there is any texture, you can easily wipe the texture and cause it to look bad... on the same note, you'll see that when you pour the paste over a surface in a thinner solution (more solvent to plastic ratio), once it hardens, it will have a very smooth, high gloss sheen... it is because the plastic has had a chance to level out... if you leave a large drop of solvent on a hair-cell (texture of lots of vacuum formed pastics) plastic, come back later and you'll have a smooth spot... this is because the plastic melts, levels itself off, and then hardens...

The problem with bondo and fiberglass and resins is that they all shrink and expand at a different rate than that of the pastic you are trying to molde together... the thinner you put the bondo/fiberglass on, the less chance of cracking... but in the hostile enviroment of the automotive world, you often have temperature ranges from below freezing all the way up to temperatures that will nearly melt the pastics you are trying to work on and molde together. You are less likely to have problems if the materials expand and contract at the same rate... but again, with the chemical bond you end up with, it is almost impossible to crack... especially if your preparation process gets ALL paint and impurities out of the way... essentially what you have in the end is ONE piece of plastic... not two peices glued together but a dissimilar glue.

You can use this process for small gaps or large gaps... the larger gaps are better to be filled with a thicker mixture... for two reasons... 1) becuase the paste is less likely to find gaps to ooze out of... and 2) so it will set up faster. When filling smaller gaps, you can use a thick or thin mixture... if you are trying to fill pits and fine pin-holes, you should use a very thin solution... sometimes you can even just use a brush with acetone or other solvent to soften the surface and make it flow smooth.

OK, I've rambled on enough... I'll post more later as I think of it... and I'll post a picture or two once my batteries are charged... TTYL!

Coach


4:


Quote:Originally Posted by Scouse Monkey
YOu want to be careful though as the vapours given off when the acetone evaporates fromy our slurry will be harmful and explosive.


Yeah... what he said... always keep in mind when working with solvents and other chemicals to work in a well ventilated area... the one chemical I mentioned above (THF) is kinda hard to get hold of due to its dangerous properties... if you read the MSDS (material saftey data sheets)... they almost all tell you that they can be flamable or explosive in high concentration and in the case of THF, it has been proven in a lab to cause or increase the chance for certain cancers! DOH! You should always use rubber gloves when working with solvents... they can soak directly into your skin... ok, enough scary stuff... its really not that bad... just use common sense if you have it! lol

Later!

Randy