Sciencemadness Discussion Board - Trouble melting plastic for recycle science project

Trouble melting plastic for recycle science project

briannacook7625 - 12-2-2018 at 18:40

I have a hot pad that should heat to 400 degrees. The plastics that I'm using are polycarbonate. When they melt they become sludgy instead of smooth and pourable. I can't get them into my molds. any suggestions? We are really limited in our labs. TIA

elementcollector1 - 12-2-2018 at 19:48

Plastics don't always have a melting point, and polycarbonate is mentioned to flow at above 155 degrees Celsius (though how much it flows, you've likely seen already).

You might have better luck with solvent casting. If you have dichloromethane or chloroform, those came up as potential solvents you could dissolve it in and evaporate it back out of instead of mucking about with viscous polymer melts.

j_sum1 - 12-2-2018 at 20:14

If you can get hold of a glass syringe (cheap on ebay) you might try injection moulding. Fill with polycarbonate pieces, heat and squeeze.

You will obviously need to be careful with both the heating and handling. I am thinking of a stand and clamp to hold the syringe, wire from an old toaster element for heating, glass wool for insulation and leather gloves when it comes time to inject. Perhaps awkward bud within the realms of poszibility.

Or switch to LDPE for the project.

Vomaturge - 12-2-2018 at 23:50

I would tend towards going with j_sum1's second suggestion. Try casting a different kind of plastic. Some plastics are just hard to work with. Some (like thermosetting resins) even scorch or turn to ashes without melting at all. I think that LDPE is better than polycarbonate anyhow for an experiment or demonstration of plastic recycling. Many throwaway plastic bags, bottles, and other commonly recycled objects are made out of it, PETe, or HDPE. In my very limited (mostly accidental) experience, Polyethylene Terephthalate can get pretty fluid, too, but needs a high temperature to do so. Wikipedia says 260C, which is close to the PETe's decomposition temperature. There are lots of other plastics you might try or at least look into. The injection syringe isn't a bad idea either, but it may be harder to control the temperature. That is basically how a hot glue gun works, though. Whichever approach you take, only get the plastic as hot as you need to melt it, and use good ventilation because you will probably have smoke and/or vapors despite your best efforts.
Good luck!

Bert - 13-2-2018 at 00:51

Try HDPE. The ones labeled "2".

This kid is compression moulding using vise and clamps in a simple wooden form at around 350 F.

Myself, I would try vacuum pressing- Bag up the mould in one of the compression bags for clothes storage and pull a vacuum to compress.

A plastic bag and your mom's vacuum cleaner can work for a lot of moulding projects

[Edited on 13-2-2018 by Bert]

Panache - 1-3-2018 at 05:20

hmm, a memory
recycling:- an expensive, but virtueous process that turns waste that nobody wants into raw materials thats nobody wants.

you really have chosen a difficult polymer. you should carry on however, a negative result is still a result and you have learnt something. Could be worse, you could have been assigned casting ptfe or one of its lesser analogues.

Engineering polymers, there is no concerted effort to recycle these things.

Side note, has anyone come into contact with the fluorinated silicon rubbers declassified a couple of years ago, performing into the 600-700C range. I read about them on defence briefs and have been waiting for a take home cast yourself kit, but to no avail.

unionised - 1-3-2018 at 05:53

Quote: Originally posted by Panache

. I read about them on defence briefs

Did they talk about alien technology?

andy1988 - 3-3-2018 at 22:18

Quote: Originally posted by briannacook7625

I have a hot pad that should heat to 400 degrees. The plastics that I'm using are polycarbonate. When they melt they become sludgy instead of smooth and pourable. I can't get them into my molds. any suggestions? We are really limited in our labs. TIA

I don't know the specifics of virgin polycarbonate, and who knows what else is in recycled pieces. Various pieces could have different plasticizers in it, or even be a blend different polymers, each polymer likely with a different glass transition temperature and melt viscosity.

Realize that the plasticizers may have a lower boiling point than virgin polycarbonate, so take care you're in a well ventilated area just in case (e.g. a plasticizer I'm looking at called EGDA has a boiling point of 178C at in a 25% EGDA/CA mix).

See this project https://hackaday.io/project/5189-shop-air-injection-molder
Specifically the talk about melt viscosity, where molten ABS has around the same viscosity as peanut butter under his operating conditions.

As for suggestions? I think the best route for recycling plastics is for manufacturers to use biodegradable polymers & additives in the first place. Maybe education on that, and through your example, why recycling non-biodegradable plastics is difficult and cost-prohibitive, would be fitting for a science project. If only governments would start regulating plastic manufacturers like they do amateur chemists! (in terms of prohibited/restricted chemicals)

You could talk & illustrate polymer compounding, glass transition temperature, etc. Also how certain extrusion processes may use up to 50% regrind (stuff trimmed off the output is ground up and fed back through), but they want largely want virgin resin or the output product will have poor/unwanted qualities. Lots of concepts you could illustrate, you don't need to have a finished product on your table IMHO.

Here's another suggestion, tabletop creation of a biodegradable polymer (by chance I was looking at this earlier today): https://sciencing.com/make-cellulose-acetate-7657800.html
I think the chloroform step is the only step which has fumes? Someone else can say more than I. Everything in the experiment looks readily available except the chloroform, and I think you don't even need to do that step. You can make glacial acetic acid yourself for cheap with vinegar and freezing weather (or your freezer) via fractional freezing: https://chemistry.stackexchange.com/questions/2506/acetic-ac...

EDIT: Another suggestion on a different type of plastic "recycling" experiment (e.g. repair broken plastic part): http://www.eng-tips.com/viewthread.cfm?qid=354893

[Edited on 4-3-2018 by andy1988]

[Edited on 5-3-2018 by andy1988]

Melgar - 8-3-2018 at 19:51

If this plastic has to be transparent, and I suspect it does since you're using it rather than some other plastic, you may want to look at polyester/PET/PETE maybe?

Also, look into clear epoxies if it doesn't have to be a thermoplastic.

For a rule of thumb, the recycle numbers on the bottoms of containers are roughly in order of how practical it is to recycle that plastic, with 1 being most worth it. (1 is PETE, with 2 being polyethylene)

aga - 9-3-2018 at 07:14

If it's for a school science project, how about expanded polystyrene dissolved in acetone ?

It should work with ethyl acetate too i guess, so polystyrene & even UK nail varnish remover.

TheNerdyFarmer - 10-3-2018 at 06:34

Not sure if it applies to this particular situation, but some plastics decompose when heated in atmospheric gasses. For this reason, polymer chemists often seal a polymer sample in a large glass tube under an inert atmosphere (often nitrogen) to test for melting point. Not sure if this applies to polycarbonate, just something I thought I would share

Fantasma4500 - 12-3-2018 at 04:08

if you need to protect from air, butane is both very easy to get and has decent properties as protective layer, heavy gas and has 95 to 5 requirement to burn with air, viscocity could be a problem but applying pressure to the plastic when "molten" could solve viscocity problems