[Khalid1]

Hello

I've done a bit Googling and couldn't find a specific answer hence the registration and post so thanks in advance for any helpful replies.

There doesn't seem to be a single recycling company that takes empty silicone tubes (also know as mastic tubes) and recycles them. As a result, here in the UK it goes to landfill. Such a shame and doesn't seem right!

The tube is made from HDPE but is contaminated with the silicone inside it, usually used for sealing windows or bathrooms.

There is a chemical solution available that will strip out the silicone by dissolving it but that doesn't make commercial sense for two reasons;

1. The cost and time involved
2. You are left with a chemical to dispose of

So, nobody wants these tubes and it has begun to annoy me!

I'm wondering if anyone could advise of the possibility / dangers of simply melting the empty tubes which result in a plastic mix of HDPE and silicone?

Would it work? Could it work?

I look forward to the replies!

[Enthalpy]

Hi Khalid1, welcome here!

A few thoughts in no special order:

• Silicone doesn't melt. It decomposes at heat like 350°C, where PE is long molten.
• I doubt you can mix PE and silicone, and that it woud give a useful result, but I feel you don't need to.
• This sort of silicone has often acetic acid as a solvent, whose evaporation hardens the silicone. No idea whether acetic acid can soften the silicone hardened in the tubes, nor at what pace. Disposing of acetic acid looks simple to my eyes.
• I wouldn't use a solvent nor heat. I'd have a motor-brush to clean the tubes previously cut open, with an additional strong stream of air (or just the centrifugal force) to remove the detached silicone.
• PE is very cheap. Do you have an efficient means to collect many empty silicone tubes?
• I doubt the recovered silicone can make anything useful, and then you have the worry of disposing of it. Burn it to silica?

[Khalid1]

Hi,

Thanks for your response, I really appreciate it.

When you say it decomposes does it evaporate or become a molten liquid?

The tubes will be empty but there's always a residue and the recyclers don't touch it because they say it interferes with the extrusion process when shredding and remedying the hdpe.

Our company alone goes through low XXXX tubes per month and we're a small company so yes I have access to lots of them.

I'm don't have a product in mind to make with the material I'm just investigating any dangers or problems. I guess in the end I'll just need to melt it and see?

[Enthalpy]

Silicone decomposes, that is, above some 350°C it transforms permanently in useless and stinky compounds like tar, toxic fumes and silica.

If you melt the dirty polyethylene it will be tainted by silicone, the result being expectedly useless. I feel seperating them is mandatory, but rather simple. Though, it needs to develop a few machines which are difficult to pay with recycled waste, hence I asked about the amount.

One polyethylene tube for silicone weighs estimated 80g. Polyethylene from 10,000 empty tubes sold for 0.8€/kg (that would be powder of guaranteed high quality, ready for injection) brings you 600€. Still interested?

[aga]

It might be practical to make a machine to cut off the top of the tubes and use the integrated piston disc to effectively remove most of the remaining silicone gel.

I'd do some experiments with a hacksaw and a hammer, weighing absolutely everything before building a machine, just to see if was worth the effort.

ISTR that the silicone is kept as a gel by ammonia, so testing for ammonia would be a good way to check how much gel is left behind.