Hello.
Do you know what adheres to cured silicone for a permanent bond ? Fresh silicone adhesive or something else ? Need to seal forever some bags, cutting the zipper off :

 

I would use a food saver bag sealer.

 

Thank you. I have a thermal sealer but suspect silicone does not fuse/melt with heat at all .

Just saw this xantopren thinghy; will see...

 

Thank you. I have a thermal sealer but suspect silicone does not fuse/melt with heat at all .

From your photo it looks like the bags have been thermally welded on the other three edges.
If you don't have a bag sealer, try it with an engineering rule and a soldering iron. Place the rule over the bag and scribe along it with the soldering iron.

 

While silicone can be heat bonded, it is not an easy operation. The temperature is critical because the softening point of typical thermoset silicone is quite high (somewhere between 200°C and 400°C depending on the formulation) while being close to the temperature that will cause degradation. And, due to the range of possible softening temperatures, the correct one for the target is critical and may only be possible to determine empirically.

Heat welding of silicone also requires pressure, so the usually methods employ a heated press. A commercial welder is an expensive option and a DIY version not a simple project. An alternative, though, is cold welding. That is, using a solvent to soften the silicone and pressure to weld it. This is easier from a DIY perspective since it is not necessary to handle material at hand-burning temperatures.

Toluene is a good candidate for a solvent since it is readily available (at least in the US) as a paint thinner and works for many silicone formulations. Obviously empirical tests will be required. Toluene is quite flammable and rather unkind to the human body so excellent ventilation (working outdoors is best) and a respirator with organic solvent cartridges are a good idea.

Xylene can also be used, and it is less hazardous—but is it also less aggressive on the silicone and so may not be as effective, or effective at all. Again, testing is everything.

As far as adhesives go, there are a number of candidates. A product called Sil-poxy is commonly used in applications such as bonding silicone molds and appliances used in theatrical work. It is reading available but not cheap. (datasheet➚)

Other options include a specially formulated cyanoacrylate-based adhesive like Guoelephant 407. This is a high viscosity, "instant" adhesive which is very effective but to get the best results it would probably be most sensible to make a jig so positioning of the parts can be achieved quickly and accurately.

 

...From your photo it looks like the bags have been thermally welded on the other three edges...

Thanks. Yes, and the clear bag is something I never saw in silicone, being mostly milky. The bag probably is typical chinese wrong misleading lie being vulgar polyethylene material. But if the zipper is silicone, it seems well joined to the bag. Asked the vendor; maybe will get clarification.