Okay, so I have various projects where there were originally two pieces of plastic, or a piece of plastic and silicone, “glued” together, but I accidentally broke the brittle “glue” and now they just won’t stick together again. I can see the remains of some sort of yellow substance that was used to bind the two non-porous, dissimilar materials together, but I can’t tell what it is exactly. If I had to give a guess, I’d say it’s epoxy. Indeed, in some cases, it is. In other cases, it is rubber cement. Still other more specialized cases use more specialized materials.
Well, taking a web search for gluing platistics together, I came to this pretty good wiki How article. Note that the hardest plastics to glue together are polyethylene and polypropylene (low coefficient of friction), some of the easiest are polystyrene (high coefficient of friction). “Poly cement” or “plastic cement” is the name of the game for plastic glues.
20191214/DuckDuckGo glue plastic together
20191214/https://www.wikihow.com/Glue-Plastic