I wanted to buy glue for my prints, today. Only realized in the shop that I forgot everything about fusing prints together and didn't know which one to buy. Remembered vaguely that maybe ABS can be fused together with acetone, but not PLA. So I bought just some fast curing glue, which is based on cyanoacrylate. At home, when I wanted to put it down at a suitable place I found the one I already had, lol. Here some article on how to glue PLA prints: https://3dinsider.com/how-to-glue-pla
Works, needs rough surface, burns into it, suboptimal shear strength.
Similarly strong to cyanoacrylate, but more flexible bonds. Can withstand most indoor and outdoor conditions. More suitable for heavy-duty applications, but should have a week to fully cure. Not useful for thin and small sections because of temperature while curing.
Might create heat, but depends on the product, same for the toxic fumes. Little bit more complex to apply, might take 72h to cure. "Bonds created by epoxy resin are extremely tough. When applied to PLA, the PLA parts are more likely to break apart before the epoxy resin bond will break."
Needs highly controlled conditions. Actually dissolves the PLA material. Dangerous for small and thin parts but extremely strong bond. Ventilation (or outdoor), eye protection and breathing protection are necessary.
>PLA 3D pen
Like a soldering iron. Very useful for filling in gaps between separate parts, but applying only a very thin layer is almost impossible. Needs skill.
>actual soldering iron
Might also work, but the molten plastic can be very hard to control. Needs even more skill and experience.