Cyanoacrylates do not form a strong bond in the same way solvent welding or structural adhesives do. With CA, the joint strength primarily depends on the adhesive layer itself - its cohesive strength and its adhesion to the surfaces. With solvent cement, the solvent softens the polymer surfaces so the two parts fuse together and form polymer chain entanglement across the interface. When done correctly with a compatible material, that can approach parent material strength.
As the OP was asking, finding a true solvent for PETG would be a strong solution if one were available and compatible. In that case, the solvent does not “create” the bond in the traditional adhesive sense - the base material does, through fusion.
Try this. Print two strips of material, PLA, PETG, etc., that are 60x15x10 mm. Glue them together in an offset manner like this:
Clamp them tightly and let the bond cure for 24 hours. Then place one side in a vise, clamp the other side with vise grips, and bend the joint. This is effectively a peel or cleavage-style test, not pure shear.
With standard superglue, you will typically see brittle fracture at the bond line. That is characteristic of CA - high stiffness, low elongation, and poor peel and impact resistance.
With a properly executed solvent weld using a solvent that genuinely softens the polymer, you will often see failure in the surrounding material rather than at the interface. That happens because the joint becomes closer to a solid piece of plastic as if it had been printed as one single piece. Which is why I prefer cement.
For certain materials like ABS, PC, and PVC with tight-fitting, well-prepared surfaces, CA can work reasonably well in light-load applications. But with most FDM 3D printed parts, the layer lines reduce true contact area and introduce stress risers. CA performs best with tight joint fit and clean surfaces; it does not require a glass-polished finish, but large gaps and rough surfaces significantly reduce performance.
So the distinction is not simply glue versus cement. Solvent cement is still an adhesive. The difference is the bonding mechanism: adhesive bonding versus polymer fusion. That mechanism difference is why, in structural thermoplastic joints, a proper solvent weld will generally outperform standard cyanoacrylate.
MEK was an important part of the welding properties and the new products is not as good.
