I use Acetone to join Acrylic. It’s a true solvent, no actual adhesive. Surfaces mated together melt and merge and the Acetone evaporates and I’m left with a joint that’s generally as strong as the surrounding plastic. To join at right angles, I’ve got a set of adjustable-angle corner clamps. Set 'em at 90º, clamp the pieces making sure the seam I’m going to bond is straight and gapless, then I hold it so the seam is vertical and I get a drop of Acetone and run it down the inside angle of the seam. If it’s a long seam, I might drip another drop or two further down the seam. Wait 10 minutes, remove clamps, parts bonded. Since I’m not clamping the parts to anything except themselves, there’s no worry about them sticking to anything. But the Acetone isn’t glue, so unless I go nuts with it there’s nothing for anything foreign to stick to.
I’ve tried to break Acetone joined pieces and often times the break occurs someplace adjacent to the seam, the seam itself doesn’t fail.
My wife’s nail polish remover can be used in a pinch, but “industrial” is best. And the stuff is cheap.