Steve, Hello
Some of the guys in the tech lab did some work trying to glue the poly decking materials a few years back, they finally gave up. You can forget any conventional wood glues. I don't think that epoxy will stick it either. They will NOT stick it.
You could try a polyurethane hotmelt, which I've seen in the woodcraft magazine, but are very expensive and requires a specialized glue gun applicator, your regular hot glue gun won't work for these. OR you could try a solvent based contact adhesive. If I had to glue poly decking, that's what I would use.
Good luck, and let us know what works.