Hi fowlerp
CNCman here from Greece, Vassilis is my name
The material use for plastic bags - i believe - is not the ideal one for 3D printing because its low viscosity.
Low viscosity means thick layers and more material waste.
High viscosity means thinner layers and i believe less material waste.
I'm on research too , so what ever i say is just thoughts with no proofs yet.
Lets hope we find something evolutionary 
Thats for start
Keep up the good work and all the best
Vassilis