This may sound crazy but can the Shredder knives be moulded from plastic?
Then you screw a then metal blade to the cutting tip.
Would a HDPE Shredder Knife be strong enough in conjunction with the metal blade not to break?
You would need to re-design the shredder knife.
So long as you are careful and dont place any heavy duty plastic in the Shredder could it possible survive?
Just thinking out side of the box!