All PC boards have a thin layer of copper that adheres to them. This copper is the wiring or traces for conveying an electrical current to all of the components that are soldered onto the board. You can recycle used PC boards, once you have removed all of the electronic components. What's left are the copper traces, which you can strip and send to any recycling center or scrap yard that deals in recycling metals.
Cut each trace of copper beginning on one end with your hobby knife.
Grasp a cut end with your pliers. It may be tricky to get beneath a copper trace, so you may need to start it by prying it up with a fingernail or the end of a hobby knife.
Pull the trace out and away from the circuit board, literally peeling it off. Repeat this procedure on all copper traces.
This method works even on nontraced copper. Just peel off a corner, grasp with pliers, and pull the copper sheet straight off.
Be careful. Hobby knives are razor sharp, so take precautions when using a tool such as this.