I had a long length of copper ground wire that was still in good condition other than the many kinks and folds caused by the way the wire had been stored. I carefully straightened the wire against a flat board using pliers, but it took a long time and I wasn’t very pleased with the results.
The other day, I stumbled across a different technique that I had never heard of to straighten copper wire. All you need to do is draw the wire, under tension, back and forth repeatedly against a rounded surface. (This only works for solid copper wire, not stranded wire.)