There are all types of plastic strengths, I've run the thick stuff and the thin stuff in my baler. The thick stuff is stronger than twine and lasts at least a year maybe 2 outside in the direct sun. If in the shade its just as strong 10 years old. Mice mostly leave it alone too.
We have a compost pile of mouldy bales. If you go back in a year you can drag a soaking wet half rotted bale out of the pile by the strings if you hook it with the forks while turning the pile.
Edit: The sisal twine is mush after a year in the compost. Nicer for going in the manure spreader.