Disclaimer, I've NOT used this tool. It does seem like a useful item for converting plastic bottles into cordage.
https://www.kickstarter.com/projects/910418035/plastic-bottle-cutterThe information is NOT sufficient to show the actual cutting blade in this device. I think I could build one of these myself, from standard hardware store items. The blade might take some experimenting to get it working correctly.
I suspect that there is a narrow "carpet" blade inside the wooden handle which could be easily fabricated.
FYI this is a kickstarter project and I don't know how long the page will continue to exist.
The kickstarter project, linked above, was successful and they have a retail website too:
https://plasticbottlecutter.com/DO WATCH THE VIDEO. This thing is FAST, cutting two liter bottle in just a few seconds.