Recycling a plastic bottle to a 20m long thread isn't rocket science. It just takes a steady hand with scissors or you can make a jig like the one pictured to cut the plastic.
You can recycling bottles, beer cans and similar cylindrical shapes objects (junk) to thread.
Thread is a raw material for production, usually for sewing or making fabric or some similar things.
PET is very strong material. 1.5mm plastic bottle thread can hold 5kg at least (I don't know exactly).
A 2l PET bottle can be recycled to 3mm thread 20m long.
This application can be used to make line as well as ribbon type strapping, it depends on your needed application. It all depends on how wide you cut your material.
When using scissors be careful and take your time, the string should to be continuous.
Follow the edge and cut width you want. (I cut 2-3mm it's hard to be absolutely precise)
Be patient and try to be precise