When in a scavenging survival situation rope and string to tie stuff up is very valuable. Trust me you can never have enough string. Here is how you can turn scrap plastic bottles into surprisingly strong string or ribbon or rope.
Step 1. Find a plastic bottle. Two liter or bigger soda bottles work great!
Step 2. Remove the label.
Step 3. Rinse out the bottle so that your string isn't sticky.
Step 4. Cut off the bottom of the bottle.
Step 5. Take your knife or scissors and cut the bottle in a spiral pattern.
Clarification: Cut the bottle starting at the bottom as if you are going to cut just a ring off of the bottom. But instead angle the first couple of inches of the cut so that the bottle is cut as a tiny thread but grows in thickness until you get the string as wide as you want it. This could be 1/32 of an inch or a 1/2 inch ribbon. You just keep slowly cutting in a spiral pattern further and further up the bottle towards the cap until you run out of bottle.
Bam, simple and relatively easy but strong cordage to tie up all kinds of stuff! You can use it just like string. You can heat up the knots you tie to melt the knot so it doesn't slip or come untied. Heating weakens the plastic a little so only do this if you need too. Also melting the knot prevents you from using that portion of the plastic string again.
Now what if you want rope? Simply use multiple strings wound together to form a rope just like regular rope is made.
How to make the plastic string the easy way!
If you want to prepare ahead of time there are a few simple devices that you can make that will make the job of making bottle string so much faster and easier. It is really simple to make too. You will need a piece of channel iron. It can be made of hard metal or something such as aluminum. The lighter the better I say. Channel iron is a simple square tubing but with one of the 4 sides missing. It will look like this |_|
Now drill a hole straight through so that the drill bit goes through two sides of the channel iron.
This hole needs to be just big enough to fit a piece of all thread through the holes.
Now take a piece of all thread and make a very slight bend in the rod. About 15 degrees should be good.
Put the all thread through the holes until the bend reaches the channel iron.
Now secure the rod in this position with washers and nuts. Now take a hacksaw and cut into the corner of the channel iron until your cut creates a hole/gap in the channel iron. Now make another cut or two just like the first close to each other but each cut will be of different sizes. This will make the string different widths. The width matches the cut/hole in the metal.
Now you will need either a regular razor blade or even the blade from a pencil sharpener. Glue or weld the blade such that the blade is inside of the channel iron and the sharp edge is in the corner where the small cuts are. The blade will effectively cover up one side of the cut slits in the channel iron.
That is it!
Here are a couple of screen shots to give you a better idea of what to make.
Now just place the bottle on the rod and cut the bottle manually to get the string started and thread it through the hole in the channel iron to simply pull until your bottle is spent.
Here are a couple of YouTube videos to watch so that you will understand better and to give credit to the ones that figured this out! The first contraption is better but slightly more involved in making the jig. The second video shows you how to do it with just a block of wood and a multi-tool.