How to sharpen knives?

Knives are considered blunted if
the nuts are tightened and the knives are rotating smoothly
but does not cut the bottle.

If the knives are blunt at the first time:
1. unscrew the nuts
2. remove both blades
3. turn knives over the other way round
4. refit (first the lower blade and then the upper blade)

Note! There are 1 or 2 thin plastic washers UNDER the lower blade.
Remember to put them in place before assembly

5. Now tighten the nuts firmly so that the lower blade rotates automatically as you twist the upper blade.
The blades should twist smoothly.

If the knives are blunt on both sides
1. remove them
2. place the sandpaper (P180…P240) on a hard surface
such as a table and press sandpapper down with your fingers
3. place the knife flat on the sandpaper
4. wipe the knife across the sandpaper lightly pressing down 20-25 times
5. turn the knife through 90* (do not turn it upside down, but rotate it)
6. rub the knife again 20 times
7. turn the knife upside down and repeat on the other side. 
8. Repeat the operation with the second knife

What I can actually do with the strips of plastic?

You can use it:

• as rope, to bind any things (including, to tow the car);
• as heat shrinkable rope, for strong connection something without bolts and screws;
• to create filament for 3D printer using recreator3d   facebook.com/groups/recreator3d
• as plastic scrubber, to clean anything strongly dirty;
• as filter media, in fish tank or pond filters;
• at any your DIY and crafts ideas, etc.

And this list will be constantly updated.

Also, we carry out researches and tests of using bottles ropes/strips as universal trimmer line for garden trimmers, and already available results are encouraging.