Paper

Paper

How is paper made? 

What is it made of? 

Why are there different types of paper that have different properties?

How is Paper Made

Paper is made from trees.

Wood Pulp

A tree's strength is from a small fibre called cellulose which is bound together by an organic glue called lignin. Paper is mainly made from this cellulose but it isn't so easy to extract. Removing cellulose from lignin is like removing chewing gum from hair.

To separate them, the wood is crunched and then boiled at high temperatures and pressures  The fibres are left over in water and this is called wood pulp. Lay this on a flat surface, let it dry and you get paper. This paper is raw and brown so to make it white, chemical bleach and white powders such as calcium carbonate are added. Additional coatings are then added to stop ink sinking too far into the cellulose because this is what causes ink to bleed.

Why Does Paper Yellow

If the paper is made from low grade wood pulp; it will still contain lignin. When in light, lignin reacts with oxygen making chromophores, which turns paper yellow over time.
Another way paper may yellow is if it contains aluminium sulfate. In the 1800s and 1900s, to increase the textual quality, paper was coated in aluminium sulfate. This creates acidic conditions however. This causes cellulose fibres to react with hydrogen ions which results in yellowing and a decrease in the strength of the paper. Many 19th and 20th century books are on "acid paper" and so appear yellow and fragile.

Other Uses Of Paper

Paper's properties make it perfect for wrapping paper.
Fibres can be partially snapped in areas to allow bending, but enough stay together to not crack and fall apart. This means wrapping objects is possible without the paper disintegrating. It can resist being torn apart very well, yet be torn easily if a point of weakness (tear) is opened up. This means presents can survive rough journeys but are easy to rip open, even for a baby.

Why Do Tills Never Run Out Of Ink?

Tills use special paper with fluoran leuco dye and acid already within it. The till then makes a spark, which causes the dye to react with the acid in the paper, darkening the dye. Till machines therefore never run out of ink and only the paper needs to be replaced.

Money

Traditional money is not made from paper. It is mostly made from cotton so you can feel the difference between real money and fake money. Another way to tell the difference is by using an Iodine pen. If the pen makes a mark; it is fake money made from normal paper. This is because the iodine reacts with starch in the cellulose. There is no starch in cotton and so no mark appears on cotton money. A watermark is also put on notes making it even harder to fake money. The watermark is given by changing the density of cotton, and can only been seen when light is going through the note.

Electronic Paper

Electronic paper displays text using ink and is read using reflected light just like a real book.

The ink used is Janus ink. Janus ink is made of dye particles that have a white side and black side. The two sides are also given opposite electric charges. Changing the distribution of charge throughout the screen changes the side of the Janus particle seen, and so it can display any page of a book. Since the particles have to change side to show different images; they are slower than liquid crystal displays on smartphones and so can't show videos as well at the moment. With the way technology is advancing however; this may be possible in some way in the future.



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Most of the information from this post is from the book Stuff Matters. Check it out if this kind of stuff interests you.

Check Out My Other Posts On Materials Science (link to all posts)

Book Review: Stuff Matters By Mark Miodownik

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