What is in paper?

It is common knowledge that paper is made of wood. Actually, it is quite a big mental shortcut. The base material for the production of paper is cellulose fibres. Of course, they are obtained mainly from wood but can also be sourced from other plants, such as grasses or cotton.

Paper has different properties depending on the kind of wood used. For example, broadleaved tree fibres are short, which provides good opacity, whereas coniferous trees have longer fibres, which gives paper more strength. The most common species of trees used for papermaking are pine, spruce, aspen, birch and eucalyptus.

There is another kind of material that can be used to make paper – wastepaper fibres. They normally require an addition of fresh fibres and have to be specially processed. Paper can be recycled as many as 5 or 7 times before the fibres become unusable. It is a cost-efficient and environmentally-friendly solution.

This may come as a surprise, but paper contains a bit of water. Between 3 and 7 per cent of its mass, depending on the kind of paper. This is why it is very important to maintain a specific level of relative air humidity in the printing room, controlled by appropriate sensors. They are located both on the shop floor and in the paper storage area.

The substances are called fillers because they essentially fill the spaces between cellulose fibres. As a result, the paper becomes smoother, softer and more flexible. These properties improve the setting of ink by the paper surface. One of the most common fillers is calcium carbonate in the form of kaolin or ground marble. The kind of filler to be used depends on the expected properties of the final product, and on the technology involved.

This is a very broad umbrella term and one that can be somewhat controversial. Consumers associate it with some unsavoury ingredients in food. Mammals (other than ruminants) cannot digest cellulose, so eating paper is not recommended whether it contains artificial additives or not. Joking aside, industrial papermaking is hardly possible without chemicals. Still, it is practically a natural product and the additives are selected in such a way as not to affect the environment adversely.

Depending on what properties the paper is to have, different additives are used. If we want the paper to be bright, optical brightening agent is used. If the paper should not absorb moisture, resin adhesives are added to the paper stock.
Also, dyes are used to ensure a consistent colour of the stock while it is undergoing different processing stages.
These are just a few examples of chemical additives used in papermaking.