Ask yourself “what is paper made from?” and let me guess your answer to this seemingly rhetorical question: trees. Easy, right? Paper is made from trees. The input to the papermaking process is trees, and the output is paper.
If only it were that simple. Paper is certainly made from trees (or other fibrous plants), but there is a whole slew of other materials that paper is “made” from. Let’s look at the kraft pulping process, which is the first step used to make the majority of paper packaging. The trees are harvested, chipped, and put in a solution called “white liquor,” which is a mixture of water, sodium sulfide, and caustic soda. Your answer to our seemingly rhetorical question has already become more educated: paper is made from trees, water, sodium sulfide, and caustic soda.
Let’s keep going. Caustic soda is produced by running electricity through salt water. Interestingly, the salt water is created by adding fresh water to salt that was produced by evaporating naturally occurring salt water, instead of using the naturally occurring salt water itself, which has too many other types of dissolved solids. Where does the sodium sulfide come from? Most of it is made by mixing ground up coal with a substance known as “salt cake.” And where does salt cake come from? About two thirds of salt cake is harvested as the mineral mirabilite, and the remainder is produced as a byproduct of hydrochloric acid production.
If the paper is white, then it’s probably been treated with chlorine (also made from running electricity through salt water), chlorine dioxide, or an alternative combination of ozone (made from running electricity through air) and hydrogen peroxide (don’t even ask how hydrogen peroxide is made. I looked it up, and found phrases like “autoxidation of a 2-alkyl anthrahydroquinone”).
Modern papermaking is a fascinating process and decades of innovations have resulted in every single input being used to its fullest extent with a minimized amount of non-paper outputs. The white liquor is recycled inside a paper mill, using lime (calcium oxide, made from limestone) and small amounts of new white liquor to reconstitute its needed properties. By amount used, trees vastly outweigh every other resource used to make paper. Nonetheless, it’s important not to oversimplify the answer to my seemingly rhetorical question.
So what is paper made from? Trees, water, salt water, coal, mirabilite, limestone, maybe 2-alkyl anthrahydroquinone. It might contain calcium carbonate (more limestone), kaolinite (clay), talc, or titanium dioxide as a filler. Perhaps a wax emulsion is used as a sizing agent. Formaldehyde could be added to improve its strength when wetted. Some paper is treated with optical brighteners, dyes, pitch control chemicals, and slimicides. It might still suffice to say that paper is made from trees, but sustainability is complicated and we shouldn’t oversimplify our concept of paper production to the point where we think that the only inputs are trees. It’s important to keep in mind that paper as we know, as well as all products, couldn’t be made without a fascinating array of other additions.