It’s a fairly regular occurrence on the internet to hear well-meaning artists comparing “cellulose” watercolor paper to “cotton” watercolor paper. They’re using “cellulose” to refer to paper made from trees.
The differences, however, between paper made from trees and that made from cotton have little to do with cellulose. Why? Because cotton is 99% cellulose.
Watercolor paper made from trees is also mostly cellulose. To make it archival, they extract from wood pulp a protein call lignin that trees use to hold their cellulose fibers together. It’s the lignin that causes cheap papers to yellow as it is acidic. This extraction is almost complete, but to get the paper completely pH neutral, a base is added to neutralize the small amount of remaining lignin. The result leaves watercolor paper made from trees mostly cellulose.
It is the case that cotton cellulose fibers are longer than wood cellulose. Cellulose itself is nothing more than glucose molecules stuck together into a long string so its length can vary. We’re talking here about the same cellulose you find in celery. It’s a basic structural component of most plants and certainly not unique to trees.
So, the next time you want to compare papers made from trees vs papers made from cotton, a more accurate nomenclature would be to talk about wood-based vs cotton paper. Better living through chemistry.