[Structures, Papermaking]

Biomolecules: Cellulose


Cellulose, the major structural component of woody plants and natural fibers such as cotton, wood, and cork, is a ß-D-glucos polymer found in vegetable matter.

cellulose molecule

The ß-glycoside linkages in cellulose give the glucose rings a different relative orientation than is found in starch. Although this difference may seem minor, it has very important consequences. Normal ether linkages are strong because the joined groups are covalent bonded and usually 'well balanced', so that there is little charge separation.

The linkage in the disaccharides is fairly easily broken, i.e., not much energy is needed to break it - because one of the Cs in the linkage is also bonded to its own O, resulting in a charge separation and thus a weaker bond. Sodium bicarbonate (NaHCO3), a safer alternative to substances such as Drano, can break the bond. The moisture in the paper reacts with sulfur dioxide (SO2) in the air or with biproducts of the papermaking process and forms an acid, which then breaks the C-O-C bonds. The breaking of the bonds is the source of the mechanism by which paper breaks down with age. Alkaline filler (buffer) is used to prevent the decomposition of the paper over time because the acid as it is formed reacts with the buffer, not the C-O-C bond.

 

The Papermaking Process

Paper, both commercial and hand-made, is produced through a similar process of mechanically reducing woody material, consisting of cellulose, into pulp, immersing the pulp in water, and then draining it in a mold. This drained pulp, made of reconstituted cellulose fibers, when pressed and fully dried, forms paper. Paper, however, is not merely aggregated wood pulp, but instead a new material made from re-bonding cellulose molecules. When the pulp is immersed in water, the oxygen and hydrogen ions in the cellulose molecules bind to the hydrogen and oxygen ions in water . Upon removal of the water, the cellulose molecules break their bonds with the water and re-bond to other cellulose molecules.

As shown in the photograph to the right, hand papermakers first break apart the cellulose fibers of woody material by mixing them with water in a machine known as a Hollander beater. The beater mechanically breaks apart the material without damaging the fibers, forming pulp. This process enables the fibers to keep their structure intact in order to bond to each other once the paper is couched. These fibers are immersed in water in a holding tank attached to the same machine. The moist pulp is collected from the tank and transported to a deckle and mold, where the pulp is drained. As the pulp is pressed and dried, the cellulose molecules in the fibers bond together to form paper.

Click on these pictures to see illustrations of the papermaking process. The first shows a deckle draining water from the pulp into a graduated cylinder. The second shows an example of the finished paper product in a mold. Go here, to learn FAQs about how you too can make home-made paper.

 


The same general process applies to commercial papermaking. To get a look at large-scale papermaking, link to the Bowater Papermaking Plant . Or to learn more about the paper making industry, link here.



Meredith Arthur, Terry Miller, and Kay Tasian 1998.