Why does Newsprint easily discolor?

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Why indeed does newsprint media discolor when left exposed to the elements? The is due to the wood compound called lignin, the natural substance that binds the cellulose fiber together in trees. Lignin is sensitive, easily degrades and turns brown when exposed to sunlight. This is the reason why paper processed through the mechanical pulp method easily discolors and the best example is the cheap and non-archival paper we all know as the newsprint. Moreover, trees contain as much as 30% lignin and therefore when not treated properly succumbs to discoloration, a paper character that is not suited for hard copy documents.

The methods used in pulp preparation affect the quality of paper and every paper mill conforms to set processes to produce the type of paper ordered for distribution.

Chemical Pulp Process. Wood chips from storage bins are directly fed into a digester and mixed with chemicals such as caustic soda and Sulfur. The mixture is then pressure cooked to remove the substance lignin which affects the color quality of paper. This process can be coined as energy self-sufficient since practically, all timber by-products are utilized to provide energy to the pulp mill power plant. The only drawback to the chemical pulping process is the resulting low fiber yield since the procedure can only deliver fiber yield from between 50% to 60%.

Mechanical Pulp Process. Logs are debarked and cut into uniform lengths of 2 meters and placed between 2 huge rotating steel disks with teeth. Adding hot water action, the process literally tears the wood apart and reduces it to a pile of wood fibers. Logs can also be made to move against grindstones, a process that produces a by-product called the ground wood pulp. Either way both mechanical pulp processes can recover a yield of at least 90%.

Newsprint is manufactured using the mechanical pulp process and is not made to undergo the chemical process of extracting lignin from the tree cellulose fiber. Along with the high fiber recovery rate of the mechanical procedure, the inferior quality of newsprint in contrast to white paper with virgin components makes sense.

Given its fiber quality, the newsprint of course would not be able to meet the required specifications for media intended for laser printing. Besides, if newsprint can resist lateral shear during printing, output will still be marred with print defects that could not be resolved even with a sufficient supply of toner powder.