Enzyme Degradation and Mechanical Damage
Enzymes are protein catalysts coded for by that very newsworthy molecule, DNA, and assembled from amino acids in the ribosomes of living cells. Enzymes such as endoglucanases and cellobiohydrolase can cleave the bonds connecting the cellulose chain at any link. This subject is really beyond the scope of our discussion, but if you are interested in additional information, your local paper conservator will be able to answer any questions you may have. Mechanical damage can result in splayed, split or broken fibers which can weaken paper just as surely as bond cleavage between the rings in the cellulose chain. Remember, the longer the chain, the stronger and less mobile the structure. The hydrogen atoms are forced into a plane close to the oxygen molecules and the hydrogen and oxygen atoms connecting the sheets are able to form better hydrogen bonds. For essentially the same reasons, the strength of Van der Waals force connecting the sheets into layers is maximized. This is the reason you should request a paper with high strength and durability even when it seems unimportant for your particular requirement. Say, for example, you are trying to choose a thick, stiff paperboard for use in making cloth wrapped book boxes. Perceived stiffness is basically a function of thickness, but a thick board constructed from multiple plys of paper with high physical strength characteristics, such as high folding endurance and tear resistance, will be manufactured from good, long fibers. This board will be much more resistant to damage over an extended period of time, and not be as likely to harbor acids from bonds broken by hydrolysis (see illustrations 10 through 13) that can migrate to historical paper artifacts stored within it.