A decade-long study shows why heat tests can mislead about paper ageing

A decade-long experiment by Estonian researchers found that a week in hot conditions can give a misleading picture of a material’s long-term durability, ERR reports in an article by Rando Tuvikene, a professor of biopolymer chemistry at Tallinn University.

The familiar smell of an old book is partly a sign of decomposition: compounds evaporate from paper as it ages. Researchers have shown that these compounds can help assess paper’s condition and sometimes estimate its age. Changes may be detectable by smell long before a page begins to crumble.

Wear and ageing are not the same. Pages can be damaged by handling, but paper also becomes more brittle while untouched on a shelf. Understanding why means looking at its molecules.

Paper is made mainly of cellulose, whose molecules form long chains of repeating glucose units. A chain can contain thousands, or even more than 10,000, units. Strong chemical bonds hold the units together.

Cellulose is a polysaccharide, a substance made up of many sugar units. Other polysaccharides include amylose, a component of starch; pectins found in fruit; and seaweed-derived thickeners and gelling agents such as agar, carrageenans and alginates. Although they are made of sugar units, long cellulose chains do not taste sweet.

The structure and length of these chains affect how strong a material is or how thick a solution becomes. Tuvikene compares the effect of chain damage to a rope hammock. If some strands break, neighbouring strands take on the load and the hammock may still hold. As more strands break, fewer remain to carry the weight, until the network eventually gives way. Much of the rope may still be present, but its integrity has changed.

Similarly, fibres and networks made of polysaccharides are widespread in nature and help materials gain strength, flexibility and the ability to bind water.