In neutral and alkaline environments paper remains stable for a long time but can deteriorate quickly if it comes into contact with acidic substances. Most modern papers contain ingredients that form acids which can cause the breakdown of cellulose. When paper deteriorates in this way it becomes very brittle and discoloured, like old newspapers, and eventually disintegrates on touch. There are certain types of papers which are more prone to rapid deterioration. Papers which are acidic or made from low quality fibres are more likely to deteriorate quickly.
Acid attacks the plant fibres in paper and weakens it.
Some impurities cause papers to darken when exposed to sunlight and oxygen from the environment. This increases the amount of acid in the paper which can lead to more rapid deterioration. Recycled paper is often more unstable than virgin paper, as it may contain impurities such as printing inks and plastics from toners used in copiers. Also, the recycling process shortens and weakens cellulose fibres which affects paper strength, limiting the amount of wear and tear it may endure. Thermal paper, which is often used for fax machines and electronic whiteboards, is treated with a heat sensitive chemical coating.