Degradation of Paper by Light
Absorption of light will not directly cleave a bond in the cellulose chain. However, certain additives, impurities, dyes, and metals such as iron (Fe++++, Fe++) will absorb energy from light which raises their electrons to a higher energy orbit. When this energy is released to the cellulose, bond cleavage can result and this, in turn, can allow oxidative degradation. Incidentally, this same mechanism is used by plants to provide the energy to grow the cellulose we use to make paper. A molecule of chlorophyll, for example, absorbs quanta of light energy from the sun, raising its electrons to higher energy levels. When the electrons fall back to lower energy levels, they release the same amount of energy they absorbed. This energy is used by the plant cell to fuel the chemical reactions which produce simple sugars.