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.