As we all know, most paper is made of plants rich in cellulose. The main components of these plants are cellulose and lignin. Cellulose is a polymer of glucose, while lignin is a complex macromolecule with phenylpropane as its basic structure. However, lignin and some cellulose are easily oxidized. Hydroxyl groups in chain cellulose are oxidized to ketones or diketones, forming chromophores. By comparing the infrared and ultraviolet-visible spectra of degraded cellulose, it was found that * * * yokone group caused the yellowing of paper.
Pure cellulose has no absorption band in the ultraviolet-visible wavelength range of about 6 eV(200 nm). On the contrary, the degraded cellulose has four absorption spectra, a broad peak around 4.8 eV(260 nm) and a long absorption tail with low energy. Degraded paper will absorb purple light, so what the naked eye sees is the complementary color of purple, yellow.
The presence of light, heat, moisture, metal cations such as Cu2+ and Fe3+, and polluted gases such as SO2 and NO2 will especially affect oxidation. It has been found that paper turns yellow after being soaked in water or exposed to the sun, because water molecules provide additional oxygen free radicals and promote the formation of ketones on glucose rings.
Similarly, high temperature is also beneficial to the oxidation of cellulose. As the paper ages, the degree of discoloration depends on the percentage of components in the paper. It should be noted that other components in paper, such as dyes, pigments, metal ions and additives, can be used as photosensitizers by absorbing light quantum and transferring its excitation energy to oxygen.
Proper storage of paper:
1, paper has strong moisture absorption characteristics, and it will be stretched and deformed after being wetted, which will seriously cause mildew and affect product quality. Therefore, the place where the paper is stacked must be clean, dry and well ventilated.
2. When the paper is stacked, it should be raised with a wooden frame, about 25mm from the ground, not too close to the wall.
3. Don't put the paper with articles that are easily deliquescent, otherwise it will easily absorb moisture and deteriorate. Used for non-sized paper, such as newsprint, straw board, box board, etc. Pay more attention to moistureproof in rainy season. In addition, if the paper is exposed to the sun, the white paper will turn yellow, the colored paper will fade, the paper will become brittle and easy to crack. Therefore, it is necessary to prevent the paper from being exposed to the sun.
4. Generally, when the paper is above 38℃, the strength will decrease obviously. In order to better ensure the quality of paper, the relative temperature of the environment for storing paper should be controlled at about 75%. When the indoor (paper bin) temperature reaches 39℃, ventilation and cooling measures should be taken to prevent paper from embrittlement and deterioration.
Official website of Shaanxi Geological Survey Institute-Mineral Knowledge.