4 kinds of paper "secrets" such as paper must use trees?

Trees are only one of the raw materials used to make paper. In ancient China, hemp, bark and bamboo were usually used to make handmade paper. In the late 18th century, after the rise of machine-made paper in Europe, trees (wood chips) were used to make paper. Therefore, the raw materials used in the modern paper industry can be divided into two categories: the first category is plant fiber, and the second category is non-plant fiber. The former includes wood, bamboo, reed, grass and so on.

The latter includes glass fiber, carbon fiber, nylon fiber, metal wire and so on. In addition, there are polymer resins (such as polypropylene), inorganic substances (such as limestone powder), etc., are also included in the second category. Plant fiber raw materials are mainly used to produce ordinary paper; Non-plant fiber raw materials are mostly used in the manufacture of specialty paper.

In China, the plant fiber raw materials used in the paper industry: wood accounted for 20%, reed accounted for 13%, bamboo accounted for 15%, rice-wheat grass accounted for 22%, waste paper accounted for 30%. In economically developed countries abroad, their paper industry uses plant fiber raw materials: wood accounts for 90%, and other (including waste paper) is only about 10%.

At present, ordinary paper, which is generally used for writing, printing and packaging, is still made of plant fiber as the main raw material, accounting for about 95% of the total production. For other papers, it's 5%. It can be seen that paper does not have to be made of trees, and there are many raw materials for paper making. Of course, because the fiber of the tree is better, the quality of the paper made from it is generally higher.

Why does the newspaper turn yellow and brittle after long standing?

The basic material of paper is pulp. Most of the general pulp is from plants - such as wood, grass, etc., after a series of treatments to get. The so-called pulp is a "collective household" composed of many single fibers and water. Those thin, silky fibers contain cellulose, lignin, hemicellulose and other chemical components.

In the paper industry, the physical and chemical processing of plant raw materials to obtain fibers is called pulping. The pulping process includes a series of operations such as slicing, screening, cooking, washing, bleaching, etc., whose purpose is to remove lignin, appropriately retain hemicellulose, and maximize the separation and extraction of cellulose. Therefore, the paper produced is generally white, but there is more or less residual lignin in the fibers in the paper (which is invisible to the naked eye). The steel printed newspaper is also white, with (acid) ink on it. Naturally, there are also wooden ropes in it.

Lignin this chemical substance, has a polymer three-dimensional structure, which contains a large active chemical group, the nature is both tenacious and sensitive. Because in the pulping process, although it is treated with strong alkali and strong acid, a part of the lignin is broken down, but it is still "tenacious resistance", so there is still a certain amount of lignin in the fiber.

In other words, the paper is also more or less "hidden" lignin. Once the paper is placed for a long time, exposed to sunlight or chemically reacted with oxygen in the air, the chemical groups in the lignin molecules that are particularly sensitive to ultraviolet light and oxygen molecules will change from colorless to colored group - yellowish brown. Add to that the acidic substances floating in the air and the erosion of the acidic ink. As a result, the newspaper turned yellow and brittle. Why isn't wet paper strong enough to break at a poke?

Paper is mainly made of plant fibers interwoven with each other. Between fibers, they are held together by hydrogen bonds formed by hydroxyl groups of cellulose macromolecules.

In the papermaking process, according to the process flow, the fiber (pulp) dispersed in water is first dehydrated, and then squeezed dry, and finally dried in the dryer. In the meantime, water molecules are used to build a "water bridge". The water bridge is a "bridge" that uses the polarity of the water molecule itself to narrow the hydroxyl group between the cellulose molecules to a very small distance, which causes the electronegativity of the oxygen atom to attract the positivity of the hydrogen atom. The chemical bond between so many hydrogen and oxygen atoms is called a hydrogen bond. The bond energy of hydrogen bonds is smaller than that of common covalent bonds, but the total energy of many, many hydrogen bonds is large. Therefore, due to hydrogen bonding, dry paper shows good strength, that is, strong and not easy to break.

If you soak the paper in water, in other words, let the water molecules push between the fibers in the paper, pushing the cellulose molecules that are already tightly bound, that is, the water molecules break the hydrogen bond, and the result is a huge damage to the fiber network. As a result, the hydrogen bond is broken, and the strength of the paper is also severely destroyed, and the wet paper becomes very weak and breaks at a poke.