Although the basic composition of paper is plant fiber, not all plants can be used to make paper. This is because the use of a raw material always takes their comprehensive conditions into consideration. For example, when the fiber content in plants is too low (the fiber content is generally required to be no less than 40%), its economics will lose its meaning, and other factors such as fiber strength, source of raw materials, price, etc. must be considered.
The following simple examples illustrate several kinds of plant fibers commonly used in my country:
Wood is one of the main raw materials for the paper industry. Generally, there are two kinds of . The former is called softwood and the latter is called hardwood. The part close to the bark is called sapwood, with light color and long fiber length (generally 5-6mm), which is a suitable material for papermaking. The part near the center is called heartwood, which is dark in color and thick in fiber, relatively poor in quality, and difficult to pulp.
Coniferous wood pulp is suitable for making various high-grade printing papers and industrial papers (such as cement bags etc.), or for the production of rayon pulp, cellophane (see the second section below), nitrocellulose , film, etc.
The fiber of reed is soft, and there is often a reed film in the pulp. After paper is made into paper, there are . Because this part has poor ink absorption, it will affect the printing effect. Commonly used to produce letterpress printing paper and glossy paper.
There are many varieties of bamboo. The fibers are slender, with an average length of 1.5-2 mm. They are soft and have good water drainage. They can be used to make high-grade paper, such as offset printing paper, letterpress printing paper, kraft paper and matches.
Bagasse, which is a product of the sugar industry, has thick and short fibers. Although it is shorter than the fibers of wood and bamboo, it is longer than the fibers of ordinary grasses. It is often used to make letterpress paper, match paper, poster paper, glossy paper, wrapping paper and wall wallpaper. It can also be used to make .
Rice straw is a relatively abundant agricultural by-product. Straw fibers are brittle and short, and contain more ash. The fiber of wheat straw is longer than that of rice straw, and its strength is higher. Wheat straw pulp is easy to change color after oxidation. Rice straw pulp is suitable for the production of glossy paper, wrapping paper, poster paper, yellow cardboard, etc. Wheat straw pulp can still be used to make newsprint and so on.
Cotton, the paper industry directly uses new cotton less, and generally uses cotton linters, waste cotton, etc. as raw materials. Cotton fibers are long, strong, and elastic, and are generally used to make high-grade paper , such as banknote paper, bond paper, and map paper.
Hemp includes hemp, flax, ramie and so on. Hemp paper has existed since ancient times. Hemp can be said to be a kind of papermaking raw material with the longest fiber . Hemp can be combined with other pulps to produce a few high-grade papers, such as cigarette paper and banknote paper.
Others such as sorghum stalks, corn stalks, scorpion grass, etc. can also be used for papermaking.
Because plant fibers are thin and long, with spindle-shaped ends, rich in flexibility and flexibility , and have a certain bonding force after being interwoven with each other, they can be processed into paper.
The composition of plant fibers is mainly cellulose, lignin and hemicellulose. Cellulose is a natural polymer compound that exists in all plant fibers and is the basic component of paper. The molecular formula of cellulose can be represented by (C6H10O5)n . We know the molecular weight of glucose, n is 162, and n is 1,506,600 and 1,134,000 for wood and wheatgrass respectively. It was pointed out that the aggregation and arrangement of such long chains in the macromolecules of fiber cords is not uniform, but loose in some places and tight in others . Thus, cellulose is considered to have a two-phase structure. That is, part is the "amorphous region" and the other part is the "crystalline region". The cohesive force of the amorphous region is small, and it is easy to be broken or penetrated by water or other solvents, while the crystalline region is more difficult.
Generally, the specific gravity of natural fibers is about 1.550.
