Why does the white paper turn yellow after a long time?

Some careful friends will find that a piece of white paper, after a period of time, will turn yellow, and the longer the time, the darker the color, so why does a clean white paper turn yellow? I believe that many friends are puzzled, in fact, this is caused by the material of the paper, and the following is the reason why the paper turns yellow.

Why does white paper turn yellow after a long time?

We know that the vast majority of paper is made from plants rich in cellulose. The main components of these plants are cellulose, hemicellulose, and lignin.

Cellulose is a long, linear polymer of glucose. Hemicellulose has a much lower molecular weight, and they are not made up of glucose alone, but are made up of units of multiple sugars linked together. Lignin is a complex macromolecule composed of phenylpropane as the basic structure.

Lignin, like cellulose and hemicellulose, is the main component of the formation of plant skeletons, second only to cellulose in quantity. Lignin acts like glue in plants, holding fibers tightly together.

But when it comes to papermaking, lignin is a harmful component. Papermaking needs to make pulp from raw materials and cook them with alkali, the main purpose is to remove lignin as much as possible, because residual lignin will reduce the strength of the paper. The white paper will turn yellow after a long time, which is caused by the lignin remaining in the paper.

Because lignin is easily oxidized, its oxidation products are yellow.

In the pulping process of the papermaking process, although most of the lignin is removed, it is impossible to completely remove the lignin, so bleaching is required to further remove the lignin. The bleaching process is divided into two types: oxidative bleaching and reductive bleaching. Under oxidative conditions, the residual lignin is converted into a soluble substance and then eluted, so this type of paper is not easy to yellow.

Under reducing conditions, it can not remove the residual lignin, but selectively destroys the chromogenic groups of colored substances and makes the paper white, so the durability of this kind of paper is relatively poor, and it is easy to yellowish after a long time, oxidized by light and air. Newsprint is more prone to yellowing than regular paper, mainly because it does not undergo a bleaching process and contains a higher level of lignin.

Cellulose-rich plants are not only used to make paper, but also to remove lignin from them when they are used to make textiles.

Because white paper is mainly made of plants, the ingredients in it are different, and some of the ingredients will be lost after too long, so it will turn yellow.

Because of the different compositions on it, we know that the vast majority of paper is made from cellulose-rich plants. The main components of these plants are cellulose, hemicellulose, and lignin.

This is related to the composition in the white paper, lignin, like cellulose and hemicellulose, is the main component of the formation of plant skeletons, second only to cellulose in quantity.

We know that the vast majority of paper is made from plants rich in cellulose. The main components of these plants are cellulose, hemicellulose, and lignin.

The yellowing of the white paper is caused by the lignin remaining inside the paper. Because lignin is easily oxidized, its oxidation products are yellow.

Because of the different compositions on it, we know that the vast majority of paper is used.

After a long time, the white paper is easy to yellow due to the oxidation of light and air.

It is caused by a chemical change in the white paper.

This is due to the material of the paper

The method of quickly turning yellow and old white paper is as follows:

Materials required: A4 paper, black tea, soft bristle brush.

Brew a cup of black tea and strain the tea leaves as long as the tea.

Take out the soft bristle brush that has been prepared. (The bristles of the brush must be soft, too hard will damage the structure of the paper and make the aging effect unnatural).

Place the prepared A4 paper horizontally on the table.

Use a brush to dip the black tea water on the paper and spread it evenly.

After applying, let the paper dry naturally. In this way, the aging effect of the paper is good.

Cracking the Falsification:

1. There are two types of paper aging: one is "dyeing paper", including using sugar water, or chestnut shell water, or tea, or other methods to dye the paper yellow-brown, and there are also smoked yellow with smoke water, in order to make the paper appear old; The second type is to use "old paper new", if the counterfeiter has ancient paper, he can print the content of the ancient book on the paper, and then bind it into "ancient books".

2. Forged preface On some duplicate engraved copies, in addition to retaining the preface of the original book, a new preface was added, describing the reason for the reprint, and the name, year and month were also written after the preface. These are indicative of the true age of the books. Counterfeiters often cut out the preface to their forgery, or alter the age of it, and also forge a new preface that is beneficial to their forgery.

Ways to make white paper turn yellow and old quickly:

1. Tools and materials.

1. A baking tray the same size as the old paper to be made;

2. Sponge brush or soft bristle brush;

3. a paper towel; 4. an oven;

5. A blank piece of paper;

6. Half a cup of hot tea water;

7. About a spoonful of instant coffee granules.

Second, the step method:

1. Crumple the paper again.

2. Turn to the lowest temperature to preheat the oven.

3. Crumple the paper into a ball, spread it out flatly, and place it on a baking sheet.

4. Sprinkle the tea evenly on the paper, brush evenly with a sponge or soft brush, and dry it in a ventilated and cool place.

5. Sprinkle tea again, sprinkle instant coffee granules, wait for about 5 minutes to wipe off the instant coffee granules with a paper towel, be careful not to pull, and dry them.

6. Put the paper in the baking tray and bake it in the oven, this process must be paid close attention to, do not burn, as long as it is almost dry.

7. After drying, take out the old paper, and it's OK.

Precautions: Be careful not to use too much force in the process of kneading, and knead the paper, do not touch back and forth when wiping the coffee grains, just dry it, and finally it is baked, pay close attention, do not roast it.

Yes, yes, after taking your advice, the new white paper does yellowed very quickly, thank you very much.

Put it outside, wind and sun

Since most of the paper is made of wood. Therefore, paper contains a lot of wood cellulose. Cellulose is originally white, but after being left in the air for a long time, it will combine with the oxygen in the air and turn yellow.

The cellulose in the paper turns yellow, and the natural paper looks yellow. Light can also cause chemical changes in the cellulose in the paper, which can make the paper yellow and brittle. Therefore, it is best to store books and newspapers in a dry and dark place.

The museum stores precious books and cultural relics in a confined nitrogen environment.

Because most of the paper is made of wood, the paper contains a lot of wood cellulose, which is originally white, but after being placed in the air for a long time, it will combine with the oxygen in the air and turn yellow.

Pulp, the raw material for papermaking, is mainly composed of cellulose, hemicellulose and lignin. The raw pulp paper that has undergone the alkali treatment process is yellow-brown in color and needs to be bleached.

There are two processes for pulp bleaching: oxidative bleaching and reductive bleaching, and the most common safe bleaching method is sulfur dioxide reduction bleaching. The principle of this bleaching is to use the reducing property of sulfur dioxide to open the double bond of the pigment in the lignin and turn it into a single bond, so that the conjugated electron cloud is broken, so as to eliminate the pigment.

Because modern paper is made by bleaching with an acidic substance, although it is neutralized before leaving the factory, there will still be residues left on it. Over time, the paper will oxidize and turn yellow.

In fact, the composition of the paper is oxidized.

Lignin is one of the main components in plant fibers, it has aromatic properties, and is a compound containing carbon, hydrogen, and oxygen. According to chemical analysis, lignin contains the following functional groups, methoxy (-och3), hydroxyl (0h), carbonyl (o = c), aldehyde (-cho), ether bond (-0-), etc.

Lignin is white or nearly white, insoluble in solvents, fragile in texture, dissolves at high temperatures, and its solution is milky white or dark brown. Because lignin contains various functional groups, its chemical properties are relatively active, such as sulfonation, so that lignin becomes soluble lignosulfonate, oxidation into soluble chlorinated lignin. Lignin is the most susceptible to oxidation, especially in the presence of light, high temperature and alkali, and the oxidation is more rapid.

Modern paper contains more lignin, so newsprint is easy to turn yellow and brittle, and it is not easy to be stored for a long time.

It can be seen that because the raw materials of papermaking contain plant fibers, especially lignin, pectin, fat, pigments and other ingredients, the potential factors for the harm of paper have been buried.

I believe that many friends don't read newspapers much now, but have you noticed that sometimes books and newspapers will slowly turn yellow after a long time? Why is that?

Because the paper is bleached with SO2 from the previous waste paper.

SO2 bleaching, on the other hand, is chemical bleaching, that is, the combination with colored substances to form colorless substances.

Over time, the paper will turn yellow.

Reducing the number of times the paper is exposed to bright light is conducive to paper preservation.

Paper is made of wood, which is mainly made up of white cellulose. Wood also contains a number of dark-colored substances called lignin, which, along with cellulose, are eventually made into paper. The reason why newspapers turn yellow is because lignin is exposed to air and sunlight.

Lignin makes wood hard and strong. You can think of it as a glue that sticks cellulose fibers together. It is a multimer that comes from the polymerization of simple molecules into macromolecules that are different from it.

Professor Hou-min Chang of the University of North Carolina at Raleigh (who studies wood and paper science) likens lignin to concrete for construction and cellulose to steel frames. Professor Zhang said that without lignin, trees can only grow to about a metre tall. Lignin also helps protect wood from pests and other attacks.

For newsprint, the lower the production cost, the better, and therefore contains more lignin than other high-grade papers. In the factory, the wood used to make newsprint is ground along with the lignin and all the other components in it.

Nonetheless, paper manufacturers take advantage of the advantages of lignin in certain types of paper. Brown kraft paper, dark brown paper used to make grocery store bags, and cardboard are all very hard and strong because they contain more lignin and are not treated with bleach. Because the content printed on these papers is very limited, their color shade does not matter.

To make high-grade white paper, the wood is treated by a chemical solvent method that separates and removes lignin. Pure cellulose is white, and paper made from it is also white and does not turn yellow.

Lignin eventually turns the paper yellow due to oxidation. To be precise, when the lignin molecule comes into contact with oxygen in the air, it begins to change and becomes unstable. Lignin absorbs more light and appears darker in color.

Professor Zhang said that if newsreel is kept in a place that is completely blocked from sunlight and air, it will remain white. However, after a few hours of contact with sunlight and oxygen, it begins to change color.