Why does the paper wrinkle when it dries in water?

Water molecules enter the paper fibers, the fiber segments become longer, the paper ligament fibers become less mobile, so they become softer, and after the water evaporates, the fiber length remains unchanged so it becomes wrinkled; Paper contains plant fibers, so some fibers swell with water and deform.

And then, when the water evaporates, there's a regain, and then it's not as straight.

The action of water causes the fibers that form the paper to dissolve and deform.

After that, the water evaporates, while the dissolution and deformation are irreversible.

Of course, if it is a better paper (such as coated paper), the impact will be a little smaller.

If it's a little bit (like straw paper), it's just a mess that dissolves into a mess.

The composition of the paper.

Paper is composed of plant fibers, fillers, rubbers, pigments, etc.

1) Plant fibers.

Plant fiber is the basic component of paper, as a raw material for papermaking, plant fiber must be easy to dissociate during pulping, high cellulose content in plant fiber, low content of wood cord; Required strength, length and width; It has sufficient elasticity and interweaving ability; ** Abundant and low cost, suitable for mass production and other conditions.

Commonly used papermaking plant fibers in China are: straw, wheat straw, reeds, bamboo, wood, hemp, cotton, etc., waste cotton, waste cloth, waste hemp, waste paper, etc. are also the main raw materials for papermaking.

In the process of manufacturing pulp, the plant fiber manager processes and removes other components such as lignin, pectin, resin, and fat contained in the plant fiber, and only retains the active components such as cellulose and hemifiber cord.

The properties of the paper, under certain conditions, depend on the physicochemical properties of the selected plant fibers, as well as the pulping method.

2) Filler The paper composed of intertwined fibers has many voids, and filler must be added to fill it to increase flexibility, reduce the transparency and elasticity of the paper, and make the surface uniform and adapt to the requirements of use.

Commonly used fillers are kaolin, talc, gypsum powder, carbonic acid and barium sulfate, etc., talc powder is used for general printing paper, and kaolin and barium sulfate are used for high-grade printing paper.

The amount of filler generally accounts for about 20%, too much filler will affect the quality of the paper, reduce the tension resistance and toughness, hinder the absorption of ink, and it is easy to lose powder during printing.

3) Rubber material is added to fill the gap on the surface of the paper, reduce the capillary effect in the paper, improve the water resistance of the paper, and improve the gloss and strength of the paper after sizing.

Commonly used rubber materials are rosin, aluminum sulfate, alum, starch, water glass, butyric acid, etc.

According to the different requirements of the use of various papers, there are various sizing methods, including paper sizing, surface sizing, heavy sizing and light sizing. The amount of sizing varies greatly, from the weight of the slurry, and the excessive sizing will also affect the ink absorption performance of the paper.

4) Pigment plant fiber has a certain color, after bleaching is still not pure white, but slightly light yellow or light green, can not meet the requirements of whitening paper, so it is necessary to add pigment for color mixing and whitening treatment.

The commonly used pigments for white-making paper are royal blue, ultramarine, etc., and a certain fluorescent brightener should be added to make high-grade paper.

In the manufacture of colored paper, pigments are also used, most of which use inorganic pigments or organic dyes.

From the above, we can see that the main components of paper are fillers, rubbers, and pigments that can be dissolved in water. After the paper has been soaked with water, these components have moved along with the movement of water. Cellulose, which makes up paper, is insoluble in water as a bone and does not shift.

This leads to folds and even gelatinization. Some high-grade paper, the filler, rubber, pigment, etc. used are materials that can withstand the test of moisture, so the deformation is smaller.

Tools: books, blotting paper, wool felt.

Here's how:

1. Sandwich the paper between absorbent materials like a sandwich. If the paper gets wet, try sandwiching the paper between two sheets of blotting paper, wool felt, or other absorbent material.

2. Sandwich the paper clamped by the above method between two heavy objects again. Once the paper is clamped with absorbent material, it is placed on a flat, hard surface. Use your hands to smooth out visible wrinkles.

3. Put a flat weight on top so that the paper is completely covered. Usually, a stack of heavy and large books is a good weight.

4. Check every day until the paper dries. When dry, the paper will be flat and most of the wrinkles will disappear. However, it will take some time to achieve such an effect.

It is advisable to check daily and replace it with a new one as soon as it is found that the absorbent material is wet. It takes 3 to 4 days for the soaked paper to dry completely. If you only spray a little water on the paper, it will dry in less than two days.

Because the internal molecular structure of the paper is disturbed when it is wet, it loses its previous arrangement, so the paper is wrinkled after drying.

Paper is an aggregate of short fibers, the fibers are absorbent, and the dehydration of the fibers starts from the two ends of the fibers, and the dry parts are different, which causes the deformation and contraction of the fibers, so the paper is uneven when looking at it as a whole.

When soaked in water, the molecules inside change a lot, so they wrinkle when they are dry.

In terms of the structure of the paper, the paper is made of plant fibers, and the fibers and other molecules are neatly arranged when they are not wet. When the paper is wet, the water molecules will destroy the arrangement of the original fiber molecules, and squeeze the fiber molecules that were originally closely packed together.

After the paper is dried, the water molecules are gone, but the fiber molecules cannot be restored to their original arrangement, but some places are dense and some places are sparse, so the paper becomes uneven, which is the so-called unevenness after drying after wetting.

If the water is on the tree and then the book is soaked, after drying, half of the book is wrinkled like a perm, you can use toilet paper, next to each page to clip on, just like a hamburger (if there is not much paper, you can divide the paper into two layers, but the effect may be poor), and then put a stack of books under the press, the next day is basically the same as not soaked, will not wrinkle, although a bit of a waste of paper.

If it is a single sheet, you can try going through the paper from the printer to make the paper balance again.

Paper towel water absorption is a capillary phenomenon where the force comes from the gaps between the tissue particles. Because the gap, that is, the molecular particles that are infinitely larger than the air, and smaller than the sum of the volume of molecular particles on the surface of the gap.

In this way, the number of air molecules in the gap is less than the number of molecules on the surface of the gap, so that the air molecules cannot meet the equilibrium requirements of the molecular attraction on the surface of the gap. That is, the force of attraction formed by the molecules on the surface of the interstitial space, which creates a residual force of attraction in the air. And the density of water is greater than that of air, so that the residual force of attraction attracts the denser water up to achieve conservation of energy.

Upstairs is so profound, let's put it simply, the paper will swell after absorbing water. But the size of the expansion is different at each position of the paper. That's why it's wrinkled.

The paper doesn't have much resilience, so it still looks crumpled when the moisture dries. Recovery, you try to iron it, hehe. But it's estimated that you can't see anything clearly, and if it's a blank piece of paper, what's the use of recovering it?!

1. The main component of paper is plant fiber, and there are a large number of hydroxyl groups on the cellulose molecule, and the strength of dried paper mainly comes from the complex hydrogen bond network formed between hydroxyl groups. The reason why paper can absorb water is also because the hydroxyl group is a hydrophilic group, and the process of volume expansion of fibroblasts after absorbing water is called fiber expansion, in this process, hydrogen bonds are formed between hydroxyl groups and water molecules to produce water bridges, and at the same time, water molecules enter the fiber cells to promote the increase of fibroid. Swelling can have two consequences:

The first is to weaken the cohesion of the fiber; The second is to create interlayer sliding between the layers of microfibers in the fibrous cell wall, so that the stiff fibers become soft and plastic.

2. If there is no external intervention, let the paper air dry naturally, the cellulose molecules are not densely dispersed due to the sliding between the layers, that is, the original tight hydrogen bond network cannot be recovered naturally, so the blistered paper will become wrinkled after drying, and other solutions can also produce such an effect, which is mainly related to the polarity of the solution molecules. The argument circulating on the Internet that crumpled paper is moistened and then compacted with a dictionary to flatten it when it dries is correct, which is similar to pulping in the papermaking process, i.e. the hydrogen bonds between cellulose molecules are better formed by applying stress.