Natural fiber fabrics, especially cotton fabrics, have the advantages of natural feel, moisture absorption and breathability, antistatic, comfortable wearing, and economical benefits, so they are deeply loved by people. Among fabric fibers, cotton fiber has the largest output and is the most widely used. However, pure cotton fabric has the disadvantages of poor elasticity, easy wrinkles, need to be ironed after washing, and is susceptible to microbial attack, resulting in fiber mildew and brittleness. In order to improve the wrinkle resistance of fabrics, anti-wrinkle finishing is required during dyeing and finishing [1]. In recent years, people advocate nature, and cotton fiber fabrics are generally popular. With the improvement of people’s living standards and the acceleration of the pace of life, people not only require clothing to be comfortable to wear, but also have higher requirements for maintaining a smooth appearance and simple cooking. Therefore, anti-wrinkle and durable press finishing have once again become a hot topic of research.
01 Reasons why cotton has poor wrinkle resistance
Cotton fiber belongs to cellulose fiber, and cellulose fiber is a polymer composed of water-losing glucose units. A cellulose molecule is a long chain composed of 6000 to 7000 units. These long-chain molecules of cellulose are arranged parallel to each other in some areas, and form hydrogen bonds and van der Waals attractions with each other. Such areas are called crystal regions. Within these regions, cellulose chains are tightly and firmly bonded to adjacent molecular chains. It is believed that in the crystal region, there is no space between cellulose molecules for water molecules and resin molecules to enter. In addition, due to the strong force between adjacent cellulose chains, the relative movement of the cellulose chains is very difficult. Even if a relative displacement of the molecules occurs, the binding force will immediately return the displaced molecules to their original positions when the stress is relieved. Therefore, it can be considered that the crystalline area is used to prevent wrinkles.
Modern theory believes that between the crystalline regions of cellulose molecular chains, there are amorphous regions with poor sequence. Because in this area, the cellulose molecules are not arranged very orderly. In the amorphous region, the distance between fiber chains is larger, and the attraction between adjacent chains is lower than that in the crystalline region. Therefore, water molecules, resin molecules, and dye molecules can all penetrate between the cellulose chains in the amorphous region. Because the attraction between adjacent fiber chains is low, the stress caused by wrinkles can cause relative displacement of the cellulose chains. Once the stress is removed, there is not enough binding force to return the cellulose molecules to their original positions, thus making the fabric Wrinkles are produced, so the wrinkles can be considered to be produced in the amorphous zone.
In order to make the fiber or fabric anti-wrinkle, it is necessary to add some connections between the cellulose molecules immediately adjacent to the amorphous zone. The fabric should maintain the desired shape while being processed. The molecules introduced in this way should have at least two groups capable of reacting with cellulose. Under appropriate catalyst conditions, such molecules, often referred to as textile resins, are actually more appropriately called “preshrunks.”
The cross-linking of cellulose chains must take into account two other factors. First, the introduced cross-bonds must be in a tight state. If the wrinkle resistance or pleat stability of fibers and fabrics under normal conditions of use is to be improved, these conditions should also be maintained during processing. Second, cellulose will swell after absorbing water. Whether it absorbs water under standard conditions, or is immersed in water or an aqueous solution, swelling is the result of water molecules entering the cellulose chains in the amorphous zone and forcing the chains apart. . If the cellulose fiber cross-linking is carried out in a highly swollen state, for example, the cellulose fabric is treated with an aqueous solution of inorganic acid and formaldehyde. When dried, the cellulose shrinks and the cross-links relax. Under dry conditions, the relative movement of cellulose molecules caused by wrinkles causes the loose cross-links to simply straighten. Since the cross-bonds are partially straightened, the resulting stress will cause the displaced molecules to return to their original positions. However, the transfer of atoms in the cross-bond around the valence bond will offset the above-mentioned restoring force, keeping the deformation at a minimum position. In fact, relaxed cross-links have no dry wrinkle resistance.
In summary, covalent bonding in a wet or other non-aqueous medium under a highly swollen state will result in wet wrinkle resistance and pleat retention, but in the dry state Little wrinkle resistance and pleat retention. Such as under high humidity.
Dry baking forms covalent bonds, which results in dry wrinkle resistance and pleat retention, as well as a certain degree of wet wrinkle resistance and pleat retention. In addition, dry baking cross-linking reduces the water absorption and swelling capacity of cellulose. Introducing cross-links in cellulose not only achieves the desired results, namely wrinkle resistance, pleat retention and ease of use, but also brings serious disadvantages, namely reduced physical strength.
The anti-wrinkle effect of cellulose fiber fabrics mainly relies on the cross-linking of a large number of reactive groups on the cellulose molecules with the finishing agent, which limits the relative displacement between structural units.
02 The reason for the formation of cotton fiber wrinkles
It is generally believed that it is due to the degeneration of fiber supramolecules after being subjected to large external forces. Each area within the structure is deformed to varying degrees by stress, and the basic structural units of the fiber are relatively displaced, causing the original hydrogen bonds to break and re-establishing a new hydrogen bond system at the new position that is difficult to recover, making the fiber structure deformed to varying degrees. The deformation of fibers or fabrics cannot be restored. Therefore, regarding the anti-wrinkle mechanism of cellulose fibers, it is generally believed that the role of finishing agents in anti-wrinkle (non-iron) finishing fluids has two aspects. On the one hand, due to the reaction between finishing agents and fiber molecules,are destroyed and replaced by covalent bonds. At the same time, some hydroxyl groups are blocked by resin molecules and cannot play the role of hydrogen bonds. Moreover, because some resins precipitate in the fibers, the cotton, which is originally highly crystalline and poor in flexibility, is The fibers become stiffer, severely limiting the free-moving properties of the molecular chains. Once stressed, it is difficult to distribute the load evenly to each fiber unit structure, resulting in load concentration. Therefore, although the elasticity of the fiber increases, the breaking strength decreases.
Synthetic resin produces cross-bonding and precipitation in the amorphous part of the fiber, changing the ease of sliding of the fiber molecular chain, thus reducing the elongation at break of the fiber. The elongation characteristics of the fiber reflect the flexibility of the fiber. If the elongation of the fiber is smaller, the brittleness will be greater. The tear strength and abrasion resistance of fabrics are related to the flexibility of the fibers. After resin finishing, the friction resistance of the yarn is increased and the free movement is restricted. When the fabric is in a tearing state, if the fiber elongation is small, the relative sliding of the yarn is restricted, and the yarn gathers at the tearing action point. The quantity is smaller, so less force is needed to tear the fabric. The abrasion resistance of fabrics is closely related to the elongation and elastic recovery of fibers. After resin finishing, the rigidity of the yarn increases, the free movement ability decreases, and the wear resistance decreases accordingly. </p
