What changes will occur in the physical properties of polyester hot melt yarn after it is damp?

What changes will occur in the physical properties of polyester hot melt yarn after it is damp?

When polyester hot melt yarn is damp, its physical properties will undergo the following changes:

1. Strength
Decrease in tensile strength: The main component of polyester hot melt yarn is polyester polymer, whose molecular chain structure is relatively tight in a dry state and can withstand large tensile forces. However, after being damp, moisture will penetrate into the fiber and interact with the ester bonds on the polyester molecular chain, resulting in the weakening of hydrogen bonds and van der Waals forces between the molecular chains. This makes the fiber more likely to break during stretching, and the tensile strength decreases significantly.
Increased elongation at break: After being damp, the molecular chain activity inside the fiber increases, and the originally tight structure becomes loose. When stretched by external force, the molecular chain can slide and stretch more freely, so the elongation at break will increase. However, this increase is at the expense of the initial modulus and overall strength of the fiber. The initial modulus of the fiber decreases and the overall strength deteriorates.

2. Modulus
Decrease in initial modulus: The initial modulus reflects the rigidity of the fiber under small deformation. After being damp, the molecular chain structure inside the fiber is destroyed, and the interaction force between the molecular chains is weakened, resulting in a decrease in the rigidity of the fiber in the small deformation stage. This means that the fiber is more likely to deform when subjected to a small external force, and its initial modulus decreases significantly.

3. Melting performance
Melting point reduction: The melting point of polyester hot melt is determined by factors such as its molecular chain structure and crystallinity. After being damp, the presence of moisture interferes with the crystallization process of the molecular chain and reduces the crystallinity. At the same time, the interaction between moisture and the polyester molecular chain reduces the thermal stability of the molecular chain, resulting in a decrease in the melting point of the fiber. This means that under the same heating conditions, polyester hot melt is easier to melt after being damp.
Melt viscosity change: After being damp, the molecular chain structure inside the fiber becomes loose, and the entanglement and interaction between the molecular chains are reduced. In the molten state, this structural change will lead to a decrease in melt viscosity. The decrease in melt viscosity will affect the bonding and processing properties of the fiber. For example, in the hot melt bonding process, the fiber after being damp may not provide sufficient bonding force, resulting in poor bonding effect.

4. Crystallinity
Decrease in crystallinity: Crystallinity is one of the important factors affecting the physical properties of fibers. After being damp, moisture will enter the fiber, destroy the orderly arrangement of the molecular chains, and make the structure of the crystallization area unstable. This will lead to a decrease in crystallinity and a decrease in the physical properties of the fiber. The decrease in crystallinity will deteriorate the strength, modulus and thermal stability of the fiber, and will also increase the hygroscopicity and thermal expansion of the fiber.

5. Dimensional stability
Increase in thermal shrinkage: After being damp, the molecular chain structure inside the fiber becomes loose, and the interaction between the molecular chains is weakened. During the heating process, the molecular chains are more likely to move and rearrange, resulting in an increase in the thermal shrinkage of the fiber. This means that during the heat treatment process, the polyester hot melt yarn after being damp is more likely to change in size, affecting its application effect in textiles.
Increase in hygroscopic expansion: Since the fiber absorbs moisture after being damp, the distance between the molecular chains increases, and the volume of the fiber will increase accordingly. This hygroscopic expansion will make the fiber more likely to change in size in a humid environment, affecting its dimensional stability and appearance quality in textiles.

6. Wear resistance
Decrease in wear resistance: After being damp, the tensile strength and initial modulus of the fiber decrease, and the molecular chain structure becomes loose. During the friction process, the fiber is more likely to deform and break, and the wear resistance decreases significantly. This will affect the service life of polyester hot melt yarn in textiles, especially in application scenarios that need to withstand greater friction, such as shoe uppers, sofa fabrics, etc.

7. Hygroscopicity
Increase in hygroscopicity: Polyester hot melt yarn itself has a certain hygroscopicity. After being damp, the fiber has absorbed some moisture inside, and its hygroscopicity will be further enhanced. This is because the internal structure of the fiber becomes looser after being damp, and the gaps between the molecular chains increase, which can more easily absorb and retain moisture. This increased hygroscopicity makes the fiber more susceptible to moisture in a humid environment, further affecting its physical properties and use effect.