Study on the influence of high humidity on the hot-melting effect of polyester hot-melt yarn

Study on the influence of high humidity on the hot-melting effect of polyester hot-melt yarn

In the textile industry, polyester hot-melt yarn, as an important functional fiber, is widely used in clothing, footwear, home textiles and other fields due to its excellent bonding performance, high strength, washability and other characteristics. However, in the actual production and application process, changes in environmental humidity, especially high humidity environment, will have a certain impact on the hot-melting effect of polyester hot-melt yarn. This article will deeply explore the influence of high humidity on the hot-melting effect of polyester hot-melt yarn, and analyze its causes, influencing factors and countermeasures.

1. Characteristics and application of polyester hot-melt yarn

Polyester hot-melt yarn is a low-melting-point fiber, mainly made of 100% polyester, and its melting point is controlled between 85℃ and 180℃ through a special production process. At room temperature, polyester hot-melt yarn is woven into fabrics with other fibers. When the temperature is higher than its melting point, the hot-melt yarn gradually melts, thereby bonding other fibers together to achieve the bonding and shaping functions of the fabric.
Polyester hot melt yarn has the following main characteristics:
Excellent bonding performance: It can quickly melt and bond to other materials at high temperatures, and form a stable bond after cooling, which is suitable for various scenarios that require strong bonding.
High strength and wear resistance: It has high tensile strength and wear resistance, and can withstand greater external pressure and friction.
Excellent washability: The hot melt bonding process combined with other fibers makes the product less likely to fall off or deform during washing.
Environmental protection and sustainability: The waste generated during the production process can be recycled and reused to reduce the impact on the environment.
Good stability and temperature resistance: It shows good stability under various temperatures and environments, and has a certain high temperature tolerance.
Polyester hot melt yarn is widely used in flyknit uppers, chenille yarn, high-end linings, trouser cuffs, knitted hats, bondi lines, socks and shoes and other fields.

2. The effect of high humidity on the hot melt effect of polyester hot melt yarn
(I) Changes in hot melt temperature
In a high humidity environment, the hot melt temperature of polyester hot melt yarn will decrease to a certain extent. This is because under high humidity conditions, moisture in the air will be adsorbed on the surface of the polyester hot melt thread to form a layer of water film. When the polyester hot melt thread is heated, this layer of water film will absorb part of the heat, causing the actual heating temperature of the polyester hot melt thread to decrease, thereby causing its hot melt temperature to decrease. For example, studies have shown that in an environment with a relative humidity of 80%, the hot melt temperature of the polyester hot melt thread is about 5℃-10℃ lower than that in an environment with a relative humidity of 30%.
(II) Decrease in bonding strength
High humidity environments will affect the bonding strength of polyester hot melt threads and reduce them. When the moisture content in the air is high, moisture will penetrate into the bonding interface between the polyester hot melt thread and other fibers. During the bonding process, the presence of moisture will hinder the mutual diffusion and entanglement of the molecular chains between the hot melt thread and the fiber, thereby reducing the bonding strength. In addition, moisture may also react with certain chemical groups in the hot melt thread to generate new substances, further affecting the bonding effect. For example, when making fabrics containing polyester hot melt yarn, if the ambient humidity is high, the peel strength and shear strength of the fabric will be significantly reduced, resulting in a decrease in the durability and reliability of the fabric.
(III) Changes in melt fluidity
High humidity will also change the melt fluidity of polyester hot melt yarn. Under normal humidity conditions, polyester hot melt yarn has good fluidity in the molten state and can be fully filled into the gaps in the fabric to achieve a good bonding effect. However, under high humidity conditions, due to the influence of moisture, the melt viscosity of the polyester hot melt yarn will increase and the fluidity will deteriorate. This makes it difficult for the hot melt yarn to be evenly distributed on the fabric surface after melting, and it is easy to have problems such as uneven and weak bonding, which affects the quality and performance of the fabric.
(IV) Extension of hot melt time
Under high humidity conditions, due to the combined effects of factors such as lower hot melt temperature, lower bonding strength, and worse melt fluidity, in order to achieve the same hot melt effect, it is often necessary to extend the hot melt time of the polyester hot melt yarn. This is because more heat is required to overcome the influence of moisture on the hot melt process, so that the hot melt yarn is fully melted and good bonding is achieved. However, too long hot melt time may cause other problems, such as thermal damage to the fabric, color change, etc., so it is necessary to make reasonable adjustments and controls in actual production.

3. Analysis of the reasons why high humidity affects the hot melt effect of polyester hot melt yarn

(I) Changes in molecular structure
Polyester hot melt yarn is mainly composed of polyethylene terephthalate (PET), and its molecular structure contains hydrophilic groups such as ester groups. In a high humidity environment, the moisture in the air will interact with these hydrophilic groups, resulting in the movement of the PET molecular chain being restricted and the hydrogen bonding effect between molecules being enhanced. This change in molecular structure causes the hot melt properties of polyester hot melt yarn to change, such as lower hot melt temperature and lower bonding strength.

(II) Changes in crystallinity
High humidity environment will also affect the crystallinity of polyester hot melt yarn. Under high humidity conditions, moisture will enter the crystal structure of polyester hot melt yarn, destroy the original crystal structure, and reduce the crystallinity. The reduction in crystallinity will lead to a lower melting point and increased melt viscosity of polyester hot melt yarn, thereby affecting its hot melt effect.
(III) Effect of hygroscopicity
Polyester hot melt yarn has a certain degree of hygroscopicity. In a high humidity environment, it will absorb more moisture. The absorbed moisture will not only affect the molecular structure and crystallinity of the hot melt yarn, but also generate vapor pressure during the hot melting process, which will hinder the melting and flow of the hot melt yarn, resulting in a poor hot melting effect.

4. Factors affecting the hot melting effect of polyester hot melt yarn under high humidity
(I) Environmental relative humidity
Ambient relative humidity is an important factor affecting the hot melting effect of polyester hot melt yarn under high humidity. The higher the relative humidity, the more moisture content in the air, and the greater the impact on the hot melting effect of polyester hot melt yarn. For example, in an environment with a relative humidity of 90%, the decrease in the hot melting temperature and the decrease in the bonding strength of polyester hot melt yarn will be greater than in an environment with a relative humidity of 70%.
(II) Temperature
Temperature and humidity work together to affect the degree of influence of high humidity on the hot melting effect of polyester hot melt yarn. At higher temperatures, the evaporation rate of water is faster, which may reduce the impact of humidity on the hot melt effect; at lower temperatures, water is more likely to condense on the surface of polyester hot melt yarn, exacerbating the negative impact of humidity on the hot melt effect.
(III) Varieties and specifications of polyester hot melt yarn
Different varieties and specifications of polyester hot melt yarn have different characteristics such as hygroscopicity, molecular structure and crystallinity, so the impact they receive in a high humidity environment will also be different. For example, fine denier polyester hot melt yarn has a relatively large surface area and strong hygroscopicity, and its hot melt effect is more easily affected in a high humidity environment; while coarse denier polyester hot melt yarn has a small relative surface area and weak hygroscopicity, and is relatively less affected.

5. Measures to deal with the impact of high humidity on the hot melt effect of polyester hot melt yarn
(I) Controlling ambient humidity
In the process of producing and using polyester hot melt yarn, the ambient humidity should be controlled within an appropriate range as much as possible. It is generally recommended to control the relative humidity between 40% and 60%. The environmental humidity can be reduced by installing dehumidification equipment, ventilation and other methods to reduce the impact of moisture on the hot melt effect of polyester hot melt yarn.
(II) Optimizing hot melt process parameters
According to different environmental humidity conditions, the hot melt process parameters, such as temperature, time and pressure, should be reasonably adjusted. In a high humidity environment, the hot melt temperature should be appropriately increased and the hot melt time should be extended to ensure that the polyester hot melt yarn can be fully melted and achieve a good bonding effect. At the same time, pay attention to controlling the hot melt pressure to avoid deformation of the fabric or excessive flow of the hot melt yarn due to excessive pressure.
(III) Selecting suitable polyester hot melt yarn varieties and specifications
According to specific use requirements and environmental conditions, select polyester hot melt yarn varieties and specifications with low hygroscopicity, high crystallinity and good thermal stability. For example, in a high humidity environment, polyester hot melt yarns that have been specially treated can be used preferentially, such as surface hydrophilic treatment, addition of anti-hydrolysis agents, etc., to improve their hot melt performance in a high humidity environment.
(IV) Surface treatment
Surface treatment of polyester hot melt yarn, such as coating with waterproofing agent, silicone oil, etc., can reduce its hygroscopicity and reduce the adsorption of water on the surface, thereby reducing the impact of high humidity on the hot melt effect. In addition, surface treatment can also improve the melt fluidity and bonding performance of polyester hot melt yarn, and improve its application effect in high humidity environment.

6. Case analysis
When a textile enterprise was producing a sports shoe fabric containing polyester hot melt yarn, it was found that when the workshop humidity was high (relative humidity greater than 70%), the bonding strength of the fabric decreased significantly, and it was easy to have problems such as debonding. After analysis, it was found that the high humidity environment was the main cause of these problems. In order to solve this problem, the company took the following measures:
Install dehumidification equipment in the workshop to control the relative humidity between 50%-60%.
Optimize the hot melt process parameters, increase the hot melt temperature by 5℃-10℃, and extend the hot melt time by 10%-20%.
The polyester hot melt yarn was treated with a waterproofing agent on the surface to reduce its hygroscopicity.
After the implementation of these measures, the bonding strength of the fabric has been significantly improved, the debonding problem has been effectively solved, and the product quality has been guaranteed.

7. Conclusion
High humidity has a significant effect on the hot melt effect of polyester hot melt yarn, which is mainly reflected in the reduction of hot melt temperature, the decrease of bonding strength, the deterioration of melt fluidity and the extension of hot melt time. These effects are caused by the changes in the molecular structure, crystallinity and hygroscopicity of polyester hot melt yarn caused by the high humidity environment. In order to cope with the influence of high humidity on the hot melt effect of polyester hot melt yarn, it can be solved by controlling the environmental humidity, optimizing the hot melt process parameters, selecting the appropriate polyester hot melt yarn varieties and specifications, and performing surface treatment. In actual production and application, various factors should be considered comprehensively according to the specific situation, and effective measures should be taken to ensure the hot melt effect of polyester hot melt yarn and the quality of fabrics.