How to control the melting characteristics of low melt FDY yarn during spinning or heat treatment?

Key strategies for controlling the melting properties of low melt FDY yarn
As a functional fiber material, low melt FDY yarn is widely used in thermal bonding, composite nonwovens, filter materials and other fields. Due to its low melting temperature, its melting properties have a direct impact on product performance and process stability during spinning and subsequent heat treatment. Reasonable control of its melting behavior is not only related to production efficiency, but also to the structural stability and safety of the final product.

Reasonable selection of raw materials and copolymer ratio
The melting properties of low melt FDY yarn first depend on its molecular structure, especially the type of polymer and the ratio of comonomers. Adding flexible segments or branched structures to polyesters, polyolefins or multi-copolyesters can effectively reduce their crystallinity, thereby achieving a lower melting start temperature. By controlling the proportion of copolymers, the problem of excessive fluidity caused by too low melting point can be avoided while maintaining hot viscosity. In addition, the selection of high-purity and thermally stable raw materials helps to improve the controllability of the melting process and prevent local melting anomalies caused by thermal degradation and impurities.

Accurately control spinning temperature and cooling conditions
In the spinning process, the control of melt temperature is crucial. Too high a melt temperature can easily degrade the polymer chain segments, affecting the subsequent thermal bonding performance; while too low a temperature can lead to spinning breakage, hairy yarns or insufficient crystallization, forming an unstable melt structure. In order to achieve a stable spinning state, the heating temperature zone should be gradually transitioned to ensure uniform melt flow. In addition, the wind speed and temperature of the cooling section should also be adjusted according to the fiber line density and the yarn outlet speed, so that the yarn forms a reasonable crystallization area during the cooling process and inhibits the pre-melting phenomenon caused by internal heat accumulation.

Control the temperature and tension during the stretching and heat setting process
During the stretching and heat setting process of low melt FDY yarn, temperature control is directly related to the orientation degree of the molecular chain and the release state of the internal thermal stress. If the stretching temperature is close to the melting point, the yarn may be adhered or melted on the surface; if the temperature is too low, it may not be fully set, affecting the thermal bonding performance of the final fiber. Therefore, segmented heating and slow temperature increase should be adopted to ensure that the fiber is moderately oriented while the structure is stable. In addition, the tension control during the setting process should also be avoided to be too large to avoid the risk of breaking when approaching the melting temperature.

Avoid overheating in secondary heat treatment
In subsequent processes, low melt FDY yarn is often used for compounding with other high melting point fibers or as a thermal bonding point. Special attention should be paid to the heating method and time at this stage to prevent the yarn from losing its shape due to excessive local temperature rise. Temperature control methods such as hot air circulation, infrared heating or electric heating plates can be used, and real-time monitoring can be carried out in combination with temperature sensing devices to keep the heating process within the critical temperature range. Especially in hot pressing, laminating or fixed width operations, the pressure and time should be reasonably controlled to avoid irregular melting caused by heat accumulation.

Consider the stability of the process environment
In addition to the process parameters themselves, the temperature and humidity stability of the external environment will also have a certain impact on the melting characteristics. Especially in high temperature and high humidity operating environments, low melt FDY yarn is more likely to soften prematurely. Therefore, production and storage should be carried out under constant temperature and humidity conditions, and avoid exposing the product to sunlight or near heat sources for a long time.