Heat Setting of Synthetic Filament Yarn

Heat Setting

Heat setting is a thermal process used to stabilize filament yarns, improving their dimensional stability, texture, and appearance. The process involves heating the yarns to a specific temperature, which varies depending on the type of fibre, and then cooling them down. The main objectives of heat setting are to:

1. Stabilize the yarn structure: This prevents the yarn from shrinking, stretching, or deforming during subsequent processing or usage.
2. Enhance physical properties: This includes improving the yarns’ elasticity, strength, and wrinkle resistance.
3. Set texture: For textured yarns, heat setting helps to maintain the crimp or bulkiness introduced during texturing processes.

Nature of Set

The nature of the set refers to the type of structural changes that occur within the yarn fibres during the heat-setting process. These changes can be classified into physical, chemical, and mechanical modifications:

1. Physical changes: Heat setting causes the polymer chains within the fibres to realign and form more stable configurations. This realignment can lead to an increase in crystallinity, which enhances the thermal and dimensional stability of the yarn.
2. Chemical changes: In some cases, chemical bonds within the fibre molecules may be broken and reformed, leading to a more stable molecular structure. This is particularly relevant for fibres like polyester, where heat setting can cause a reduction in the internal stresses within the polymer.
3. Mechanical changes: The heat-setting process can also relieve internal tensions within the yarns introduced during spinning, drawing, or texturing. This results in a more relaxed and stable yarn structure.

Degree of Set

The degree of set refers to the extent to which the desired properties and stability are achieved through the heat setting. It can be measured using various parameters, such as:

1. Dimensional stability: The ability of the yarn to maintain its dimensions (length and width) after being subjected to heat and mechanical forces.
2. Elastic recovery: The ability of the yarn to return to its original shape after being stretched.
3. Tensile properties: Changes in the strength and elongation of the yarn after heat setting.
4. Crimp stability: For textured yarns, the ability to maintain crimp or bulkiness after repeated mechanical stresses.