Textile Dyeing and Dyes: Lecture #10 – Dyeing Synthetic Fibers: The Stretch of Elastane (Spandex/Lycra)

Today, we will discuss the dyeing of elastane fibers, also known as spandex or Lycra. Elastane is a unique synthetic fiber prized for its exceptional elasticity and recovery properties, often used in blends with other fibers. Dyeing elastane presents specific challenges due to its chemical nature and the need to maintain its elastic properties.

Understanding Elastane Fiber for Dyeing:

Elastane is a segmented polyurethane fiber composed of long, flexible polyether or polyester segments and short, rigid urethane segments. Key aspects of elastane’s chemistry relevant to dyeing include:

Hydrophobicity: The long polyether or polyester segments contribute to the hydrophobic nature of elastane.
Lack of Strong Ionic Sites: Elastane lacks significant inherent ionic binding sites for acid or basic dyes.
Sensitivity to High Temperatures and Harsh Chemicals: The elastic properties of elastane can be easily damaged by prolonged exposure to high temperatures and strong chemicals. Dyeing processes must be mild to preserve its functionality.
Blend Dyeing: Elastane is rarely used on its own and is typically blended with other fibers like cotton, polyester, or nylon. Therefore, dyeing often involves achieving a uniform shade on both components of the blend.

Key Dye Classes for Elastane:

Dyeing elastane, especially in blends, often requires a careful selection of dye classes that are compatible with both the elastane and the blend component:

Disperse Dyes: Due to the hydrophobic nature of the polyether/polyester segments in elastane, disperse dyes are commonly used. They offer a wide range of shades with acceptable fastness properties when applied under carefully controlled conditions. Lower dyeing temperatures are preferred to prevent damage.
- Application: Applied at relatively lower temperatures (typically 95-105°C) compared to dyeing 100% polyester. Longer dyeing times may be necessary for adequate penetration.
- Mechanism: Dissolution in the fiber and entrapment through hydrophobic interactions and van der Waals forces.
Acid Dyes: For elastane blended with nylon or wool, acid dyes can be used to dye the polyamide or protein component. However, the dyeing conditions must be mild enough to avoid significant degradation of the elastane. Careful selection of acid dyes with good compatibility is essential.
Reactive Dyes: When blended with cellulosic fibers like cotton, reactive dyes can be used to dye the cotton component. Again, the dyeing conditions (temperature, pH) must be optimized to minimize damage to the elastane.
Metal-Complex Dyes: Similar to acid dyes, metal-complex dyes can be used for blends with nylon or wool, offering improved fastness properties under mild dyeing conditions.

The Elastane Dyeing Process (General Steps):

The dyeing of elastane, especially in blends, requires careful control:

Fiber Preparation: Cleaning to remove any processing aids.
Dyebath Preparation: Selecting compatible dyes for the blend components and preparing the dyebath with appropriate auxiliary chemicals (leveling agents, pH buffers) for the chosen dye classes.
Dye Application: Introducing the elastane blend to the dyebath. The temperature is gradually raised to a moderate level (typically below 105°C) and maintained for a longer time to promote level dyeing without damaging the elastane.
Dye Exhaustion: Allowing sufficient time for the dyes to be absorbed by the respective fibers in the blend.
Rinsing: Removing excess unfixed dye.
After-treatments: Applying finishing agents to improve fastness or handle, ensuring they are compatible with elastane.
Drying: Drying at low temperatures to prevent damage to the elastane.

Conclusion:

Dyeing elastane, particularly in blends, requires a delicate approach to balance achieving the desired color on all fiber components while preserving the unique elastic properties of the elastane. Disperse dyes are commonly used for the elastane itself, while acid, reactive, and metal-complex dyes are selected based on the blend composition, with careful control of dyeing conditions being paramount.